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K E Ragozzino

Publications and source records attributed to K E Ragozzino.

3 recordsLinked to original sources

Dorsal striatal head direction and hippocampal place representations during spatial navigation.

Several theories of basal ganglia function describe a striatal contribution to learning that is independent of hippocampal function. This study examined the question of whether the striatum should be regarded as functioning independently of or acting in concert with limbic structures. Dorsal striatal head direction cells and hippocampal place cells were recorded in parallel while rats performed a hippocampal-dependent radial maze task. Changes in the directional preference of head direction cells and the location of place fields were compared following alterations of the sensory environment. When familiar visual cues were presented in new spatial arrangements, or when new visual cues were placed in a familiar environment, rotations of directional preferences were consistent with the mean place-field response. When familiar visual and nonvisual cues were presented in conflict, or when rats were exposed to novel environments, the responses of the two cell types were inconsistent relative to each other. This pattern suggests that current perceptions and expectations of familiar spatial contexts may dynamically modulate the relationship between hippocampus and dorsal striatum.

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Convergence of head direction and place information in the CA1 region of hippocampus.

The hippocampus has long been considered critical for spatial learning and navigation. Recent theoretical models of the rodent and primate hippocampus consider spatial processing a special case of a more general memory function. These non-spatial theories of hippocampus differ from navigational theories with respect to the role of self-motion representations. The present study presents evidence for a new cell type in the CA1 area of the rat hippocampus that codes for directional heading independent of location information (i.e. the angular component of self-motion). These hippocampal head direction cells are controlled by external and idiothetic cues in a similar way as head direction cells in other brain areas and hippocampal place cells. Convergent head direction information and location information may be an essential component of a neural system that monitors behavioral sequences during navigation. Conflicts between internally generated and external cues have previously been shown to result in new hippocampal place representations, suggesting that head direction information may participate in synaptic interactions when new location codes are formed. Combined hippocampal representations of self-motion and external cues may therefore contribute to path integration as well as spatial memory processing.

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Hippocampal representational organization and spatial context.

The hippocampus appears to undergo continual representational reorganization as animals navigate their environments. This reorganization is postulated to be reflected spatially in terms of changes in the ensemble of place cells activated, as well as changes in place field specificity and reliability for cells recorded in both hilar/CA3 and CA1 regions. The specific contribution of the hilar/CA3 region is suggested to be to compare the expected spatial context with that currently being experienced, then relay discrepancies to CA1. The properties of CA1 place fields in part reflect the spatial comparisons made in the hilar/CA3 area. In addition, CA1 organizes the input received from the hilar/CA3 place cells according to different temporal algorithms that are unique to different tasks. In this way, hippocampus helps to distinguish temporally one spatial context from another, thereby contributing to episodic memories.

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