Abstract
Repetitive transcranial magnetic stimulation (rTMS) induces lateralized speech arrest consistent with cerebral dominance for language. Studies of language cerebral dominance in differently handed healthy subjects have been limited. Using a focal magnetic coil, we examined the degree of consistency between handedness as evaluated by the Stanley Coren Score and hemispheric dominance for language as determined by rTMS in 25 right- and 25 left-handed medical students. They were categorized according to the score into 24 strongly right-handed, 1 moderately right-handed, 19 strongly left-handed, 3 moderately left-handed and 3 ambidextrous (equally-handed). In the strongly right-handed subjects, left-sided language cerebral dominance was recorded in 87.5% of the subjects, and bilateral cerebral representation in 8.2%, and right-sided language cerebral dominance in 4.2%. In the strongly left-handed subjects, 73.7% had left-side language cerebral dominance, 15.8% had bilateral cerebral representation and 10.5% had right-side cerebral language dominance. In mixed handed subjects (moderately right, left and ambidextrous), bilateral cerebral representation was observed in 57% and left-side cerebral language dominance in 43%. There were 27 subjects who developed speech arrest at 140% of motor threshold, the others developed speech arrest at lower intensities. Speech lateralized to the left-side cerebral dominance in strongly right- and left-handed subjects, but bilateral cerebral representation was frequent in mixed handedness and right-sided cerebral dominance rarely occurred.