Objective To compare the effects of paired associative stimulation (PAS) and repetitive transcranial magnetic stimulation (rTMS) on motor cortex excitability.Methods The baseline corticospinal excitability of the left hemispheres of 10 healthy subjects was measured in terms of resting motor threshold (RMT) and other indicators of motor evoked potentials (MEP).On the following day they received PAS composed of trascranial magnetic stimulation (TMS) to the motor cortex of the left hemisphere and electric stimulation (ES) of the median nerve contralateral to the motor cortex,with an interval of 10ms between the TMS and ES (termed PAS10).The PAS10 was delivered at a frequency of 0.05 Hz and an intensity of 120％ of the RMT,for a total of 90 pulses.The MEP amplitude,MEP latency and RMT were evaluated one minute after the stimulation.After the PAS intervention,an interval of one week was allowed to eliminate any effect of PAS on motor cortex excitability.Then rTMS was delivered to the subjects' left motor cortex at the same time of day at a frequency of 1 Hz and an intensity of 120％ of the RMT,for a total of 1000 pulses.MEP amplitude,MEP latency and RMT were evaluated one minute after the stimulation.The two interventions were compared in terms of MEP amplitude,MEP latency and RMT.Results The average MEP amplitude,MEP latency and RMT at baseline were (2.93 ± 0.99) mV,(20.97 ± 1.67) ms,and (46.06 ±5.32) ％,respectively.One minute after PAS10,the MEP amplitude,MEP latency and RMT were (1.14 ± 0.76) mV,(21.87 ± 1.09) ms and (52.06 ±4.20) ％,respectively.One minute after rTMS,the MEP amplitude and latency and the RMT were (2.24 ± 0.79) mV,(20.88 ± 1.94) ms,and (49.00 ± 4.54) ％,respectively.The differences in MEP amplitude,MEP latency and RMT pre-and post-intervention were (0.69 ± 0.10) mV,(0.09 ±0.05) ms and (3.94 ± 0.93) ％,respectively for rTMS.For PAS10 they were (1.83 ± 0.14) mV,(0.90 ± 0.26)ms and (6.00 ± 1.13)％,respectively.The differences in MEP amplitude decrease and MEP latency lengthening between the two stimulation protocols were significant,but the difference in RMT elevation was not.Conclusion Both PAS10 and low frequency rTMS suppressed motor cortex excitability,but the suppressive effect of PAS10 is more significant.

Objective To investigate the effects of paired associative stimulation (PAS) on the recovery of upper limb motor function in stroke patients,and to analyze the relationship between the change of motor cortex excitability in the contralesional hemisphere and the recovery of motor function in the affected upper limb.Methods Thirty hemiplegic stroke patients were divided randomly into a treatment group and a control group.Both groups were given routine rehabilitation therapy,but the treatment group also received PAS consisting of transcranial magnetic stimulation (TMS) of the intact motor cortex and electrical stimulation (ES) of the median nerve at the wrist of the intact arm with an interval of 10 ms between the TMS and ES (PAS10).The PAS10 was delivered at a frequency of 0.05 Hz and an intensity of 120％ the resting motor threshold (RMT),once daily for 30 minutes,five times a week for 4 weeks.Corticospinal excitability was measured using motor evoked potentials (MEP) and the RMT.The FuglMeyer upper limb assessment (FMA),Brunnstrom staging and the modified Barthel index (MBI) were also applied before and at the end of the 4 weeks of treatment.Correlation was sought between any changes in MEP amplitude,the RMT of the contralesional hemisphere and changes in the FMA results.Results Before the intervention there were no significant differences between the two groups in terms of any of the assessments.After 4 weeks of treatment,all the assessments had changed significantly compared to those before the treatment,but there were still no significant differences between the two groups in terms of any the assessments.After 4 weeks of treatment,the differences in MEP amplitude from the contra-lesional hemisphere and the differences in FMA scores were positively and significantly correlated with a correlation coefficient of r =0.431.The lesioned hemisphere was also positively correlated with the differences in FMA scores with a significant correlation coefficient of r =0.608.Conclusion PAS10 can facilitate the recovery of upper limb motor function.The change in motor cortex excitability of the contra-lesional hemisphere significantly correlates with functional recovery in the upper limb.