Tuesday, February 7, 2017

The crimes against dopamine


Dopamine is in the cultural zeitgeist. Want to lose weight? Eat the Dopamine Diet. Want to dress happy? Try Dopamine Dressing. Want to be a Silicon Valley hi-tech entrepreneur genius? Boost your dopamine. Want to feel constant pleasure? Stuff as much dopamine in your noggin as you can.
Craving that dopamine hit? Then check your phone. Read a story. Watch an advert. Or visualise something good happening.

Dopamine will enhance your mental prowess, give you the figure you always dreamed of, and make you happy. Not bad for a lowly chemical sloshing around in your brain. And all of it utter rubbish.
Here’s what it does. Dopamine either changes fast or slow. Fast changes are an error signal. Slow changes are a motivation signal. That’s it.

Dopamine: fast and slow. Error and motivation. These correspond to two different ways dopamine is released. One way is a precise, short, large spike in the amount of dopamine, in a small region of brain. The other way is all the time, creating a constant, low concentration soup of dopamine sitting around in many regions of your brain.

(A couple of things to get out of the way. Dopamine is in many places in the brain. There’s some in your eyeball, for example. But when the media says “dopamine” it means the dopamine releasing neurons in small groups in the middle of the brain. And they also mean where those neurons release their dopamine: a big brain region tucked up nice and warm just under your cortex: the striatum).
How is that precise, short, large spike an error signal? Say you wandered into my house unannounced and, instead of throwing you out on your ear, I offered you a chocolate biscuit (McVities, obviously). Your dopamine neurons would burst into life, spiking dopamine. They signalled the error between what you predicted (being forcibly ejected with a hoof to the bum) and what you received (a nice biscuit). This prediction error was in your favour – it was a positive error.

Say I asked you to turn up at my house at 3 o’clock so I could you give you a chocolate biscuit. You turn up at 3 o’clock, and I give you the promised biscuit. What do your dopamine neurons do? Sod all. You predicted you’d get a biscuit at 3 o’clock, you got a biscuit at 3 o’clock; all is right with the world. Nothing surprising is going on. There was no error.

What if, when you turned up at 3 o’clock, I didn’t give you that chocolate biscuit? What if I just blithely ignored your presence instead? Then your dopamine neurons would briefly pause their activity, stopping the release of dopamine. They signalled the error between what you predicted (a chocolate biscuit) and what you received (nothing). This prediction error was not in your favour – it was a negative error.

This is what fast dopamine does: it signals the error between what you predicted and what you got. That error can be positive, negative, or zero.
It is not reward. Dopamine neurons do not fire when you get something good. They fire when you get something unexpected. And they sulk when you don’t get something you expected. Rewards make you happy. Dopamine does not.

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