ANTICIPATORY HEAD DIRECTION SIGNALS IN ANTERIOR THALAMUS - EVIDENCE FOR A THALAMOCORTICAL CIRCUIT THAT INTEGRATES ANGULAR HEAD MOTION TO COMPUTE HEAD DIRECTION

Several regions in the rat brain contain neurons known as head-directi on cells, which fire only when the rat's head is facing in a specific direction. Head-direction cells are influenced only by the direction o f the head with respect to the static environmental surroundings, and not by the position of the head relative to the body. Each head-direct ion cell has its own preferred direction of firing, so that together, the population of cells provides a continuous signal of momentary dire ctional heading. Here, head-direction cells were recorded from the pos tsubicular cortex (PSC) and anterodorsal nucleus (ADN) of the thalamus of freely moving rats. Cell activity was analyzed in relation to both momentary head direction, and the angular velocity of head turns. Hea d-direction cells in PSC maintained the same directional firing prefer ence, regardless of the angular head velocity. By contrast, head-direc tion cells in ADN systematically shifted their directional firing pref erence, as a function of angular head velocity. The ADN cells always s hifted their directional tuning peak to the left during clockwise head turns, and to the right during counterclockwise head turns. These res ults suggest that ADN neurons anticipate the future direction of the h ead, whereas PSC neurons encode the present direction of the head. Bas ed on these findings, we hypothesize that neurons in PSC and ADN are r eciprocally connected to form a thalamocortical circuit, which compute s the directional position of the rat's head by integrating the angula r motion of the head over time.