t a h , Salt Lake City, UT 841 12 U . S . A .
Many models (e.g., working memory, declarative memory, explicit memory, attributeidata-based memory, spatial cognitive map. temporal context, and configural associations) have been proposed to account for the apparent ubiquitous role of the hippocampus in subserving mnemonic information. These models vary on at least two critical dimensions as they attempt to account for a role of the hippocampus in coding and representing information.
One dimension concerns the nature or attributes that are coded in the hippocampus. One view has been presented by O' Keefe andNadel (1978) and Nadel (1991). They propose that the hippocampus codes and stores exclusively spatial information in the form of an allocentric spatial cognitive map (i.e., spatial maps that are independent of the body axes). This spatial cognitive map can be used for place recognition, navigation, and coding of context. The allocentric map is to be differentiated from egocentric or taxic and praxic orientations, which are subserved by different neural systems. This cognitive map model of the hippocampus suggests that the hippocampus codes only spatial information.
A somewhat different view is provided by the temporal context model (Rawlins, 1985). The model states that the hippocampus serves as a multisensory, multistructural processor for temporally discontiguous data. The hippocampus is involved in processing information whenever two or more stimuli, regardless of sensory modality, are separated in time but must be associated with one another in order to solve a task correctly. Thus, the hippocampus codes only temporal information.
In the attribute memory model (Kesner, 1990), it is proposed that the hippocampus in animals codes only spatial and temporal attributes. In humans, the right hippocampus mediates spatial and temporal attribute representations, and the left hippocampus mediates verbal and temporal attribute representations.
Other models (e.g., working, explicit, and declarative memory models) propose that the hippocampus codes all information, including spatial, temporal, nonspatial (sensory cues), and egocentric spatial attributes (Olton, 1983;Squire, 1987;Schacter, 1987). Finally, the configural association model proposes that the hippocampus codes higher-order interactions among any of the spatial and nonspatial attributes of information processing (Sutherland and Rudy, 1989). Thus, models of hippocampal function vary greatly on the nature of information or attributes that are processed, coded, or represented in the hippocampus, each model emphasizing the importance of spatial, temporal, spatial and temporal, verbal and temporal, or all spatial, temporal, and nonspatial attri-