HF, and CL lesions on acquisition and retention of place learning. Table 3.1 indicates that the model has difficulty simulating the effect of HF lesions on explicitly unpaired extinction and conditioned inhibition. Also as indicated in Table 3.1, the model makes numerous novel predictions about the effects of HP on many learning paradigms.
In addition to simulating behavioral effects of brain lesions, the model also describes hippocampal activity in normal animals. Because the model suggests that the hippocampus computes aggregate predictions of environmental events in time and space, it correctly predicts that hippocampal activity reflects the topography of the CR during classical conditioning ( Berger & Thompson, 1978) and the spatial location of the US ( Breese et al., 1989) during place learning.
In conclusion, this chapter suggests how different regions of the hip pocampal formation and the neocortex might participate in the formation of both temporal maps during classical conditioning and spatial maps during place learning.
Schmajuk and DiCarlo ( 1992) and Schmajuk and Blair ( 1993) presented a neural network model capable of generating predictions of future events in time and space. In the context of this model, accurate generation of predictions depends on the processes of configuration and competition. Configuration refers to the combination of simple stimuli into a complex stimulus, which represents a pattern of stimuli that better predicts the future than its individual constituents do. Competition refers to the selection of the stimulus best predicting the future from among different simple and complex stimuli.
In the context of the network, the hippocampus is assumed to provide error signals that control the formation of configurations in cortical regions, and to compute the aggregate prediction signal that regulates competition in subcortical areas. According to the model, whereas aspiration lesions of the hippocampus eliminate both cortical configuration and sub cortical competition, ibotenic acid lesions of the hippocampus abolish only cortical configuration. The model correctly describes the effects of hippocampal aspiration and ibotenic acid lesions on several temporal (classical conditioning) and spatial learning paradigms.
This project was supported in part by contract N00014-91-J- 1664 from the Office of Naval Research.