Objective To observe the plasticity between hand and face representations of the motor cortex of healthy volunteers after electroacupuncture(EA) at Hegu(LI4)

so as to provide a scientific basis for the theory of "Hegu is indicated for orofacial problems". Methods Using a cross-over design(self-controlled study)

10 healthy volunteers were randomly assigned to an acupuncture group and a sham acupuncture group(two-weeks wash-out period between the two groups). Subjects in the acupuncture group received EA stimulation(2 Hz

0.5 to 1 mA

30 min) at LI4 on their left hands. Adhesive pads sticked on the left hands of subject in the sham acupuncture group

thus

the placebo needle provided participants with a similar appearance to that in the acupuncture group but no skin penetration

and the placebo needles were connected to an EA device with a broken wire inside. Using transcranial magnetic stimulation technology

the motor evoked potentials(MEPs) of the first dorsal interosseous muscle and the orbicularis oculi muscle in hand and face representations in the contralateral motor cortex were recorded before and after EA and sham EA

and the total amplitude

effective stimulation area and center of gravity of MEPs were calculated. Results Compared with that before intervention

for acupuncture group

the total amplitude of MEPs in hand representation in the contrala-teral motor cortex was significantly increased(P<0.05)

while the total amplitude of MEPs in face representation was significantly decreased(P<0.05). The effective stimulation area in hand representation was significantly increased(P<0.01)

and there was no difference in face representation(P>0.05). The difference in the center of gravity of the X-axis in hand representation was statistically significant(P<0.05)

with the center of gravity moved an average of 0.6 cm to the outside

and there was no difference in face representation(P>0.05). There was no difference in the center of gravity of the Y-axis in hand and face representations(P>0.05). For sham acupuncture group

there were no differences in total amplitude of MEPs

effective stimulation area and the center of gravity in hand and face representations(P>0.05). Conclusion EA at LI4 can induce plasticity between the hand and face representations of the motor cortex in healthy volunteers(exciting the hand representation of the motor cortex

while inhibiting the motor cortex representation)

which provides a scientific basis for treating facial and mouth diseases by acupuncture at LI4 and the theory of selecting acupoints of the corresponding meridian distal to the disease location.