Effect of lesion of the lateral geniculate body on the EEGs and photically evoked potentials in the cerebral visual, somatosensory and association areas of unanesthetized cat.

Visually evoked potentials and background EEGs in the cerebral visual, somatosensory, and association areas (lateral suprasylvian gyrus), as well as in the lateral geniculate body (GL) and mesencephalic reticular formation were studied before and after unilateral destruction of the GL of unanes-thetized cat. Autocorrelograms and power spectra of background EEGs in various areas mainly showed activities of less than 5 c/s. Unilateral GL destruction caused considerable depression of the ipsilateral EEG activities and mild depression in the contralateral EEGs in most regions except the somatosensory area, where some augmentation was observed. Unilateral putamen destruction resulted in augmented EEG activities in various areas. GL activity seemed to augment EEG activities in the cerebral visual and association areas, while it seemed to depress the activity in the somato-sensory area. Summation average of evoked potentials in the association area likewise manifested quite similar diphasic deflections within 130 msec after flashing light stimulus. The initial positive deflection P1 led bipolarily in the medial visual association area was found to be longer in duration than in the medial visual area. Peak latencies of the second positive-negative deflection (P2N2) and third positive deflection P3 in the association area were about 10 msec longer than those in the visual area and this was proven to be statistically significant. Amplitudes of the initial and second diphasic deflections in the medial visual area were higher than those in the posterior visual and medial association areas, whereas amplitudes of the third and fourth deflections in the medial visual area were lower than those in the association area. Almost complete destruction of the GL resulted in disappearance of the initial and succeeding diphasic deflections, and there remained a slow negative wave with a crest at about 70 msec after the flashing stimulus which presumably had been masked by the above deflections prior to GL * • Î –ì • @ " O destruction. After partial destruction of the GL, the initial and succeeding deflections were sustained, but prolonged in their peak latencies and decreased in their amplitudes. It was suggested, therefore, that the association area (medial lateral suprasylvian gyrus) may have intimate interaction with the lateral geniculate body, and that the slow negative wave following the initial positive deflection may have been brought out through the indirect nonspecific projection system.