USC Brain Project: Hippocampus and Navigation Group

The TAM-WG Model: Head Direction

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Theoretical background:

Cells that show a unimodal tuning to head direction independent of location and relative to a "compass direction" have been reported in several areas of the rat brain, including the postsubiculum (Taube et al., 1990a,b) and the posterior parietal cortex - PPC (Chen et al., 1994a,b). Head direction cells provide the animal with an internal representation of the direction of its motion. When landmarks in a familiar environment are rotated about the animal, tuning curves of head direction cells rotate accordingly (Taube et al., 1990b; McNaughton et al., 1994b; Goodridge and Taube, 1995; Knierim et al., 1995; Taube, 1995), which suggests that the compass direction can be determined by familiar landmarks. However, in unfamiliar environments, vestibular information dominates and the rat does not respond to the rotation of landmarks. Like place cells (McNaughton et al., 1989; Quirk et al., 1990; Markus et al., 1994), head direction cells continue to fire in the dark. But if the animal wanders about in a darkened circular arena with no other positional cues available, they eventually drift. Hippocampal place fields appear to drift in synchrony with the head direction system (Knierim et al., 1983; McNaughton et al., 1994b). For Touretzky and Redish (1996), the information conveyed by head direction cells contributes to the operation of a path integrator. As proposed by McNaughton et al. (1996; Samsonovich, 1996; Samsonovich & McNaughton, 1997), head direction is responsible for the implementation of angular path integration.

For more information on head direction, please refer to the cited papers, or to our papers listed in the Hippocampus and Navigation Group homepage.

Representing head direction ...

Place cells show direction-dependent firing fields only in some specific types of tasks, particularly those with restricted movement paths. For example, place fields tend to be directional on a radial arm maze (McNaughton et al., 1983), while directional place fields are rarely seen in an open arena (Muller et al., 1991; Muller et al., 1994). In this case, however, a task requiring restricted movement paths produces more directional place fields than one with unrestricted paths (Markus et al., 1995). Although the directionality of place fields is yet to be fully understood, the WG model incorporates the role of head direction cells into its computation. This information, like the other perceptual inputs, will be coarse coded as a bump of activity over a linear array of cells, our head direction perceptual schema. Below, we show the activation of the head direction perceptual schema when the rat is facing 8 possible directions. It is worth mentioning that west, for example, may not mean the magnetic west, but the allocentric direction based on the rat's internal, e.g., landmark-based, compass.

East

Northeast

North

Northwest

West

Southwest

South

Southeast

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University of Southern California Brain Simulation Lab
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Author: Alex Guazzelli <aguazzel@rana.usc.edu>