Numbers up for dopamine myth

I’ve just read an elegant study on the neuroscience of gambling that wonderfully illustrates why the dopamine equals pleasure myth, so often thrown around by the media, is too tired to be useful.

I have seen countless news reports that claim that some activity or other causes dopamine to be released; that dopamine is the ‘pleasure chemical’; and that it’s also released by ‘drugs’, ‘sex’, ‘gambling’ and ‘chocolate’ (a quartet I have named the four dopamen of the neurocalypse).

Normally, this breathless attempt to make something sound sexy is followed by a slightly sinister bit where they say that this dopamine activity is also likely to make it ‘addictive’.

Dopamine is involved in drug addiction, but the over-extended clich√© is drivel, not least because the dopamine neurons start firing in the nucleus accumbens when any reward is expected. Whether it be heroin, a glass of water when you’re thirsty, or your favourite book on calculus – if that’s what floats your boat.

And herein lies the subtlety. Our best evidence tells us that while the dopamine system has many functions, it’s not really a reward system – it’s most likely a reward expectancy system of some kind. Theories of exactly what form this takes differ in the details, but it certainly seems to be active when we’re expecting a reward, whether it actually turns up or not.

The study on gambling, led by neuroscientist Luke Clark, demonstrates that this is true even when the actual experience is unpleasant.

The research team looked at the activity differences in the dopamine-rich mesolimbic system in a gambling task – comparing wins, misses and near-misses. Near-misses were where the reels on a slot machine just missed the payout.

It turns out that near-misses activate almost exactly the same dopamine circuits as actual wins – but here’s the punchline – they were subjectively experienced as the most unpleasant outcome, even worse than total misses.

In other words, the dopamine system was firing like a rocket display but the experience was awful.

Interestingly, although near-misses were experienced as aversive they increased the desire to play the game but only when the person had some perception of control, by choosing what the ‘lucky’ picture would be.

Of course, like choosing ‘heads or tails’, it’s only an illusion of control because the outcome is random anyway.

But because of reward expectancy the dopamine system is most active when we think we can control the outcome and modify our strategy next time, even if that sense of control is completely false.

Link to full-text of study on near-misses and dopamine.
Link to good coverage of study from Quirks and Quarks.