Cortical and subcortical responses to flicker in cats

Abstract

Gross potential responses to 400-msec flicker trains (7.5–100 Hz) were measured from lateral geniculate body, optic radiation, optic tract, and cortex in adult anesthetized cats. A typical response sequence consisted of an “on” response, followed by about 100 msec of little or no activity (entrainment latency), and then frequency-specific (entrained) responses. Latency to entrainment reflects recovery from rapid adaptation to the first few stimuli in a flicker train. The subcortical entrained response had fast rise and decay times and exhibited response “doubling” at low frequencies and oscillatory potentials after the stimulus was terminated. The cortical entrained response had slower rise and decay times and was not easily distinguishable from base line. It was also highly sensitive to barbiturate anesthetic levels. At low frequencies and intensities, and under light anesthesia, cortical responses also exhibited response doubling. Quantitative analysis of the data revealed better frequency following for depth structures than for cortex. Entrained response amplitude was attenuated at high frequencies in cortex and subcortex.