Effects of left ventro-dorsal stream stimulation on novel tool use

Mechanical problem solving enables using novel tools without primarily recalling semantic knowledge. In our previous fMRI study, the left ventro-dorsal stream, with clusters in the anterior supramarginal gyrus and ventral precentral gyrus, was active as healthy participants used novel tools. By using transcranial magnetic stimulation, the current study investigates the regions' causal contributions. Participants were stimulated in the left anterior supramarginal gyrus or ventral precentral gyrus while planning to use novel tools to lift a cylinder. Each participant completed the tasks once under verum and once under sham stimulation. Performance accuracy and hand kinematics were assessed. Overall task performance remained unaffected by the stimulation at either site. However, stimulating the anterior supramarginal gyrus during early planning processes tended to reveal longer reaching paths and reduced velocity magnitudes when preparing the tool's attachment. Stimulating the ventral precentral gyrus during later planning stages resulted in delayed movement initiation and extended deceleration as the tool approaches and lifts the cylinder. Kinematic compensation behavior may allow successful task performance despite the stimulation. The need for compensation may arise from subtle challenges in decision-making and tool-cylinder-matching processes, supported by the anterior supramarginal gyrus during early processing stages. A more detailed analysis of the tool-cylinder match may be needed when later processes supported by the ventral precentral gyrus are disrupted.