Functional organisation of the facial motor system in man

To investigate human corticobulbar projections, electromyographic responses from orbicularis oculi and orbicularis oris muscles were recorded in II he althy subjects after transcranial magnetic stimulation. Selective activatio n of lower facial motoneurones of one hemisphere was reached with the round coil 4 cm lateral to the vertex on, a line to the external auditory meatus with stimulus intensities from 45 to 55% (100% = 1.5 T). The mean latency of the OR muscle teas 11.5 +/- 1.77 ms contralaterally. Ip silateral cortical responses were observed in 5 subjects (45%) at a mean la tency of 13.88 +/- 2.17 ms. Corticobulbar innervation may have affected bil ateral responses in the lower facial muscles as those persisted even after lidocaine blockade of both supraorbital nerves. The functional importance o f ipsilateral projections to the lower facial muscles in man is lower than that of the contralateral projections,as evidenced by the fact that they ca nnot be observed in all subjects or in all motor units. The influence of th e trigeminal sensory afferents was excluded from the study after blockade o f both supraorbital nerves.