Brain (1992), 115, 711-733
VISUOSPATIAL ATTENTION IN DEMENTIA OF THE ALZHEIMER TYPE by RAJA PARASURAMAN, 1 PAMELA M. GREENWOOD, 1 JAMES V. HAXBY2 and CHERYL L. GRADY1 {From the 'Cognitive Science Laboratory and Department of Psychology, The Catholic University of America, Washington, DC and the ^Laboratory of Neurosciences, National Institute on Aging, Bethesda, MD, USA)
Cue-directed shifts of spatial attention were examined for a letter-discrimination task in 15 patients with mild to moderate dementia of the Alzheimer type (DAT) and 15 healthy, age-matched controls. Spatial cues were valid, invalid or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7° to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200 ms and 2000 ms. Reaction time (RT) benefits conferred by valid cues did not differ between the DAT group and the controls. However, RT costs incurred by invalid cues were significantly greater in the DAT group than in the control group. Group differences in RT costs plus benefits occurred at short SOAs (500 ms) for central cues. Reaction time costs plus benefits were correlated with right-left asymmetry in resting levels of cerebral glucose metabolism in the superior parietal lobe for DAT patients but not for controls. The results indicate that focusing of attention to spatial location is intact in early DAT, whereas the disengagement of visuospatial attention is impaired. Automatic attention shifts elicited by peripheral cues reveal abnormalities earlier than attention shifts initiated 'effortfully' by central cues. Intact focusing and impaired disengagement of visuospatial attention may be linked to dysfunction in early DAT of cortico-cortical networks linking the posterior parietal and frontal lobes.
INTRODUCTION
There has been little formal study of attentional functioning in persons with dementia of the Alzheimer type (DAT), despite the recognition that attention deficits may constitute a significant aspect of the cognitive impairment in this disease (Jorm, 1986; Parasuraman and Nestor, 1986, 1991; Broks et al., 1988; Nebes and Brady, 1989). The relative neglect of attention is surprising for at least three reasons. First clinical observations have long pointed, albeit in a general way, to the moderating influence of attention on the neuropsychological test performance of patients with dementia (Lezak, 1983). Secondly, there is an extensive literature indicating that attentional processes are affected by normal adult aging (Craik and Byrd, 1982; Plude and Hoyer, 1985; Salthouse, 1988). Given the overlap in cognitive functioning between normal aging and the very early, mild stages of DAT (Corkin et al., 1984; McKhann et al, 1984; Rubin et al., 1989; Storandtand Hill, 1989), it would be important to know if the effects on attention of aging and dementia differ, and if so, whether quantitatively or qualitatively. Thirdly, many of the neural Correspondence to: Raja Parasuraman, Department of Psychology, The Catholic University of America, Washington, DC 20064, USA.
© Oxford University Press 1992
Downloaded from http://brain.oxfordjournals.org/ by guest on November 11, 2015
SUMMARY
712
R. PARASURAMAN AND OTHERS
Attention and cognition in dementia What role does attention play in DAT? Two general views have been proposed. One sees attention as an intrinsic property of mental operations in general; for example, memory search, retrieval or response selection, and postulates that the efficiency of cognitive operations is dependent upon the efficient allocation of attention to those operations (Nebes et al, 1984; Oberet al., 1985; Hartman, 1991; Nestor
VISUOSPATIAL ATTENTION IN DEMENTIA OF THE ALZHEIMER TYPE by RAJA PARASURAMAN, 1 PAMELA M. GREENWOOD, 1 JAMES V. HAXBY2 and CHERYL L. GRADY1 {From the 'Cognitive Science Laboratory and Department of Psychology, The Catholic University of America, Washington, DC and the ^Laboratory of Neurosciences, National Institute on Aging, Bethesda, MD, USA)
Cue-directed shifts of spatial attention were examined for a letter-discrimination task in 15 patients with mild to moderate dementia of the Alzheimer type (DAT) and 15 healthy, age-matched controls. Spatial cues were valid, invalid or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7° to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200 ms and 2000 ms. Reaction time (RT) benefits conferred by valid cues did not differ between the DAT group and the controls. However, RT costs incurred by invalid cues were significantly greater in the DAT group than in the control group. Group differences in RT costs plus benefits occurred at short SOAs (500 ms) for central cues. Reaction time costs plus benefits were correlated with right-left asymmetry in resting levels of cerebral glucose metabolism in the superior parietal lobe for DAT patients but not for controls. The results indicate that focusing of attention to spatial location is intact in early DAT, whereas the disengagement of visuospatial attention is impaired. Automatic attention shifts elicited by peripheral cues reveal abnormalities earlier than attention shifts initiated 'effortfully' by central cues. Intact focusing and impaired disengagement of visuospatial attention may be linked to dysfunction in early DAT of cortico-cortical networks linking the posterior parietal and frontal lobes.
INTRODUCTION
There has been little formal study of attentional functioning in persons with dementia of the Alzheimer type (DAT), despite the recognition that attention deficits may constitute a significant aspect of the cognitive impairment in this disease (Jorm, 1986; Parasuraman and Nestor, 1986, 1991; Broks et al., 1988; Nebes and Brady, 1989). The relative neglect of attention is surprising for at least three reasons. First clinical observations have long pointed, albeit in a general way, to the moderating influence of attention on the neuropsychological test performance of patients with dementia (Lezak, 1983). Secondly, there is an extensive literature indicating that attentional processes are affected by normal adult aging (Craik and Byrd, 1982; Plude and Hoyer, 1985; Salthouse, 1988). Given the overlap in cognitive functioning between normal aging and the very early, mild stages of DAT (Corkin et al., 1984; McKhann et al, 1984; Rubin et al., 1989; Storandtand Hill, 1989), it would be important to know if the effects on attention of aging and dementia differ, and if so, whether quantitatively or qualitatively. Thirdly, many of the neural Correspondence to: Raja Parasuraman, Department of Psychology, The Catholic University of America, Washington, DC 20064, USA.
© Oxford University Press 1992
Downloaded from http://brain.oxfordjournals.org/ by guest on November 11, 2015
SUMMARY
712
R. PARASURAMAN AND OTHERS
Attention and cognition in dementia What role does attention play in DAT? Two general views have been proposed. One sees attention as an intrinsic property of mental operations in general; for example, memory search, retrieval or response selection, and postulates that the efficiency of cognitive operations is dependent upon the efficient allocation of attention to those operations (Nebes et al, 1984; Oberet al., 1985; Hartman, 1991; Nestor
