Association between reward-related activation in the ventral striatum and trait reward sensitivity is moderated by dopamine transporter genotype

Nucleus accumbens response to incentive stimuli anticipation in children of alcoholics: relationships with precursive behavioral risk and lifetime alcohol use

Children of alcoholics (COAs) are at elevated risk to develop alcohol and other substance use disorders. The neurobiological underpinnings of this heightened vulnerability are presently not well understood. This study investigated whether, in humans, COAs have different functioning of the mesolimbic reward circuitry beyond previous substance use confounds and examined potential group differences in neural response in relation to alcohol use and behavioral risk. We studied 20 18- to 22-year-old COAs and 20 controls, developmentally well characterized for substance use and selected to match on sex, age, IQ, lifetime substance use and associated problems, and precursive (ages 12-14 years) externalizing behavioral risk. None met criteria for Diagnostic and Statistical Manual of Mental Disorders IV diagnosis. Neural responses to anticipation of reward and loss were assessed using functional magnetic resonance imaging during a monetary incentive delay task. Overall, COAs showed reduced ventral striatum activation during anticipation of monetary reward and loss compared with controls. However, additional analysis revealed that blunted nucleus accumbens (NAcc) response was only observed in COAs who have not demonstrated any problem drinking behavior. In addition, uniquely in COAs, NAcc activation was positively correlated with precursive externalizing risk, as well as current and lifetime alcohol consumption. These findings suggest a multilevel developmental process whereby lower precursive behavioral risk appears protective of later problem alcohol use in COAs, which is further associated with a blunted NAcc response to incentive anticipation, potentially reflecting a resilience mechanism. Moreover, the results suggest that a close association between motivational responses, alcohol consumption, and behavioral risk may underlie addiction vulnerability in COAs.

Test-retest reliability of evoked BOLD signals from a cognitive-emotive fMRI test battery

Even more than in cognitive research applications, moving fMRI to the clinic and the drug development process requires the generation of stable and reliable signal changes. The performance characteristics of the fMRI paradigm constrain experimental power and may require different study designs (e.g., crossover vs. parallel groups), yet fMRI reliability characteristics can be strongly dependent on the nature of the fMRI task. The present study investigated both within-subject and group-level reliability of a combined three-task fMRI battery targeting three systems of wide applicability in clinical and cognitive neuroscience: an emotional (face matching), a motivational (monetary reward anticipation) and a cognitive (n-back working memory) task. A group of 25 young, healthy volunteers were scanned twice on a 3T MRI scanner with a mean test-retest interval of 14.6 days. FMRI reliability was quantified using the intraclass correlation coefficient (ICC) applied at three different levels ranging from a global to a localized and fine spatial scale: (1) reliability of group-level activation maps over the whole brain and within targeted regions of interest (ROIs); (2) within-subject reliability of ROI-mean amplitudes and (3) within-subject reliability of individual voxels in the target ROIs. Results showed robust evoked activation of all three tasks in their respective target regions (emotional task=amygdala; motivational task=ventral striatum; cognitive task=right dorsolateral prefrontal cortex and parietal cortices) with high effect sizes (ES) of ROI-mean summary values (ES=1.11-1.44 for the faces task, 0.96-1.43 for the reward task, 0.83-2.58 for the n-back task). Reliability of group level activation was excellent for all three tasks with ICCs of 0.89-0.98 at the whole brain level and 0.66-0.97 within target ROIs. Within-subject reliability of ROI-mean amplitudes across sessions was fair to good for the reward task (ICCs=0.56-0.62) and, dependent on the particular ROI, also fair-to-good for the n-back task (ICCs=0.44-0.57) but lower for the faces task (ICC=-0.02-0.16). In conclusion, all three tasks are well suited to between-subject designs, including imaging genetics. When specific recommendations are followed, the n-back and reward task are also suited for within-subject designs, including pharmaco-fMRI. The present study provides task-specific fMRI reliability performance measures that will inform the optimal use, powering and design of fMRI studies using comparable tasks.

Randomness of resting-state brain oscillations encodes Gray's personality trait

Randomness of functional Magnetic Resonance Imaging (fMRI) resting-state time-series has recently been used as a biomarker for numerous disorders including Alzheimer's and Parkinson's disease as well as autism. To date, however, it remains unknown whether and to what degree personality traits are associated with the randomness of resting-state temporal dynamics. To investigate this question, we estimated the Hurst exponent - a measure of the randomness of a time-series - during resting-state fMRI in brain areas previously associated with trait Impulsivity as defined in Gray's Reinforcement Sensitivity Theory of Personality in 15 healthy individuals. The Hurst exponent in the ventral striatum as well as in the orbitofrontal cortex (OFC) was significantly associated with the measure of Gray's trait Impulsivity. Specifically, more random resting-state neural dynamics corresponded to higher Impulsivity scores both in the ventral striatum (r(15)=-.71; p=.003) and the OFC (r(15)=-.81; p<.001). In summary, we provide evidence for an association between individual differences in Gray's Impulsivity and randomness in key areas of the reward system which have previously been associated with this personality trait. Based on evidence from fMRI and electroencephalographical studies, we suggest that this association might arise from resting-state fluctuations constraining task-related neural responsiveness. Thereby, we outline a potential mechanism linking randomness of resting-state dynamics and personality.

Impulse control disorders in Parkinson's disease: seeking a roadmap toward a better understanding

The development of an impulse control disorder (ICD) is now recognized as a potential nonmotor adverse effect of dopamine replacement therapy in Parkinson's disease (PD). Here, recent epidemiological, neurophysiological and genetic advances are summarized to outline potential mechanisms involved. It is safe to say that dopaminergic drugs, particularly dopamine agonists, are able to induce ICDs only in a minority of patients, while the majority are somehow protected from this adverse effect. While it seems clear that men with early-onset PD are more vulnerable, other predisposing factors, such as various current or pre-PD personality traits, are a matter of debate. In terms of neurophysiological advances, one may find striking analogies to the addiction literature suggesting a causal chain beginning with certain predisposing conditions of striatal dopamine synapses, an "unnatural" increase of dopamine stimulation and a characteristic pattern of resulting functional changes in remote networks of appetitive drive and impulse control. Future prospects include potential add-on medications and the possible identification of genetic predispositions at a genome-wide scale. Functional imaging of pharmacogenetic interactions (imaging pharmacogenomics) may be an important tool on that road.