Reward Dependence - Brain Physiology

Brain Physiology

Cloninger describes reward dependence as being a prime component of the Behavior maintenance System (BMS). Norepinephrine (NE), apart from producing alertness and arousal, is seen as influencing the brain reward system by aiding in the learning of new paired associations.

According to Cloninger, the norepinephrine neurotransmitter has its major ascending pathways arising in the locus coeruleus in the pons, projecting onward to the hypothalamic and limbic structures, and then branching upwards to the neocortex.

• Reward dependence has been linked to "dissociable connectivity streams" in the brain. Striatal projections and Tracts between the prefrontal cortex predict our individual differences in reward processing, reward dependence and reward-guided behaviors. These findings suggest that personality traits may be affected by the strength of limbic-striatal connectivity.

High reward dependence is characterized by learning from reward signals, persisting repetition of actions that are associated with rewards, increased sociability and a need for social approval. The striatum, especially the dorsal regions, is necessary to carry out these functions.

• Using Positron Emission Tomography (PET) researchers have shown that reward dependence is linked to opiate receptor binding (the endorphine system) in the bilateral ventral striatum: a core substrate of the reward circuit which is strongly implicated in addictive behavior development. These findings demonstrate that people with high reward dependence (who feel a greater need for social rewards and verbal approval) have more opiate receptors found in the ventral striatum, whereas people with low reward dependence have a lower concentration of receptors. It is then suggested that increased ventral striatal opiate receptors could provide the biological link between personality traits and substance abuse risk.

• fMRI studies have shown that individuals with immature development of the inferior part of the frontal lobe around the midline inner surface of the brain, showed greater reward dependence. People with social reward dependence personalities were also seen to have brains with far less tissue in the fronto-striatal section of the brain (e.g. damage to the fronto-striatal area is often linked to autism and schizophrenia). Relationship between concentration of grey matter (brain-cell containing tissue) in different brain regions and social reward dependence was also studied. It was found that the greater the concentration of tissue in the orbitofrontal cortex (the outer strip of the brain just above the eyes), and in the ventral striatum (a deep structure in the centre of the brain), the higher they tended to score on the social RD measure. The researchers warn that these studies are only correlational and cross-sectional and none of this research is definitive in proving that brain structure determines personality but it could be that personality, through experience, may help in determining the structure of the brain.

• Social Reward Dependence has also been associated with the temporal lobes, the caudate Grey Matter Density (GMD) in the orbitofrontal cortex and the basal ganglia of the ventral striatum. These structures, which are rich in dopamine receptors, are known to play a crucial role in reward receipt, Incentive anticipation and simple and discrete primary and secondary rewards prediction errors. These significant findings show a correlation between primary reward processing circuits and reward dependence, keeping with the fMRI research studies that demonstrated that, following the experience of complex rewards the activation of the striatal circuits occur.

Primary reward processing has also been associated with the orbitofrontal cortex and the grey matter density in the ventral striatum, whereas higher RD scores were associated with the interactions between dopamine projections, neuropeptides and opiates in the ventral striatum. It is demonstrated here, then, that there is evidence for a structural disposition of the brain towards social interactions, and that both sensitivity to salient social reward cues and primary reward processing share the same brain systems.

In addition to these findings, the bilateral temporal poles were also identified in which gray matter density correlated with reward dependence. The medial prefrontal cortex and orbitofrontal cortex, along with other temporal structures, project to the temporal pole, enabling reward stimuli information between the two regions to be integrated. In an fMRI study, the temporal poles and the ventral striatal areas have been shown to be activated in response to social rewards (such as humor) and also in looking forward to simpler rewards (such as money).