TYPE OF RESPONSE TO STEADY ILLUMINATION AND LEVEL OF NEURONAL DARK DISCHARGE IN CENTRAL VISUAL PATHWAYS

1. (1) In anesthetized (Nembutal) and unanesthetized pretrigeminal cats the possibility of predicting the direction of the change in frequency of the maintained discharge in response to steady, diffuse illumination was investigated in geniculocortical (G.C.) and corticofugal (C.F.) fibers. 2. (2) In a selected population, it was found that the direction of the change in frequency during illumination was conditioned by the level of the discharge during the immediately preceding dark adaptation period. 3. (3) When the whole population of G.C. and C.F. fibers was considered, the direction of the change in frequency of the maintained discharge was found to be conditioned entirely by the level of the discharge during the preceding dark adaptation period only when the mean frequency of the discharge in the dark immediatel preceding the illumination was higher than the mean frequency of the discharge calculated over all the dark periods of that particular fiber. In the opposite case, the relationship was present only in 50% of the trials. 4. (4) The occurrence of a statistical correlation between the levels of the maintained neuronal activities in dark and light adaptation and the possibility of expressing the prediction in numerical form are discussed. © 1969.