Transcranial magnetic stimulation disrupts eye-hand interactions in the posterior parietal cortex.
ABSTRACT Recent neurophysiological studies have started to shed some light on the cortical areas that contribute to eye-hand coordination. In the present study we investigated the role of the posterior parietal cortex (PPC) in this process in normal, healthy subjects. This was accomplished by delivering single pulses of transcranial magnetic stimulation (TMS) over the PPC to transiently disrupt the putative contribution of this area to the processing of information related to eye-hand coordination. Subjects made open-loop pointing movements accompanied by saccades of the same required amplitude or by saccades that were substantially larger. Without TMS the hand movement amplitude was influenced by the amplitude of the corresponding saccade; hand movements accompanied by larger saccades were larger than those accompanied by smaller saccades. When TMS was applied over the left PPC just prior to the onset of the saccade, a marked reduction in the saccadic influence on manual motor output was observed. TMS delivered at earlier or later periods during the response had no effect. Taken together, these data suggest that the PPC integrates signals related to saccade amplitude with limb movement information just prior to the onset of the saccade.
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ABSTRACT: Execution of a saccadic eye movement towards the goal of a hand pointing movement improves the accuracy of this hand movement. Still controversial is the role of extra-retinal signals, i.e. efference copy of the saccadic command and/or ocular proprioception, in the definition of the hand pointing target. We report here that hand pointing movements produced without visual feedback, with accompanying saccades and towards a target extinguished at saccade onset, were modified after gain change of reactive saccades through saccadic adaptation. As we have previously shown that the adaptation of reactive saccades does not influence the target representations that are common to the eye and the hand motor sub-systems (Cotti J, Guillaume A, Alahyane N, Pelisson D, Vercher JL. Adaptation of voluntary saccades, but not of reactive saccades. Transfers to hand pointing movements. J Neurophysiol 2007;98:602-12), the results of the present study demonstrate that extra-retinal signals participate in defining the target of hand pointing movements.Behavioural brain research 03/2011; 218(1):248-52. · 3.22 Impact Factor
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ABSTRACT: Posterior parietal cortex (PPC) plays an important role in the planning and control of goal-directed action. Single-unit studies in monkeys have identified reach-specific areas in the PPC, but the degree of effector and computational specificity for reach in the corresponding human regions is still under debate. Here, we review converging evidence spanning functional neuroimaging, parietal patient and transcranial magnetic stimulation studies in humans that suggests a functional topography for reach within human PPC. We contrast reach to saccade and grasp regions to distinguish functional specificity and also to understand how these different goal-directed actions might be coordinated at the cortical level. First, we present the current evidence for reach specificity in distinct modules in PPC, namely superior parietal occipital cortex, midposterior intraparietal cortex and angular gyrus, compared to saccade and grasp. Second, we review the evidence for hemispheric lateralization (both for hand and visual hemifield) in these reach representations. Third, we review evidence for computational reach specificity in these regions and finally propose a functional framework for these human PPC reach modules that includes (1) a distinction between the encoding of reach goals in posterior-medial PPC as opposed to reach movement vectors in more anterior-lateral PPC regions, and (2) their integration within a broader cortical framework for reach, grasp and eye-hand coordination. These findings represent both a confirmation and extension of findings that were previously reported for the monkey.Experimental Brain Research 07/2012; 221(1):1-18. · 2.22 Impact Factor
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ABSTRACT: Modification or suppression of reaches occurs in everyday life. We argue that a common modular architecture, based on similar neural structures and principles of kinematic and kinetic control, is used for both direct reaches and for their on-line corrections. When a reach is corrected, both the pattern of neural activity in parietal, premotor and motor cortex and the muscle synergies associated with the first movement can be smoothly blended or sharply substituted into those associated with the second one. Premotor cortex provides the early signalling for trajectory updating, while parietal and motor cortex provide the fine-grained encoding of hand kinematics necessary to reshape the motor plan. The cortical contribution to the inhibitory control of reaching is supported by the activity of a network of frontal areas. Premotor cortex has been proposed as a key structure for reaching suppression. Consistent with this, lesions in different nodes of this network result in different forms of motor deficits, such as Optic Ataxia in parietal patients, and commission errors in frontal ones.Neuroscience & Biobehavioral Reviews 01/2014; · 9.44 Impact Factor