Mental health issues currently affect a significant portion of the population, with approximately 1 in 5 adults in the US experiencing symptoms associated with at least one mental health disorder each year. In 2021, only 47.2% of these individuals received treatment or intervention¹. One of the most disruptive mental health issues is addiction. According to the Oxford Languages Dictionary, addiction is defined as “being addicted to a particular substance, entity, or activity”². Addictive behavior should not be viewed as a singular condition but rather as a complex condition impacted by both intra- and interpersonal factors.

For a majority of individuals who engage in forms of gambling, it is a healthy means of recreational entertainment. However, for some individuals, gambling moves beyond a healthy form of entertainment and becomes an addictive behavior. A recent report found that about 10 million people have reported a gambling addiction in the past year³. Approximately 85% of American adults have gambled at least once in their lives, and 60% in any given year, according to the National Council on Problem Gambling [1] . In addition, 86% of Americans consider gambling as an acceptable form of entertainment, as suggested by the American Gaming Association [2] . In the United States, gambling has gained significant popularity over the past few decades, especially in the form of online gambling, since the global pandemic of COVID-19. The estimated increase in online gambling is between 11% and 20%, excluding the highest and lowest estimates from 8 different studies in various countries [2] .

Both the vast number of participants and the increasing trend in gambling call for additional research and methodology development for managing pathological gambling behavior. Given the remarkable amount of information available concerning drug addiction (compared to what we know about gambling addiction), a comparison between these two might provide important insights. As the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, or DSM-V suggests, an individual can be accurately diagnosed as having an addiction if they meet two of the following 10 criteria: tolerance, withdrawal, hazardous use, social or interpersonal problems related to use, neglected major roles due to use, use of larger amounts over time, repeated attempts to quit or control use, increased time spent using, physical or psychological dependence problems related to use, and giving up other activities to use⁴.

Gambling encompasses a range of activities, providing individuals with opportunities to participate in games of chance for entertainment or monetary rewards. The most prevalent forms include casino gambling, sports betting, lottery games, and online gambling; whereas social gambling, including bingo and raffles, is also popular. Each form of gambling also includes various types. In casino gambling, for example, betting includes games such as slot machines, roulette, blackjack, craps, baccarat, and poker, which can be played in brick-and-mortar locations or in online casinos.

Table 1 presents the ten DSM-V diagnostic criteria for drug addiction, their definition, and an example of how each relates to gambling addiction. Of note, is the compelling connection between gambling and drug addictions, suggesting a similar neural mechanism for both pathologies.

Despite the similar neural mechanisms involved in all types of addiction, there exist both similarities and differences between substance and behavioral addictions⁵. Perhaps in a different way, compared to drug addiction or alcoholism, behavioral addiction is an impulse control disorder described as being seized by the compulsion to take part in specific behavior or behaviors on a repeated basis, while neglecting potential physical, mental, or financial consequences. Gambling

addiction falls into this category. Although a full diagnostic model has not yet been developed targeting this type of behavioral addiction, it is recognized that even some seemingly harmless activities can contribute to this phenomenon. In this way, it is theoretically possible for gamblers to become addicted without there being obvious physical evidence of addiction, as the changes occur from the dysfunction in the reward circuitry of the brain. On the other hand, substance addiction, in which an individual becomes physically dependent on external chemical substances, can cause more obvious physical symptoms that will require medical assistance. In short, though behavioral addiction and substance addiction share similar neural mechanisms, behavioral addictions receive much less attention as their effects are not as obvious in the short term. To better help gamblers with their specific type of behavioral addiction, a more thorough understanding of the neural origin of the reward system will be discussed.

The VTA is a small brain region within the brainstem that produces dopamine, a neurotransmitter associated with reward. When a rewarding experience or behavior occurs, dopamine projections from the VTA to the NAcc become active. Neurons in the VTA not only respond to the presence of rewards, but their response also depends upon whether the reward was expected [5] . To elaborate, Schultz and colleagues (1997) showed that dopamine neurons were most responsive to the delivery of a reward when that reward was unexpected, and they were least active when a reward that was expected was not delivered.

Thus, rather than simply being a reward detector, the function of the VTA is much more complex; being guided by the prediction value of environmental cues that precede the potential subsequent delivery of a reward (or lack thereof). Given these data showing that the VTA is most responsive to outcomes related to uncertain reward; and when compared to other data showing that the NAcc is responsive to reward per se; it has been suggested that VTA neurons may be involved in anticipation of rewards, while NAcc neurons may be involved in the experience of reward [6] [7] .

To complicate matters, this increase in dopamine also produces the release of other neurotransmitters, such as glutamate and opioids, which are responsible for pleasurable feelings. Over time, the brain adapts to the increased levels of dopamine and becomes less sensitive to it [3] [4] . This means that people who engage in addictive behaviors, such as substance use or gambling will be a) highly sensitive to cues associated with the availability of reward via VTA activity, and b) will be highly activated by the delivery of reward requiring more and more to achieve the same level of pleasure via the NAcc.

The PFC is a region of the brain that is involved in decision-making and impulse control. The NAcc also sends projections to the PFC, alerting this part of the reward system about the presence of a reward, purportedly so the system can learn more about the environmental contingencies that led to this reward. It is thought that the PFC plays a role in avoiding addiction by helping people resist the temptation to use drugs or gamble (i.e. regulate their reaction to reward). However, in people who are addicted to drugs or gambling, the PFC is often less active, meaning they have trouble placing their knowledge about the negative consequences of their addictive behavior (e.g. lost social relationships, criminal offenses) ahead of their desire for the drug or to gamble [3] [4] . Thus, behavioral addiction is thought to be related to dysfunction within the PFC leading to the observed impulse control disorder.

Functional magnetic resonance imaging (fMRI) based research, which reveals the small hemodynamic changes that are associated with brain activity, can be used to examine which parts of the brain are carrying out critical functions during a given behavior [8] .

These studies have identified neural circuits that support positive and negative emotions; specifically, the PFC and the amygdala are thought to play key roles. Emotions are important in guiding actions and organizing behaviors toward goals. The PFC supports affective working memory, whereas the amygdala plays a crucial role in the perception of emotional cues and production of emotional responses.

In a research study, eighteen individuals diagnosed with cocaine addiction and eighteen individuals diagnosed with gambling addiction were asked to perform a probabilistic reversal learning task during fMRI. Both cocaine users and pathological gamblers exhibited reduced ventrolateral PFC signal during the task, suggesting a neural marker associated with both gambling and cocaine addictions. These results also resonate with the suggested function of the PFC in affective working memory [9] .

By understanding the neural mechanisms behind addictions, pathological gambling is quickly recognized to also be a “brain disorder”; one related to an underlying neurobiological abnormality [10] involving the neural circuitry that underpins gambling-related decision-making, including the ventral striatum, ventromedial PFC, VTA, and insula. The pathophysiology of gambling disorder manifests as a clinical disorder through the debilitating consequences of pathological gambling behavior. The behaviors follow known psychological features, including sensitivity to variable ratio schedules, near-misses, “losses disguised as wins”, and the illusion of control. All of these features arise from the core decision-making circuitry that is perturbed in gambling disorder [10] . This information might help in the design of tools aimed at applying neuroscience to reverse such phenomena.

Interestingly, it has been noted that many individuals who have become addicted to drugs or other behaviors report that, though they no longer derive the pleasure they used to receive through addictive behaviors, they continue to maintain their addictive behavior. In response, Berridge (2007) [11] has proposed that drug addiction involves a disruption of the balance between “wanting” and “liking”. Wanting is a motivational state that drives us to seek out rewards. It is associated with the anticipation of pleasure and the urge to act. Wanting is thought to be mediated by the VTA and NAcc. Liking is the subjective experience of pleasure that we feel when we consume a reward. It is associated with the release of dopamine in the brain. Liking is thought to be mediated by a system of PFC brain regions, that include the orbitofrontal cortex (OFC). In individuals addicted to drugs, the wanting system becomes hyperactive, while the liking system becomes hypoactive. This leads to a situation where these individuals are driven to seek out drugs (i.e. increased wanting), even though they no longer derive pleasure from them (i.e. decreased liking).

Together, these studies elucidate the involvement of three brain regions in the reward system that play a role in the production of dopamine and reward prediction (VTA), the processing of rewards (NAcc), and final decision-making (PFC). The overall loop is illustrated in Figure 1.

There exists little doubt that addictive drug use is related to the abnormal functional organization in the brain of the user, as shown by fMRI data. For example, compared with controls, chronic heroin users showed increased functional connectivity between the NAcc and ventral/rostral anterior cingulate cortex (ACC) in the PFC, between nucleus accumbens and OFC, and between the amygdala and OFC [12] .

Several fMRI studies have localized specific brain regions related to various types of addiction. Neurosynth is an online platform for large-scale, automated synthesis of fMRI data. A search for studies related to various types of addiction produced, one hundred and thirty-five studies. The following is a summary of three that best relate to behavioral (i.e. non-substance) addiction and their associated brain regions.

Individuals with internet addiction disorder (IAD) are susceptible to a greater interference or “Stroop” effect and exhibit greater activation of the anterior and posterior cingulate cortices in the PFC during fMRI. This may underlie the diminished efficiency of response-inhibition processes in IAD [13] . Internet pornography addiction, one type of IAD, has also been found to be linked to increased ventral striatum activity (where the NAcc is located), especially when the

images shown to participants are closer to their preferences [14] . There is also an increase in the functional coupling between the ventral striatum and bilateral amygdala in gamblers with impulse control disorders (ICDs) compared to controls [15] .

Trait-based inventories assess relatively stable, or long-term personality or behavioral traits, reflecting individual differences in patterns of thoughts, feelings, and behaviors that are consistent and stable. Inventories exist that can address an individual’s predisposition for engaging in addictive behaviors. For example, addiction susceptibility and the Big 5 Personality traits are correlated; specifically, neuroticism and openness are positively correlated with addiction susceptibility, whereas the traits of extraversion, agreeableness, and consciousness are negatively linked to addiction susceptibility [16] .

In addition to trait-based assessments of addictive tendencies, there exists a body of inventories that specifically target assessments of gambling addiction. These include the Problem Gambling Severity Index, proposed by the Canadian Centre on Substance Abuse [17] . This index includes nine questions, each offering four choices classified according to severity. This inventory offers an opportunity for gamblers to realize the severity of their addiction and discover potential measures to be taken.