Experience Of Musical Pleasure And Reward In Congenital Amusia: An EEG Study

Objective:We aimed to explore if the amusics and the controls have the same ability to get pleasure from music by combining questionnaires,behavioral tasks and EEG.Methods:We selected 26 amusics and 25 controls using the Montreal Battery of Evaluation of Amusia（MBEA）.All participants filled out the questionnaires related to musical preference,physical anhedonia,and current emotional states.We also evaluated the IQ（Intelligence quotient）of every participant.Then,we used the real-time rating tasks and auction paradigm to evaluate their ability to obtain pleasure from music and their motivation to obtain musical reward again.Meanwhile,the electroencephalogram was recorded.The data analysis focused on the pressing time in the real-time rating tasks,the times of successful purchase in the auction paradigm,the power spectral density values for alpha and theta frequency bands,the alpha frontal asymmetry,beta to alpha ratio,and theta phase-synchronization.We used the independent-samples T test,repeated measures ANOVA,and the Mann-Whitney U test to compare these indices of the two groups.Finally,regression analysis was conducted to explore the relationship between EEG indices and the MBEA score.Results:General demographic data showed no significant difference between the two groups in terms of gender,age,years of education,initial pre-experimental mood state,the scores of Chinese Version of Revised Physical Anhedonia Scale（RPAS-C）,and music preference.But the IQ of the amusia group is significantly higher than that of the control group.The behavioral results showed no significant difference either in the pressing time in the real-time rating tasks under five different pleasure levels or in the total pressing time of three pleasant levels in the real-time rating tasks.There was also no significant difference in the number of successful purchases in the auction task.The results of theta power spectral density showed that the power spectral density of theta band in the left prefrontal lobe region under the conditions of“high pleasure”and“low pleasure”in the amusia group was higher than that in the control group(t _{high pleasure}=-2.91,p=0.009;t _{low pleasure}=-2.12,p=0.046),the power spectral density of theta in the“high pleasure”condition in the right prefrontal region was higher than that in the control group(t _{high pleasure}=-2.74,p=0.013),the power spectral density values of theta in the left frontal region in“musical chill”,“high pleasure”and“unpleasant”conditions were higher than those in the control group(t _{musical chill}=-2.25,p=0.036;t _{high pleasure}=-2.34,p=0.030;t _unpleasant=-2.11,p=0.048)and theta power spectral density values in the“high pleasure”condition in the left and right temporal regions were higher than that in the control group(t _{high pleasure（left）}=-2.18,p=0.042;t _{high pleasure（right）}=-2.18,p=0.042).The results of theta phase synchronization showed that when experiencing musical chill,the phase synchronization between the P2 and OZ electrodes in the control group was significantly higher than that in the amusia group.In the amusia group,the phase synchronization between frontotemporal electrodes under the condition of“musical chill”was significantly lower than that of the other three conditions“high pleasure”,“low pleasure”,“neutral”and“unpleasant”.In the control group,the degree of phase synchronization between frontotemporal electrodes under the“musical chill”was significantly higher than that under the"low pleasure","neural",and"unpleasant"conditions.The results of the power spectral density of the alpha band showed the power spectral density of the alpha band in the right prefrontal region under the“high pleasure”condition in the amusia group was higher than that in the control group(t _{high pleasure}=-2.30,p=0.033)and the power spectral density of the alpha band in the right prefrontal region under the“high pleasure”condition in the amusia group was also higher than that in the control group(t _{high pleasure}=-2.12,p=0.047).The results of alpha asymmetry showed that there was a significant difference in the alpha asymmetry of the prefrontal lobe between the amusia group and the control group under the"unpleasant"condition（Mann-Whitney U=157.000,p<0.05）,which showed that the left side of the control group was significantly different.The alpha power of the lateral prefrontal lobe was greater than that of the right prefrontal lobe,while the alpha power of the right prefrontal lobe was greater than that of the left prefrontal lobe in the amusia group.The results of the beta/alpha ratio showed that there was no significant difference in the beta/alpha ratio of the frontal lobe between the two groups.Besides,theta power spectral density in the left prefrontal region under“high pleasure”and“low pleasure”conditions and the alpha power spectral density under“high pleasure”conditions can negatively predict MBEA scores.Conclusions:（1）There is abnormal pitch perception in amusia,but compared to the controls,there is no significant difference in the length of pleasure experience they obtained from music.This result suggests that music processing in congenital amusia may reflect the developmental dissociation between music perception and music appreciation;（2）under pleasant conditions,weak theta and alpha activity in the frontal lobe region of the congenital amusia reflects weaker activation of the reward system when they obtained the pleasure and rewarding experience from music;（3）The results of alpha asymmetry showed that there were abnormalities in emotional valence recognition in the amusia group,which may be because they could not detect the less different acoustic features;（4）The phase synchronization results of the amusia group in the frontotemporal area showed that their reward processing did not involve the process of anticipation and prediction error.