Background: The schizophrenia-like psychoses of epilepsy (SLPE) might represent a secondary form of schizophrenia in which the pathology is relatively confined to the temporal lobe. To test this possibility we have compared the neuropsychological profile of schizophrenia and SLPE. Our main hypothesis was that both psychotic groups would show deficits of temporal lobe function but that prefrontal impairment, as measured by tests of executive function, would be found only in the primary schi ophrenic group.
Methods: Four groups were studied: (1) patients with SLPE (N = 25); (2) patients with epilepsy but not psychiatric history (N = 24); (3) patients with schizophrenia (N = 22); and (4) healthy volunteers (N = 24). Neuropsychological testing comprised measures of pre-morbid IQ, current verbal and performance IQ, information processing, digit span, motor speed, verbal and visual learning and memory, verbal fluency, the Wisconsin Card Sorting Task, the Stroop test and the trail making task.
Results: Patients with schizophrenia and those with SLPE had almost identical neuropsychological profiles, with impairments of attention, episodic memory (verbal > visual) and executive function. The epileptic controls showed similar though less severe impairments of memory and of some tests of executive function.
Conclusions: Our results do not support the hypothesis that the pathophysiology of SLPE and schizophrenia are distinct. While our findings suggest an important role for dominant temporal lobe abnormality in schizophrenia, both in its primary form and in that occurring in patients with epilepsy, they also implicate generalized cognitive impairment, manifest in particular as attentional deficits, in both forms of the disorder.