Contribution of the retrosplenial cortex to temporal discrimination learning

Abstract

The retrosplenial cortex (RSC) has an important role in contextual learning and memory. While the majority of experiments have focused on the physical context, the present study asked whether the RSC is involved in processing the temporal context. Rats were trained in a temporal discrimination procedure where the duration of the intertrial interval (ITI) signaled whether or not the next tone conditioned stimulus would be paired with food pellet reinforcement. When the tone was presented after a 16-min ITI it was reinforced, but when it was presented after a 4-min ITI it was not. Rats demonstrated successful discrimination in this procedure by responding more to the tone on reinforced trials than on non-reinforced trials. Pre-training electrolytic lesions of the RSC attenuated acquisition of the temporal discrimination. The results are the first to demonstrate a role for the RSC in processing temporal information and in turn extend the role of the RSC beyond the physical context to now include the temporal context.

Keywords: episodic memory; retrosplenial; temporal context.

Figure 1

(a) Photomicrograph of a representative RSC lesion at 3.0 mm posterior to bregma. The dotted line indicates the boundaries of RSC. (b) Schematic diagram indicating the rostro-caudal extent and the largest (gray) and smallest (black) lesions of RSC. Abbreviations: RSC, retrosplenial cortex; M2, secondary motor cortex; V2, secondary visual cortex; fmj, forceps major corpus callosum. Figure 1b is adapted from The Rat Brain in Stereotaxic Coordiantes (6^th edition), G. Paxinos and C. Watson, 2007. Copyright 2007, with permission from Elsevier.

Figure 2

Responding during the tone over 20 sessions for controls (upper panel) and RSC lesions (lower panel). R = reinforced (following 16 m ITI), N = nonreinforced (following 4 m ITI). Dashed vertical line indicates first vs. second half of training. Data are mean ± standard error.