Averaged sensory evoked potentials were recorded from the outer molecular layer of the dentate gyrus (OM AEP) in freely moving rats trained to criterion performance in a two-tone differential discrimination paradigm. OM AEPs showed consistent fluctuations in amplitude based on the acquired significance of the tones through their association with reward (CS+) or non-reward (CS-). However, the relationship between tone significance and OM AEP configuration was dependent upon the sequence of trials preceding the evoked potential, irrespective of whether the potential was evoked by a CS+ or CS-. Specifically, when the preceding sequence contained an increased number of CS- trials, the amplitude of the initial negative component (N1) of the OM AEP was increased, while that of the slower (N2) component was reduced; conversely, when the preceding sequence contained an increased number of CS+ trials, the amplitude of N1 was reduced, while that of N2 was increased. The results suggest that the transmission of sensory information into the dentate gyrus is biased by prior experience.
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