[Significance of theta-rhythm phases for excitatory transmission in the cerebral cortex]

The dependence of the number of motor reactions on the phase of theta-rhythm in the cerebral cortex, during which photic stimuli were presented was studied on unanaesthetized rabbits. Single flashes were presented to animals with 1--15 min intervals when theta-rhythm was dominant in the visual cortex. Each experimental session included 10--45 photic stimuli. It was found that the probability of rabbit's motor reaction to a photic stimulus depends on the phase of the theta-rhythm with which it coincides. The onset of a motor reaction to light in the majority of cases coincided with the positive phase of the theta-rhythm, which seems to be an optimal condition for the transmission of excitation in the cortex. The number of movements in response to light increases when the amplitude of the positive theta-rhythm oscillation is greater than the negative one. Recurrent inhibition in neural systems of the cerebral cortex seems to limit irradiation of excitation in case of big theta-rhythm amplitudes.