Two functional components of the hippocampal memory system

Abstract

There is considerable evidence that the hippocampal system contributes both to (1) the temporary maintenance of memories and to (2) the processing of a particular type of memory representation. The findings on amnesia suggest that these two distinguishing features of hippocampal memory processing are orthogonal. Together with anatomical and physiological data, the •neuropsychological findings support a model of cortico-hippocampal interactions in which the temporal and representational properties of hippocampal memory processing are mediated separately. We propose that neocortical association areas maintain shortterm memories for specific items and events prior to hippocampal processing as well as providing the final repositories of long-term memory. The parahippocampal region supports intermediate-term storage of individual items, and the hippocampal formation itself mediates an organization of memories according to relevant relationships among items. Hippocampal-cortical interactions produce (i) strong and persistent memories for events, including their constituent elements and the relationships among them, and (ii) a capacity to express memories flexibly across a wide range of circumstances.It has been known for decades that the hippocampal system plays a prominent role in learning and memory. Only recently has it become clear that only certain properties of memory processing depend on hippocampal system function and that these can be distinguished operationally from other aspects of memory that do not. It has proved difficult, however, to arrive at an understanding of memory rich enough to characterize both the nature of memory that is dependent on the hippocampal system and memory that is independent of this processing, and to tie them to underlying neural mechanisms. The earliest reports of amnesia emphasized the timelimited role of the hippocampal region in memory, focusing on its critical function in "consolidation" processes that bridge between immediate memory and the longterm store (Scoville & Milner 1957). This temporal distinction is most striking: amnesic patients and animals with hippocampal system damage show normal retention at short delays and increasingly impaired retention with longer delays. Recently, some have argued that virtually all aspects of memory processing by the hippocampal system can be attributed to its function as a temporary memory store or buffer (e.g., Rawlins 1985). However, a large body of data indicates that the loss of consolidation or memory-buffer functions cannot account for the full pattern of impaired and spared memory performance observed after hippocampal system damage; some memory capacities are intact in amnesia even across very long temporal intervals, whereas other aspects of memory performance are grossly impaired even over relatively short retention intervals. The buffer hypothesis also fails to account fully for a number of relevant observations on the stable, long-lasting functional correlates of hippocampal neuronal activity (see sect. 5). To accommodate a ...

The hippocampus and memory for orderly stimulus relations

“…However, this account would not be consistent with other functional dissociations, indicating that parahippocampal damage, but not FX or hippocampal damage, results in a deficit on recognition memory performance (16)(17)(18)(19)(20). By contrast, the combination of these and other findings is consistent with a suggested parcellation of functions mediated by hippocampal region structures (23). Although the parahippocampal region may play a unique role in recognition memory, the hippocampus itself is critical to the memory processing that underlies relational organization and declarative memory expression.…”

The Temporal Context Model in Spatial Navigation and Relational Learning: Toward a Common Explanation of Medial Temporal Lobe Function Across Domains.

“…Eichenbaum (2001Eichenbaum ( , 2000 hypothesized that the hippocampus could accomplish many of the functions ascribed to it by forming a "memory space." If the hippocampus could support the rapid development of a stimulus representation that captures the temporal and contextual relationships among stimuli, this representation would presumably be extremely useful in the "flexible re-expression" of memory (Eichenbaum, Otto, & Cohen, 1994;Cohen & Eichenbaum, 1993 …”

Stimulus–outcome learnability differentially activates anterior cingulate and hippocampus at feedback processing

“…There is substantial neuropsychological evidence for the existence of multiple memory systems, which are functionally and neurally distinct (Cohen and Squire 1980;Squire 1992;Eichenbaum et al 1994;Gabrieli et al 1997;Packard and Knowlton 2002;White and McDonald 2002). The striatum, which supports a number of forms of skill learning and stimuli-response learning, is implicated in procedural memory.…”