[Role of the midbrain central gray substance in the performance of a conditioned reflex]

The conditional placing reflex was studied in chronic experiments on cats. Neuronal activity of the midbrain periaqueductal grey matter was recorded under conditions of extinction, differentiation and conditional inhibition. Neuronal reactions preceded the conditioned and voluntary movements by 400-800 ms and lasted for 1-2 s in 69 units from total numbers 182 (36.7%). This reactions appeared 200 ms earlier than corresponding neuronal reactions of the motor cortex. 58 neurons (30.9%) were excited by auditory stimuli with latencies 10-50 ms for 2-6 s. 19 neurons (10.1%) were activated by auditory stimuli and conditioned movement. Responses to isolated auditory stimulation were absent in 42 neurons (22.3%), but some of the neurons showed long-lasting (minutes) changes of the background activity under repeated conditioned stimulation. The extinction, differentiation and conditioned inhibition caused specific changes in activity of different neuronal groups. A conclusion is made that the periaqueductal grey matter participated in reflex performance as well as in its inhibition. The functional independence of the first and second neuronal groups in extinction and restoration of conditional reflex is shown.