Memory encoding in the primate brain: The role of the basal forebrain
The neural structures underlying the encoding of memories have long been a subject of investigation. Studies in human patients in the mid-1950s indicated that damage to structures in the medial temporal lobe resulted in a severe memory impairment that did not aﬀect other cognitive abilities. The early focus of investigation in these patients was the hippocampus, but more recent work has suggested that the role of the hippocampus is limited primarily to the encoding of episodic memories. Further patient groups, with damage to other structures of the brain but with similar severe amnesia, can help shed light on the structures that interact to allow encoding of memories. These investigations have given rise to several diﬀerent explanations about the cause of severe anterograde amnesia in humans. Similarly, lesion studies in animals have shown that there are multiple memory systems in the brain, underlying diﬀerent aspects of memory, and consensus is not yet reached over the relative importance of either structures or systems. In this chapter, we review the literature and then our recent work, which suggests that none of the brain areas that store the elements of memories are able to encode information without modulation of their activity by the cholinergic cells of the basal forebrain.