Motor hand representation in cortical area 44

Objective: To elucidate whether area 44 of human frontal cortex is essential for the organization of voluntary hand movements or not, the authors examined effects of single transcranial magnetic stimulation (TMS) of human area 44 on voluntary hand movement and electromyography (EMG) activities in hand muscles. Method: Surface EMG responses were recorded from the thenar muscles of 10 normal subjects following TMS over area 44. Stimuli were applied 2 cm anterior to the primary tongue motor area. Results: Single TMS over area 44 could easily interrupt target-oriented hand movements. Human area 44 has facilitatory and inhibitory effects over both tonic and phasic finger movements. It is shown that single TMS of area 44 produces motor evoked potential from hand muscles. Conclusion: Human area 44 is involved in voluntary hand movements and has direct fast-conducting corticospinal projections.