Direction-selective neurons in macaque V4

In mammalian visual system, direction-selective (DS) neurons prefer visual motion in a particular direction and are specialized for visual motion processing. In area V4 of the macaque, about 13% neurons are direction-selective and form clusters (DS domains). The functional role of DS neurons in this form-processing area is still unknown. We implanted electrode arrays targeting these DS domains and recorded neurons' responses to moving stimuli such as gratings and simple shapes. We found that DS neurons were similar to non-DS neurons in their receptive field sizes and orientation-selectivity properties. However, population-wise, DS neurons responded slower and had lower firing rates than non-DS neurons, contrary to their traditional role in motion processing. In addition, direction selectivity of V4 neurons was stimulus-dependent (i.e., not invariant). DS neurons identified with grating stimuli may not exhibit direction selectivity to other types of stimuli such as random dots or contour shapes. These results suggest that, unlike DS neurons in other areas, V4 DS neurons may have a unique origin for their direction selectivity and nontraditional roles in visual motion processing.<b>NEW & NOTEWORTHY</b> The functional role of direction-selective (DS) neurons in the ventral pathway is unclear. We studied DS neurons in area V4 of awake macaques. Interestingly, these neurons have slower responses and lower firing rates than those non-DS neurons. In addition, direction selectivity of these neurons was stimulus-type dependent. DS neurons in V4 may play a functional role different from those typical DS neurons in V1 or MT.