Electrical activation of visual pathways substitutes for tonic light input in triggering EEG correlates of food reward during conditioned behavior in cats.

Cats trained to press a lever for 1 cc of milk reward normally show during the consummatory response high voltage 6--8 c/sec EEG synchronization associated with epicortical positive steady potential shift over the primary and secondary visual projections. The emergence of this postreinforcement synchronization (PRS) and Reward Contingent Positive Variation (RCPV) is known to depend upon appropriate gustatory input and presence of ambient light, although visual perception of reward and/or environment is not essential as shown in cats wearing translucent "milky" contact lenses. Training the animals in a paradigm in which a "light-off" cue signaled the availability of reward, and thus assigned positively reinforcing quality to the dark condition, also failed to restore the PRS-RCPV phenomenon in the absence of light. However, brief electrical stimuli applied to either the optic tract or the lateral geniculate nucleus substituted for unpatterned light input and fully restored the PRS-RCPV in the dark. The suprathreshold stimuli were effective only during the consummatory response. Maximum effect could be produced during a brief time period between 0.8 and 1.5 sec after the onset of consummatory response as judged by lapping activity, thus showing the specificity of the effect of visual input. Even during a relaxed wakefulness after satiation or during slow wave sleep or REM sleep the same electric stimuli were ineffective although they produced well-developed evoked potentials with all characteristic wave components. The results indicate that brain pathways utilize unpatterned i.e. noisy visual input in complex integrative processes involving gustatory input.