A study of individuals with amphetamine use disorder has found that they have altered neural response patterns when anticipating rewards or losses compared to individuals without this disorder. This potentially reflects an impairment in dopamine function, which may influence their decision-making. The research was published in the Journal of Psychopharmacology.
Amphetamines are potent stimulant drugs that affect the central nervous system. Some amphetamines are prescribed by medical professionals to treat conditions such as attention-deficit/hyperactivity disorder (ADHD) and narcolepsy (uncontrollable urge to sleep). Other types of amphetamines, such as methamphetamine (colloquially referred to as “speed”), are illicit drugs, produced and sold illegally for their stimulating effects.
Amphetamines can be highly addictive and dangerous if misused, particularly when taken in amounts exceeding those prescribed. This misuse can lead to amphetamine use disorder, a condition defined by compulsive use of amphetamine-type substances despite negative consequences. This disorder causes individuals to develop a psychological dependence on amphetamines, resulting in increased tolerance and withdrawal symptoms when the drugs are not used.
In the United States, approximately 2.4 million adults over the age of 26 reportedly used methamphetamine in the past year, with about 1.4 million meeting the criteria for amphetamine use disorder.
Study author April C. May and her colleagues noted that one of the theories explaining addictive behaviors posits that the brains of individuals with these behaviors have an impaired ability to react to rewards. To compensate for this deficit, these individuals seek out stronger rewards and often find them in illicit drugs.
To examine whether this might be the case, the researchers analyzed data from the Tulsa 1000 project, a naturalistic study that includes individuals with substance use disorders, as well as those with mood, anxiety, and eating disorders. They compared the neural activity of individuals with and without amphetamine use disorder as they anticipated rewards or losses.
The study involved 46 individuals with amphetamine use disorder and 90 without this disorder. The latter group did not meet criteria for any diagnosis except past major depressive disorder.
Each participant completed two rounds of the monetary incentive delay task, which consisted of 45 trials each. This task required participants to respond to cues signaling the chance to win or lose varying amounts of money based on their performance in responding to a target stimulus. During this task, a white triangle was displayed, and participants had to press a button within a specified time frame to win $0, $1, or $5, or to avoid losing these amounts. Their brain activity was recorded using functional magnetic resonance imaging while they completed the tasks.
The results indicated that individuals with amphetamine use disorder were generally slower in their reactions compared to those without the disorder. They also tended to be less educated and had poorer reading abilities. Reaction times were quicker when the potential gains were higher, especially in contrast to trials with no monetary incentive.
Those with amphetamine use disorder displayed lower activity in the caudate and putamen regions of both brain hemispheres, as well as in the left nucleus accumbens region, compared to the control group. They exhibited higher activity in the right amygdala region when anticipating large wins.
When tasked with avoiding losses, these individuals showed reduced activity in the caudate, putamen, and nucleus accumbens regions of both hemispheres and in the left amygdala region compared to the control group. They showed increased activity in the left fusiform gyrus when anticipating large losses, and lower activity in the left caudate, left putamen, and right amygdala when anticipating small losses.
The study authors concluded that individuals with amphetamine use disorder “have altered neural processing and response patterns during reward and loss anticipation, potentially reflecting impairments in dopamine function, which may influence their decision-making and reactions to different win/loss scenarios.”
“Alterations in reward processing contribute to the persistence of SUD [substance use disorders] by: (1) leading individuals to seek out stronger rewards (i.e., illicit substances) because they under-value primary incentives when anticipating the potential rewarding effects; and (2) perpetuating the cycle of poor decision-making due to an attenuated neural response to loss anticipation and underappreciation of the potential of negative consequences.”
The study sheds light on the neural specificities of individuals with amphetamine use disorder. However, it is important to note that the study’s design does not allow for cause-and-effect conclusions about the relationship between amphetamine use and neural activity. Whether the altered neural activity patterns are a contributing cause or a consequence of amphetamine use disorder, or if the nature of this association is of a different kind, remains unclear.
The paper, “Amphetamine use disorder is associated with striatum hypoactivation during anticipation of loss and reward,” was authored by April C. May, Kaiping Burrows, Rayus Kuplicki, Martin P. Paulus, and Jennifer L. Stewart.
