PLACE-DEPENDENT DISCRIMINATION OF TRACE INTERVAL IN CLASSICAL EYEBLINK CONDITIONING

S. Kawahara^1,2*; M. Tatsuno^3,4; J.A. Dees³; K.M. Bohne³; E.R. Lindstedt³; F.P. Houston³; B.L. McNaughton^2,3

1. Lab Neurobiophysics, Univ Tokyo, Tokyo, Japan
2. JST CREST, Kawaguchi, Japan
3. NSMA, Univ Arizona, Tucson, AZ, USA
4. Lab Math Neurosci, RIKEN BSI, Wako, Japan

An intact hippocampus is necessary for classical conditioning when an interval is present between the tone CS and US ("trace conditioning"). In addition to its selectivity for spatial position (within a given behavioral context at least), several lines of evidence suggest that hippocampal information processing is modulated during eyeblink conditioning and that it generates a predictive neural response. In this experiment, we addressed the question of whether rats can use spatial location as a contextual cue in order to acquire two different trace intervals involving the same CS-US pairs. Rats were first trained to shuttle on a circular platform and then received CS-US pairs at 50% probability, with different trace intervals (250 ms or 500 ms) at different specific regions. When the start point of the CS was fixed, the rat showed the conditioned response (CR) with an apparent adaptive timing. But the rat also blinked without the tone CS, when it passed the place where the US delivery was anticipated. After a few days of conditioning, the rat began to show the CR only after the tone CS. Another rat, to which the CS was delivered at a random place within a particular region, acquired the CRs with an adaptive timing to each trace interval. In this case, the rat first acquired the CRs with no difference in the timing of the CR between the two paradigms. After several days of conditioning, the rat acquired adaptive timing to each trace interval. These results suggested that, in the random-place CS presentation conditioning, the rat learned successfully the contextual discrimination of the trace interval. In the fixed-place task, it appears that the rat first learned a spatial response and later learned to modulate that response using the CS as a contextual cue.

Support Contributed By: JST CREST & MH01565

hippocampus, cerebellum, context, motor learning