Viewing distance related sensory processing in the ascending tract of deiters vestibulo-ocular reflex pathway

The firing behavior of seven antidromically identified ascending tract of Deiters (ATD) neurons was recorded in one alert squirrel monkey trained to pursue moving targets and to fixate visual targets at different distances from the head during whole body rotation. 2. ATD cells generated signals related to contralateral horizontal smooth pursuit eye movements and to ipsilateral angular and linear head velocity. Most ATD neurons reversed the direction of their response to head rotation when the vestibulo-ocular reflex was canceled by fixation of a head stationary target. 3. ATD unit gains in respect to linear head velocity increased dramatically (> 4x) when a near, earth stationary target (10 cm from the eyes) was fixated, compared to the response recorded during fixation of a far target (130 to 170 cm from the eyes). Since the viewing distance related changes in the responses of ATD neurons closely parallel the changes in the responses of the eyes, the ATD appears to be an important premotor pathway for producing viewing distance related changes in the gain of the vestibulo-ocular reflex.