Effects of Repetition and Dark Adaptation on Visual Evoked Responses in the Rat

Rats chronically implanted with monopolar electrodes in the primary visual cortex were used to evaluate progressive changes occurring in the amplitude of visual evoked responses to repeated visual stimuli. It was found that if the rats were dark-adapted prior to testing, no consistent changes occurred in the early components of the evoked response. Without sufficient dark-adaptation, however, progressive increases in these components were observed. Contrary to these changes, the later evoked response components exhibited reliable changes over trial blocks, regardless of whether prior dark adaptation was given. It was concluded that these latercomponent changes are best explained as correlates of central nervous system habituation. These data may be taken into account in hyperbaric experiments in which the averaged evoked response is used as a measure of neural functioning, thus often alleviating the need for certain costly control conditions. Also, they may provide an additional tool for research programs interested in assessing the effects of hyperbaric environments on simple neurobehavioral processes.