Input-output organization of the foot motor area in humans

OBJECTIVE A well-organized input-output relation similar to that of the monkey motor cortex has been demonstrated in the human hand motor area (Terao Y, Ugawa Y, Uesaka Y, Hanajima R, Gemba-Shimizu K, Ohki Y, Kanazawa I. Input-output organization in the hand area of the human motor cortex, Electroenceph clin Neurophysiol 1995;97:375-381). The aim of this study is to investigate the input-output organization of the human foot motor area. METHODS We studied the effect of tactile stimuli given to the toe tip on the sizes of following responses; motor evoked potentials (MEPs) elicited by transcranial magnetic or electrical stimulation (TMS or TES) over the motor cortex and magnetic stimulation at the foramen magnum level. RESULTS Air stimuli applied to the toe tip facilitated magnetically evoked MEPs of mainly the muscle attached to that toe, although a less prominent facilitation was also noted in muscles attached to the adjacent toes. Neither responses evoked by TES, nor those by stimulation at the foramen magnum level, were affected by air stimuli. These results suggest that the observed facilitatory effect occurs at the cortical level. CONCLUSION A fairly well-organized input-output relation is present also in the foot motor area in humans, although the facilitatory effect is not so topographically restricted as is noted for the hand motor area.