The neural underpinnings of haptically guided functional grasping of tools: An fMRI study

The neural bases of haptically guided interactions with tools are largely unknown. Whereas in the visual domain there is clear evidence for left lateralization of the networks underlying the guidance of actions involving tools, comparable evidence in haptic modality is missing. Therefore, we examined whether the temporo-parieto-frontal networks responsive to interactions with tools also support haptically guided functional grasping. We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity while, in the absence of vision, 21 right-handed participants performed the following tasks with either their dominant or non-dominant hands: haptic exploration of real 3-D tools or size-matched control objects, subsequent planning of functionally appropriate grasps of tools and most convenient grasps of non-tools, and the resulting grasp execution. As predicted, haptic exploration of tools (vs. non-tools) was associated with significant asymmetrical/left-lateralized increases of activity in temporo-parieto-frontal networks. While grasp planning did not reveal differences between tools and control objects, the execution of functional grasping of tools (as compared to control grasps) re-recruited mainly dorsal cortical regions engaged earlier during the exploration phase. These results demonstrate that haptically guided grasping of tools invokes only subsets of cortical regions typically associated with tool-directed actions. They also call for a re-interpretation of what we assumed would be happening during the exploration phase, as this early stage of processing most likely included preliminary grasp planning. After all, the requisite integration of structural and conceptual tool features, as well as relevant action knowledge mediated at the neuronal level by the temporo-parietal projections in the early stage of processing, is not then critical for the execution of the preprogrammed functional grasp.