21 April 2009

How bad do you want it? (update 1)

Deep brain stimulation (DBS) electrodes offer a window into regions of the human brain that would otherwise, for obvious ethical reasons, not be available for scientific analysis. Interesting activity related to sensation, cognition and behavior can, for example, be recorded from DBS electrodes placed in the subthalamic nucleus for the purpose of treating Parkinson's disease (e.g. Balaz et al 2008, Bronte-Stewart et al 2009).

More and more, DBS is being applied to the human reward circuit to treat obsessive-compulsive disorder and depression (see previous blog post). Specifically, the nucleus accumbens (ventral striatum) is being targeted. Dopamine release into the nucleus accumbens is the strongest reward-signal we know of; it is core to the generation of motivation and learning.

So, what will we see when we start recording from DBS electrodes placed in the human nucleus accumbens? I'll bet my boots that we'll be able to detect changes in dopamine release and reward-processing with MUCH higher precision than when we use brain scanners. Averaged over many trials and patients, recordings like that could allow us to quantify the reward value of things in the world, and relate the activity of the human reward circuit not just to sensation but also to cognition and behavior.

Monkey reward circuit neurons respond to a liquid reward. How exactly would the human reward circuit respond to a liquid reward? Or an invitation to a BBQ? Or two political candidates? Or heroin? Or boredom? Or praise? Or coffee? Or any of the various reinforcers that shape our behaviour, thoughts and feelings? I think we're about to find out.

Edit: publications exploring this line of research are already available: M√ľnte et al 2008, Cohen et al 2009, Zaghloul et al 2009, Cohen et al 2008.
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