Foveal tracking cells in the superior temporal sulcus of the macaque monkey.

Visual responses were recorded from neurons in the superior temporal sulcus (STS) of awake, behaving cynomolgus monkeys trained to fixate a small spot of light. Visual receptive fields, directionality, and responses during visual tracking were examined quantitatively for 50 cells in the foveal portion of the middle temporal (MT) visual area and surrounding cortex. Directionality indices and preferred directions for tracked and nontracked stimuli were compared. Eighteen cells (18/50 = 36%) were found to respond preferentially during tracking (tracking cells), 7 within MT, 9 in area FST on the floor of the STS, and 2 in unidentified areas. Three distinctly different tracking response profiles (VTS, VTO, and T) were observed. VTS and VTO cells had foveal receptive fields and gave directionally selective visual responses. VTS cells (3 in foveal MT, 6 in FST, 1 in an unidentified area) had a preferred visual direction that coincided with the preferred tracking direction, and began responding 50-100 ms before the onset of tracking. VTO cells (4 in foveal MT, 0 in FST, 1 in an unidentified area) had a preferred visual direction opposite to the preferred tracking direction, and began responding 0-100 ms after the onset of tracking. T cells (0 in MT, 3 in FST) had no visual responses and began responding simultaneously with the onset of tracking. It is suggested that this region of the brain could be the primary location for converting direction-specific visual responses into signals specifying at least the direction of an intended pursuit movement.