Cortical representation of conditioned eye blink in the rabbit studied by a functional ablation technique

Abstract

Conditioned eye blink was established in rabbits by reinforcing visual or auditory conditioned stimulus (CS) (400 msec) with corneal air puffs (UCS). After 90% correct responses had been attained, single waves of cortical spreading depression (CSD) were elicited by microinjection of 25% KCl into the frontal or occipital cortex and the slow potential change (SPC) was recorded with implanted Ag AgCl electrodes. Frontal injection into the hemicortex contralateral to the blinking eye suppressed the conditioned eye blink as soon as the negative SPC invaded the motor cortex. Recovery started 4 min later and was completed after 18 or 23 min when using auditory or visual CS respectively. Occipital injection of KCl caused a deep but incomplete suppression of the visually conditioned eye blink and a much weaker impairment of the auditory CS. Complete blockade of the conditioned eye blink developed when CSD reached the frontal cortex. CSD in the ipsilateral hemisphere had similar but less pronounced effects. It is concluded that the cortical projection of the CS is important but not indispensable for the performance of the conditioned eye blink.