[Magnetic stimulation using double coils--methodology and normal findings].

Magnetic stimulation of the motor cortex and spinal nerve roots was investigated in a group of 45 normal subjects using double coils. Figure of eight coils allows for an isolated excitation of the motor cortex of one hemisphere which cannot be achieved with circular coils. To evoke compound responses in hand muscles the optimal position of the figure of eight coil is with its centre about 5 cm lateral of the vertex and contralateral to the target muscle. The coil handle is in frontal position (occipito-frontal direction of the stimulation current in the coil; physical current definition is used resembling the electron flow from - to +). For the excitation to leg muscles the double coil centre is over the vertex with the handle contralateral to the target muscle (frontal current direction). Cervical roots can easily be stimulated using figure of eight coils with the handle contralateral to the target muscle and the coil centre over the root segment.