Objective
To investigate the characteristics of the motor cortex map for abductor pollicis brevis muscle (APB) using transcranial magnetic stimulation (TMS) in normal subjects.

Method
Ten adults without neurological disorder were studied. A piece of cloth which marked at 1 cm interval was fixed on the head of the subject. The motor cortex mapping for APB was done with butterfly magnetic stimulator, and then with round magnetic stimulator.

Results
The average optimal scalp position for left APB was located on lateral 6.2 cm, anterior 0.1 cm from Cz and that for right APB was located on lateral ⁣6.0 cm, anterior 0.1 cm from Cz when stimulated with butterfly magnetic stimulator. The differences between hemispheres were less than 1 cm in the location of optimal scalp position and less than 10% in excitatory threshold (ET) irrespective of magnetic stimulator. The ipsilateral motor evoked potential (MEP) was not evoked in all subjects. The ET when stimulated with butterfly magnetic stimulator was higher to that when stimulated with round magnetic stimulator.

Conclusion
We conclude that TMS using butterfly and round magnetic stimulator is useful for the motor cortex mapping.