Functional connectivity from area 5 to primary motor cortex via paired-pulse transcranial magnetic stimulation

In non-human primates area 5 is dominated by the representation of the hand and forelimb, and has direct connectivity with primary motor cortex (M1) implicating its role in the control of hand movements. To date, few studies have investigated the function of area 5 in humans or its connectivity with M1. Using paired-pulse TMS, the present study investigates the functional connectivity between putative area 5 within the medial superior parietal lobule and ispilateral M1 in humans. Specifically, the motor evoked potential (MEP) from the first dorsal interosseous muscle of the right hand was quantified with and without conditioning TMS stimuli applied to left-hemisphere area 5. The timecourse of functional connectivity was examined during cutaneous stimulation applied to the thumb and index finger and also during rest whereby no somatosensory processing demands were imposed. Results indicate that area 5 facilitates and inhibits the MEP at 6 and 40 ms, respectively, during somatosensory processing. No net influence of area 5 on M1 output was observed during rest. We conclude that area 5 has a task-dependent and temporally specific influence on M1 output, and suggest that the interaction between these areas presents a novel path with which to alter the motor output, and possibly movement of hand muscles.