Task preparation and neural activation in stimulus-specific brain regions: an fMRI study with the cued task-switching paradigm.

Brain and Cognition 87 (2014) 39–51

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Task preparation and neural activation in stimulus-specific brain regions: An fMRI study with the cued task-switching paradigm Yiquan Shi a,b,⇑, Thomas Meindl c, Andre´ J. Szameitat a, Hermann J. Müller a,d, Torsten Schubert a,e,⇑ a

Department of Psychology, Ludwig-Maximilians-University, Munich, Germany Neuroimaging Center, Department of Psychology, Dresden University of Technology, Dresden, Germany c Department of Clinical Radiology, University Hospitals–Grosshadern, Ludwig-Maximilian-University, Munich, Germany d Department of Psychological Sciences, Birkbeck College, University of London, UK e Department of Psychology, Humboldt-University, Berlin, Germany b

a r t i c l e

i n f o

Article history: Accepted 5 March 2014 Available online 27 March 2014 Keywords: Preparatory modulation Stimulus-specific regions Selective enhancement Functional connectivity Residual activation

a b s t r a c t To investigate the role of posterior brain regions related to task-relevant stimulus processing in task preparation, we used a cued task-switching paradigm in which a pre-cue informed participants about the upcoming task on a trial: face discrimination or number comparison. Employing an event-related fMRI design, we examined for changes of activity in face- and number-related posterior brain regions (right fusiform face area (FFA) and right intraparietal sulcus (IPSnum), respectively), and explored the functional connectivity of these areas with other brain regions, during the (preparation) interval between cue onset and onset of the (to-be-responded) target stimulus. The results revealed task-relevant posterior brain regions to be modulated during this period: activation in task-relevant stimulus-specific regions was selectively enhanced and their functional connectivity to task-relevant anterior brain regions strengthened (right FFA – face task, right IPSnum – number task) while participants prepared for the cued task. Additionally, activity in task-relevant posterior brain regions was influenced by residual activation from the preceding trial in the right FFA and the right IPSnum, respectively. These findings indicate that, during task preparation, the activation pattern in currently task-relevant posterior brain regions is shaped by residual activation as well as preparatory modulation prior to the onset of the critical stimulus, even without participants being instructed to imagine the stimulus. Ó 2014 Elsevier Inc. All rights reserved.

1. Introduction A fundamental characteristic of executive control is that in a changing environment, humans can selectively prepare for a specific task even prior to the presentation of the task-critical stimulus. Such task preparation is crucial for flexible and precisely timed behavior in many situations. Much of the previous work on this issue has focused on the neural correlates of the task preparation process in general, and specifically on localizing activation foci for critical components of task preparation, such as task configuration and rule activation, in the prefrontal cortex (PFC) and the parietal cortex (e.g., Bode & Haynes, 2009; Brass & von Cramon, 2002, 2004; Gruber, Karch, Schlueter, Falkai, & Goschke, 2006; Luks, Simpson, Feiwell, & Miller, 2002; Shi, Zhou, Müller, & Schubert, 2010; Sohn, Ursu, Anderson, Stenger, & Carter, ⇑ Corresponding authors. Address: Department of Psychology, Ludwig-Maximilians-University Munich, Leopoldstraße 13, 80802 Munich, Germany. E-mail addresses: [email protected] (Y. Shi), torsten.schubert@psychologie. hu-berlin.de (T. Schubert). http://dx.doi.org/10.1016/j.bandc.2014.03.001 0278-2626/Ó 2014 Elsevier Inc. All rights reserved.

2000; but see Wylie, Javitt, & Foxe, 2006). However, little effort has been expended on investigating the role of posterior brain regions that are related to task-relevant stimulus processing during task preparation. This is surprising because it has long been suggested that the PFC and the parietal cortex modulate stimulus processing during task performance in posterior brain regions in a goal-directed manner (e.g., Corbetta, Kincade, Ollinger, McAvoy, & Shulman, 2000; Corbetta, Kincade, & Shulman, 2002; Desimone & Duncan, 1995; Hopfinger, Buonocore, & Mangun, 2000; Miller & Cohen, 2001; Serences, Schwarzbach, Courtney, Golay, & Yantis, 2004). Therefore, in the present study, we aimed to elucidate the characteristics of the preparation-related changes in those posterior brain regions that are related to the processing of the task-relevant and task-irrelevant stimuli. The mechanisms and neural substrate of task preparation have often been investigated using the cued task-switching paradigm (e.g., Bode & Haynes, 2009; Brass & von Cramon, 2002, 2004; Gruber et al., 2006; Luks et al., 2002; Meiran, 1996, 2000; Shi et al., 2010; Sohn et al., 2000; Sudevan & Taylor, 1987; Wylie et al., 2006). In this paradigm, participants have frequently to

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Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

switch between two tasks, requiring them to repeatedly prepare for a new task. For instance, participants may be presented with a face which is overlaid with a digit, and they have to indicate the gender of the presented person (i.e., male or female) on some trials and the magnitude (i.e. larger or smaller than 5) of the presented digit on other trials. A task cue, in the present example: the word ‘gender’ or ‘digit’, is presented before the target stimulus to indicate the upcoming task, thus permitting anticipatory task preparation. This paradigm makes it possible to temporally dissociate the task preparation (time interval from cue presentation until target presentation) from the task execution period (following target presentation) (e.g., Meiran, 1996). It has been shown that in the cued task-switching paradigm, participants’ performance benefits from a prolonged cue–target interval (CTI), with the overall reaction time becoming faster and the error rate and the cost of task switching lower with increasing CTI (e.g., over CTI durations from 0 to about 1000 ms). These benefits are suggestive of task preparation occurring within the cue–target interval (e.g., Meiran, 1996, 2000). However, extending the time allowed for task preparation by increasing the CTI even further does not usually translate into increased performance gains, possibly because such long CTIs may pose extra demands on working memory and so discourage active task preparation (Brass & von Cramon, 2002; Monsell, 2003) The components involved in task preparation in the paradigm sketched above are commonly thought to include: task-relevant stimulus processing and retrieval, or pre-activation, of stimulus–response (S–R) rules (see Kiesel et al., 2010, for review). Assuming that preparation for a specific task includes task-relevant stimulus-specific processing, this processing should be associated with pre-activation of posterior brain regions that are specifically involved in task-relevant stimulus processing. Recent neuroimaging studies have provided reliable evidence for the existence of several, separable stimulus-specific brain regions in posterior cortices (e.g., Dehaene, Piazza, Pinel, & Cohen, 2003; Kanwisher, McDermott, & Chun, 1997; Liu, Harris, & Kanwisher, 2010; Tootell et al., 1995; Zeki et al., 1991). Based on the findings of these studies, it becomes possible to investigate the neural activity in posterior stimulus-specific brain regions during the task preparation processes in the cued task-switching paradigm. Note that most fMRI studies that employed this paradigm did not localize the task-relevant stimulus-specific regions to examine for neural activation related to stimulus processing during task preparation (Brass & von Cramon, 2002, 2004; Gruber et al., 2006; Luks et al., 2002; Shi et al., 2010; Sohn et al., 2000; but see Wylie et al., 2006). These studies consistently revealed a fronto-parietal network to be activated in cued task-switching, including the lateral frontal cortex, the pre-supplementary motor area, and the inferior parietal lobule during task preparation (Brass & von Cramon, 2002, 2004; Gruber et al., 2006; Luks et al., 2002; Shi et al., 2010; Sohn et al., 2000). Some of these studies also reported preparatory activation in posterior brain regions in extrastriate cortical areas (e.g., fusiform gyrus, inferior, superior occipital, and the lingual gyri) and striate cortical areas (e.g., calcarine sulcus). However, it is not clear from these reports whether the observed posterior brain activations relate to sensory processes involved in the encoding of the task cue after its presentation, or to specific preparation for the upcoming task. An exception is the study of Wylie et al. (2006), who required participants to switch between a motion and a color task; however, this study yielded only partial evidence of preparation for the critical stimuli for the color (but not the motion) task, and for rather long preparation periods (2 or 4 s), which makes it difficult to generalize the findings to other task situations with shorter preparation times. There is good evidence for the existence of posterior stimulusspecific regions that are sensitive to specific stimulus information such as faces, houses, motion, or numbers. While these regions

may be activated by the presentation of the region-specific stimuli, it has been shown that their degree of activation may additionally be modulated by selective attention or demands to imagine, expect, or hold the stimulus in memory (e.g., Chelazzi, Miller, Duncan, & Desimone, 1993; Esterman & Yantis, 2010; Fuster & Jervey, 1981; Lepsien & Nobre, 2007; Miller, Li, & Desimone, 1993; Miller & Desimone, 1994; Miyashita & Chang, 1988; O’Craven and Kanwisher, 2000; Puri, Wojciulik, & Ranganath, 2009; Serences et al., 2004; Stokes, Thompson, Nobre, & Duncan, 2009; Yantis & Serences, 2003). For example, Serences et al. (2004) presented participants with a stream of faces with overlapping houses and asked them to selectively attend to either the face or the house for a certain period of time. Activity in the house-specific region was found to be increased when participants were asked to pay attention to houses as compared to faces, and vice versa. While this pattern shows that activation in posterior stimulus-specific brain regions may indeed be modulated by the allocation of attention to the relevant stimulus or object, it is not conclusive as to whether prior activation occurs during the preparation for a task in the taskswitching paradigm. In this paradigm task, preparation may start at different points in time, for example, immediately upon presentation of the task cue, at some time before, or only at the onset of the target stimulus. Because there is no specific instruction to, for instance, actively imagine the upcoming stimulus, whether pre-activation of posterior brain regions occurs at all and, if it does, at which point in time is likely to depend on whether or not participants actually intend to prepare for the task in advance (Shi et al., 2010). On this background, the present study was designed to investigate whether pure preparation for an upcoming task induces cuerelated changes (commencing with or after the task cue) of neural activity in stimulus-specific regions even prior to the presentation of the actual target stimulus. To examine this, we employed a face discrimination and a number comparison task in a cued taskswitching paradigm in which the upcoming task was indicated by a symbolic pre-cue. The fusiform face area (FFA) is known to be associated with the processing of faces, relative to other stimuli such as houses (e.g., Kanwisher et al., 1997); and a region in the horizontal segment of the intraparietal sulcus (IPS), the IPSnum, is systematically activated whenever numbers are manipulated, independently of number notation (e.g., ‘one’ or ‘1’; Dehaene et al., 2003). We identified each individual participant’s taskrelevant region in the FFA and IPSnum and analyzed the activity changes in these regions both during the time interval between pre-cue and target onset (i.e., the task preparation period) and during the task execution period. Given that task preparation processes are thought to involve task-relevant stimulus processing (Kiesel et al., 2010), we expected selective pre-activation patterns in the face- and number-specific brain regions, respectively. We were able to analyze the neural activation specifically related to the task preparation period by presenting different types of trials, namely: cue–target trials and cue-only trials, in randomly intermixed fashion (e.g., Brass & von Cramon, 2002, 2004; Corbetta et al., 2000, 2005; Shi et al., 2010; Weissman, Gopalakrishnan, Hazlett, & Woldorff, 2005). Most of the trials (see Section 2) were cue–target trials in which participants responded to the target depending on the task cue. However, the sequence of trials also included some (cue-only) trials on which only the pre-cue was presented without any target. Because participants did not know in advance whether or not a target would follow the cue, they had to prepare for the task on every trial, including cue-only trials. Consequently, analysis of the activation on cue-only trials (compared with null trials, i.e., trials in which no target stimulus but only the central fixation point was presented) permitted the activation related to task preparation to be calculated. In particular, we analyzed the activation in the face- and number-specific regions during the task preparation period, to examine whether or not


the activation in the respective stimulus-specific region would be selectively enhanced while preparing for the task. Execution-related processes are revealed by contrasting activity between cue–target and cue-only trials. Because the activation on cue–target trials consists of both activation related to task preparation and activation related to task execution, subtracting the cuerelated activation from the activation on cue–target trials would isolate the execution-related activation. We analyzed the faceand number-specific regions’ activation in the task execution period, to examine whether or not the activation in the respective stimulus-specific region would be selectively enhanced while performing the task. What must also be taken into account is that the activation in posterior brain regions during preparation for an upcoming task may not only be influenced by processes related to the active preparation for this (new) task. Rather, there may also be residual activity relating to processes on the preceding trial, which may influence the current-trial activity in posterior stimulus-specific brain regions through carry-over mechanisms (e.g., Yeung, Nystrom, Aronson, & Cohen, 2006). Behavioral evidence shows that as a result of ‘task set inertia’, the preceding task settings may continue to persist during processing of the current (changed) task (Allport, Styles, & Hsieh, 1994; Wylie & Allport, 2000; Yeung & Monsell, 2003a,b). If residual activation from the previous trial were indeed affecting current-trial activation, then the preparatory activation of a certain task-stimulus-specific region on the current trial should be modulated by whether or not the preceding task was the region-specific task. To illustrate, consider the FFA: if the preceding task was a face task, rather than a number task, then residual activation from the preceding task would enhance FFA activation by carry-over (and analogously for the IPSnum region if the preceding task was a number task). To address this, we examined whether task-specific prior activation would still be observed even if the preceding task was different from the current task. In addition, we explored whether or not task preparation engenders an anticipatory modulation of the functional connectivity between posterior stimulus-specific regions and other brain regions, by examining for Psychophysiological Interactions (PPI; Friston et al., 1997). Previous studies had already demonstrated changes in functional connectivity as a result of participants operating cognitive control in Stroop (Egner & Hirsch, 2005a) and dualtask situations (Stelzel, Brandt, & Schubert, 2009). However, with regard to the cued task-switching paradigm, there is as yet (to our knowledge) no evidence for an anticipatory modulation of the functional connectivity between task-relevant brain regions. 2. Methods 2.1. Participants Fourteen healthy right-handed volunteers with normal or corrected-to-normal vision took part in the experiment (six males; age range 19–33 years, mean: 24.9 years, SDV: 4.4 years) after obtaining informed consent according to the Declaration of Helsinki. Each participant was paid 20 €. The data of two participants were excluded from further analysis owing to their exceedingly high error rates (>20%). Thus, ultimately, the data sets of 12 participants were available for analysis (six male; age: mean [±standard deviation] 24.4 [±4.6] years, range 19–33 years). 2.2. Task procedure 2.2.1. Procedure for the main task The task to be performed by the participants was either gender discrimination (female vs. male) or number comparison (larger vs.

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smaller than five, ‘large’ vs. ‘small’ in short). There were three types of trials: two of them were event trials, namely, cue-only and cue–target trials; the other type was null trials. Each event trial began with the presentation of a cue for a fixed duration of 1200 ms, which was considered to be sufficiently long to permit task preparation (e.g., Rogers & Monsell, 1995; Meiran, 1996). For addressing a question not directly related to the primary focus of the present study, we used two kinds of cues, both displaying instruction information about the up-coming task: task cues and rule cues (Fig. 1c). In addition to specifying the task to be performed, the latter cues provided precise information about the stimulus–response (S–R) mapping required for performing the task correctly (e.g., for the face task, the task rule information [male ? left button; female ? right button] was given explicitly; please refer to Fig. 1 for the exact protocol). Shi et al. (2010) had shown that rule cues can be more efficient in evoking rule activation during task preparation than task cues. Given this, a comparison between the two cue conditions was expected to be informative about whether or not activity changes in posterior stimulus-specific regions are additionally affected by the rule information specified in the cue display. On cue-only trials, cue offset was followed by a blank black screen (rather than a face/number word stimulus) which lasted for 600 ms, and there was no need for participants to make a response (Fig. 1b). In contrast, on cue– target trials (Fig. 1a), the cue was followed by a target presented for 600 ms. The target was a picture of a face with a number word located in the region of the depicted person’s nose. Two male and two female face pictures were used (Collection of Facial Images: Faces94; http://cswww.essex.ac.uk/mv/allfaces/faces94.html); the number could be ‘‘EINS’’ (one), ‘‘ZWEI’’ (two), ‘‘ACHT’’ (eight), or ‘‘NEUN’’ (nine). As a result, 16 face-&-number pictures were employed as target stimuli. The stimuli (cue stimuli and target stimuli) were presented on a black background in the center of the screen and subtended 5° of visual angle. Participants responded, as fast and as accurately as possible, to either the face or the number, depending on the task instruction provided by the cue. Participants made a two-alternative forced-choice response using either their left or their right index finger, with response sets counterbalanced across participants. For half the participants, the S–R mapping rule was male ? left, female ? right (face task) and, respectively, large ? left, small ? right (number task). This mapping was reversed for the other half of the participants. Response times (RTs) were recorded only if they were faster than 1800 ms. On null trials, only the central fixation marker was presented for 1200 ms, followed by a 600-ms black screen. After the 600-ms black screen (on null or cue-only trials) or the offset of the target picture (on cue–target trials), respectively, there was a variable interval of 1800, 2500, 3100, 3900, or 4600 ms before the next trial started. The next trial could then either be an event trial or a null trial. In total, there were 200 cue-only trials (100 face and 100 number tasks, with the same number of rule cue and task cue trials for each task; e.g., the face task rule cue condition included 50 cue-only trials), 280 cue–target trials (140 face and 140 number tasks, again with the same number of rule cue and task cue trials for each task; e.g., the face task rule cue condition included 70 cue–target trials), and 140 null trials. Since one study aim was to examine for possible residual activation from the preceding trial, the factor ‘task transition’ was also considered. Depending on the instruction cue presented prior to the target, the current trial was classified as a repetition trial if the current task was identical with that on the previous event trial, independently of whether the trial (i.e., current or previous) was a cue-only trial or a cue–target trial. Similarly, the current trial was classified as a switch trial if the current task was different from the preceding one independently of whether the trial was a cue-only or a cue–target trial. We presented equal numbers of task switch

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Fig. 1. Illustration of the experimental procedure and details of the cue displays. Panel (a) panel shows a cue–target trial (of the number task, rule-cue condition). Panel (b) shows a cue-only trial (of the number task, task-cue condition). In the bottom panel (c), the rule-cue and task-cue displays are illustrated. In both cue conditions, the upcoming task was indicated by the German words ‘‘ANZAHL’’ (number) and ‘‘GESICHT’’ (face), respectively. In the rule-cue condition (upper row), additional information indicated the assignment of the response keys to the stimulus categories male and female in the gender task, and larger and smaller in the number task.

and repetition cue-only and cue–target trials for both the face and number tasks. In sum, there were three factors in the main task: task (number vs. face), cue type (rule cue vs. task cue), and task transition (switch vs. repetition). For the resulting eight conditions, there were each 25 cue-only trials and 35 cue–target trials. Task order was pseudo-randomized. All event trials (n = 480) and null trials (n = 140) were assigned to four runs each lasting 12 min 40 s. Participants took a short break, of one or two minutes, between two runs. At the beginning of each run, the word ‘‘Achtung’’ (Attention) was presented for 2 s to remind participants of the tasks to be performed.

presented as sole targets (i.e., the stimuli displayed only a face or only a number). Accordingly, target stimuli could be presented without prior cues (specifying the task) in the localizer tasks, and participants responded blockwise to the presented face or, respectively, number stimuli. Larger activity in the FFA was expected in the face compared to number localization task; and vice versa, larger activity was expected in the IPSnum in the number compared to the face localization task (see section Determination of ROIs below for the methodological details of defining the individual face and number ROIs).

2.3. fMRI measurement 2.2.2. Task procedure for the localization task In order to identify the individual task-relevant regions, FFA and IPSnum, participants performed an independent localization task after the main task. In this task, participants responded to the picture containing either only a face or only a number word in alternating blocks of trials without presentation of a pre-cue. Participants performed 18 alternating task blocks to localize the FFA and the IPSnum, respectively. Each block consisted of 8 trials, with a trial duration of 2 s. Accordingly, the resulting whole run lasted 9 min, 36 s. On each trial, stimulus duration was 600 ms (as in the main experiment). In the face blocks, participants performed the face discrimination task, and in the number blocks they performed the number discrimination task, using the same response rules as in the main experiment. There were four face pictures (2 female and 2 male) and four number words (‘‘EINS’’, ‘‘ZWEI’’, ‘‘ACHT’’, ‘‘NEUN’’), each of which also appeared in the main task. Importantly, in the localization task, the target pictures were

Imaging was performed employing a SIEMENS TRIO 3-Tesla scanner at the Klinikum Großhadern (Institute for Clinical Radiology), Ludwig-Maximilians-Universität München. T2⁄-weighted echo-planar images (EPI) with blood oxygenation level-dependent contrast were acquired (TR = 1500 ms, TE = 30 ms, flip angle = 80°, matrix size = 64 64 voxels). Twenty-three axial slices (thickness = 4 mm, spacing = 1 mm) were acquired parallel to the AC-PC plane, covering the whole cortex. The order of acquisition of the slices was interleaved. The first four volumes (dummy volumes) were discarded because of possible instabilities in the magnetic field at the beginning of a run. Stimuli were displayed on a back-projection screen mounted in the bore of the magnet behind the participant’s head, by using an LCD projector. Participants viewed the screen by wearing mirror glasses. The four runs of the main task were scanned first; then the run of the localization task was scanned.


2.4. fMRI data analysis 2.4.1. Preprocesses and data modeling Preprocessing of all functional images (of main task and localization task) was carried out using SPM5 (Wellcome Department of Cognitive Neurology, London, UK). Images of the main task were interpolated in time to account for the differences in acquisition time between slices (slice timing). All images were spatially realigned to the first volume for head movement correction, and then normalized into MNI space (images were re-sampled to 2 2 2 mm3 isotropic resolution) with default normalization estimation. The data were then smoothed with a Gaussian kernel of 8 mm full-width half-maximum to account for inter-participant anatomical variability. Then for the main task, the image data were modeled by applying a general linear model (Friston et al., 1995). In event-related single-participant analyses, the 8 cue-only and the 8 cue–target conditions – resulting from the factorial combination of the two task types (face vs. number), two cue types (rule cue vs. task cue), and two types of task transition (switch vs. repetition) – were modeled. These 16 events were locked with the onsets of the (rule or task) cues. In addition, the null trials, all error trials, and the periods with the instruction word ‘Attention’ at the beginning of each run, were modeled separately. The resulting 19 conditions were modeled as events of zero duration; they were convolved with the hemodynamic response function (HRF) to generate 19 corresponding regressors, and then beta values of these regressors were estimated according to the ordinary least-squares (OLS) method. As activation parameters for the preparation period activation, we calculated the beta values of the cue-only trials minus the beta values for null trials; as parameters for the execution-related activation, we calculated the beta values for the cue–target trials minus the beta values for their cue-only trials (e. g., Shi et al., 2010). 2.4.2. Region(s)-of-Interest (ROI) analysis The FFA, typically the right side, has been shown to be consistently involved in the processing of faces (e.g., Kanwisher, 2000; Kanwisher et al., 1997). In numerous earlier studies, the bilateral IPSnum has been shown to be consistently involved in the processing of number categories; however the right-hemisphere activation was stronger than that in the left hemisphere in the number comparison task (e.g., Chochon, Cohen, van de Moortele, & Dehaene, 1999; Pinel, Dehaene, Riviere, & Le Bihan, 2001). Given this, we identified the individual task-relevant ROIs in the right FFA and right IPSnum. The precise ROIs for each participant were determined based on the localization task. For this task, all the face and, respectively, number task trials were modeled as events; next, these two conditions were convolved with the HRF to generate the two regressors, and the beta values of the regressors were estimated according to the OLS method. Then, for the whole-brain group analysis, onesample t-tests of contrast maps across participants (randomeffects model treating participants as a random variable) were calculated to ascertain whether the differences between conditions were significant. The contrast ‘face – number’ and the reversed contrast ‘number – face’ were calculated to find the group activity peaks in the right FFA and right IPSnum, respectively; a statistical threshold of p < 0.05, FDR corrected, was used, with 10 continuous voxels. Starting from the group peaks, we then localized individual face-specific and number specific-regions as ROIs in the right FFA and right IPSnum, respectively; for determining these individual ROIs we used a more relaxed statistical threshold of p < 0.001, uncorrected, with 10 continuous voxels. We determined the nearest peak (relative to the corresponding group peak) per participant (for the individual contrasts of

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‘face – number’ and ‘number – face’) as the center of the individual cube ROI mask (6 mm side length). From the voxels covered by these masks, we extracted the parameter estimates from the time series of every individual participant for all 16 task conditions (produced by the beta values). The 8 activation parameters obtained for the preparation period, which were of most interest for the current questions at issue, were examined by an analysis of variance (ANOVA) with the factors task type (face vs. number), cue type (rule cue vs. task cue), and task transition (task switch vs. task repetition). The 8 parameters for the cue–target trials, after following subtraction of the corresponding cue-only-trial parameters to provide the parameters for execution period activation, were also subjected to an ANOVA with the factors task type, cue type, and task transition. 2.4.3. PPI analysis We conducted a Psychophysiological Interaction (PPI) analysis (Friston et al., 1997) to examine the functional connectivity between posterior and other brain regions (see also Egner & Hirsch, 2005a; Stelzel et al., 2009). The aim of a PPI analysis is to explain the neural responses in one brain region in terms of the interaction between the neural responses in another brain region and a specific psychological context. In the present study, we investigated whether a given posterior task-relevant region (FFA or IPSnum) was differentially coupled with other brain regions during the preparation for its relevant and, respectively, the irrelevant task. We used the FFA and IPSnum ROIs of each participant as ‘‘seed regions’’ and extracted the time courses from these seed regions (with SPM’s VOI module). Separately for the two regions, SPM’s PPI module was used (i) to obtain the seed regions’ neural signals by de-convolving the extracted time courses with HRF; (ii) these de-convolved time courses and the respective psychological variable (for FFA: face compared to number task preparation; for number: number compared to face task preparation) were used to generate the psychophysiological interaction term. Then, for each seed region, all three variables generated by the PPI module (deconvolved time course in seed region, psychological variable, and the interaction term) were entered into a new general linear model. This way, we could identify regions that were significantly correlated with the activity in the sensory seed regions depending on whether participants prepared for a seed-region-relevant or an irrelevant task. In particular, there might be enhanced functional connectivity between FFA and another brain region during the preparation for the face, compared to the number, task, while there might be enhanced functional connectivity between IPSnum and other brain regions during the preparation for the number, compared to the face, task. A statistical threshold of p < 0.001, uncorrected, was used, with an extent threshold of 10 voxels. This threshold is commonly used in studies of cue-related processing and PPI analyses for exploratory purposes (see, e.g., Egner & Hirsch, 2005b; Ruff & Driver, 2006; Wendelken, Bunge, & Carter, 2008). 3. Results 3.1. Behavioral results Mean RTs and error rates were submitted to separate 2 2 2 repeated-measures ANOVA, with the factors task type (face or number), cue type (rule cue or task cue), and task transition (switch or repetition) (see Fig. 2). For RTs, we did not find a significant effect for the factor task type (F(1, 11) = 0.1, p = 0.76), nor any significant interaction between the factor task type and the other two factors (both Fs < 0.22, ps > 0.65). Therefore, the data of the two tasks were merged; see Fig. 2 for the (merged) data. RTs showed a tendency

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Fig. 2. Reaction times (RT) as a function of task transition and cue type (left graph); error rates as function of task type, task transition, and cue type, separately for the face and the number task (middle and right graphs, respectively). Error bars show one standard error of mean.

for being faster in the rule cue than in the task cue condition (main effect of cue type, F(1, 11) = 4.30, p < 0.06, the rule cue benefit was 18 ms), which indicates that participants effectively utilized the rule cue information during the preparation period. In addition, RTs were significantly slower for task switch than for task repetition trials (main effect of task transition, F(1, 11) = 10.70, p < 0.01), with switch costs amounting to 22 ms on average. Finally, the interaction between cue type and task transition was non-significant (F(1, 11) = 1.64, p = 0.13). For error rates, no significant effect was found for the factors task type (F(1, 11) = 0.96, p = 0.35) and task transition (F(1, 11) = 1.94, p = 0.19). A significant effect was found for the factor cue type (F(1, 11) = 12.1, p < 0.005): the error rate was lower in the rule cue compared to the task cue condition (3.8% vs. 5.3%), indicating that the additional rule information provided by the rule cue helped to reduce errors. The interaction between task type and cue type was significant (F(1, 11) = 11.2, p < 0.01). Further analyses with separate t-tests revealed a significant benefit for the rule cue compared to the task cue condition during performance of the face task (mean benefit of 3%, t(11) = 5.47, p < 0.0001), but not of the number task (mean benefit of 0.1%, t(11) = 0.12, p = 0.90). This indicates that participants utilized the rule cue information more effectively for the preparation of the face task, as compared to the number task. 3.2. Imaging results We analyzed activity changes in the right FFA and IPSnum ROIs and the changes of their functional connectivity during the task preparation period. In addition, we analyzed activation changes in the execution period and the possible influence of residual activation from the preceding task. Considering the limited sample size of the study, all these analyses were conducted after checking whether our data are reliable in terms of in replicating the typical pattern of findings in cued task-switching paradigms, namely, switch-related brain activation and the general task preparation network (e.g., Brass & von Cramon, 2002, 2004; Dove et al., 2000; Gruber et al., 2006; Luks et al., 2002; Shi et al., 2010; Sohn et al., 2000). Consistent with previous findings, right inferior frontal gyrus, bilateral precuneus, right superior parietal lobule, bilateral cingulate gyrus, right lentiform nucleus, and thalamus exhibited higher activation in the task switch vs. repeat conditions of cue–target trials. Furthermore, the general preparation network, including lateral frontal cortex, pre-supplementary motor area, and inferior parietal lobule, was activated during the cue interval in the present study. Because the present design did not include a short (e.g., 300-ms) preparation interval, we were unable to assess task preparation by comparing long vs. short intervals.

However, the fact that the general preparation network was activated points to successful preparation actually taking place during the preparation interval in the present experiment. 3.2.1. Determination of ROIs We calculated the contrasts of ‘face – number’ and ‘number – face’ for the data of the localization tasks and determined the corresponding ROIs by focusing on the group peaks in the right FFA and bilateral IPSnum, respectively. For the individual face-task relevant ROIs, the group peak in the right FFA in the ‘face – number’ contrast was located at MNI coordinates (46, 44, 24), (Fig. 3a). All twelve participants showed significant activation in the ‘face – number’ contrast near this peak (mean distance = 11.6 mm). The nearest individual peak was identified for each participant, then all significant activation voxels within a cube mask of 6 mm side length were selected to define that participant’s specific ROI for face. Next, the activations in these ROIs were extracted for the subsequent ROIs analysis. For the individual number-task-relevant ROIs, the group peak in the right IPSnum in the ‘number – face’ contrast was located at MNI coordinates (56, 30, 50), (Fig. 3b). Eleven of the twelve participants showed significant activation in the ‘number – face’ contrast near this peak in the right IPSnum (mean distance = 16.5 mm). The nearest individual peak to the right IPSnum was determined for those eleven participants, and then all significant activation voxels within a 6-mm side length cube mask were selected to define a given participant’s specific ROI for number processing. Next, the activations in the eleven right-sided ROIs were extracted for the subsequent analysis. Note that the only one participant who did not exhibit number dominant activation in the right IPSnum showed such activation in the left IPSnum. We also extracted this participant’s data from the left IPSnum and checked the pattern of results: it does not change if the data of this participant are included in the data set. 3.2.2. Activation in the preparation period Participants’ individual activation parameters for cue-only trials were subjected, separately for the right FFA and the right IPSnum regions, to 2 2 2 repeated-measures ANOVAs with the factors task type (face or number), cue type (rule cue or task cue), and task transition (switch or repetition). For both regions, there was a significant main effect of task type on the activation values during the preparation period; this is illustrated in Fig. 4. In particular, in the FFA, preparation-period-related activation was larger for the face task compared to the number task (F(1, 11) = 6.25, p < 0.05, çp2 = 0.362); conversely, in the right IPSnum, activation was larger for the number task compared to the face task (F(1, 10) = 5.56, p < 0.05, çp2 = 0.357). No significant main effect of cue type was


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Fig. 3. Panels (a) and (b) show group activation in the localization runs (p < 0.05, FDR corrected, with 10 continuous voxels). Illustrated are the peaks of the FFA and IPSnum activations in MNI coordinates (for details, see Section 2). Panel (c) examples of target pictures in the localization runs: face task (left) and number task (right).

Fig. 4. Right FFA and IPSnum’s activity in preparation period for the relevant and irrelevant task. Preparation period activation was detected by calculating the beta values of the cue-only trials minus the beta values for null trial. Error bars show one standard error of mean (only positive).

found for either ROI (the FFA and IPSnum regions) (both Fs < 0.33, both ps > 0.5). Task transition (switch vs. repetition) had no significant effect on the activation in either the right FFA or the right IPSnum ROIs (both Fs < 1.27, both ps > 0.2). For the interactions, we found a significant interaction between current task type and task transition for the FFA region (F(1, 11) = 10.00, p < 0.01, çp2 = 0.476). Other interactions were not significant (all Fs < 3.12, all ps > 0.1). In more detail, for both ROIs, we checked whether or not they showed selective enhancement during the preparation for the different tasks, and then we examined for possible effects of residual activation and of task transition on the activation in the current trials.

3.2.2.1. Preparation for the task. As mentioned, there was a significant main effect of task type on the activation values during the preparation period for both regions (both ps < 0.05). In order to further test whether FFA and IPSnum showed increased activity compared to null trials exclusively while participants prepared for the region-specific relevant task, but not to the other, region-nonspecific task, separate follow-up t-tests were performed. These tests showed that in the FFA region, both the task cue and the rule cue elicited significant activity, compared to null trials, during the preparation for the face task (both ts > 1.9, both ps < 0.05); by contrast, no significant FFA activity was found during the preparation for the number task in either cue type condition (both ts < 1.34,

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ps > 0.2). In the IPSnum region, both the rule cue (t(10) = 1.77, p = 0.05) and the task cue (t(10) = 1.58, p < 0.08) elicited or tended to elicit increased activation compared to null trials during the preparation for the number task; by contrast, the activation values in the IPSnum were not significantly increased during the preparation for the face task, in either cue type condition (both ts < 1.08, ps > 0.3). Thus, with regard to the task information, both types of cue (rule cue and task cue) elicited prior activation in the ROI of the task-relevant stimulus, whereas the additional rule information in the rule, as compared to the task, cue did not yield any additional activation in the ROI of the task-relevant stimulus. These results indicate that the FFA and IPSnum regions can be selectively enhanced during the preparation period for the respective relevant task. Furthermore, the amount of preparatory activation in posterior stimulus-specific brain regions is not influenced by the type of cue (rule cue or task cue), which may indicate that the rule information is not represented in the stimulus-specific regions; rather, it is more likely represented in the PFC and/or the parietal cortex (Bode & Haynes, 2009; Bunge, Kahn, Wallis, Miller, & Wagner, 2003; Montojo & Courtney, 2010; Sakai & Passingham, 2003, 2006; Woolgar, Thompson, Bor, & Duncan, 2011). 3.2.2.2. Effects of residual activation. The residual activation from the preceding task is illustrated in Fig. 5. We found a significant interaction between current task type and task transition for the FFA region (F(1, 11) = 10.00, p < 0.01), which reflects an influence of the residual activation on the current trial. Further t-tests revealed that when the current task was a face task, the FFA tended to show stronger activation in the task preparation period when the previous task was also a face task, rather than a number task (repetition > switch, t(11) = 1.75, p < 0.06); note, though, that when the current task was the number task, the FFA showed also stronger activation in the preparation period when the previous task was a face task (switch > repetition, t(11) = 2.96, p < 0.01). In other words, no matter which task was to be performed on the current trial (face or number), the right FFA showed increased activation during the preparation period when the preceding task had been a face task. This is likely due to residual activation from the preceding face task, in spite of the current task type (Fig. 5, left). The examination of the interaction between task type and task transition in the right IPSnum revealed an activation pattern that was

similar to that exhibited by the FFA; however, the interaction was statistically non-significant (F(1, 10) = 0.84, p = 0.38) (see Fig. 5, right). We also examined the correlation between the amount of neural activity and behavioral performance during task switching. Eight variables were used for representing neural activity: FFA and IPSnum activation in the task preparation period for the face and the number task, respectively (yielding 2 2 = 4 variables); and the difference between task switch and repeat trials for the two tasks in FFA and IPSnum, respectively (accounting for the other 2 2 = 4 variables). As parameters for behavioral performance, we used four parameters: mean reaction time and switch costs for the face and number tasks, respectively. Correlations were calculated between each one of the eight neural activity variables and each one of the four performance parameters. These analyses revealed only one correlation to be significant: that between the activation in the FFA_number task_(switch-repeat) (Fig. 5, the 2nd two-bars group) and the switch costs in the number task (Pearson correlation coefficient r = 0.606, p < 0.05) This finding indicates that it was the more difficult to switch (from the preceding face) to the current number task the greater the residual activation (from the preceding face task) that existed in FFA. Importantly, this finding is consistent with an observation by Yeung et al. (2006), that switch cost magnitude correlates significantly with activity in the (after the change) task-irrelevant posterior brain region of preceding trial. Finally, it is worth noting that neural activity in the corresponding ROIs was nevertheless significantly increased even if participants prepared for a switch trial. This was revealed by an additional analysis in which we extracted the right FFA’s activation on face switch trials (i.e., during preparation for the face task when the preceding task was a number task) and compared this activation with that on null trials: the resulting activation was still significant (t(11) = 2.06, p < 0.05). Similarly, when the preceding task was a face task, the activation in the right IPSnum during the preparation for the upcoming number task was still significantly higher than that on null trials (t(10) = 1.83, p < 0.05). These latter effects indicate that the task-specific prior activation in the right FFA and the right IPSnum was induced by active preparation processes for the respective relevant task, rather than being attributable solely to residual activity from the previous trial.

Fig. 5. Activation in the preparation period as a function of preceding and current task type; the number task is denoted by N and the face by F; NF means that the preceding task is a number task and the current task a face task. Error bars show one standard error of mean (only positive).


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Fig. 6. Functional connectivity between activation in posterior ROIs (regions-of-interests) and other (anterior) brain regions in the preparation period (psychophysiological interaction analysis; for details, see text). Panel (a) Stronger functional connectivity between right FFA and rACC (peak at MNI 4, 30, 2) was found during preparation for the face, compared to the number, task. Panel (b) Stronger functional connectivity was found between right IPSnum and right anterior part of SFG (peak at MNI 22, 50, 8) during the preparation for the number, compared to the face, task.

3.2.2.3. Task transition effects. Task transition (switch vs. repetition) had no significant effect on the activation in either the right FFA or the right IPSnum ROIs (both Fs < 1.27, both ps > 0.2). In addition to the ROI-based analysis of task transition effects, we examined also whether brain regions other than the right FFA and the IPSnum would show larger activity on switch compared to repeat trials, by performing a whole-brain analysis (task switch vs. task repeat, p < 0.001, uncorrected, with 10 continuous voxels.). This analysis revealed larger activity during the preparation for switch compared to repeat trials in the left medial superior frontal gyrus (meSFG, MNI ( 10, 14, 44)), left medial frontal gyrus (meFG, MNI ( 8, 0, 60)), and right superior temporal gyrus (STG, MNI (52, 34, 6)). 3.2.3. Execution-related activation The parameters for the execution-related activation in the right FFA and, respectively, the right IPSnum were subjected to separate 2 2 2 repeated-measures ANOVAs, with the factors task type (face vs. number), cue type (rule cue vs. task cue), and task transition (switch vs. repetition). No main effect of task type was found in either region (all Fs < 1.52, ps > 0.2); that is, unlike the period of preparing for the task to be performed, there was no selective enhancement of activation in task-relevant stimulus processing regions while actually executing the task. Further t-tests disclosed significant additional activity compared to null trials in the right FFA and the right IPSnum for both component tasks (i.e., the face and the number task) and for the two cue conditions (i.e., rule cues and task cues) (all ts > 2.47, ps < 0.05). This finding likely reflects the fact that the current target display contained both face and number stimulus information, giving rise to increased activation simultaneously in both task-relevant regions during the execution of each individual task. Furthermore, the observed pattern of an undifferentiated increase of activation during task execution in the face and number task regions may indicate that the task-relevant region had already been sufficiently up-modulated during the task preparation period, doing away with a need for an additional task-specific activation increase during task execution. Another possibility would be the assumption that the resolution was occurring ‘downstream’ in processing – for example, in response-related areas. 3.2.4. PPI analysis To assess the functional connectivity between the activation in posterior task-relevant brain regions and other brain regions during task preparation, we conducted a PPI analysis (see Fig. 6). For

the number-task-relevant region, the right IPSnum, this analysis revealed increased functional connectivity with the right anterior SFG (MNI coordinates 22, 50, 8) during the preparation for the number, compared to the face, task (p < 0.001). With a lower significance threshold (p < 0.005), a further important region in the left inferior parietal lobule (MNI coordinates 58, 32, 50) was found to show increased functional connectivity to the right IPSnum during the preparation for the number, compared to the face, task. For the face-task-relevant region, the right FFA, increased functional connectivity was revealed during preparation for the face, as compared to the number, task with the rostral anterior cingulated cortex (rACC; MNI coordinates 4, 30, 2). Lowering the significance criterion to p < 0.005 did not change the PPI data pattern with respect to the FFA region. 4. Discussion In the present study, we found that the neural activation in stimulus-specific posterior brain regions is modulated during the preparation for a cued-face and, respectively, a cued-number task (presented in random order) in a cued task-switching paradigm. Activity in the right FFA was significantly increased, compared to null trials, in the preparation period for the face task, and the functional connectivity between the right FFA and the rACC was increased. Analogously, activity in the right IPSnum region was significantly increased, compared to null trials, in the preparation period for the number task, and the functional connectivity between the right IPSnum region and the right anterior SFG was increased. These findings indicate that even without presentation of the task-relevant stimulus, task preparation can modulate the neural signals within specific posterior regions, and these regions’ connectivity with other brain regions, which are related to the processing of the task-relevant stimulus. The results show further that in addition to the preparatory modulation, there is another factor that can influence prior activation in task-relevant posterior brain regions, namely: (residual) activation from the preceding task-relevant posterior brain region persisting into the preparation period for the current trial in the right FFA and tending to persist in the right IPSnum. Thus, both preparatory modulation and residual activation shaped the activation pattern in the current task-relevant, and task-irrelevant, posterior regions: activation in the current taskrelevant, as compared to the task-irrelevant, region was enhanced by preparatory modulation; at the same time, residual activation

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from the preceding task set persisted to influence the activation in the relevant posterior region. 4.1. Preparatory modulation in posterior task relevant stimulus specific regions Previous studies had shown that the presentation of certain specific stimuli can activate posterior stimulus-specific brain regions (e.g., Dehaene et al., 2003; Kanwisher et al., 1997; Liu et al., 2010; Tootell et al., 1995; Zeki et al., 1991), and that the degree of activation in these regions can be modulated by processes of attentional selection (e.g., Serences et al., 2004). For example, in the study of Serences et al. (2004), participants were presented with ambiguous stimuli, such as pictures of faces with overlaid houses, and told to attend to either faces or houses for a certain period of time; the face-specific region’s activity was found to be increased while participants had to attend to faces compared to houses, and vice versa (see also Esterman & Yantis, 2010; Lepsien & Nobre, 2007; O’Craven & Kanwisher, 2000; and others). There are studies that investigated the stimulus-specific regions’ activation while no stimulus was physically presented in the relevant task conditions. In these studies, however, participants were asked either to imagine the stimulus (e.g., O’Craven & Kanwisher, 2000) or to maintain the stimulus in memory (e.g., Corbetta et al., 2005; Lepsien & Nobre, 2007) for a certain period of time (usually more than 10 s). The results of the present study extend these earlier findings because, during task preparation, no specific stimuli were actually presented in the current paradigm and there was no (explicit) instruction to imagine or expect specific stimuli or maintain them in memory. Nevertheless, the presentation of a cue (without presentation of specific stimuli) indicating the up-coming task led rapidly to pre-activation in posterior stimulus-specific brain regions. These findings show that even without presenting specific stimuli, preparatory attention on its own can bias the activation in these regions. In addition, the current findings add to several prior studies that have pointed to the possibility of preparatory modulation in posterior brain areas for certain attention tasks, such as selection of spatial locations (Corbetta et al., 2000; Kastner, Pinsk, De Weerd, Desimone, & Ungerleider, 1999; Hopfinger et al., 2000; Ress, Backus, & Heeger, 2000; Serences, Yantis, Culberson, & Awh, 2004; but see Corbetta et al., 2005). For example, in the study of Hopfinger et al. (2000), a cued spatial-attention task was used, with the cue display consisting of two arrows, one yellow and one blue, pointing in opposite directions. Participants were required to covertly orient their attention to a location in the visual hemifield indicated by an arrow of a certain color (e.g., the yellow one). The attentional control centers (e.g., in superior frontal and inferior parietal cortex) were activated by the directional cue in the task preparation period, and their activations were accompanied by activity changes in location-specific posterior brain regions (e.g., right extrastriate-cortex activation was found with left- vs. right-ward pointing cues). Shulman et al. (1999) found preparatory modulation of feature processing in a task in which participants had to discriminate the direction of coherent motion in visual displays of moving dots, where coherent-motion displays were presented randomized with some (catch) trials on which no coherent motion was present. Activation in motion-related brain regions (e.g., MT+) was found to be increased during the preparation period, that is, in response to a directional arrow pre-cue arrow pointing left or right to indicate the direction of the coherent dot motion, compared to a neutralcue (fixation cross) condition. The present study extends these earlier findings of locationspecific modulations and feature-relevant preparation in

single-task situations, by showing that when switching between two different discrimination tasks, the mere preparation for one or the other task specified by a pre-cue can modulate activity in the respective stimulus-specific posterior brain regions. 4.2. Modulation of activation in posterior task relevant regions: task preparation and task execution In the current study, selective modulation of activity occurred in both the FFA and the IPSnum specifically during task preparation. However, later on during the task execution period, we did not find any selective enhancements in either region above the level that had already been reached before. Arguably, this is so because the modulation of activation in posterior task-relevant regions may not necessarily occur exclusively in either the task preparation or the task execution period. The specific point in time at which the modulation may occur and the degree to which participants prepare during the cue period depend on several factors, such as the time available for preparation, the amount of explicit task information provided by the cue, and participants’ task strategies (e.g., Brass & von Cramon, 2002; Gruber et al., 2006; Meiran, 1996, 2000; Shi et al., 2010). Recent neuroimaging studies have shown that the extent to which the experimental settings allow, or encourage, preparation for an upcoming task strongly influences the degree to which preparatory processes are actually engaged, as well as having a bearing on the strength of the processes operating in the subsequent task execution period (Brass & von Cramon, 2002; Gruber et al., 2006; Shi et al., 2010). For instance, in the study of Gruber et al. (2006), the cue–target interval (CTI) varied between 0 and 1500 ms. When the CTI was long (i.e., 1500 ms), a network of frontal and parietal brain areas was activated during advance preparation for the upcoming task, and the subsequent processes of task execution were associated with activation in areas involved in visual processing and motor execution. By contrast, when the CTI was too short to permit effective advance preparation, the same network of frontal and parietal brain areas was activated – though only later, during the task execution period. These findings suggest that the point in time at which the preparation-related control network is activated depends on when control is demanded (rather than this network being activated exclusively in either the task preparation or the task execution period). Temporal flexibility of modulation processes in posterior brain regions has also been revealed in studies using different paradigms (e.g., Corbetta et al., 2005; Shulman et al., 2002). For instance, Corbetta et al. (2005) employed a matching-to-sample task in which the sample picture to be remembered could be either a face or a place. The test screen, presented after a delay, contained four pictures including two faces and two places, and participants had to decide whether or not the sample picture was present. Similar to the current pattern of findings, Corbetta et al. observed neural activation in the FFA to be selectively enhanced in the delay (preparation) period of the face (as compared to the place) task, but not in the test (task execution) period. In contrast, and different to the current data pattern, no selective enhancement of activation was found in the place-related region (parahippocampal place area, PPA) during the task preparation period; rather, an enhancement manifested only later during the test (task execution) period (Corbetta et al., 2005). Taken together, various studies indicate a considerable degree of flexibility in the timing of task preparation, which is likely to contribute to the specific patterns of preparatory modulatory influence on neural activity in posterior task-relevant regions. The modulation may not necessarily take place exclusively in either the task preparation or the task execution period. Rather, if control processes are sufficiently effective to induce the requisite modulation


of activation in the posterior task-relevant region already during the preparation period, there would be no need for (re-) engaging this modulation in the task execution period, and vice versa. Further studies are required to examine the particular factors that permit the timing of task preparation processes to be controlled precisely during task performance (Corbetta et al., 2005; Shulman et al., 2002). 4.3. Functional connectivity during task preparation Earlier work had shown that the functional connectivity between the activity in posterior stimulus-specific regions and in anterior executive-control regions or other task-relevant regions may change during task processing (e.g., Egner & Hirsch, 2005a; Li et al., 2010; Prado, Carp, & Weissman, 2011; Prado & Weissman, 2011; Stelzel et al., 2009). With respect to the cued task-switching paradigm, it was still an open question whether or not task preparation leads to modulations of the functional connectivity between the respective posterior stimulus-specific region and other brain regions. During preparation for number comparison (as compared to the face discrimination) task, the present findings suggest increased functional connectivity between the right IPSnum and the right anterior SFG; and between the right IPSnum and the left inferior parietal lobule at a lower threshold (p < 0.005). This fits well with findings of previous imaging studies that inferior parietal lobule and prefrontal cortex are involved in the number comparison task (e.g., Chochon et al., 1999; Dehaene, Spelke, Pinel, Stanescu, & Tsivkin, 1999; Pinel et al., 2001; Pesenti, Thioux, Seron, & De Volder, 2000) and that bilateral IPS and anterior portions of the right PFC are critical for processes of approximate calculation (Kucian et al., 2006). Most importantly, however, the present findings show that the functional connectivity between the critical regions for the number comparison task (i.e., right IPSnum, right anterior SFG, and left inferior parietal lobule) was increased specifically during the preparation for the number comparison task. Considering the different functions of these regions, it is tempting to speculate that they may have played different roles in the current task situation. For instance, the bilateral IPS may play a major role in the representation of numbers (e.g., Dehaene et al., 1999, 2003) and the PFC may implement abstract response strategies required for basic mathematical operations (Bongard & Nieder, 2010). During the preparation for the face (as compared to the number) task, the functional connectivity between the right FFA and the rACC was increased. Face perception would not appear to be a process primarily associated with the rACC. However, several findings suggest a role of the rACC in emotional processing and social awareness/cognition (e.g., Bush, Luu, & Posner, 2000; De Martino, Kalisch, Rees, & Dolan, 2009; Lieberman, 2007; Satpute & Lieberman, 2006; Amodio & Frith, 2006). Here, we speculate that the increased functional connectivity between the FFA and the rACC while preparing for the face, as compared to the number, task may represent those aspects of task preparation that are related to social task ‘reflection’ and social awareness. 4.4. The residual activity from preceding trials in the posterior brain regions In the present study, we found that residual activation in the preceding task-relevant posterior brain region still persisted during the preparation period for the current trial in the right FFA and tended to persist in the right IPSnum. There are many behavioral reports of an influence of the preceding task set on the performance of the current task, which has been attributed to (residual) task set inertia (e.g., Allport et al., 1994; Allport & Wylie, 1999, 2000; Yeung & Monsell, 2003a,b). The persistent activity in the

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posterior brain regions observed in the present study fits well with this interpretation. It has been shown that the persistent activity can be a source of task switching costs, because it interferes with the performance of the current task if this is different from the preceding task (e.g., Allport et al., 1994; Allport & Wylie, 1999, 2000; Yeung et al., 2006). In the present study, we found that the greater the residual activation from the preceding face task that persisted in the right FFA, the more difficult it became to switch to the current number task, likely owing to interference. This finding is consistent with Yeung et al. (2006) findings: their study revealed the magnitude of switch costs to be significantly correlated with the level of activity in the (after the change) task-irrelevant posterior brain region of the preceding trial (Yeung et al., 2006). Arguably, however, task set inertia can be at least partially overcome by intentional task preparation. For example, Wylie et al. (2006) had participants switch between a color and a motion task, and observed larger cue-related activation in the switch, compared to the repetition, condition of the color task in the color-specific region. Importantly, there was no evidence of a behavioral switch cost in the color task, suggesting that the increased (cue-related) activity during the preparation period reflects enhanced efficiency with which the new task is set up in a switch situation. 4.5. Switch-related activation in the preparation period The effect of task transition (i.e., task switch vs. repetition) was not significant in either region. A reason for this observation may be that the activation in the posterior regions can depend on the performance in the behavioral tasks. For instance, in the already mentioned study of Wylie et al. (2006), for the color task, participants prepared effectively on the switch trials, permitting them to react as fast and accurately on switch trials as on repeat trials. Correspondingly, successful preparation was associated with robust preparatory activity in color-related regions, which was even higher than the activity on the repeat trials. In contrast, participants showed relatively slower reaction times (on average more than 100 ms slower compared to the color task) and considerable switch costs in the motion task, with motion-processing areas exhibiting no activation during the preparation period. The findings of activation during the current preparation period strongly suggest that participants did prepare for the respective task prior to target presentation in the current study (recall the finding of prior activation in the FFA during preparation of the face task, and in the right IPSnum during preparation of the number task). Also, participants expended more effort on preparing for a switch trial compared to a repeat trial. In the present study as well as a previous one of our group (Shi et al., 2010), we consistently found higher activation in the pre-SMA during preparation for switch trials, compared to repeat trials. This pattern is consistent with the assumed operation of a task reconfiguration process (e.g., Monsell, 2003). However, the effort may not have been sufficient to evoke additional activation in posterior brain regions. Such activation may be an important precondition for observing a reduction or even abolishment of behavioral switch costs (e.g., see Wylie et al., 2006). 5. Conclusions The findings of the present study provide evidence for preparatory modulations of task-relevant posterior brain regions. In particular, the activation of task-relevant stimulus-specific brain regions can be enhanced and their functional connectivity to other (task-relevant) anterior brain regions strengthened during task preparation. These findings clearly demonstrate the task-relevant

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posterior brain regions’ role in task preparation, significantly extending our understanding of task preparation processes. Acknowledgments This research was supported by grants from Cluster of Excellence ‘‘Cognition for Technical Systems (CoTeSys)’’ Grant No. 439 to T.S. and by a grant of the German Research Foundation to T.S. and H.M. We thank Ute Coates (Department of Clinical Radiology, LMU Munich) for her help with data collection. References Allport, D. A., Styles, E. A., & Hsieh, S. (1994). Shifting intentional set: Exploring the dynamic control of tasks. In C. Umilta & M. Moscovitch (Eds.), Attention and performance XV (pp. 421–452). Cambridge, MA: MIT Press. Allport, D. A., & Wylie, G. (1999). Task-switching: Positive and negative priming of task-set. In G. W. Humphreys, J. Duncan, & A. Treisman (Eds.), Attention, space, and action: Studies in cognitive neuroscience (pp. 273–296). Oxford: Oxford University Press. Allport, D. A., & Wylie, G. 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