Excitotoxic perirhinal cortex lesions leave stimulus-specific habituation of suppression to lights intact.

Previous experiments demonstrate a normal decline in unconditioned responding in rats with perirhinal cortex lesions but attenuated performance on spontaneous object recognition (SOR), a finding supporting the assertion that distinct systems support these phenomena. This finding informs on the nature of these two fundamental forms of learning and may be taken as support for certain contemporary theories of memory. However, we cannot quantify the relative contributions of genuine habituation and alternative, trivial sources in response decline from effector fatigue and sensory adaptation in these demonstrations. An important implication of this problem is that previous reports may have missed perirhinal-dependent habituation. We report perirhinal cortex lesions to be without effect in rats' habituation of suppression to lights when any influence of effector fatigue and sensory adaptation is eliminated. Theoretical implications of this finding are discussed.