Neural activation to monetary reward is associated with amphetamine reward sensitivity

Lack of effect of methamphetamine on reward-related brain activity in healthy adults

INTRODUCTION

Stimulant drugs are thought to alter processing of rewarding stimuli. However, the mechanisms by which they do this are not fully understood.

METHOD

In this study we used EEG to assess effects of single doses of methamphetamine (MA) on neural responses during anticipation and receipt of reward in healthy volunteers. Healthy young men and women (N = 28) completed three sessions in which they received placebo, a low MA dose (10 mg) or a higher MA dose (20 mg) under double blind conditions. Subjective and cardiovascular measures were obtained, and EEG was used to assess brain activity during an electrophysiological version of the Monetary Incentive Delay (eMID) task.

RESULTS

EEG measures showed expected patterns during anticipation and receipt of reward, and MA produced its expected effects on mood and cardiovascular function. However, MA did not affect EEG responses during either anticipation or receipt of rewards.

CONCLUSIONS

These findings suggest that the effects of MA on EEG signals of reward processing are subtle, and not related to the drug's effects on subjective feelings of well-being. The findings contribute to our understanding of the neural effects of MA during behaviors related to reward.

Methamphetamine alters nucleus accumbens neural activation to monetary loss in healthy young adults

RATIONALE

Stimulant drugs like methamphetamine (MA) activate brain reward circuitry, which is linked to the development of problematic drug use. It is not clear how drugs like MA alter neural response to a non-drug reward.

OBJECTIVES

We examined how acute MA impacts neural response to receipt of a monetary reward relative to a loss in healthy adults. We hypothesized that MA (vs. placebo) would increase mesolimbic neural activation to reward, relative to loss.

METHODS

In a within-subject, randomized, cross-over, double-blind, placebo-controlled design, 41 healthy adults completed the Doors monetary reward task during fMRI after ingestion of placebo or 20 mg MA. We examined drug effects on neural response to reward receipt (Win vs. Loss) using a priori anatomical striatal regions of interest (nucleus accumbens (NAcc), caudate, putamen).

RESULTS

MA decreased NAcc BOLD activation to reward vs loss compared to placebo (p=.007) without altering caudate or putamen BOLD activation. Similar effects for reward vs. loss were obtained using whole brain analysis. Additional exploratory ROI analysis comparing reward and loss activation relative to a neutral "fixation" period indicated that MA increased NAcc BOLD activation during loss trials, without decreasing activation during win trials.

CONCLUSIONS

This preliminary evidence suggests that MA increases NAcc neural response to the receipt of monetary loss. Additional studies are needed to replicate our findings and clarify the mechanisms contributing to altered mesolimbic neural response to reward and loss receipt during stimulant intoxication.

Embodied decision biases: individually stable across different tasks?

In everyday life, action and decision-making often run in parallel. Action-based models argue that action and decision-making strongly interact and, more specifically, that action can bias decision-making. This embodied decision bias is thought to originate from changes in motor costs and/or cognitive crosstalk. Recent research confirmed embodied decision biases for different tasks including walking and manual movements. Yet, whether such biases generalize within individuals across different tasks remains to be determined. To test this, we used two different decision-making tasks that have independently been shown to reliably produce embodied decision biases. In a within-participant design, participants performed two tasks in a counterbalanced fashion: (i) a walking paradigm for which it is known that motor costs systematically influence reward decisions, and (ii) a manual movement task in which motor costs and cognitive crosstalk have been shown to impact reward decisions. In both tasks, we successfully replicated the predicted embodied decision biases. However, there was no evidence that the strength of the biases correlated between tasks. Hence, our findings do not confirm that embodied decision biases transfer between tasks. Future research is needed to examine whether this lack of transfer may be due to different causes underlying the impact of motor costs on decisions and the impact of cognitive crosstalk or task-specific differences.

A narrative review of reward sensitivity, rash impulsivity, and food addiction in adolescents

Adolescence represents a neurodevelopmental period characterised by heightened reward drive and weaker inhibitory control that may increase vulnerability to compulsive overconsumption of highly-palatable foods and food addiction. This narrative review aimed to summarise research investigating the presence of food addiction in adolescents and establish the role that impulsivity traits (i.e., reward sensitivity and rash impulsivity), previously linked to substance and behavioural addictions, play in contributing to food addiction in this cohort. It was found that the prevalence of food addiction was typically higher in studies that recruited adolescents who were overweight/obese or from clinical populations. Overall, impulsivity was found to be more consistently associated with food addiction, while the relationships between measures of reward sensitivity and food addiction were mixed. Findings of this review suggest trait impulsivity may contribute to food addiction in adolescents, however, further longitudinal and prospective research is recommended to confirm these findings and to investigate the potential interactive effects of reward sensitivity and rash impulsivity.

Valuation system connectivity is correlated with poly-drug use in young adults

Poly-drug consumption contributes to fatal overdose in more than half of all poly-drug users. Analyzing decision-making networks may give insight into the motivations behind poly-drug use. We correlated average functional connectivity of the valuation system (VS), executive control system (ECS) and valuation-control complex (VCC) in a large population sample (n = 992) with drug use behaviour. VS connectivity is correlated with sedative use, ECS connectivity is separately correlated with hallucinogens and opiates. Network connectivity is also correlated with drug use via two-way interactions with other substances including alcohol and tobacco. These preliminary findings can contribute to our understanding of the common combinations of substance co-use and associated neural patterns.

Subjective responses predict d-amphetamine choice in healthy volunteers

BACKGROUND

It is commonly believed that drugs, including stimulants, are used recreationally because of their ability to induce pleasurable subjective effects. However, recreational drug use sometimes occurs in the absence of positive subjective effects, suggesting that other factors contribute. Here, we examine the extent to which the direct subjective effects of amphetamine, a commonly misused stimulant, predict subsequent choice of the drug vs placebo.

METHODS

Healthy adults (N = 112) participated in a five-session amphetamine choice study. On the first four sessions, participants sampled either 20 mg d-amphetamine or placebo in color-coded capsules two times each. On the fifth session, they chose which color (d-amphetamine or placebo) they preferred. We examined the choice of drug vs placebo in relation to demographic characteristics, baseline mood states, personality and subjective and cardiovascular responses to acute administration of the drug.

RESULTS

Eighty-one participants chose amphetamine (Choosers) while 31 chose placebo (Non-choosers). Overall, amphetamine produced typical stimulant-like effects on subjective questionnaires, and it elevated heart rate and blood pressure vs placebo. Choosers reported greater positive mood, elation and stimulant-like effects following amphetamine compared to Non-choosers. The Choosers also exhibited a greater increase in systolic blood pressure, but not heart rate. The groups did not differ on demographic characteristics, mood states before drug administration or personality.

CONCLUSIONS

These findings support the idea that pleasurable subjective responses to amphetamine, including positive mood, elation, and stimulant-like effects influence behavioral choice of the drug.

A role for reward valuation in the serotonergic modulation of impulsivity

RATIONALE

Impulsive behavior is a deleterious component of a number of mental health disorders but has few targeted pharmacotherapies. One contributing factor to the difficulty in understanding the neural substrates of disordered impulsivity is the diverse presentations of impulsive behavior. Defining the behavioral and cognitive processes which contribute to different subtypes of impulsivity is important for understanding the neural underpinnings of dysregulated impulsive behavior.

METHODS

Using a mouse model for disordered impulsivity, our goal was to identify behavioral and cognitive processes that are associated with increased impulsivity. Specifically, we were interested in the facets of impulsivity modulated by serotonin signaling. We used mice lacking the serotonin 1B receptor (5-HT_1BR) and measured different types of impulsivity as well as goal-directed responding, extinction, habitual-like behavior, cue reactivity, and reward reactivity.

RESULTS

Mice lacking expression of 5-HT_1BR had increased levels of impulsive action, goal-directed responding, and motivation, with no differences seen in rate of extinction, development of habitual behavior, delay discounting, or effort-based discounting. Interestingly, mice lacking 5-HT_1BR expression also showed an overall increase in the choice of higher value rewards, increased hedonic responses to sweet rewards, and responded more for cues that predict reward. We developed a novel paradigm to demonstrate that increasing anticipated reward value could directly increase impulsive action. Furthermore, we found that 5-HT_1BR KO-induced impulsivity could be ameliorated by decreasing the reward value relative to controls, suggesting that the increased 5-HT_1BR-associated impulsive action may be a result of increased reward valuation.

CONCLUSIONS

Taken together, these data show that the effects of serotonin on impulsive action are mediated through the modulation of hedonic value, which may alter the reward representations that motivate action. Overall, this data supports a role for reward value as an important substrate in impulsive action which may drive clinically relevant increases in impulsivity.

Neural activation during anticipation of monetary gain or loss does not associate with positive subjective response to alcohol in binge drinkers

BACKGROUND

Alcohol use disorder (AUD) remains an unresolved source of morbidity and mortality. Psychopharmacological challenge studies and neuroimaging experiments are two methods used to identify risk of problematic substance use. The present study combined these two approaches by examining associations between self-reported stimulation, sedation, liking or wanting more after a dose of alcohol and neural-based responses to anticipation of monetary gain and loss.

METHODS

Young adult binge drinkers (N = 56) aged 21-29, with no history of Substance Use Disorder completed five experimental sessions. These included four laboratory sessions in which they rated their subjective responses to alcohol (0.8 g/kg for men, 0.68 g/kg for women) or placebo, and a single functional magnetic resonance imaging session in which they completed a monetary incentive delay task. During the scan, we recorded neural signal related to anticipation of winning $5 or $1.50 compared to winning no money (WinMoney-WinZero), losing $5 or $1.50 compared to losing no money (LoseMoney-LoseZero), and winning $5 or $1.50 compared to losing $5 or $1.50 (WinMoney-LoseMoney), in reward related regions.

RESULTS

There were no significant associations between subjective ratings of "Feel Drug Effect", "Like Drug Effect", "Want More", stimulation or sedation following the acute alcohol challenge and neural activation in reward related regions during anticipation of monetary gain or loss.

CONCLUSIONS

These results suggest that sensitivity of neural reward circuits is not directly related to rewarding subjective experiences from alcohol. Taken together with previous studies, the present findings indicate that the association between the subjective effects of drugs and reward-related brain activity depends on the drugs, tasks or subject samples under study.

Striatal activation to monetary reward is associated with alcohol reward sensitivity

One well-known phenotypic risk factor for the development of alcohol use disorder is sensitivity to the rewarding effects of alcohol. In the present study, we examined whether individuals who are sensitive to alcohol reward are also sensitive to nondrug rewards, thereby reflecting a broader individual difference risk factor. Specifically, we tested the hypothesis that subjective response to acute rewarding effects of alcohol would be related to neural activation during monetary reward receipt relative to loss (in the absence of alcohol). Community-recruited healthy young social drinkers (N = 58) completed four laboratory sessions in which they received alcohol (0.8 g/kg) and placebo in alternating order under double-blind conditions, providing self-report measures of subjective response to alcohol at regular intervals. At a separate visit 1-3 weeks later, they completed a reward-guessing game, the 'Doors' task, during fMRI in a drug-free state. Participants who reported greater motivation (i.e., wanting) to consume more alcohol after a single moderate dose of alcohol also exhibited greater neural activation in the bilateral ventral caudate and the nucleus accumbens during reward receipt relative to loss. Striatal activation was not related to other subjective ratings including alcohol-induced sedation, stimulation, or pleasure (i.e., feeling, liking). Our study is the first to show that measures of alcohol reward are related to neural indices of monetary reward in humans. These results support growing evidence that individual differences in responses to drug and nondrug reward are linked and together form a risk profile for drug use or abuse, particularly in young adults.

Males are more sensitive to reward and less sensitive to loss than females among people with internet gaming disorder: fMRI evidence from a card-guessing task

BACKGROUND

Many studies have found an interesting issue in the Internet gaming disorder (IGD): males are always observed to be the majority. However, there are little research to exploring the differences in the neural mechanisms between males and females in decision-making process among people with IGD. Therefore, explore the reward/loss processing between different gender with IGD could help in understanding the underlying neural mechanism of IGD.

METHODS

Data from functional magnetic resonance imaging (fMRI) were collected from 111 subjects (IGD: 29 males, 25 females; recreational internet game user (RGU): 36 males, 21 females) while they were performing a card-guessing task. We collected and compared their brain features when facing the win and loss conditions in different groups.

RESULTS

For winning conditions, IGD group showed hypoactivity in the lingual gyrus than RGU group, male players showed hyperactivity in the left caudate nucleus, bilateral cingulate gyrus, right middle frontal gyrus (MFG), right precuneus and inferior parietal lobule relative to the females. And significant sex-by-group interactions results showed higher brain activities in the thalamus, parahippocampal gyrus and lower brain activities in Inferior frontal gyrus (IFG) were observed in males with IGD than females. For losing conditions, IGD group showed hypoactivity in the left lingual gyrus, parahippocampal gyrus and right anterior cingulate cortex (ACC) compared to the RGU group, male players showed hyperactive left caudate nucleus and hypoactive right middle occipital gyrus relative to females. And significant sex-by-group interactions results showed that compared to females with IGD, males with IGD showed decreased brain activities in the IFG and lingual gyrus.

CONCLUSIONS

First, there appeared to be no difference in reward processing between the IGD and RGU group, but IGD showed less sensitivity to loss. Secondly, male players showed more sensitivity to rewards and less sensitivity to losses. Last but not least, males and females showed opposite activation patterns in IGD degree and rewards/losses processing. And male IGD subjects are more sensitive to reward and less sensitive to loss than females, which might be the reason for the gender different rates on IGD.

Stability of acute responses to drugs in humans across repeated testing: Findings with alcohol and amphetamine

BACKGROUND

Controlled drug challenge studies provide valuable information about the acute behavioral effects of drugs, including individual differences that may affect risk for abuse. One question that arises in such studies is whether a single administration of a drug (and placebo) provides an accurate measure of response to the drug.

METHODS

Here, we examined data from two studies, one with alcohol and one with amphetamine, in which participants received two administrations of the drug and placebo. In this analysis we assess the stability of acute subjective and cardiovascular responses to the drugs across the two administrations. We examine i) systematic increases or decreases to the drugs from the first to the second administration, ii) test-retest reliability within individuals and iii) the accuracy of the acute drug responses to predict drug choice in a later session.

RESULTS

Responses were largely stable across sessions, although on the second session amphetamine "liking" was higher, and subjective responses to placebo including "liking" and "want more" decreased in both studies. Test-retest reliability within individuals was high. Responses during the first drug administration were as accurate in predicting drug choice as responses during both administrations combined.

CONCLUSIONS

Our findings indicate that a single administration of drug (and placebo) provides a good index of an individual's responses to alcohol or amphetamine, when participants are tested under controlled experimental conditions.

Anticipation of monetary reward in amygdala, insula, caudate are predictors of pleasure sensitivity to d-Amphetamine administration

BACKGROUND

Drug addiction and dependence continue as an unresolved source of morbidity and mortality. Two approaches to identifying risk for abuse and addiction are psychopharmacological challenge studies and neuroimaging experiments. The present study combined these two approaches by examining associations between self-reported euphoria or liking after a dose of d-amphetamine and neural-based responses to anticipation of a monetary reward.

METHODS

Healthy young adults (N = 73) aged 19 and 26, without any history of alcohol/substance dependence completed four laboratory sessions in which they received oral d-amphetamine (20 mg) or placebo, and completed drug effect questionnaires. On a separate session they underwent a functional magnetic resonance imaging scan while they completed a monetary incentive delay task. During the task, we recorded neural signal related to anticipation of winning $5 or $1.50 compared to winning no money (WinMoney-WinZero), in reward related regions.

RESULTS

Liking of amphetamine during the drug sessions was related to differences in activation during the WinMoney-WinZero conditions - in the amygdala (positive), insula (negative) and caudate (negative). In posthoc analyses, liking of amphetamine was also positively correlated with activation of the amygdala during anticipation of large rewards and negatively related to activation of the left insula to both small and large anticipated rewards.

CONCLUSIONS

These findings suggest that individual differences in key regions of the reward network are related to rewarding subjective effects of a stimulant drug. To further clarify these relationships, future pharmacofMRI studies could probe the influence of amphetamine at the neural level during reward anticipation.

Neural correlates of inhibition and reward are negatively associated

Individuals with impulsive and addictive disorders, including drug addiction, binge eating/obesity, and problem gambling, exhibit both impaired control over behavior and heightened sensitivity to reward. However, it is not known whether such deviation in inhibitory and reward circuitry among clinical populations is a cause or consequence of the disorders. Recent evidence suggests that these constructs may be related at the neural level, and together, increase risk for engaging in maladaptive behaviors. The current study examined the degree to which brain function during inhibition relates to brain function during receipt of reward in healthy young adults who have not yet developed problem behaviors. Participants completed the stop signal task to assess inhibitory control and the doors task to assess reactivity to monetary reward (win vs loss) during functional magnetic resonance imaging (fMRI). Brain activation during response inhibition was negatively correlated with brain activation during reward. Specifically, less brain activation in right prefrontal regions during inhibition, including the right inferior frontal gyrus, middle frontal gyrus, and supplementary motor area, was associated with greater brain activation in left ventral striatum during receipt of monetary reward. Moreover, these associations were stronger in binge drinkers compared to non-binge drinkers. These findings suggest that the systems are related even before the onset of impulsive or addictive disorders. As such, it is possible that the association between inhibitory and reward circuitry may be a prospective marker of risk.

Gender differences in the behavioral and subjective effects of methamphetamine in healthy humans

RATIONALE

Methamphetamine (MA) use is steadily increasing and thus constitutes a major public health concern. Women seem to be particularly vulnerable to developing MA use disorder, as they initiate use at a younger age and transition more quickly to problematic use. Initial drug responses may predict subsequent use, but little information exists on potential gender differences in the acute effects of MA prior to dependence.

OBJECTIVE

We examined gender differences in the acute effects of MA on subjective mood and reward-related behavior in healthy, non-dependent humans.

METHODS

Men (n = 44) and women (n = 29) completed 4 sessions in which they received placebo or MA under double-blind conditions twice each. During peak drug effect, participants completed the monetary incentive delay task to assess reaction times to cues signaling potential monetary losses or gains, in an effort to determine if MA would potentiate reward-motivated behavior. Cardiovascular and subjective drug effects were assessed throughout sessions.

RESULTS

Overall, participants responded more quickly to cues predicting incentivized trials, particularly large-magnitude incentives, than to cues predicting no incentive. MA produced faster reaction times in women, but not in men. MA produced typical stimulant-like subjective and cardiovascular effects in all participants, but subjective ratings of vigor and (reduced) sedation were greater in women than in men.

CONCLUSIONS

Women appear to be more sensitive to the psychomotor-related behavioral and subjective effects of MA. These findings provide initial insight into gender differences in acute effects of MA that may contribute to gender differences in problematic MA use.