Low frequency damped oscillations of cat visual cortical neurones

A synchronizing volley of excitation was delivered to cells from the primary visual cortex of the anaesthetized cat by an electrical pulse stimulation of the optic radiations. In intracellular records, this resulted in an initial, fast depolarization of the membrane potential followed by a longer lasting (266 ms) hyperpolarization, and then to small amplitude damped oscillations of the membrane potential. In different cells the number of peaks ranged from 3 to 6, and the amplitude of the first oscillation averaged 3.5 mV. If the pulse stimulation was repeated during visual drive with an optimal bar stimulus, the membrane potential fluctuations were non-linearly enhanced with spike bursts recorded during the depolarized states of the membrane potential. The amplitude of the first oscillation in these cases averaged 6.9 mV. The mean frequency of damped oscillations was 9.9 Hz. The results suggest that these oscillations are mediated by the waxing and waning of the excitatory drive to the recorded neurone.