Visual Properties of Hand-manipulation-related Neurons in Macaque Monkey

A previous study reported that neurons in the rostral part of the intra-parietal sulcus (area AIP) of the monkey discharge specifically during object manipulation. We studied the visual properties of these neurons during fixation and manipulation of eight different simple three-dimensional objects and two different complicated objects. We also examined the orientation selectivity of neurons using 4 of these objects. Object type neurons were activated by the sight of objects during fixation as well as object manipulation and some were highly selective for complicated objects, such as a knob or plate in a groove. These neurons appear to discriminate the shape of objects. Some neurons showed selectivity for the orientation of the long axis or the surface of objects of different shapes. Moreover, some object type neurons were highly selective for a certain object and its orientation in three-dimensional space. Non-object type neurons were not activated during fixation. However we also recorded from non-object type neurons that responded to complicated objects, these neurons required manipulating hand image to respond. Some non-object type neurons showed orientation selectivity during object manipulation. The visual properties of hand-manipulation-related neurons in area AIP suggest that they are coding object shape and/or orientation, and play an essential role in matching and monitoring the hand shape and orientation for the manipulation of objects.