Parietal conditioning enhances motor surround inhibition

BACKGROUND: Motor surround inhibition (mSI) is a phenomenon supportive for executing selective finger movements, wherein synergist muscles are selectively facilitated while surround muscles are inhibited. Previous studies of conditioning inputs to several intracortical and cortico-cortical inhibitory networks did not show an influence on mSI. The inhibitory posterior parietal-motor network, which is crucial for executing fine movements, however, has not been studied. OBJECTIVE/HYPOTHESIS: To investigate the role of inhibitory posterior parietal-motor network in mSI. We hypothesized that conditioning this inhibitory network would enhance mSI. METHODS: 11 healthy adults completed study. mSI was elicited by applying a TMS pulse over the motor cortex coupled with or without a conditioning input to an inhibitory spot in the posterior parietal cortex at 2 or 4 ms interval. RESULTS: Conditioning input to the posterior parietal cortex increased mSI by ~20% CONCLUSION: The inhibitory posterior parietal-motor network appears to contribute to the genesis of mSI.