does dopamine equal reward?

Bradley Voytek at Oscillatory Thoughts Blog has a great posting (here). It is about Jonah Lehrer’s book on creativity (sort of). More important, it is about how misleading neuroscience can be. The great thing for me was that he very clearly discussed why it is not reasonable to assume that dopamine equals reward.

… And that’s assuming that the “dopamine = reward” hypothesis is even true. Most people–neuroscientists included–take this as gospel truth. Of course dopamine equals reward! Dopamine neurons fire in response to rewarding stimuli, and the neurons “learn” to predict the rewards! Addicts’ brains show activity in dopaminergic regions when shown images of drug paraphernalia. And on and on. … dopaminergic neurons don’t get any sensory inputs early enough to make a “decision” about the reward value of visual stimuli. In fact, they’re probably encoding salience (relevance). Which explains why drug users have increased activity when shown pictures of drug paraphernalia, and mothers pictures of their children, or even iPhone users pictures of iPhones versus Androids: because those things are more familiar and relevant to them.
To really hammer this point home, there is one disease we know of that is caused by the death of dopaminergic neurons: Parkinson’s disease. It seems to me the clearest support for the argument that “dopamine = reward” would be seen in people missing most of their dopamine. Parkinson’s patients shouldn’t be able to experience any reward/pleasure because that whole system is obliterated.
Clinically, not feeling pleasure from experiences is known as “anhedonia”, and a systematic review of the literature on Parkinson’s and anhedonia in 2011 was inconclusive. In that review the authors found that, if anything, any signs of anhedonia in Parkinson’s patients was likely caused by their associated depression.

Voytek has more to say about simplistic conclusions on the posting – link above.

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