Involvement of the trisynaptic hippocampal pathway in generating neural representations of object-place associations (an analytical review)


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Abstract

The possible mechanisms by which neural representations of object-place associations are generated in different parts of the network consisting of the hippocampus and the parahippocampal complex are analyzed. Spatial and non-spatial information arrives in the hippocampus via two streams from the parahippocampal complex, which consists of the perirhinal, postrhinal, and entorhinal areas of the cortex. It can be suggested that because there are no connections between the lateral and medial areas of the entorhinal cortex, these representations, as particular patterns of connected and discharging neurons, are generated mainly in the hippocampus, though they may also be generated in the entorhinal cortex because of the input from the postrhinal cortex. As both information streams converge on neurons in the dentate gyrus and field CA3, the trisynaptic pathway through the hippocampus may play a key role in generating these representations. As spatial information arrives in the neocortex and passes from there via the parahippocampal complex to the hippocampus about 20 msec earlier than non-spatial information, spatial information is processed first in the dentate gyrus and field CA3. Later, because of the return of excitation from field CA3c to the dentate gyrus, neural representations of object-place associations start to be generated in the dentate gyrus. Signals are transferred from the dentate gyrus to field CA3, where information arriving from the entorhinal cortex is superimposed on the neuronal patterns activated by these signals. As a result, more complex neural representations are generated in field CA3 and signals are sent to field CA1. In the dorsal (ventral) part of field CA1, non-spatial (spatial) information arriving from the lateral (medial) part of the entorhinal cortex is superimposed on the activated neuronal pattern. The result is that higher-order representations are generated in field CA1. In the parahippocampal cortex, the generation of neuronal representations of object-place associations can result from the transfer of activity from the dorsal part of hippocampal field CA1.

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