The Effects Of Aerobic Exercise On Decision-making Of Methamphetamine Dependents And The Brain Processing Characteristics

Purpose: Decision-making,as a high-level cognitive function,is an essential part of human survival.Drug dependents often decide to choose the former between immediate rewards such as temporary euphoria and pleasure and potential penalties such as personal health and family and social status destruction.Methamphetamine(MA)is currently the most abused type of stimulant drug in the world.It has strong neurotoxicity,and long-term use will damage the nervous system of the brain.Previous studies have found that 75% of stimulant drug addicts will relapse within half a year after withdrawal.This type of relapse behavior with high probability is essentially a decision-making disorder.In recent years,as more and more scientists in the field of drug dependence pay attention to the decision-making of drug dependents and their brain mechanisms have gradually been directed to the prefrontal lobe especially the orbitofrontal cortex(OFC),and the dorsolateral prefrontal cortex(DLPFC)was found to play an important role in decision making.It is urgent to find effective ways to improve the decision making of drug dependents.Of all the treatments,aerobic exercise is gaining attention as an economical and green method.It has been widely accepted that suitable aerobic exercise can improve the memory function,inhibition ability and emotional mediating function of the brain of MA dependent people,but there is less research on aerobic exercise directly on decision-making ability,especially on its brain mechanism the study.The purpose of this study was to explore the effects of aerobic exercise on the decision making of MA dependents and their brain processing characteristics through two interventions: acute aerobic exercise and long-term aerobic exercise.Methods: This study was conducted in SHILIPING Compulsory Drug Rehab Center in Zhejiang Province.In the first study,28 MA dependents during the rehabilitation and consolidation period were given acute aerobic exercise intervention with different intensities,and a control group was set up: control group(n=9,living in a normal rehab life),moderate-aerobic exercise group(n=10,65-75% HRmax),and high-aerobic exercise group(n=9,75-85% HRmax).Exercise intervention was performed using stationary exercise bicycles(SH-5000 U)of corresponding intensity.Each intervention lasted for 45 minutes(including 5-minute warm-up,5-minute acceleration,25-minute target heart rate maintenance,5-minute deceleration on the bike and 5-minute relaxation time).Exercise interventions were conducted under the guidance of professionals and under the supervision of police.If MA dependents experience discomfort during exercise,they would take a rest or seek medical attention immediately.Except for the time of exercise intervention,the subjects in the exercise group lived the same regular life as the control group during the whole experiment period.Before and after the intervention,a classic psychological decision-making test paradigm,Iowa Gambling Task(IGT),was used to test the decision-making of MA dependents.And the changes in the concentration of oxygenated hemoglobin(HbO)in the dorsal lateral prefrontal cortex(DLPFC)and orbitofrontal cortex(OFC)during the IGT were detected by functional near-infrared spectroscopy system(fNIRS).In the second study,of 53(mean age: 32.83 ± 6.52 years)MA dependents completed the whole experiment.The subjects were randomly divided into 3 groups: the control group(n = 15),the moderate-intensity aerobic exercise group(n = 21),the high-intensity aerobic exercise group(n = 17),and the two exercise groups were subjected to the corresponding intensity.The exercise intervention method of the two exercise groups is the same as the first study,which lasts for 12 weeks,3 times per week,45 minutes each time,and the control group lived a regular rehab life for 12 weeks.At an interval of 12 weeks,both before and after the intervention,the subjects were tested for decision-making using a computer version of IGT,while fNIRS was used to detect the hemodynamics of subjects' DLPFC and OFC during the task.What's more,the subjects' drug craving was evaluated by visual analog scale(VAS).Results: The behavioral results of the first study showed that there was no significant difference in IGT performance among the three groups in the pretest,and the net score of each block was negative.The repeated measures ANOVA of 2(pretest,posttest)* 3(3 groups)* 5(5 blocks)found that only the IGT performance of high-intensity aerobic exercise group had significantly improved in the post-test(P = 0.002).The results of the fNIRS study showed that there was no statistical difference between DLPFC and OFC between groups or before and after intervention.The behavioral results of the second study showed that there was no statistically significant difference in IGT performance between the three groups of subjects in the pre-test,and the net scores were all negative.Repeated measures ANOVA of 2(pretest,posttest)* 5(5 blocks)was performed on the net scores of each group,respectively.The results showed that IGT performance of subjects in the high-intensity aerobic exercise group was significantly superior after 12 weeks of different interventions to that in the pretest(P =0.037).The results of the fNIRS showed that there were no significant differences between groups in the HbO concentration levels in DLPFC and OFC in the pretest.After 12 weeks of different interventions,the DLPFC in the high-intensity aerobic exercise group showed a significant difference between the pretest and posttest: the HbO concentration in the left DLPFC in the fifth block was significantly higher in the posttest than that in the pretest(P = 0.01);the HbO concentration in the third block in the right DLPFC was significantly higher in the posttest than that in the pretested(P = 0.003).The OFC of the moderate-intensity aerobic exercise group showed a significant difference of hemodynamics between pretest and posttest: the HbO concentration of block 4 was significantly higher in the posttest of OFC than that in the pretest(P = 0.043).Additionally,In the moderate-intensity aerobic exercise group,the degree of drug craving of MA in posttest was significantly lower than that in the pretest(P = 0.015),while the control group increased significantly(P = 0.04).Conclusions: With the help of IGT and fNIRS,this study first conducted a preliminary exploration of the effects of aerobic exercise on the decision-making of MA dependents through acute aerobic exercise intervention,and then further research was carried through a long-term aerobic exercise intervention.Combining the findings of previous studies and the results of this study,the following conclusions can be drawn: aerobic exercise can improve the decision-making ability of people dependent on MA,and high-intensity aerobic exercise may improve the decision-making of MA dependents with more efficiency by enhancing the activity of DLPFC.