Hippocampectomy and feature-positive discrimination.

The effects of hippocampal lesions on feature-positive discrimination were investigated using the nictitating membrane response preparation. During training, animals received a simultaneous reinforced compound as the conditioned stimulus (CS+) and a non-reinforced element as the CS-. The compound consisted of a tone and a light, with the tone being more salient than the light. The light and tone served as the CS- in Expts. 1 and 2, respectively. There were no significant differences between hippocampectomized animals and the controls (cortical and sham) when the CS- was the light; however, when the more salient tone stimulus was the CS-, hippocampectomized animals exhibited high levels of responding to both the CS+ and CS- and failed to acquire the discrimination. The results are discussed in terms of attentional and response inhibition theories of hippocampal function.