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Abstract:
According to the nowadays preferred integrative hybrid model for planning and
executing goal-directed movements, an initial motor plan is calculated prior to
movement onset and subsequently feedback information is used to update this plan
continuously during movement execution. In this continuous online control of the
movement, the posterior parietal cortex (PPC) is involved critically. To enable a
detailed and comprehensive research of the processes and brain areas involved in
reaching, a virtual reality environment with the possibilities for manipulating visual
and proprioceptive feedback information is set up, and equipment for transcranial
magnetic stimulation (TMS) is integrated. The setup offers the possibility to study the
chronometry of the processes and the localization of crucially involved brain areas.
Five main conditions are implemented: Undetected displacement of the visual target,
undetected displacement of visual hand feedback, rotation of visual hand feedback,
application of a force to the hand and (as control) no alteration of visual or haptic
scene. All conditions can be conducted with and without hand feedback and with
and without TMS stimulation. As proof of concept, a pilot study is conducted that
replicates the study of Desmurget, Epstein, Turner, Prablanc, Alexander, and Grafton
(1999). In this study, they could show that the updating of a reaching movement
towards an unconsciously displaced target can be disturbed by applying TMS over
the contralateral PPC. Additionally to the replication of this disturbance, the
possibility to localize the affected cortical area more precisely than in the original
study is demonstrated in the pilot study.
