The Development And Functional Roles Of Beta Rhythm In Motor Cortex

Beta(15~30 Hz)and mu(8~14 Hz)rhythm in the human motor cortex are closely related to motion behavior of human.Power of beta and mu rhythm significant decrease during active movement,passive movement,motor preparation,motor imagery and observing movement.Beta rhythm and mu rhythm are not two sub-components of one EEG mechanism.Upon the completion of a movement,the mu rhythm slowly returns to its baseline,but the beta rhythm shows a power “rebound” that reaches above the baseline level and lasting for a while.This phenomenon is called post-movement beta rebound(PMBR).Currently,the functional role of PMBR is still under debate,hypotheses that try to explain it includes: Idling hypothesis,termination of somatosensory afferents,resetting the motor system,the confidence in internal feed forward estimation and updating the forward model.Experiment 1 compared PMBR of children who are at age 5 to 9 with that of adults.The result shows that PMBR is found in adults but not found in children.We use an EEG approach and independent component analysis in this experiment and the result is consistent with an earlier study that used a Magneto encephalography(MEG)approach.This result does not support Idling hypothesis and hypothesis of termination of somatosensory afferents.The result shows that PMBR may represent an acquired motor-related mental process.Experiment 2 compared PMBR of one movement with that of movement combination.This experiment is designed to examine the hypothesis of resetting the motor system.The experiment set two key conditions to compare: 1)one movement condition: participants do not need to connect the next motor after the first motor;2)combined movement condition: participants need to connect the next motor after the first motor.Through the analysis of EEG data,the result shows that power of PMBR in combined movement condition is not significantly higher than that in one movement condition in general.This seems that this result does not support the hypothesis of resetting the motor system.However,after further analysis we found the power of PMBR significantly reduces with the advancement of the experiment process in the condition of one movement,but the power of PMBR in each stage has no significant difference in the condition of movement combination.This result shows that PMBR may be modulated by the connection between movements so that it remains at a relatively high level.This result supports the hypothesis of resetting the motor system.We discussed the result by combining with the other hypothesis of PMBR,and we believe this result still provides evidence for the hypothesis of resetting the motor system.