Automatic motor cortex activation for natural as compared to awkward grips of a manipulable object

It has been suggested that, relative to natural objects, man-made object representations in the brain are more specifically defined by functional properties that reflect how an object is used and/or what it is used for (Warrington and Shallice 1984). We recorded 123-channel event-related potentials (ERP) in healthy participants during a mental rotation task involving a manipulable (hammer) and a non-manipulable (church) object. Both stimuli had standard and mirror-image versions rotated in four different orientations, resulting for the manipulable object in some natural and some awkward grips. Using spatial cluster analysis, time periods were determined during which the ERP maps differed between stimulus conditions. Specific maps appeared for natural versus awkward grips with the manipulable object at a very early stage (60-116 ms) as well as during a later stage (180-280 ms). Source estimations derived from the topographic data indicated that during the second time window the left motor cortex was significantly activated in the case of natural grips. We argue that the motor programs that are semantically associated with the object are automatically activated when it is presented in graspable orientations.