Modulation Of Movement-Related Beta Power By Predictability Of Keypress Time And Location

Beta-band rhythm of motor cortex(13-30Hz)is of great significance in human movements.Compared with the baseline,the power in beta band starts to decrease about 500ms before movement,and this decline process will continue until the end of the movement,which is called movement-related beta decrease(MRBD).However,after the end of movement,the power of beta rhythm quickly rises to a level higher than the baseline within a time window of about 500ms,and this phenomenon of energy rebound is called post-movement beta rebound(PMBR).On the basis of previous studies focusing more on the relationship between beta activities and current action execution,more recent studies have begun to explore the possible relationship between beta in the next action to be performed.This study combines the predictability of time and position to explore the influence of predictability of time and position of the button-press dimensions on movementrelated beta power changes,so as to further promote the understanding of the functional meaning of beta.A total of 29 college students were tested(average age 21.13±2.25 years).The adapted series reaction time task(SRTT)paradigm was used and the experimental data was recorded synchronously through Electroencephalograph(EEG)during the completion of the task.SRTT paradigm is usually used in the study of implicit sequence learning.It is applied in this study because it can simultaneously manipulate the response to stimulus interval(Response to Stimulus Interval,referred as RSI below)—the time predictability level,and the position of the button-press—the spatial predictability level.There are three dependent variables in this experiment.The first dependent variable is RSI,including 1000ms/1500ms/2000ms three.The second dependent variable is the fixity of the response to stimulus interval(RSI),which includes two levels:fixed condition and random condition.By comparing the changes of beta power under RSI fixed conditions and RSI random conditions,we examined the impact of time predictability on beta power.The third dependent variable is the spatial predictability level of visual stimuli.It can be divided into three levels—high,middle and low—by manipulating the sequence length.By comparing the beta power under different spatial predictability conditions,we can get the change of beta power brought by spatial predictability.The dependent variables of the experiment are the correct rate and reaction time of the key press,and the peak value and latency of beta power during the task execution.The experiment was divided into two times according to the fixity of RSI,and the experimental order of RSI fixed and RSI random was balanced among all subjects.The hypothesis for this study is that if beta power is stronger under the RSI fixed condition or at the high predictability level,it indicates that time predictability or the predictability of button-press position has affect on beta power.In addition,for MRBD,we assume that the time process of MRBD will change as the length of RSI changes under the condition of RSI fixed.In this study,the time period from zero to the peak of beta power is defined as PMBR,and the time period from the peak of beta energy to the next valley is defined as MRBD.The statistical analysis of behavior data shows that the predictability of time and position of the button-press and the length of RSI have interactive effects on reaction time.Generally speaking,the shorter the RSI,the more prominent the promotion of time predictability to reaction time.Based on the behavioral results,we further hypothesized that the promoting effect of the predictability of time and position of the button-press may be reflected in the energy change of beta,while the statistics of EEG data mainly showed the effect of time predictability,but no predictable effect of position of the button-press on beta energy change was observed.And the effect of time predictability is mainly manifested in the decline rate of beta power in MRBD stage.We believe that the change of the decline rate of MRBD is the result of the joint participation of feedforward estimation and sensory feedback in the process of movement.And the slower decline rate in the early stage reflects the stage of feedforward estimation,while the significant increase in the decline rate after the turning point reflects the adjustment of the feedforward model by sensory feedback caused by visual stimulus.To sum up,this study draws the following conclusions:1)Between the end of the action and the execution of the next action,the predictability of the position of the button-press will significantly affect the speed of the reaction time,but does not adjust the change of beta power;2)The power decay process represented by MRBD is regulated by RSI,which supports that beta power is related with time predictability;3)However,the decay of MRBD may depend not only on the advance prediction of the internal feedforward model,but also on the external effective visual feedback.We speculate that its bias is sensitive to RSI,and the shorter the RSI is,the more likely it is to rely on the time prediction of the feedforward model.