BRAIN INJURY,
1992, VOL. 6, NO. 6, 509-520
Brain Inj Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Event-related potential measurement of deficits in information processing following moderate to severe closed head injury C.R. CLARK, A.P. O’HANLON, M.J. WRIGHT and G.M. GEFFEN Cognitive Neuroscience Laboratory and Neuropsychology Research Unit, The Flinders University of South Australia &Julia Farr Centre, Adelaide, Australia (Received 10 September 1991; accepted 22 October 1991)
Event-related potentials may offer more precision than behavioural measures for understanding the extent and timing of information processing difficulties that follow closed head injury (CHI). Behavioural tests consistently indicate a general reduction in cognitive function but lack adequate &agnostic or prognostic function. This study compares a group of seven CHI patients, in which time since injury varied between 1 and 5 years following injury, with 10 matched controls on a three-tone discrimination task. Abnormality in the processing of tones as early as 200 ms following their onset, as measured by the P2 and N2 components of the event-related potential, indicated a general dificulty with tone discrimination. This abnormality was obtained despite differing damage profiles over patients and is likely to be due to the ditfuse aspects of damage normal in CHI. These results also indicate that functional deficits in CHI patients can extend up to 5 years or more. A correlation between P2/N2 amplitudes and time since injury, however, suggests that both these components normalize with the passage of time and offers the prospect of a sensitive, non-behavioural measure of recovery in cognitive processing.
Introduction Behavioural studies of the consequences of closed head injury (CHI) commonly report impairments in the processing of information. Impairments have been described in terms of arousal, concentration, problem solving, learning, memory, attention [1-51 and processing speed [l, 6, 71. The generality of processing deficits to such a wide range of function would seem to accord with the relatively non-specific nature of physical damage to the brain following CHI. This damage commonly involves shearing injury to the neural mass in the brain stem, impact injury to the fiontal and temporal poles and some loss of integrity to myelinated structures such as the corpus callosum [2]. Event-related potentials (ERPs) provide scope for understanding the extent and timing of processing difficulties with more precision and offer some insight from scalp topography into their regional origins. T h e work carried out so far using event-related potentials supports this prospect, with reports of abnormally negative N2 and P3 components and of delays in their latencies [8-121. In general terms, these results accord well with behavioural data that indicate impaired cognition. The delays indicate slower stimulus processing [13, Address correspondence to: Dr C.R. Clark, Psychology Discipline, School of Social Sciences, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia 5001. 0269-9052/92 $3.00 0 1992 Taylor & Francis Ltd.
C.R. Clark et al.
Brain Inj Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
510
141 while abnormal negativity in amplitude in these two components is consistent with increased mental effort [15, 161 and reduced capacity for evaluating the significance of stimuli [ 171. The present study set out to address three specific issues. First, whether the P2 as well as the successive N 2 and P3 components are associated with CHI. An attenuated P2 has been reported in a number of other clinical populations (e.g. depressives, alcoholics) in which a general reduction in information processing capacity is symptomatic [18, 191. To date, P2 measurements from CHI patients have not been reported although there is some suggestion of attenuation in the waveforms shown in some of the reports cited above [121. The second issue relates to the functional significance of abnormal N2 reported in CHI patients. In the most recent study [12], an abnormal N2 to the occurrence of rare target tones in a two-tone discrimination task was taken to reflect difficulty with stimulus categorization. It is unclear from t h s study, however, whether the abnormal N2, or the associated functional impairment, is related to the rarity of these tones or to their target significance. In the present study, this matter is addressed by employing a three-tone discrimination task involving the occurrence of both rare target and rare non-target tones. In this way, the capacity of patients with CHI to detect target tones as well as to discriminate rare from common tones is separately assessed. Further, direct comparison between behavioural and electrophysiological measures will be made possible by requiring patients to respond overly to target tones. In the related study by Rugg et al. [12], target response time was measured in a separate four-choice reaction time task. Third, previous event-related potential studies of CHI have tested patients shortly after [9, 111 or at most 2 years [12, 201 following injury, as the behavioural tests used conventionally in clinical neuropsychological assessment seem to indicate little improvement in cogrutive function beyond 2 years. In the present study, time since injury ranged from 1 to 5 years, providing some potential to assess whether deficits could be discerned after longer delays.
Method Subjects Eight male closed head injury patients participated in the study as paid volunteers. All were living in the community. AU had suffered a moderate to severe CHI (post-traumatic amnesia [PTA] 2 13 days) at least 12 months prior to testing and had CT scan evidence of brain damage. PTA was assessed from the hospital file notes of a retrospective clinical interview [21] conducted by the consulting neurosurgeon. Estimates of PTA obtained in this way have recently been shown to correlate positively (Y = 0.77, y
1992, VOL. 6, NO. 6, 509-520
Brain Inj Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
Event-related potential measurement of deficits in information processing following moderate to severe closed head injury C.R. CLARK, A.P. O’HANLON, M.J. WRIGHT and G.M. GEFFEN Cognitive Neuroscience Laboratory and Neuropsychology Research Unit, The Flinders University of South Australia &Julia Farr Centre, Adelaide, Australia (Received 10 September 1991; accepted 22 October 1991)
Event-related potentials may offer more precision than behavioural measures for understanding the extent and timing of information processing difficulties that follow closed head injury (CHI). Behavioural tests consistently indicate a general reduction in cognitive function but lack adequate &agnostic or prognostic function. This study compares a group of seven CHI patients, in which time since injury varied between 1 and 5 years following injury, with 10 matched controls on a three-tone discrimination task. Abnormality in the processing of tones as early as 200 ms following their onset, as measured by the P2 and N2 components of the event-related potential, indicated a general dificulty with tone discrimination. This abnormality was obtained despite differing damage profiles over patients and is likely to be due to the ditfuse aspects of damage normal in CHI. These results also indicate that functional deficits in CHI patients can extend up to 5 years or more. A correlation between P2/N2 amplitudes and time since injury, however, suggests that both these components normalize with the passage of time and offers the prospect of a sensitive, non-behavioural measure of recovery in cognitive processing.
Introduction Behavioural studies of the consequences of closed head injury (CHI) commonly report impairments in the processing of information. Impairments have been described in terms of arousal, concentration, problem solving, learning, memory, attention [1-51 and processing speed [l, 6, 71. The generality of processing deficits to such a wide range of function would seem to accord with the relatively non-specific nature of physical damage to the brain following CHI. This damage commonly involves shearing injury to the neural mass in the brain stem, impact injury to the fiontal and temporal poles and some loss of integrity to myelinated structures such as the corpus callosum [2]. Event-related potentials (ERPs) provide scope for understanding the extent and timing of processing difficulties with more precision and offer some insight from scalp topography into their regional origins. T h e work carried out so far using event-related potentials supports this prospect, with reports of abnormally negative N2 and P3 components and of delays in their latencies [8-121. In general terms, these results accord well with behavioural data that indicate impaired cognition. The delays indicate slower stimulus processing [13, Address correspondence to: Dr C.R. Clark, Psychology Discipline, School of Social Sciences, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia 5001. 0269-9052/92 $3.00 0 1992 Taylor & Francis Ltd.
C.R. Clark et al.
Brain Inj Downloaded from informahealthcare.com by Chulalongkorn University on 12/31/14 For personal use only.
510
141 while abnormal negativity in amplitude in these two components is consistent with increased mental effort [15, 161 and reduced capacity for evaluating the significance of stimuli [ 171. The present study set out to address three specific issues. First, whether the P2 as well as the successive N 2 and P3 components are associated with CHI. An attenuated P2 has been reported in a number of other clinical populations (e.g. depressives, alcoholics) in which a general reduction in information processing capacity is symptomatic [18, 191. To date, P2 measurements from CHI patients have not been reported although there is some suggestion of attenuation in the waveforms shown in some of the reports cited above [121. The second issue relates to the functional significance of abnormal N2 reported in CHI patients. In the most recent study [12], an abnormal N2 to the occurrence of rare target tones in a two-tone discrimination task was taken to reflect difficulty with stimulus categorization. It is unclear from t h s study, however, whether the abnormal N2, or the associated functional impairment, is related to the rarity of these tones or to their target significance. In the present study, this matter is addressed by employing a three-tone discrimination task involving the occurrence of both rare target and rare non-target tones. In this way, the capacity of patients with CHI to detect target tones as well as to discriminate rare from common tones is separately assessed. Further, direct comparison between behavioural and electrophysiological measures will be made possible by requiring patients to respond overly to target tones. In the related study by Rugg et al. [12], target response time was measured in a separate four-choice reaction time task. Third, previous event-related potential studies of CHI have tested patients shortly after [9, 111 or at most 2 years [12, 201 following injury, as the behavioural tests used conventionally in clinical neuropsychological assessment seem to indicate little improvement in cogrutive function beyond 2 years. In the present study, time since injury ranged from 1 to 5 years, providing some potential to assess whether deficits could be discerned after longer delays.
Method Subjects Eight male closed head injury patients participated in the study as paid volunteers. All were living in the community. AU had suffered a moderate to severe CHI (post-traumatic amnesia [PTA] 2 13 days) at least 12 months prior to testing and had CT scan evidence of brain damage. PTA was assessed from the hospital file notes of a retrospective clinical interview [21] conducted by the consulting neurosurgeon. Estimates of PTA obtained in this way have recently been shown to correlate positively (Y = 0.77, y
