NEUROPSYCHOLOGICAL AND COGNITIVE STUDIES IN EPILEPSY

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We have been performing imaging studies of language organization in normal controls and patients with epilepsy. Using PET, activation of cerebral blood flow (CBF) associated with word and object recognition, auditory comprehension, and phoneme, word, and sentence production are localized in the brain. Investigations are being conducted on classical conditioning and implicit and explicit memory performance. Data from subdural stimulation, PET, and MRI are integrated using digital image processing techniques. The combined stimulation and PET data allow us to study the relation between activation and disruption of cognitive activity, and to form more accurate concepts of the organization of cerebral function. These studies will elucidate the function of regions such as the basal temporal language area, which are of clinical importance when surgery for uncontrolled seizures is planned. Digital signal processing techniques are used to confirm anatomic localization of functional mapping. Using surface fitting algorithms, PET, CT, MRI, and subdural electrode positons are aligned. In PET experiments, rest conditions are averaged and subtracted from activated conditions, in order to reveal regions of increased blood flow during task performance. Extensive speech deficits following inferior frontal gyrus (IFG) lesions have been explained by IFG involvement in either oromotor sequence planning, or syntactical and semantic processing. We recorded CBF in 6 normal volunteers using PET. Each performed 2 resting tasks and 4 speech tasks All tasks led to increased CBF in orofacial primary cortex, including the supplementary speech area. But left IFG was active only when a prose passage was read. This suggests IFG plays a role in language processing, as well as planning oromotor sequences. We found that verbal and performance intelligence scores did not differ between patients with left and right temporal foci. Interictal discharges did not affect neuropsychological test scores. However, Boston Naming test scores, indicative of language function, were significantly lower in patients with left temporal seizure onset. These scores were not significantly lower after left temporal lobectomy.