THE USE OF A CAP-SHAPED COIL FOR TRANSCRANIAL MAGNETIC STIMULATION OFTHE MOTOR CORTEX

A cap-shaped coil is introduced as a superior design for inducing tran scranial magnetic motor evoked potentials for spinal cord monitoring. Evaluation of the magnetic characteristics of the cap coil showed high er induced electrical fields at and below the depth of the cortical su rface. compared to a 9-cm, butterfly-shaped coil. Twenty normal adults were stimulated with the cap coil and a 9-cm round coil in three posi tions. Compound muscle action potentials were recorded from the left a nd right abductor digiti minimi and anterior tibialis muscles. The cap coil induced potentials with higher intensities and lower variability between consecutive stimuli. The cap coil was also more able to simul taneously induce motor evoked potentials from the four muscles studied . This coil design should provide superior means of inducing transcran ial magnetic motor evoked potentials in multiple muscles.