When reaching for a target, the information provided by different sensory channels is continuously processed to supervise the ongoing movement. If a discrepancy between predicted end-point of movement and target location is detected, the arm trajectory is modulated to preserve reaching accuracy. Desmurget et al. (1999) showed that the left posterior parietal cortex (lPPC) is crucial for this online control when the visual target is displaced. We investigate further the localization of involved brain areas in the lPPC and expand the paradigm to other visual and proprioceptive perturbations (visual hand feedback displacement and force impulse application to the reaching arm).
An fMRI study served as localizer task. All subjects showed strong activation in the lPPC when correcting for any visual perturbation.
Using event-related TMS, we subsequently tested the site of strongest fMRI activation on the lPPC and some adjacent control sites. The goal was to disrupt online corrections occurring with a target displacement.
Despite huge inter-individual differences in the location of the strongest BOLD activation, we could demonstrate spatial localized TMS effects in congruence with the site of each participant’s individual fMRI activation in the lPPC. The next goal is to find the dedicated cortical sites for the other perturbations.