Behavioral impairment in the monkey following implantation of aluminum hydroxide on the temporal cortex: The role of cortical destruction

A further attempt has been made to determine whether defective visual discrimination performance in monkeys with discharging epileptic lesions is more strongly associated with the frequency of paroxysmal discharges in the EEG or with the presence of bilateral cortical damage. Performance was assessed on four visual tasks, two given preoperatively and postoperatively, two given only postoperatively. Animals either remained unoperated; or received unilateral ablations of inferotemporal cortex; or had an epileptogenic chemical agent implanted unilaterally on this cortex; or had the same chemical agent implanted bilaterally on their cortex; or had implanted bilaterally the caps which in other animals contained the chemical but which in these animals remained empty. The EEG recordings were taken systematically (at weekly intervals during postoperative training). The majority of animals with unilateral epileptogenic implants gave evidence of paroxysmal discharges in the secondary hemisphere. Nonetheless, the frequency of such secondary discharges was lower than the frequency of discharges recorded from the corresponding hemisphere of animals with bilateral implants. The animals with unilateral implants were only slightly, if at all, impaired on behavioral tests, whereas the animals with bilateral implants were more severely impaired. Correlations between behavioral impairment and the frequency of abnormal EEG discharges indicated a nonsignificant (but weak) association. It was concluded that the greater behavioral impairment of the animals with bilateral implants was predominantly a consequence of their bilateral tissue destruction rather than of their more frequent paroxysmal discharges.