Left and right cerebral hemisphere differences in the occurrence of epilepsy.

Differences in function between the cerebral hemispheres are well documented for normal subjects and, in diseased states, these are used to lateralize and localize a dysfunction. However, the difference in frequency of occurrence of left vs. right hemisphere lesions and the greater likelihood of epilepsy occurring on the left have received scant attention. In the present study patients with a diagnosis of meningioma or cerebral abscess were identified from the EEG computer file. After operation the meningioma patients with predominantly left-sided tumours showed a statistically significant greater chance of developing seizures, similarly those with left-sided cerebral abscess. Considering a larger group of patients with temporal lobe epilepsy from a variety of causes, a left-sided EEG focus occurred more frequently - and was statistically significant - than a right-sided or bilateral disturbance. The full explanation of these results is not clear but they suggest that the hemispheres function differently in patients with a cerebral disorder like epilepsy, as is known to be the case in normal subjects.