Neural Mechanism For Impairment OfEmotional Decision Making In Chronic Pain Patients

Accumulating evidence from both clinical and preclinical studies indicates that,in addition to sensory dysfunctions,chronic pain is often accompanied by multiple comorbidities,such as cognitive deficits,mood disorders and decreased motivation.The impact on patients' quality of life caused by these comorbidities is even worse than the pain itself.Elucidating the underlying mechanisms for mental and cognitive dysfunctions associated with chronic pain would help our understanding towards the nature of chronic pain,and ultimately facilitating the development of novel methods for clinical intervention.Previous studies have revealed impaired emotional decision making in chronic pain patients,however the underlying neural mechanism remains unclear yet.The present study aimed at exploring the underlying neural mechanism for impaired decision making in patients by examining patterns of brain activities in chronic pain patients performing Iowa gambling task,a card game developed to study emotional decision making,using noninvasive techniques of functional magnetic resonance imaging(fMRI)and electroencephalogram(EEG).In consistent with previous studies,we observed impaired decision-making performance in chronic pain patients.Patients made more disadvantageous decisions than healthy control subjects in the Iowa task.We also performed an experiment to rule out the possibility that the alteration in emotional decision making in the patients could be due to the effect of the experience of ongoing pain.Subjects with acute pain elicited by topical capsaicin did not cause significant impairment in the Iowa task performance.One of the main findings from our mechanistic studies is that the brain activities in response to reward-or punishment-related feedback stimuli were enhanced in chronic pain patients,as indicated by the EEG data showing enhanced feedback-related negativity in patients.This finding is consistent with the observation from our fMRI experiments that the insula,parietal lobe and cingulate cortex showed significantly stronger activation during the decision-making task in patients,as compared with healthy subjects.In particular,the elevated activities in both insula and parietal lobe were associated with the conditions in which the choices were made for decks of cards with high frequency of penalty.Moreover,increased activity at medial prefrontal cortex and striatum in patients(compared with healthy control subjects)was found associated with the conditions in which the choices were made for decks of cards with larger magnitude of reward.Thus,these results suggest that the impairment of emotional decision making is likely associated with abnormality of reward-and punishment-related emotional processing in chronic pain patients.Another main finding is that the brain activities associated with disadvantageous choices exhibited a trend of increase as compared with advantageous choices in chronic pain patients,as indicated by enhanced decision-preceding negativity(DPN)as well as increased anticipation P300.In contrast,no significant difference in the amplitude of either the DPN or P300 was observed between advantageous and disadvantageous choices in healthy subjects.These results are in accordance with those from our fMRI study.Thus,the activity at posterior cingulate cortex was higher for disadvantageous choices than that for advantageous choices in patients,while no significant difference was found in healthy subjects.These results suggest that the value representation/preference for different types of choices is altered in chronic pain patients.We conclude that the abnormality in neural activities in the brain areas associated with reward/punishment and value/anticipation may underlie the impairment of emotional decision making in chronic pain patients.The alteration in the neural processing was likely due to plasticity changes in the circuitries related to reward and punishment in the chronic pain condition.This speculation needs to be testified in future studies.As a pilot study,our work provides important information for the understanding of the neural mechanism for the impairment of decision making in chronic pain patients,as well as for developing clinical intervention.