Modulation Of To-be Executed Movement On PMBR Associated With The Current Movement

A large number of studies have shown that beta rhythms(15?30 Hz)and mu rhythms(6?14 Hz)derived from the primary motor cortex and sensorimotor cortex are related to multiple processes of movement.From 500ms before the movement,the power of the two rhythms will start to show a significant decrease relative to the baseline,and throughout the movement execution.After the end of movement,the power of the beta rhythm quickly rises to a level higher than the baseline in a time window of about 500ms.This phenomenon of power rebound is called post-movement beta rebound(PMBR).Many researchers have explored the functional significance of PMBR,but there has not been given clear conclusion yet.Unlike the one-step movement task used in most previous studies,the current study required the subjects to complete a two-step action in one trial,focusing on how the PMBR of the current action would be regulated by whether the action is followed by a planned action next and the execution time of the planned action.The purpose is to investigate whether the internal organizational process of the planned follow-up actions can be reflected by PMBR,in order to further promote the understanding of the functional significance of PMBR.In the first experiment,23 college students(average age 19.65 ± 0.57 years)were recruited and required to complete a task included a single action and a combined two-step action(with a time interval in between).The brain activity of the subjects during the task would be simultaneously recorded using electroencephalograph(EEG).After independent component analysis(ICA)of the pre-processed EEG data and cluster analysis of independent components across subjects,the independent component clusters of the motor cortex area were selected,and their activities were further compared between experimental conditions.We found that a key result in the PMBR comparison between the single action and the first action in the combined action,when adults was performing an action using the right hand(All subjects are right-handed),the power of the PMBR that accompanies the end of the first action in the combined action is significantly higher than the PMBR of the single action.This result shows that the to-be executed movement plan will affect the power of the PMBR after the end of the current action.This study believes that the enhanced PMBR may reflect the adult's further movement plan during the action interval to efficiently respond to the next stimulus.Based on Experiment 1,Experiment 2 focuses on how the length of the time interval between two step actions in the combined action will regulate the PMBR after the end of action 1.In addition,because previous studies have shown that the change of PMBR showed a trend from scratch with age,and the internal organization and characterization process of action 2 in the combined action after the end of action 1 may also be accompanied by changes in development,Therefore,in the second experiment,we also considered the development factors.In the Experiment 2,a total of 31 adults(average age 18.61 ± 0.67)and 19 children(average age 8.38±1.31,of which 78.95%were above 8 years old)were recruited.In this experiment,participants were required to complete a game task within two actions should be executed in succession in a trial.The inter-stimulus interval(ISI)was 500ms\1000ms\1500ms\2000ms,and the adult and children's performance during the game with the corresponding brain activity would be simultaneously recorded using electroencephalograph(EEG).Similar to Experiment 1,through independent component analysis and cluster analysis of independent components across subjects,we focused on comparing the power and peak latency of PMBR in the motor cortex after the end of action 1 of the adult and the child under each ISI condition.The main results showed that:1)Both adults and children between 8 and 10 years of age exhibit significant PMBR with a significantly lower power in children than in adults.2)ISI has no effect on the peak power of PMBR no matter whether the subject is an adult or a child.3)However,there is a clear developmental difference in the peak latency period of PMBR.Specifically,the adult's PMBR reaches its highest power around 1000ms after the end of the action.This peak changes slightly with the increase of ISI,and is significantly earlier than the next stimulus.The peak power of children's PMBR appears around the next stimulus,and the peak latency is not statistically different from ISI.We believe that these results support the PMBR reflecting the planning process of subsequent actions within the brain.The difference in the peak latency period of PMBR between adults and children in this process may be related to the adult being more complete,rapid,and more dependent on the internal storage of information to form the next action plan.Based on the results of the above two experiments,this study draws the following conclusions:1)For adults,the follow-up action plan can enhance the power of PMBR after the end of the current action;2)Children's PMBR is generally lower than adults';3)For both children and adults,the time interval between the two actions has no effect on the power of PMBR;4)ISI regulates the peak latency period of PMBR during the action.However,the mode of influence on adults and children is different;the peak latency period of PMBR of adults is earlier and independent of the time when the subsequent action information appears.This may be related to the internal representation of the action plan.However,the child 's peak latency of PMBR is later and depends on the time when the subsequent information appears,which may reflect that the follow-up action plan's itinerary still depends on the input of external information.