RESEARCH QUESTION
Is pathological gambling (PG) related to a deficiency of the mesolimbic dopaminergic reward system?
PURPOSE
The mesolimbic reward system is thought to play a crucial role in the development and maintenance of drug addiction. Evidence suggests that drug addicts have a deficient reward system and that drug intake is an attempt to compensate for this deficit. It has been speculated that PG might also be related to a deficiency of the mesolimbic dopaminergic reward system. The purpose of the present study was to examine reward processing in PG.
HYPOTHESIS
None stated.
PARTICIPANTS
Participants were 12 pathological gamblers (PGs) (100% male; average age = 37 years) and 12 matched healthy controls (100% male; average age = 32 years) living in Germany. The PGs had been gambling for 13 years and mainly played slot machines. All controls were free of active substance abuse and known psychiatric, neurological, and medical disorders.
PROCEDURE
The PGs were recruited through advertisements and through the behavioural therapy clinic at the University Hospital Hamburg-Eppendorf. Participants underwent a structured interview performed by a psychiatrist and completed self-report questionnaires related to depression and PG. All participants were medication free and instructed not to use any substance of abuse (other than cigarettes or coffee) on the day of the scan. Participants were studied using functional magnetic resonance imaging (fMRI) while they completed a guessing task known to activate the ventral striatum (i.e., area of the brain associated with reward). To control for familiarity of the stimulus material, an abstract guessing task unknown to all participants was chosen. The task involved 3 sessions with 79 guessing trials in each. Each trial began with the presentation of the backside of two playing cards. Participants were told that one of the cards was red and that they had to guess which card that was by pressing a left or right button. Each correct guess led to a reward of €1.00 (approx. $1.29 Cdn) and each incorrect guess to a penalty of €1.00. Participants started with a balance of €15.00 and were informed that they were to receive the entire balance in cash at the end of the session. The pre-determined sequence of wins and losses over the total 237 guessing trials was identical for all participants. The fMRI was performed on a 3T system (Siemens Trio) with a gradient–echo EPI T2* sensitive pulse sequence in 38 axial slices (2 mm thickness with 1 mm gap, TR 2.2s, TE 25ms, flip angle 90°, field of view 192 x 192 mm2, matrix 64 x 64).
MAIN OUTCOME MEASURES
PG was assessed using Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV) criteria as well as with a more detailed 20-item German gambling questionnaire similar to the South Oaks Gambling Screen. Depression was assessed via the Beck Depression Inventory and DSM-IV criteria. Alcohol and drug abuse were assessed using DSM-IV criteria. Brain activity during wins and losses was recorded.
KEY RESULTS
PGs were more depressed than were controls. PGs and controls consumed alcohol, but did not fulfill the criteria for diagnosis of alcohol abuse or dependence. Three controls had previous experience with marijuana. Greater activity in the ventral striatum was observed during winning than during losing in both groups. A direct comparison of both groups showed lower activation of the right ventral striatum in PGs than in controls. The opposite comparison (testing for greater activation in PGs than in controls) revealed no differences. PGs showed weaker activation in the ventromedial prefrontal cortex of the brain. Severity of gambling in the PGs was negatively associated with response in the right ventral striatum and the response in the ventromedial prefrontal cortex. This finding remained consistent even when controlling for depression and smoking. In sum, analyses revealed a reduction of ventral striatal and ventromedial prefrontal activation in the PGs that was negatively associated with gambling severity, linking hypoactivation of those areas to disease severity.
LIMITATIONS
A smaller difference between winning- and losing-related blood oxygenation level–dependent signals in the ventral striatum of PGs could have stemmed from a higher blood oxygenation level–dependent signal during loss trials in that group.
CONCLUSIONS
Overall, decreased activation of the ventral striatum, which is a hallmark of drug addiction, and decreased ventromedial prefrontal cortex activation, which is related to impaired impulse control, suggest that PG is a non-substance-related addiction.
