The Modulation Of Motor Imagery On Continuous Enhancement Of The Motor Cortex Excitability And Its Mechanism

Continuous enhancement of motor cortex excitability plays a primary role in motor learning,memory and functional rehabilitation of patients with nerve injury.Therefore,how to continuously enhance motor cortex excitability has become an important issue for cognitive neuroscience.Paired associative stimulation at interstimulus interval of 25ms(PAS25) can induce continuous enhancement of motor cortex excitability,but the magnitude and direction of excitability changes induced by PAS25 in the motor cortex are modulated by other plasticity protocols.Based on human studies,the primary motor cortex excitability increased and the intracortical inhibition decreased during motor imagery.However,how motor imagery modulates the continuous enhancement of motor cortex excitability induced by PAS25 and the mechanism of intracortical inhibition on the motor cortex excitability induced by motor imagery remain unclear.In this study,PAS25 was used as the inducement protocol for continuous enhancement of motor cortex excitability,and motor imagery was used as the adjustment protocol.Transcranial magnetic stimulation technique was used to investigate the modulation of motor imagery on the continuous enhancement of motor cortex excitability induced by PAS25 and its physiological mechanism.Study 1 investigated the effects of motor imagery alone on the excitability and intracortical inhibition of motor cortex.Study 2 examined the interaction between motor imagery and PAS25 through two experiments.The physiological aspect examined whether the modulation of motor imagery on the continuous enhancement of the motor cortical excitability induced by PAS25 depends on the order between the two protocols.The behavioral aspect examined the effects of motor imagery combined with the subsequent PAS25 intervention on motor learning,confirming the consistency of the motor cortex excitability changes and behavioral changes.Study 3 investigated the effects of short-interval intracortical inhibition and short latency afferent inhibition on the motor cortex excitability induced by motor imagery,and to reveal the physiological mechanism of the motor cortex circuits activated by motor imagery.The results of the study showed:(1)Motor evoked potentials(MEPs)after motor imagery intervention were significantly greater than baseline,while short-interval rntracortical inhibition was the opposite.MEPs were significantly greater immediately and 20 min after motor practice intervention than those after motor imagery intervention;(2)MEPs immediately,20,40 and 60 min were significantly greater for motor imagery combined with subsequent PAS25 coirpared to those induced by PAS25 alone.On the contrary,short-interval intracortical inhibition immediately,20 min after motor imagery combined with subsequent PAS25 was significantly smaller than those induced by PAS25 alone.There was no statistic difference between MEPs after PAS25 combined with subsequent motor imagery intervention and those after PAS25 intervention;(3)The peak acceleration of the grasp actions after motor imagery combined with PAS25 intervention was significantly faster than that after motor imagery intervention;(4)The MEP amplitude after giving short-interval rntracortical inhibition intervention during motor imagery was smaller than that after motor imagery intervention,while short-interval intracortical inhibition was the opposite;(5)The MEP amplitude after giving short latency afferent inhibition intervention during motor imagery is smaller than that after motor imagery intervention.Conclusions:(1)the motor cortex excitability continuously increased after motor imagery intervention,whereas short-interval intracortical inhibition continuously decreased;(2)the modulation of motor imagery on the continuous enhancement of the motor cortex excitability induced by PAS25 depended on the order between motor imagery and PAS25;(3)the extent of intracortical inhibition plays an lirportant role in regulating the amplitude and direction of motor cortex excitability changes induced by motor imagery.