| The rhinal cortices constitute the major input-output path for hippocampo-neocortical dialogue. Substantial evidence suggests that this network is intricately involved in encoding and consolidating declarative memory, defined as knowledge of facts and events. Interestingly, emotional arousal has been reported to facilitate the consolidation of declarative memory and pharmacological data implicates the basolateral complex of the amygdala (BLA) in this effect. In fact, post-training treatments that presumably increase BLA activity can similarly facilitate learning. Conversely, disrupting BLA activity immediately after training, using lesions or infusions of inhibitory drugs, was shown to reduce performance on declarative memory tasks. Since the amygdala is heavily interconnected with the rhinal cortices, it is possible that the amygdala facilitates memory by affecting spike transfer across the rhinal cortices. However, the way in which BLA neurons influence rhinal targets has not been systematically studied. Thus, this thesis investigated the relations between the amygdala and the rhinal cortices using multiple simultaneous electrophysiological recordings of evoked and spontaneous neuronal activity in unanesthetized and anesthetized cats. Using these methods, it was discovered that even though axons from the lateral nucleus of the amygdala must travel variable distances to reach different rostrocaudal levels of the perirhinal cortex, their conduction time was uniform irrespective of distance to target. These results suggest that the lateral amygdala can produce synchronous time-windows of depolarization throughout the entire rostro-caudal extent of the perirhinal cortex. A second series of experiments demonstrated little correlated activity between the different structures of the rhinal cortices. Therefore, the rhinal cortices appear to limit the transfer of synaptic responses between the neocortex and hippocampus. Interestingly, a third series of experiments showed that electrical stimulation of the lateral amygdala enhanced the firing probability of perirhinal neurons to neocortical shocks. However, in spite of this increase in transfer probability from the neocortex to the perirhinal cortex, lateral amygdala stimulation had no effect on entorhinal responsiveness to neocortical impulses. Ongoing experiments suggest that BLA firing can enhance correlated activity between perirhinal and entorhinal units. Therefore, an amygdala-mediated increase in transmission probability between the neocortex and hippocampus is a possible candidate mechanism for the facilitation of declarative memory observed following emotional arousal. |
