Several regions of the rat brain contain neurons known as head-direc(cid:173) tion celis, which encode the animal's directional heading during spatial navigation. This paper presents a biophysical model of head-direction cell acti vity, which suggests that a thalamocortical circuit might com(cid:173) pute the rat's head direction by integrating the angular velocity of the head over time. The model was implemented using the neural simulator NEURON, and makes testable predictions about the structure and func(cid:173) tion of the rat head-direction circuit.
1 HEAD-DIRECTION CELLS As a rat navigates through space, neurons called head-direction celis encode the animal's directional heading in the horizontal plane (Ranck, 1984; Taube, Muller, & Ranck, 1990). Head-direction cells have been recorded in several brain areas, including the postsubicu(cid:173) lum (Ranck, 1984) and anterior thalamus (Taube, 1995). A variety of theories have pro(cid:173) posed that head-direction cells might play an important role in spatial learning and navigation (Brown & Sharp, 1995; Burgess, Recce, & O'Keefe, 1994; McNaughton, Knierim, & Wilson, 1995; Wan, Touretzky, & Redish, 1994; Zhang, 1995).
1.1 BASIC FIRING PROPERTIES
A head-direction cell fires action potentials only when the rat's head is facing in a particu(cid:173) lar direction with respect to the static surrounding environment, regardless of the animal's location within that environment. Head-direction cells are not influenced by the position of the rat's head with respect to its body, they are only influenced by the direction of the
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