CORTICAL RESPONSE TO STIMULATION OF LATERAL GENICULATE BODY AND THE POTENTIATION THEREOF BY CONTINUOUS ILLUMINATION OF RETINA

Abstract

Cortical response to stimulation of the lateral geniculate body of cat is similar in pattern to the cortical response to optic nerve stimulation. Cortical response to geniculate stimulation can be greatly potentiated by continuous illumination of retina with light. The effect of photic potentiation develops progressive-ly to a max. in about 5 sec. and remains at that level as long as the illumination is continued. Both at the onset and at the cessation of illumination there appears an immediate de-pression accompanied by a concomitant periodic variation of excitability lasting for about 1 sec. During continuous retinal illumination spontaneous electrical waves of the cortex are suppressed, which is interpreted as a result of postexcitatory depression caused by the intense discharge of cortical neurons. The site where the potentiation mechanism takes place is demonstrated to be in the lateral geniculate body. In addition to the changes in cortical excitability caused by the sudden change of photic stimulation, the spontaneous periodic variation of brain excitability in general is also described as a factor affecting the efficiency of cortical activity.