Abstract
Visuomotor transformations for grasping have been associated with a fronto-parietal network in the monkey brain. The human homologue of the parietal monkey region (AIP) has been identified as the anterior part of the intraparietal sulcus (aIPS), whereas the putative human equivalent of the monkey frontal region (F5) is located in the ventral part of the premotor cortex (vPMC). Results from animal studies suggest that monkey F5 is involved in the selection of appropriate hand postures relative to the constraints of the task. In humans, the functional roles of aIPS and vPMC appear to be more complex and the relative contribution of each region to grasp selection remains uncertain. The present study aimed to identify modulation in brain areas sensitive to the difficulty level of tool object - hand posture matching. Seventeen healthy right handed participants underwent fMRI while observing pictures of familiar tool objects followed by pictures of hand postures. The task was to decide whether the hand posture matched the functional use of the previously shown object. Conditions were manipulated for level of difficulty. Compared to a picture matching control task, the tool object – hand posture matching conditions conjointly showed increased modulation in several left hemispheric regions of the superior and inferior parietal lobules (including aIPS), the middle occipital gyrus, and the inferior temporal gyrus. Comparison of hard versus easy conditions selectively modulated the left inferior frontal gyrus with peak activity located in its opercular part (Brodmann area (BA) 44). We suggest that in the human brain, vPMC/BA44 is involved in the matching of hand posture configurations in accordance with visual and functional demands.
Highlights
In humans, goal based object-related movements play a significant role in our every day lives
In this study we will focus on the grasp part of the action, more in particular on the selection of the proper hand posture to functionally interact with a tool object
The aim of the present study was to focus on tool object – hand posture matching and to determine which brain areas would respond to increased matching demands
Summary
Goal based object-related movements play a significant role in our every day lives. Visuomotor transformations for grasping have been associated with two key cortical areas: area F5 or the rostral part of the monkey ventral premotor cortex, and area AIP or the rostral part of the intraparietal sulcus [6] Inactivation studies of both areas resulted in impaired shaping of the hand relative to the object’s size and shape [7,8]. Based on the characteristics of neurons in F5 and AIP, Fagg and Arbib proposed a model in which AIP uses visual input to highlight object features that are relevant for grasping it, whereas area F5 serves to select the most appropriate grasp in function of relevant constraints (visual information, task information, instructions) This decision is relayed back to the AIP which focuses on the selected grasp and continually reinforces its inputs while F5 governs the motor execution and monitors the planned preshape and grasp [9]
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