Multi-finger Prehension Synergy: Exploration with Transcranial Magnetic Stimulation

The control of hand action is commonly viewed as based on a two-level hierarchy (Arbib et al. 1985): (1) The task is shared between the thumb and a virtual finger (VF, an imagined digit with the mechanical effect equal to that of the four fingers); and (2) VF action is shared among the actual fingers. Synergies at both levels can be studied as patterns of co-variation of its elements that stabilize the overall output (Zatsiorsky and Latash, 2004). We used single-pulse transcranial magnetic stimulation (TMS) as a perturbation to explore the stability of the three components of the prehension synergies: (a) internal forces, (b) resultant force, (c) moment of force exerted on the hand-held object.