Low frequency damped oscillations of cat visual cortical neurones

A synchronizing volley of excitation was delivered to cells from the primar y visual cortex of the anaesthetized cat by an electrical pulse stimulation of the optic radiations. In intracellular records, this resulted in an ini tial, fast depolarization of the membrane potential followed by a longer la sting (266 ms) hyperpolarization, and then to small amplitude damped oscill ations of the membrane potential. In different cells the number of peaks ra nged from 3 to 6, and the amplitude of the first oscillation averaged 3.5 m V. If the pulse stimulation was repeated during visual drive with an optima l bar stimulus, the membrane potential fluctuations were non-linearly enhan ced with spike bursts recorded during the depolarized states of the membran e 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 th e excitatory drive to the recorded neurone. NeuroReport 11:1243-1247 (C) 20 00 Lippincott Williams & Wilkins.