Neural correlates for angular head velocity in the rat dorsal tegmental nucleus

Many neurons in the rat lateral mammillary nuclei (LMN) fire selectively in relation to the animal's head direction (HD) in the horizontal plane indep endent of the rat's location or behavior. One hypothesis of how this repres entation is generated and updated is via subcortical projections from the d orsal tegmental nucleus (DTN). Here we report the type of activity in DTN n eurons. The majority of cells (75%) fired as a function of the rat's angula r head velocity (AHV). Cells exhibited one of two types of firing patterns: (1) symmetric, in which the firing rate was positively correlated with AHV during head turns in both directions, and (2) asymmetric, in which the fir ing rate was positively correlated with head turns in one direction and cor related either negatively or not at all in the opposite direction. In addit ion to modulation by AHV, some of the AHV cells (40.1%) were weakly modulat ed by the rat's linear velocity, and a smaller number were modulated by HD (11%) or head pitch (15.9%). Autocorrelation analyses indicated that with t he head stationary, AHV cells displayed irregular discharge patterns. Becau se afferents from the DTN are the major source of information projecting to the LMN, these results suggest that AHV information from the DTN plays a s ignificant role in generating the HD signal in LMN. A model is proposed sho wing how DTN AHV cells can generate and update the LMN HD cell signal.