The authors sought to determine whether errors of action committed by patients with closed head injury (CHI) would conform to predictions derived from frontal lobe theories. In Study 1, 30 CHI patients and 18 normal controls performed routine activities, such as wrapping a present, under conditions of graded complexity. CHI patients committed more errors even on the simplest condition; but, except for a higher proportion of omitted actions, their error profile was very similar to that of controls. Study 2 involved a subset of patients whose performance in Study 1 was within normal limits. When these high functioning patients were asked to perform the routine tasks under still more taxing conditions, they, too, committed errors in excess of the control group. Accounts based on frontal mechanisms have a difficult time explaining the overall pattern of findings. An alternative based on limited-capacity resources is suggested.

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The underlying mechanisms for impaired output on letter (F, A, and S) and category (e.g., animal) word list generation (WLG) tasks in subcortical ischemic vascular dementia (IVD) were investigated. Normal control (NC) and Alzheimer's disease (AD) participants were also studied. IVD and NC participants performed better on category than letter WLG tasks, whereas the opposite was observed among AD participants. IVD participants produced fewer responses than AD participants on letter WLG tasks, but there was no difference between AD and IVD participants on the "animal" WLG task. AD participants scored lower than IVD and NC participants on animal WLG indexes measuring semantic knowledge. There were few differences between IVD and NC participants. The reduced output on the animal WLG task for IVD participants is consistent with search-retrieval deficits. The reduced output of AD participants may be caused by degraded semantic knowledge.

Perseverative behavior has not been extensively studied in patients with dementia. In this study, perseverative behavior was elicited with the dementia version of the Graphical Sequence Test. A control group and participants with Alzheimer's disease (AD) and subcortical ischemic vascular dementia (IVD) were studied. A factor analysis revealed a 3-factor model consisting of perseverations related to semantic knowledge, motor functioning, and a third, intermediary factor. IVD participants made more total perseverations than did AD participants. Perseverations made by AD participants were correlated with deficits on tests of semantic knowledge, whereas the perseverations made by IVD participants were correlated with motor and frontal systems tests. Results are consistent with the view that perseverative behavior is hierarchically arranged in terms of specific levels of cognitive complexity and the overall pattern of cognitive deficits associated with each type of dementia.

We report the case of a 67-year-old woman who experienced a sudden onset of psychotic illness (i.e., prominent delusions and hallucinations) that has endured for approximately 3 years. As part of her neurobehavioral work-up, a SPECT scan revealed right frontal and left anterior temporal-lobe hypoperfusion. Serial neuropsychological evaluations obtained 2 years apart demonstrated a steady decline on tests of executive control (monitoring, allocation of attention, perseveration) and visuospatial abilities, whereas performance in other areas of cognitive functioning have remained steady and in the normal range for the patient's age. Over this same period of time, serial EEG, MRI, and neurology examinations have been within normal limits. Thus, there was little evidence with which to diagnose dementia. It is suggested that concomitant impairment in executive control, coupled with a degraded capacity to process perceptual information, can give rise to enduring psychotic behavior.

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We report a subject who, subsequent to closed head injury, demonstrated a severe left hand ideational apraxia and apraxic agraphia, consistent with callosal disconnection syndrome. In contrast to the left hand, performance of the right hand was unimpaired on traditional tests of gesture to command, sight of object, and with actual object use, but proved deficient on tests of spatial and constructional ability. We examined the consequences of these hand-specific deficits for the performance of naturalistic action tasks. The patient made errors with each hand; however, the right hand performed more poorly than the left hand. In addition, the types of errors made by each hand differed in a manner consistent with the results of neuropsychological testing and indicative of disconnection phenomena. We suggest that unlike gesture, naturalistic action requires the contribution of the specialized abilities of each hemisphere, integrated across callosal structures. Traditional testing of gesture may underestimate the right hemisphere's capacity for action programming.