| Neuroanatomical studies have defined two relatively separate corticohippocampal processing streams that contribute substantially to medial temporal lobe function. Among the cortical regions providing significant input to these processing streams is the retrosplenial cortex (RSP). Outside of an established involvement in spatial navigation, relatively little is known about the role of RSP in learning and memory, although recent converging evidence suggests RSP might play a role in contextual learning and memory. The experiments described in this dissertation were designed to further characterize the involvement of RSP in learning and memory.;A combination of lesion techniques was utilized to examine the role of RSP in contextual fear conditioning. The results indicate that damage to RSP selectively impairs contextual fear conditioning, while leaving cue-specific fear conditioning in intact. Furthermore, this effect was consistent across signaled and unsignaled fear conditioning paradigms, suggesting a general involvement of RSP in contextual processing. Moreover, damage to RSP 28 days after training similarly impaired contextual fear conditioning, indicating a prolonged involvement for RSP in contextual memory. These results were substantiated by elevated expression of the immediate-early gene c-fos following reexposure to the training context and following exposure to novel contexts.;Based on the involvement of RSP in spatial and contextual learning, it was hypothesized that these distinct functions might be subserved by a more fundamental role in processing overlapping, or simultaneously presented stimuli. This notion was supported by evidence that damage to RSP severely impaired a compound feature negative discrimination, a task involving concurrent processing of phasic conditioned stimuli. However, consistent with involvement of RSP in the processing of multiple, but not individual, stimuli, damage to RSP had no effect on appetitive conditioning to a single visual stimulus.;These findings support the view that RSP plays an important role in learning that involves the processing of overlapping or simultaneously presented stimuli. Implications for understanding the functional relationship of the hippocampus and RSP are discussed, as well as the clinical significance of RSP function with respect to Alzheimer's Disease and diencephalic amnesia. |
