Hippocampal lesions prevent trace eyeblink conditioning in the freely moving rat

The effect of hippocampal aspiration lesions on trace eyeblink conditioning was examined in young, freely-moving Fl hybrid rats (Fisher 344 x Brown No rway). Rats which received either bilateral neocortical or bilateral hippoc ampal aspiration lesions were compared with each other or with sham lesione d control rats. The rats were trained with a 250 ms tone conditioning stimu lus (CS), a 250 ms stimulus free trace interval and a 100 ms corneal airpuf f unconditioned stimulus (US). Rats with lesions of the hippocampus were si gnificantly impaired relative to the neocortical and sham lesioned control rats. Analyses of different behavioral parameters (e.g. percent conditioned responses, amplitude, and area of response) indicated that all of the meas ures for the conditioned response were significantly impaired by the hippoc ampal lesion. The unconditioned response was not significantly affected by the lesion, and there was no significant difference among the groups after 2 days of subsequent conditioning with the delay paradigm (zero trace inter val). We conclude that the hippocampus is required for rats to learn the as sociation between a tone CS and an airpuff US when a 250 ms trace interval is interposed between the two stimuli. (C) 1999 Elsevier Science B.V. All r ights reserved.