Effects Of Unilateral Electroacupuncture Stimulation On The Adaptability Of Hemispheric Hemispheres In Human Brain

Background: Chronic unilateral resistance training increased trained and untrained contralateral homologous muscle strength significantly, which is called cross-education. In recent years, cross-education has been applied in the rehabilitation of clinical disease, which can significantly improve motor function in patients. Currently mechanism of cross-education is no unified conclusion. There is some evidence to suggest that adaptive changes of interhemispheric connectivity for motor cortex may be one of the neural mechanisms of cross-education, but whether unilateral electric acupuncture inducing cross-education via interhemispheric pathway for motor cortex has not been reported. Objective: In this study, we utilized TMS-EMG-EEG joint inspection and evaluation technology, and adopted the experiment intervention, a 4-week electric acupuncture stimulation at Zusanli(ST-36) and Xiajuxu(ST-39) of right leg, for subjects. Before and after the intervention, we measured the maximal voluntary contraction(MVC) strength of bilateral tibialis anterior muscles, as well as interhemispheric connectivity for motor cortex. We aimed to investigate the adaptive influence of electric acupuncture on interhemispheric connectivity of motor cortex, so that which can provide neurophysiological mechanisms in cortical level for electric acupuncture inducing cross-education. Furthermore, the results of this research can provide experimental evidences for the application of cross-education in the field of rehabilitation treatment. Methods: Twenty right-footed healthy males(age range = 19-26 years, age = 22.33±2.18 years) are volunteered for the study. The subjects were randomly assigned into the double groups: electric acupuncture group(EACU, N = 10) and control group(CON, N = 10). The subjects in EACU group received 30 minutes of electric acupuncture at IV Zusanli(ST-36) and Xiajuxu(ST-39) of right leg, 5 sessions per week for 4 weeks. In each session, parameters for electric acupuncture are non-symmetry of the pulses at a frequency of 50 Hz, square-wave, pulse width of 200 ms, constant current, and in the form of intermittent wave, working 15 s and pausing 5s, with a gradually increased intensity up to the maximal level the subjects could tolerate. Subjects in the CON group kept their normal daily activities without any additional intervention. Before the intervention and 48 h after the last intervention, all subjects participated the following tests: maximal voluntary contraction(MVC) strength of tibialis anterior muscles, interhemispheric signal propagation(ISP), ipsilateral silent period(ip SP), global mean field amplitude(GMFA), as well as N100, the late component of TMS evoked cortical potential(TEP). Results :(1) EACU group acquired significant and similar MVC gains(30.70 N increasement in right leg and 45.10 N increasement in left leg, p<0.001),while CON group not(7.53 N increasement in right leg and 8.17 N increasement in left leg, P>0.05). Post hoc analyses indicated that significant difference of MVC between EACU and CON group.(2) EACU group has significant and similar reduction for ISP(22.56% reduction when TMS stimulated left M1 and 20.35% reduction when TMS stimulated right M1, P<0.05), while CON group not(0.34% reduction when TMS stimulated left M1 and 1.91% reduction when TMS stimulated right M1, P>0.05). Post hoc analyses revealed no significant difference of ISP between EACU and CON group.(3) When TMS stimulated left M1, EACU group significantly reduced 25.83 ms for ip SP( P<0.05), while CON group increased 0.61ms(P>0.05). Post hoc analyses indicated that significant difference of ip SP between EACU and CON group. When TMS stimulated right M1, EACU group reduced 9.15 ms for ip SP( P>0.05), while CON group increased 3.00ms(P>0.05). Post hoc analyses revealed no significant difference of ip SP between EACU and CON group.(4) Whenever TMS stimulated left M1 or right M1, neither EACU nor CON group has significant difference for GMFA(P>0.05).(5) When TMS stimulated left M1, EACU group has some reduction in different degree for the amplitude of N100(7.67μv reduction in C1, P>0.05; 9.30μv reduction in C2, P<0.05; 13.34μv reduction in FC1, P<0.05; 11.75μv reduction in FC2, P<0.05), while CON group not(C1,C2,FC1 and FC2,p>0.05). Post hoc analyses indicated that some different significances of ip SP between EACU and CON group(P>0.05 in C1 and FC2; P<0.05 in C2 and FC1;). When TMS stimulated right M1, neither EACU nor CON group has significant difference for the amplitude of N100(P>0.05). Whenever TMS stimulated left M1 or right M1, neither EACU nor CON group has significant difference for the latency of N100(P>0.05). Conclusion: 4-week electric acupuncture stimulation at Zusanli(ST-36) and Xiajuxu(ST-39) of right leg can significantly enhanced the strength of interhemispheric connectivity for motor cortex, as well as significantly decreased interhemispheric inhibition from left M1 to right M1, induced synaptic plasticity in bilateral primary motor cortex and supplementary motor area, and resulted in long-term potentiation. That may be one of the neural mechanisms of cross-education induced by chronic unilateral electric acupuncture.