Aberrant Reward Anticipation Processing In Abstinent Heroin Dependence:Evidence From Monetary Incentive Delay(MID)Task

Long-term abuse of heroin and other addictive drugs would result in serious damage to the cognitive process system in the brain,leading to an extremely strong motivation and drug craving for abusers when facing drug-related stimuli.It’s still ambiguous whether long-term heroin intake would impair cognitive process and behavioral regulation on general rewards such as money.Here we combined the Event-related Potential(ERP)and source localization(sLORETA)techniques to compare the reward process mechanism of abstinent heroin dependence group(AHD group)with the healthy control group(HC group)using Monetary Incentive Delay Task(MID-task),and analyzed distinct stages of cognitive process and brain activities to provide a theoretical basis for the abnormal reward process and decision-making behavior in AHD group.As for the de-noising method of EEG signal in the non-ocular reference condition,we proposed an automatic removal of ocular artifacts based on the combination of discrete wavelet transform(DWT),Kalman filter and adaptive noise canceller(ANC),which could remove ocular artifacts effectively but preserving EEG signals as much as possible.The main conclusions of this study are as follows:(1)Based on the DWT,Kalman filter and ANC,an automatic de-noising model was proposed in this paper.The innovation of the proposed model is that the wavelet coefficients are processed according to the kurtosis of each sub-component obtained by wavelet transform of the original signal.So we could construct the rough EOG signal,and then the Kalman filtering was used to predict the accurate EOG artifacts based on the previous rough EOG.Finally,the removal of ocular artifacts and the tracking of real EEG signals are realized by an ANC.This study verifies the effectiveness of this model by comparing the simulated pure EEG signals and theEEG signals after de-noising.At the same time,we compared this method with the wavelet de-noising model and adaptive de-noising model,and further verified the advantages of this model from time domain and frequency domain.Through the above analysis,we apply this model to the artifact process for EEG signals in the subsequent experimental data processing.(2)In the MID task,the behavioral results showed that the average reaction time(RT)to the target stimulus of AHD group was much shorter than that of HC group,indicating that AHD group were more impulsive when facing the target stimulus.In addition,the RT of AHD group for the positive target was significantly shorter than that for the negative target,which did not occur in HC group.So we could infer that AHD group were more likely to focus on instant rewards but neglect the potential losses.ERP results showed that Cue-related P300,related to the clue cognitive process,did not differ significantly between the two groups.And the right hemisphere lateralization effect of SPN component,associated with the outcome expectation,disappeared in AHD group.The amplitude of FRN,associated with the outcome evaluation,was modulated by the monetary cue stimuli.The source localization results showed that there were differences between these two groups at distinct stages of reward process.Therefore,we could conclude that AHD group had abnormal neural mechanism of monetary reward,and the defects of behavioral expectation and strategy adjustment would result in the abnormality in evaluating the clue stimulus and the expectation process in AHD group.In addition,damage to the anterior cingulate cortex and temporal cortex of AHD group would lead to the defects in error monitoring and feedback regulation,so that they could not perform the task based on environmental information and prior experience.In summary,the results of our study indicated that AHD group would only focus on instant reward but neglect the potential penalties when confronted with the monetary incentives.ERP results indicated that the abnormalities in behavior were associated with defects in cognitive process during each stage of reward process,and the sLORETA results further confirmed the intrinsic link between the cognitive process deficits and the impairment in reward-related brain regions associated with long-term heroin intake.