Subcortical Reward System Research Articles

On the relationship between the social brain, social connectedness, and wellbeing.

The emergence of social neuroscience in the past two decades has offered a useful neurocognitive framework for understanding human social behavior. Of importance, social neuroscience research aimed to provide mechanistic explanations for the established link between wellbeing and social behavioral phenomena-particularly those reflective of social connectedness. Here, we provide an overview of the relevant literature focusing on recent work using functional magnetic resonance imaging (fMRI). In general, fMRI research demonstrated that aspects of social connectedness that are known to either positively (e.g., social acceptance) or negatively (e.g., social isolation) impact wellbeing also modulated the activity of subcortical reward system accordingly. Similar modulatory influence was found for the activity of other brain regions such as the medial prefrontal cortex, which are typically regarded as components of the "social brain" that support a wide range of functions related to social cognition and behavior. Elucidating such individual differences in brain activity may shed light onto the neural underpinnings of the link between social connectedness and wellbeing.

Neural substrates of deficient cognitive control in individuals with severe internet gaming disorder

Background and aimsInternet gaming disorder (IGD) is rapidly becoming a worldwide health concern. The prefrontal-subcortical model of self-regulation emphasizes that an impaired prefrontal cognitive control system and an overwhelming subcortical reward-seeking system are both crucial factors in health problems, including addiction. This study focused on the cognitive control system of IGD, aiming to investigate whether cognitive control is altered and the underlying neural correlates in college students with IGD. Methods: Thirty college students with IGD and twenty-five matched healthy controls were asked to complete a stop-signal task that measures cognitive control while being monitored by functional magnetic resonance imaging (fMRI). Results: Compared to the controls, only the college students with severe IGD, rather than those with mild IGD, had deficient brain activity involved in inhibitory control and response execution (specifically, the inferior frontal gyrus, anterior cingulate cortex and primary motor cortex); this result implies that cognitive control deficits are closely linked to addiction severity in individuals with IGD. Regarding performance monitoring function, college students with IGD exhibited unabated behavioral and brain activity, as did the control group. Conclusions: Combined with our previous finding that the subcortical reward system was enhanced in individuals with IGD, the present findings extend the prefrontal-subcortical model of self-regulation from the perspective of IGD in a college student population and thus provide useful insight for the effective prevention and treatment of IGD.

White Matter Microstructure Reflects Individual Differences in Music Reward Sensitivity.

People show considerable variability in the degree of pleasure they experience from music. These individual differences in music reward sensitivity are driven by variability in functional connectivity between the nucleus accumbens (NAcc), a key structure of the reward system, and the right superior temporal gyrus (STG). However, it is unknown whether a neuroanatomical basis exists for this variability. We used diffusion tensor imaging and probabilistic tractography to study the relationship between music reward sensitivity and white matter microstructure connecting these two regions via the orbitofrontal cortex (OFC) in 38 healthy human participants (24 females and 14 males). We found that right axial diffusivity (AD) in the STG-OFC connectivity inversely correlated with music reward sensitivity. Additionally, right mean diffusivity and left AD in the NAcc-OFC tract also showed an inverse correlation. Further, AD in this tract also correlated with previously acquired BOLD activity during music listening, but not for a control monetary reward task in the NAcc. Finally, we used mediation analysis to show that AD in the NAcc-OFC tract explains the influence of NAcc activation during a music task on music reward sensitivity. Overall, our results provide further support for the idea that the exchange of information among perceptual, integrative, and reward systems is important for musical pleasure, and that individual differences in the structure of the relevant anatomical connectivity influences the degree to which people are able to derive such pleasure.SIGNIFICANCE STATEMENT Music is one of the most important sources of pleasure for many people, but at the same time there are important individual differences in the sensitivity to musical reward. Previous studies have revealed the critical involvement of the functional connectivity between perceptual and subcortical brain areas in the enjoyment of music. However, it is unknown whether individual differences in music sensitivity might arise from variability in the structural connectivity among these areas. Here we show that structural connectivity between supratemporal and orbitofrontal cortices, and between orbitofrontal and nucleus accumbens, predict individual differences in sensibility to music reward. These results provide evidence for the critical involvement of the interaction between the subcortical reward system and higher-order cortical areas in music-induced pleasure.

Sexual Attractiveness: a Comparative Approach to Morphological, Behavioral and Neurophysiological Aspects of Sexual Signaling in Women and Nonhuman Primate Females

Objective and MethodsThis review focuses on comparative data in nonhuman primates and humans in relation to signaling secondary sex characteristics (SSC), sexual behavior, and neurophysiology of sexuality during the female cycle.ResultsIn monkeys and apes no clear distinction can be drawn between sex as a reproductive, social, or a pleasurable activity. Although female sexual behavior is not limited to a specific phase of the menstrual cycle, changes in body morphology and in behavior and psychology (for example, in feeding, risk taking, and mood) can occur across the cycle. In human and nonhuman primates, homologous biological mechanisms including specific areas of the brain, sex steroids, and receptors are involved in regulating female sexuality. Important aspects of this regulation include the interaction between the subcortical reward system and the social brain network and its projection to the prefrontal cortex. In humans, females advertise SSC permanently after the onset of puberty, but without significant changes across the cycle, whereas in other primate species, female sexual signaling can vary significantly across cycle stages and in fertile and non-fertile phases of the life cycle.ConclusionA great deal is now known about the regulation of female sexuality in primates and the use of sexual signals in terms of their variable expression and their information content for males. Human research has also elucidated the cultural mechanisms through which women communicate about their sexuality, including clothes and make-up. A full understanding of female sexuality in humans, therefore, requires knowledge of culture-biology interactions.

The Influence of Different Kinds of Incentives on Decision-Making and Cognitive Control in Adolescent Development: A Review of Behavioral and Neuroscientific Studies.

A number of recent hypothetical models on adolescent development take a dual-systems perspective and propose an imbalance in the maturation of neural systems underlying reward-driven and control-related behavior. In particular, such models suggest that the relative dominance of the early emerging subcortical reward system over the later emerging prefrontal-guided control system leads to higher risk-taking and sensation-seeking behavior in mid-adolescents. Here, we will review recent empirical evidence from behavioral and neuroscientific studies examining interactions between these systems and showing that empirical evidence in support for the view of a higher sensitivity to rewards in mid-adolescents is rather mixed. One possible explanation for this may be the use of different kinds and amounts of incentives across studies. We will therefore include developmental studies comparing the differential influence of primary and secondary incentives, as well as those investigating within the class of secondary incentives the effects of monetary, cognitive, or social incentives. We hypothesized that the value of receiving sweets or sours, winning or losing small or large amounts of money, and being accepted or rejected from a peer group may also changes across development, and thereby might modulate age differences in decision-making and cognitive control. Our review revealed that although developmental studies directly comparing different kinds of incentives are rather scarce, results of various studies rather consistently showed only minor age differences in the impact of incentives on the behavioral level. In tendency, adolescents were more sensitive to higher amounts of incentives and larger uncertainty of receiving them, as well as to social incentives such as the presence of peers observing them. Electrophysiological studies showed that processing efficiency was enhanced during anticipation of incentives and receiving them, irrespective of incentive type. Again, we found no strong evidence for interactions with age across studies. Finally, functional brain imaging studies revealed evidence for overlapping brain regions activated during processing of primary and secondary incentives, as well as social and non-social incentives. Adolescents recruited similar reward-related and control-related brain regions as adults did, but to a different degree. Implications for future research will be discussed.

The Role of Reward in Word Learning and Its Implications for Language Acquisition

The exact neural processes behind humans' drive to acquire a new language--first as infants and later as second-language learners--are yet to be established. Recent theoretical models have proposed that during human evolution, emerging language-learning mechanisms might have been glued to phylogenetically older subcortical reward systems, reinforcing human motivation to learn a new language. Supporting this hypothesis, our results showed that adult participants exhibited robust fMRI activation in the ventral striatum (VS)--a core region of reward processing--when successfully learning the meaning of new words. This activation was similar to the VS recruitment elicited using an independent reward task. Moreover, the VS showed enhanced functional and structural connectivity with neocortical language areas during successful word learning. Together, our results provide evidence for the neural substrate of reward and motivation during word learning. We suggest that this strong functional and anatomical coupling between neocortical language regions and the subcortical reward system provided a crucial advantage in humans that eventually enabled our lineage to successfully acquire linguistic skills.

Philosophical reflections on therapeutic brain stimulation.

Neurostimulation techniques have contributed to neural models of motor, cognitive, affective and volitional functions by elucidating their biophysical underpinning. Deep brain stimulation (DBS) is particularly significant in this regard because it can both probe and modulate activity in dysfunctional neural circuits in patients with neurological and psychiatric disorders (Lozano and Lipsman, 2013) These are increasingly being understood as disorders caused by overactivity or underactivity in critical nodes of these circuits. DBS can restore circuit integrity in motor disorders such as Parkinson's disease and mood disorders such as major depression when they have been resistant to pharmacological treatment. Unilateral or bilateral stimulation of the subthalamic nucleus and globus pallidus interna to modulate dysfunction in the basal ganglia has resulted in significant improvement in motor function for many patients with Parkinson's and other movement disorders. Although it is still experimental for treating psychiatric disorders, stimulation modulating overactive regions of the prefrontal cortex and underactive regions of the subcortical reward system has resulted in improved mood and relief of anhedonia and avolition in some patients with depression.

Prefrontal transcranial direct current stimulation alters activation and connectivity in cortical and subcortical reward systems: A tDCS‐fMRI study

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique used both experimentally and therapeutically to modulate regional brain function. However, few studies have directly measured the aftereffects of tDCS on brain activity or examined changes in task-related brain activity consequent to prefrontal tDCS. To investigate the neural effects of tDCS, we collected fMRI data from 22 human subjects, both at rest and while performing the Balloon Analog Risk Task (BART), before and after true or sham transcranial direct current stimulation. TDCS decreased resting blood perfusion in orbitofrontal cortex and the right caudate and increased task-related activity in the right dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) in response to losses but not wins or increasing risk. Network analysis showed that whole-brain connectivity of the right ACC correlated positively with the number of pumps subjects were willing to make on the BART, and that tDCS reduced connectivity between the right ACC and the rest of the brain. Whole-brain connectivity of the right DLPFC also correlated negatively with pumps on the BART, as prior literature would suggest. Our results suggest that tDCS can alter activation and connectivity in regions distal to the electrodes.

Enduring Effects of Adolescent Drug Exposure

Enduring Effects of Adolescent Drug Exposure

Neuronal correlates of reward and loss in Cluster B personality disorders: A functional magnetic resonance imaging study

Decision making is guided by the likely consequences of behavioural choices. Neuronal correlates of financial reward have been described in a number of functional imaging studies in humans. Areas implicated in reward include ventral striatum, dopaminergic midbrain, amygdala and orbitofrontal cortex. Response to loss has not been as extensively studied but may involve prefrontal and medial temporal cortices. It has been proposed that increased sensitivity to reward and reduced sensitivity to punishment underlie some of the psychopathology in impulsive personality disordered individuals. However, few imaging studies using reinforcement tasks have been conducted in this group. In this fMRI study, we investigate the effects of positive (monetary reward) and negative (monetary loss) outcomes on BOLD responses in two target selection tasks. The experimental group comprised eight people with Cluster B (antisocial and borderline) personality disorder, whilst the control group contained fourteen healthy participants. A key finding was the absence of prefrontal responses and reduced BOLD signal in the subcortical reward system in the PD group during positive reinforcement. Impulsivity scores correlated negatively with prefrontal responses in the PD but not the control group during both, reward and loss. Our results suggest dysfunctional responses to rewarding and aversive stimuli in Cluster B personality disordered individuals but do not support the notion of hypersensitivity to reward and hyposensitivity to loss.

Instrumental responding for rewards is associated with enhanced neuronal response in subcortical reward systems

The response of human reward systems to different reinforcers, including food, drugs and money, has been investigated in a number of recent functional neuroimaging studies. They have varied, however, in terms of whether or not a behavioural response was required to obtain rewards. The aim of the present study was to determine whether neuronal responses to financial reward are significantly modulated by the requirement to make a behavioural response. Twelve subjects were scanned using functional magnetic resonance imaging (fMRI) while performing a simple target detection task. Certain targets acted as cues predicting financial reinforcement; some additionally required that a movement be executed, while others did not. There were also targets that required a movement but were not predictive of reward. We observed, as expected, responses within motor and reward systems associated with main effects of movement and reward, respectively. Critically, the reward responses were significantly modulated by the requirement to make an intervening behavioural response. Blood oxygenation level-dependent (BOLD) responses in the amygdala and striatum were significantly enhanced when a movement was required, while reward-related response in the orbitofrontal cortex was independent of movement. These results suggest important dissociations within human reward systems, reflecting different properties of rewards. The striatum and amygdala may mediate the function of rewards in eliciting goal-directed behaviour, while the orbitofrontal cortex mediates incentive value.