Academic journal article Canadian Journal of Experimental Psychology

Growth Points in Research on Memory and Hippocampus

Academic journal article Canadian Journal of Experimental Psychology

Growth Points in Research on Memory and Hippocampus

Article excerpt

Abstract

We present an overview of two of our ongoing projects relating processes in the hippocampus to memory. We are trying to understand why retrograde amnesia occurs after damage to the hippocampus. Our experiments establish the generality of several new retrograde amnesia phenomena that are at odds with the consensus view of the role of the hippocampus in memory. We show in many memory tasks that complete damage to the hippocampus produces retrograde amnesia that is equivalent for recent and remote memories. Retrograde amnesia affects a much wider range of memory tasks than anterograde amnesia. Normal hippocampal processes can interfere with retention of a long-term memory stored outside the hippocampus. We conclude that the hippocampus competes with nonhippocampal systems during memory encoding and retrieval. Finally, we outline a project to understand and manipulate adult hippocampal neurogenesis in order to repair damaged hippocampal circuitry to recover lost cognitive functions.

For the past five years, since the opening of our new research building, the Canadian Centre for Behavioural Neuroscience at the University of Lethbridge, much of the research in our laboratory has focused on an uncomfortably wide range of topics. Thankfully all of them are related in that they connect processes in the hippocampus to memory. For a behavioural or cognitive neuroscientist, say, the first author here, entering the field in the 1980s, progress on understanding the hippocampus is astounding. In the properties of this "three-layered" region of cerebral cortex, we have seen the rapid development of information at all levels of description, from gene and protein to synaptic and computational processes to long-term memory, all of it with a unique and impressive degree of consilience. Here we limit ourselves to two themes: Why does damage to the hippocampus cause retrograde amnesia? and, What is the function of adult neurogenesis in the hippocampus? It is the intention of this paper to outline some of the main issues and questions addressed by work in our laboratory and to describe the current relevant state of conceptual and empirical progress. We apologize that it is not our plan to comprehensively review the contemporary literature, but only to introduce the issues that are centrally important to our work.

In 1957, Scoville and Milner reported that bilateral damage to the hippocampus causes memory loss for recently, but not remotely, acquired information. This phenomenon is termed temporally graded (or temporally limited) retrograde amnesia. Not all types of memories are equally affected following hippocampal damage. Temporally graded amnesia has been reported in humans for memories for personal episodes and public information (Corkin, 1984; Rempel-Clower, Zola, Squire, & Amaral, 1996). In nonhuman animals, temporally graded retrograde amnesia following hippocampal damage has been found in several memory tasks, including object discrimination (Zola-Morgan & Squire, 1990), contextual fear conditioning (Anagnostaras, Maren, & Fanselow, 1999; Kirn & Fanselow, 1992), and socially transmitted food preference (Clark, Broadbent, Zola, & Squire, 2002; Winocur, McDonald, & Moscovitch, 2001). For example, in a cleverly designed study, Anagnostaras and colleagues (1999) conditioned rats to fear two different contexts prior to damaging the dorsal region of the hippocampus. Importantly, conditioning in one context occurred 50 days before surgery, whereas in the other context the conditioning occurred 1 day before surgery. Thus, each rat acquired a remote and recent memory before the hippocampus was damaged. When tested for retention, the rats with hippocampal damage only showed fear responses in the context that corresponded to the most remote memory (i.e., with the 50-day conditioning-to-surgery interval), suggesting that the hippocampal damage caused temporally graded retrograde amnesia for contextual fear conditioning. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.