Object representation in the ventral premotor cortex (area F5) of the monkey

Visual and motor properties of single neurons of monkey ventral premotor cortex (area F5) were studied in a behavioral paradigm consisting of four conditions: object grasping in light, object grasping in dark, object fixation, and fixation of a spot of light. The employed objects were six different three-dimensional (3-D) geometric solids. Two main types of neurons were distinguished: motor neurons (n = 25) and visuomotor neurons (n = 24). Motor neurons discharged in association with grasping movements. Most of them (n = 17) discharged selectively during a particular type of grip. Different objects, if grasped in similar way, determined similar neuronal motor responses. Visuomotor neurons also discharged during active movements, but, in addition, they fired also in response to the presentation of 3-D objects. The majority of visuomotor neurons (n = 16) showed selectivity for one or few objects. The response was present both in object grasping in light and in object fixation conditions. Visuomotor neurons that selectively discharged to the presentation of a given object discharged also selectively during grasping of that object. In conclusion, object shape is coded in F5 even when a response to that object is not required. The possible visual or motor nature of this object coding is discussed.