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Schlagwörter:
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Zusammenfassung:
Introduction:
Regions in the posterior parietal cortex and the premotor cortex contribute to online control in reaching and grasping. Structural connectivity suggests the division of parieto-frontal networks into two neuronal circuits. The dorsomedial circuit connects the superior parietal occipital cortex (SPOC) and medial intraparietal sulcus (mIPS) with the dorsal part of the premotor cortex (PMd) (Tanne-Gariepy, Rouiller, Boussaoud, 2002), and is associated with reaching. The dorsolateral circuit includes the aIPS, which is highly interconnected with the ventral part of the premotor cortex (PMv) (Tanne-Gariepy et al., 2002; Tomassini et al., 2007), and is associated with grasping. However, recent findings question a strict functional distinction between both circuits, but rather suggest that the functional connectivity between these circuits is influenced by the required amount of online control during reach-to-grasp movements (Grol et al., 2007). Here, we used a perturbation paradigm to clearly separate the fMRI activity reflecting online control from that of the planning phase. We tested the reaction to changes of target location, target size, or both at movement onset. In a preceding experiment, the amount of online control required for the correction of grasp and reach perturbations was matched.
Methods:
Sixteen participants were tested in a 3T scanner with their heads tilted and elevated to allow for a natural sight of the hand. Two target objects were mounted above the participant's hip. Participants had to grasp the illuminated target (unperturbed trials). When reaching was perturbed, the illumination of the object was extinguished and the other object was illuminated, thus changing the location of the target. When grasping was perturbed, the extent of target illumination changed, changing the size of the target. Reaction (RT) and movement times (MT) as well as eye and hand movements were recorded.
Whole-brain functional images were collected (GR EPI with TR/TE = 2130/35ms; 3.0 x 3.0mm² in-plane resolution, 3.5mm slice thickness, 33 slices). Using a slow event-related design, eight experimental runs with 32 trials each were acquired per participant.
Effector-specificity during the movement phase was tested in a two stage-approach: First, two sets of regions-of-interests (ROIs) were identified using the contrasts reaching perturbed > unperturbed and grasping perturbed > unperturbed, respectively, in combination with anatomical landmarks (Fig. 1). Using this procedure, the ROIs were optimally located to capture the activity increases due to one of the two perturbation types. Second, within the ROIs, we tested whether the activity for reaching perturbed and grasping perturbed differed significantly from each other.
Conclusions:
None of the areas involved in online control showed activation differences between perturbed reaching and perturbed grasping. These results support the suggestion that the aIPS and the SPOC are not strictly effector-specific organized. In contrast, we found that mIPS, mIPS2, and the right PMd show different activation patterns if the grip is corrected into a different target size, indicating that these cortical areas are influenced by the amount of required online control.
