Complex tools and motor-to-mechanical transformations.

The ability to use complex tools is thought to depend on multifaceted motor-to-mechanical transformations within the left inferior parietal lobule (IPL), linked to cognitive control over compound actions. Here we show using neuroimaging that demanding transformations of finger movements into proper mechanical movements of functional parts of complex tools invoke significantly the right rather than left rostral IPL, and bilateral posterior-to-mid and left anterior intraparietal sulci. These findings emerged during the functional grasp and tool-use programming phase. The expected engagement of left IPL was partly revealed by traditional region-of-interest analyses, and further modeling/estimations at the hand-independent level. Thus, our results point to a special role of right IPL in supporting sensory-motor spatial mechanisms which enable an effective control of fingers in skillful handling of complex tools. The resulting motor-to-mechanical transformations involve dynamic hand-centered to target-centered reference frame conversions indispensable for efficient interactions with the environment.

The human dorsal stream adapts to real actions and 3D shape processing: a functional magnetic resonance imaging study.

We tested whether the control of real actions in an ever-changing environment would show any dependence on prior actions elicited by instructional cues a few seconds before. To this end, adaptation of the functional magnetic resonance imaging signal was measured while human participants sequentially grasped three-dimensional objects in an event-related design, using grasps oriented along the same or a different axis of either the same or a different object shape. We found that the bilateral anterior intraparietal sulcus, an area previously linked to the control of visually guided grasping, along with other areas of the intraparietal sulcus, the left supramarginal gyrus, and the right mid superior parietal lobe showed clear adaptation following both repeated grasps and repeated objects. In contrast, the left ventral premotor cortex and the bilateral dorsal premotor cortex, the two premotor areas often linked to response selection, action planning, and execution, showed only grasp-selective adaptation. These results suggest that, even in real action guidance, parietofrontal areas demonstrate differential involvement in visuomotor processing dependent on whether the action or the object has been previously experienced.

What does the brain do when you fake it? An FMRI study of pantomimed and real grasping.

Given that studying neural bases of actions is very challenging with fMRI, numerous experiments have used pantomimed actions as a proxy to studying neural circuits of real actions. However, the underlying assumption that the same neural mechanisms mediate real and pantomimed actions has never been directly tested. Moreover, the assumption is called into question by neuropsychological evidence suggesting that real actions depend on the dorsal stream of visual processing whereas pretend actions also recruit the ventral stream. Here, we directly tested these ideas in neurologically intact subjects. Ten right-handed participants performed four tasks: 1) grasping real three-dimensional objects, 2) reaching toward the objects and touching them with the knuckle without hand preshaping, 3) pantomimed grasping in an adjacent location where no object was present, and 4) pantomimed reaching toward an adjacent location. As expected, in the anterior intraparietal area, there was significantly higher activation during real grasping than that during real reaching. However, the activation difference between pantomimed grasping and pantomimed reaching did not reach statistical significance. There was also no effect of pantomimed grasping within the ventral stream, including an object-selective area in the lateral occipital cortex. Instead, we found that pantomimed grasping was mediated by right-hemisphere activation, particularly the right parietal cortex. These results suggest that areas typically invoked by real actions may not necessarily be driven by "fake" actions. Moreover, pantomimed grasping may not tap object-related areas within the ventral stream, but rather may rely on mechanisms within the right hemisphere that are recruited by artificial and less practiced actions.