Tuesday, December 09, 2008

Novelty Seeking and Reward Dependence: the dopamine white matter connection.

I had earlier wrote extensively on Cloninger's personality temperaments and proposed that dopamine lies behind the trait Novelty Seeking; while norepiniphrine lies behind Reward Dependence trait. New research , as reported in Nature Neuroscience makes me rethink some of that simplistic schema.

As per Cohen et al, they have found a double dissociation between white matter connectivity between dopamine and sub-cortical and cortical regions and found that these white matter connectivities differentially predict and correlate with traits novelty seeking and reward dependence. Let me quote from the article:

Myriad cognitive, emotional and motor functions of the brain rely on the integrity of the striatum and on interactions between the striatum and other cortical and subcortical networks1, 2, 3. Lesion work in animals supports the idea that fronto-striatal connectivity is crucial for aspects of behavioral adaptation and learning. In these cases, it is clear that anatomy constrains function. Here, we investigated whether anatomical connectivity underlies more global aspects of behavioral and cognitive organization: human personality. We found that the strength of connectivity between two different striatum-related networks predicted individual differences in self-reported personality traits in humans.

Then they go on to show which two networks they studied and found the dissociation in.

In humans, novelty seeking is characterized by impulsivity, exploratory drive and excitability, and has been proposed to be driven by individual differences in dopamine system sensitivity. In rats, both striatal dopamine and hippocampus inputs modulate novelty seeking, linking these structures into a network for novelty detection. The hippocampus may support novelty seeking in part by signaling when sensory input differs from memory-driven expectations (that is, a sensory prediction error), whereas the amygdala may support novelty seeking by modulating hippocampal and striatal activity in novel environments or during emotional memory encoding. Our findings provide additional support for this novelty-loop theory by demonstrating that the hippocampus– and amygdala–ventral striatal pathways are related to stable individual differences in novelty seeking personality.

High reward dependence is characterized by several cognitive, emotional and social facets, including enhanced learning from reward signals, persistence in repeating actions associated with rewards, high sociability and reliance on social approval. These functions recruit the striatum, including dorsal regions. Indeed, the tracts predicting reward dependence were not confined to one particular subregion of the striatum, but were instead observed in striatal areas in which there were strong inputs from these seed regions . This suggests that the white-matter circuits subserving reward dependence are distributed throughout multiple cortico-striatal loops. These loops have been linked to processes ranging from reward learning to cognitive control to action selection.

From the above it is clear that the striatal dopamine system is implicated in both Novelty seeking and Reward dependence. While the implicit, first-line, sub-cortical 'emotional' and unconscious processes sub served by hippocampus and amygdala may be the white tract inputs to the striatum that result in Novelty seeking behavior; the explicit, second-order, cortical, 'cognitive' and conscious processes sub served by frontal cortex may be the white matter inputs to the striatum that result in reward dependence behavior.

This indicates that the stage theories are true!! If one considers the sub-cortical responses to be immature and the cortical responses to be more mature than moving from novelty seeking focus to reward dependence focus is a move up the stages. What I propose is that each stage marks a movement from sub-cortical input reliance to cortical input reliance and also involves novel mechanisms and systems.

Thus, as per my theory, in the first stage of personality development, or for the trait Harm Avoidance, the white matter connections implicated should be between sub-cortical regions and raphe nucleus ( the serotonin system).

In stage 2, or for trait Novelty seeking, the white matter tracts involved should be between cortical regions and Raphe nucleus (serotonin system). Also as the earlier serotonin system comes moer and more unedr cortical control, the second system based on dopamine becomes active but is under sub-cortical control. Thus, white matter tracts involving sub-cortical regions and striatum/ VTA should also be involved.

In stage 3, or for trait Reward Dependence, the white matter tracts should be between cortical regions and striatum/ VTA as the earlier dopamine system predominance us reigned in and a new system based on nor-epinepherine replaces it. This nor-epinepherine will be under sub-cortical control and white matter tracts from sub-coritcal regions to locus ceruleus should also be involved.

And this same scheme should go on for fourth (epinepherine), fifth (histamine/ melatonin), sixth, seventh and eighth stages/ personality traits.

All these are testable hypothesis and can be easily verifed. If verified, they can shed immense light on how perosnality develops and what do temperaments/ character strengths really mean.

Hat tip: Neurological correlates

Michael X Cohen, Jan-Christoph Schoene-Bake, Christian E Elger, Bernd Weber (2008). Connectivity-based segregation of the human striatum predicts personality characteristics Nature Neuroscience DOI: 10.1038/nn.2228

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Ward said...

very nice and interesting post.

I was thinking about writing a piece on this paper - but I glad I waited because you did a nicer job than I would probably have done.



Swivelchair said...

Nice job SG, and your developmental framework makes a lot of sense - and what a good framework to correlate the organic, the personality traits and the development/maturity level of the corresponding connections.