Tuesday, July 12, 2011

Varies of reward in the brain.

Smith et al. do some interesting tracking of the different circuits that are active in different kinds of reward in the brain. Here is their summary (which is a bit less technical than the abstract pointed to by the link):

Reward can be separated into several components, which include sensory pleasure (liking), incentive motivation triggered by related cues (wanting), and predictive associations that allow cues to raise expectations of the pleasure to come (learning). Attraction to food in the refrigerator when hungry, for example, involves learned predictions of tasty treats, motivation to eat, and finally, pleasure enjoyed on eating. In the brain, signals for each of these components are funneled together through looping pathways connecting the nucleus accumbens with the ventral pallidum (VP), which form a circuit mediating motivation, behavior, and emotions. This circuit is crucial for healthy reward processing, and its dysfunction plays a special role in pathological drug addiction, eating disorders, and emotional disorders. However, it is not known how the different reward components are kept separate within this circuit. If they are funneled together, how are they independently encoded as distinct signals? Here, we report that distinct signatures of neuronal firing in the VP track each reward component. We also report that selective enhancements of liking vs. wanting brought about by specific neurochemical activations in nucleus accumbens can be tracked independently from one another in downstream firing of VP neurons, all without distorting signals related to prediction of reward.


Charles said...

Thank you! You’re turning out to be one of the best resources on Twitter.

Lee Charles Kelley said...

You do realize, don't you, that there's no such thing as a "reward pathway" in the brain? That dopamine is released when we experience changes in the environment, both positive and negative? simple pattern recognition?

The behavioral science literature is very clear that positive reinforcements can only be determined after the fact by reviewing the scientific data and examining it for statistical trends in terms of a particular behavior's "response strength, meaning that whether a bit of food or words of praise act as a reward is dependent solely on how one reads the data. So if positive reinforcements are theoretical/statistical constructs, not tangible objects, events or markers, then how can an animal be rightly said to engage in a "reward-seeking" behavior? (True, positive reinforcements are technically not the same thing as "rewards," but that's not something that's easily explainable to the average dog owner, and even if it were, it's not something that's understood at all by the average dog!)

The pleasure principle -- the idea that organisms gravitate toward behaviors that provide pleasure and avoid those that cause pain -- actually gives us a more solid explanation for both "survival" and "reward-seeking" behaviors: animals are simply seeking pleasure and avoiding pain. (Interestingly, what the brain actually rewards is the act of paying attention to both positive and negative experiences.)


If my memory serves me, you're a cat lover, but I'm still curious as to your thoughts on this.


Deric said...

How do you explain why drugs addicts continue to obsessively seek drugs after their pleasure effect has entirely habituated and vanished. Or, that some people seems quite content with grimly repeating work habits or hobbies like bridge, evidencing and reporting no pleasure in the activity?

Lee Charles Kelley, said...

I could just as easily ask why drug addicts continue to obsessively seek drugs after the "rewarding" effect has worn off? Are addicts seeking rewards when, after time, none are being provided by their drug of choice? Either way, they're not getting what they're looking for. But if we use Freud's definition of pleasure, which also includes the sudden release of internal tension, I think we'd be closer to the mark.

As to habitual repetition of behavioral patterns, that too is explained by Freud. "There really does exist in the mind a compulsion to repeat which overrides the pleasure principle." ("Beyond the Pleasure Principle," The Freud Reader,, 605) And: "Repetition, the re-experiencing of something identical, is clearly in itself a source of pleasure." (611)

Freud has gotten a bad rap for some of his theories, yet modern neuroscience is starting to validate some of the core principles of his psychology. He also predicted the discovery of the very neurochemicals found in the brain's "reward system."

My area of interest is dog training. So the management of compulsive behavior operates along simpler lines than what psychologists are faced with in human behavior. But in dogs it's pretty easy to see that these kinds of behaviors -- OCD or PTSD -- can be explained quite thoroughly by the idea that the animal is seeking a release of internal tension or stress. When the compulsive behavior doesn't provide that relief, the behavior continues or worsens. When the dog is given an alternative outlet/release for its internal tension, one that satisfies the dog's prey drive, the "dysfunctional" behaviors disappear.

In either case, human or dog, I don't think we can rightly say that the individual is seeking rewards, but rather a release of internal tension or stress. And they'll keep coming back to a behavior or object (snorting cocaine, chasing a cyclist) that previously brought about that feeling of release.


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