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Jody C. Culham, Stacey L. Danckert, Melvyn A. Goodale; fMRI reveals a dissociation of visual and somatomotor responses in human AIP during delayed grasping. Journal of Vision 2002;2(7):701. doi: 10.1167/2.7.701.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We previously reported that the anterior intraparietal (AIP) region of humans shows a greater response to visually-guided grasping than reaching. If, as proposed, human AIP is the homologue of macaque AIP, it too should respond both to the visual presentation of an object to be grasped as well as to the grasping action. We used functional magnetic resonance imaging (fMRI) to dissociate the visual response and somatomotor responses during delayed grasping and reaching. Methods: We measured the fMRI response over a series of single trials (20 sec each). On each trial, the subject viewed the target object (250 msec) with no immediate motor response. After a 10 sec delay, the fixation point changed color (250 msec) to cue the subject to make either a reaching or grasping response, followed by a 10 sec interval before the next trial. Subjects either used a precision grip to grasp the objects or reached with the arm to touch the object without preshaping the hand. Results: The area at the junction of the intraparietal sulcus (IPS) and postcentral sulcus (PCS) that we previously found activated during immediate grasping (vs. reaching) may in fact contain two subregions. In the delayed tasks, an anterior subregion in the PCS showed a large somatomotor response but little visual response; whereas, a more posterior subregion just behind the PCS, in the anterior IPS, showed both visual and somatomotor responses. The posterior subregion showed a greater response to grasping than reaching for both the visual and somatomotor components. Conclusions: Only the more posterior subregion of grasping activation may correspond to AIP-proper. The greater visual response during grasping (than reaching) is likely related to the object processing required to preshape the hand. Given behavioural evidence that delayed grasping involves a different network than immediate grasping, further analyses will investigate activity in ventral stream areas such as the lateral occipital complex.
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