Septal Regulation of the Hippocampal -- Entorhinal Network: Memory Formation and Failure
J. J. Chrobak A. L. Vi G. Buzsäki Rutgers University
A limbic forebrain network that includes septal, hippocampal, and entorhinal neurons supports the mammalian brain's ability to make memories. Considerable evidence demonstrates that this network supports only certain kinds of memory and only for certain durations ( Isaacson, 1975; Squire, 1992). Highly processed sensory information is channeled into the hippocampus via the entorhinal cortex (EC). This cortical input provides the hippocampus with multimodal representations of ongoing sensory events or episodes. These representations may then be integrated with information about the organism's internal (limbic) environment, from brainstem, hypothalamic, and septal neurons, which are channeled via the fimbria-fornix and supracallosal fibers to the hippocampus and EC. The hippocampus thus serves as an interface for integrating multimodal sensory representations with information about the emotive state of the organism (see Isaacson, 1982). This interface would seem to be a logical antecedent for the role of this network in forming memories of recent, spatiotemporally unique, sensory events.
The hippocampal-entorwnal network seems to serve a dual role in the formation of memories. "The hippocampal formation appears to play a role in assessing the relevance or significance of newly processed sensory stimuli, then exerts an equally significant role in determining whether they be registered in other parts of the cortex" ( Van Hoesen, Hyman, & Damasio, 1991, pp. 2-3). The network would seem to be involved in the initial encoding and subsequent consolidation of recent memories.