Neurons with radial receptive fields in monkey area V4A: evidence of a subdivision of prelunate gyrus based on neuronal response properties

In recordings from two awake, behaving macaque monkeys we found that neurons in the crown of the prelunate gyrus differed in their responsiveness to simple visual stimuli. Neurons in the posterior part of the gyrus (area V4) responded strongly to stationary or moving bars, while neurons in the anterior part (area V4A) responded only weakly to such stimuli. Most receptive fields in area V4A were elongated with long axes oriented radially towards the fovea. These neurons were sensitive to radial movements, especially to sudden shifts of real 3D objects. The border between areas V4 and V4A coincided with the representation of the horizontal meridian. Area V4A extended into the posterior bank of the superior temporal sulcus, where its border corresponded to the representation of the vertical meridian. The sequence of the representations of the horizontal and vertical meridians over the prelunate gyrus suggests the existence of another area between V4A and V4t.