Post-tetanic changes in background gamma oscillations in interhemisphere interactions

Experiments conducted on the motor cortex of anesthetized rats were performed to study the effects of high-frequency microstimulation of one of the hemispheres on oscillation parameters in neuronal networks containing callosal cells. Before tetanization, there were three modes in the distribution of gamma oscillation periods, corresponding to frequencies of 40-60, 70-100, and 100-200 Hz. In cells active in pre-tetanization background conditions, the three modes were retained after tetanization; there was a relative increase in the number of oscillatory interactions in that part of the gamma range (40-60 Hz) which dominated before tetanization. The distribution of oscillation periods in neurons which became active in background conditions after tetanization contained the same three modes. Tetanization resulted in a relative decrease in the number of oscillatory interactions and the number of neuron pairs in which additional synchronization occurred, along with a reduction in the extent of oscillations, which is evidence of reduced synchronization. Existing modeling data taken together with the present results led to the suggestion that these post-tetanization changes were based on a modification of the efficiency of excitatory and inhibitory inputs to neurons in both hemispheres.