Motor cortical representation of the diaphragm in man

1. Transcranial magnetic stimulation was performed using a figure-of-eight-shaped coil over the right motor cortex with the aim of identifying those areas involved with activation of the diaphragm. 2. The response of the right and left hemi-diaphragms was recorded using surface electrodes in either the 7th or 8th intercostal spaces 3 cm lateral to the anterior costal margin on either side. 3. The compound muscle action potentials recorded over the left diaphragm in response to transcranial magnetic stimulation were maximal when the centre of the figure-of-eight coil was placed approximately 3 cm to the right of the mid-line and 2-3 cm anterior to the auricular plane. 4. The amplitude of the response recorded from the diaphragm depended upon the angulation of the figure-of-eight coil and hence the direction of the stimulating current. 5. The response of the inspiratory muscles to magnetic stimulation of one side of the brain was predominantly contralateral but a small response was seen on the ipsilateral side. Ultrasonic techniques confirmed that the diaphragm was responding contralaterally and not ipsilaterally.