"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...
And that slow dopamine? The slowly changing, but always low, concentration soup of dopamine? It signals how motivated you are to work. The higher the concentration of this dopamine soup, the harder rats work for food. Take that dopamine soup right down, and rats won’t budge off their backsides to work for food. Dopamine soup is for wanting; is for signalling to your neurons: commit to this course of action. Not happiness...
There’s no getting away from the fact that the way dopamine works in the brain is complex. We know that this fast and slow split is not as simple as we’d like. For example, it seems there are some dopamine neurons that use their fast firing to affect movement. On the one hand, this is potentially fantastic, as it helps make sense of why the loss of dopamine neurons in Parkinson’s disease causes movement problems. On the other, it does not fit with an error signal. It seems that the error signal is carried by a separate set of dopamine neurons."
So, I have this imediate reaction like 'no, dopamine is incredibly core and important!'. But I realize that my education never started from first principles on neurotransmitters, it presented the chemicals that are historically important to neuroscience research and the ones that are a focus of study right now. But I couldn't say which are the most widespread of involved in the most functions or cause the most dysfunction when absent... Or whatever quality would make a neurotransmitter particularly special.
But anyway, this is a Great description of what I think is cool and compelling about dopamine.
FB: "There are so many other brain chemicals to chose from, we can guarantee the current fixation on dopamine is just a fad. Mark my words, soon it will by neuropeptide Y: NPY Diet! NPY Dressing! NPY Brain Training! Many more crimes are yet to be committed against poor defenseless brain chemicals."
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