Your brain is smarter than you: how it tells you when you made a mistake
Dopamine, your inner critic.
Do you ever get the feeling your brain is smarter than you? That your consciousness is just the dumb tip of a smart, subconscious iceberg? When we do something wrong, we catch our brains in the act of being smarter than us.
Try this. Sing a line from a favourite song. Or at least a song you know well (we all know those are not the same thing).
For the parents of young children, how about that extraordinary note Idina Menzel not just hits but belts in “Let It Go”: “Let the storm rage ONNNNNNNNNN”. (E flat 5, if you’re wondering).
Or how about Jeff Buckley’s peerless rendition of “Hallelujah”? (Peerless in case you’re thinking of Alexandra Burke’s career-launching version with a sodding key-change a minute before the end straight out of a bad 90s boy-band single and a choir massacring an intimate solo song about the elusive muse of songwriting. And don’t get me started on Rufus Wainwright mumbling his way through it on the Shrek soundtrack.)
Did you hit every note? Thought not.
When you sing a note wrong, you know it was wrong. It was you that sang the note, yet it was your brain that told you it was wrong. Your brain knows the difference between what you wanted to do, and what you actually did. It is smarter than you.
Now a wonderful recent study published in Science has shown us where the brain computes the difference between what you did and what it wanted you to do. And in doing so it lets us catch a glimpse of the subconscious, smarter brain in action.
Gadagkar, Goldberg and colleagues hit upon a fabulous way to do find this difference signal. They turned to nature’s best warblers, song birds (in this case zebra finches). To find the difference signal in a lab, you can’t wait around for the bird to make a mistake – you could be waiting forever. These little guys sing the same song over and over and over again, flawlessly. Instead you need to be able to fool the bird’s brain into thinking the wrong note was sung, even when it wasn’t. Gadagkar and co fooled the birds by sometimes playing back to them a corrupted version of the note they had just sung. Just sometimes, and only on some notes in the song they were repeating over and over and over again. So even though the bird sang the right note, sometimes it heard the wrong note. The birds sang away, oblivious. And while this was going on the experimenters recorded from the birds’ dopamine neurons (*).
What Gadagkar, Goldberg and co saw was elegantly simple. A small handful of dopamine neurons cared about the wrong note. And they all cared in the same way. When the wrong note was heard, the dopamine neurons stopped firing, briefly. When that note rolled around again in the next cycle of the song, and wasn’t wrong, the dopamine neurons burst with activity. And on all the other notes, the ones that were right all the time, the dopamine neurons didn’t respond. They didn’t increase or decrease their firing – the note was just right. So the firing of these dopamine neurons directly signalled the difference between what the bird heard and what it was expecting to hear.
Why dopamine neurons? This is where it gets really cool. We already know that, in mammals, these neurons signal the difference between what you expected to receive and what you actually got. When you were expecting nothing and someone gives you a chocolate biscuit, your dopamine neurons do a little dance of joy, bursting with activity. When you were expecting a chocolate biscuit, and get a chocolate biscuit, your dopamine neurons are oblivious, firing away as though nothing happened. But when you were expecting a chocolate biscuit, and someone gives you half a soggy Rich Tea biscuit instead, then, as you’re fighting to hide your crushing disappointment, your dopamine neurons are depressed, and they stop firing for a little while. Dopamine neurons, in other words, signal a prediction error: the error between what you predicted you would get and what you actually got.
This type of prediction error is entirely about outside events: things that happen outside of you. It is an external prediction error. The brilliance of Gadagkar and colleagues’ work is that they thought: hang on a minute, what if some dopamine neurons also care about what is going on entirely inside of you? What if they care about an internal prediction error?
Their work shows that some dopamine neurons do care about an internal prediction error. Those neurons paused when the bird’s brain heard the wrong note – when the predicted note was wrong; they didn’t change their firing on notes that were never wrong – they were correctly predicted; and those neurons fired more when it unexpectedly got the note right. So the dopamine story gets ever more interesting: some neurons are for external prediction error; some are for internal prediction error; some are even for movement. What else might they be for? And how many kinds of internal prediction error do they care about? Just singing? Speaking too? Anything involving sound? Movement errors too? Like juggling? Juggling with fire? Juggling with swords on fire? (Presumably those internal error neurons go off the moment you reach for the swords — “Noooooooo you imbecile you’re making a terrible mistake!”).
Here we catch science in the act of moving faster than we can make sense of it, new findings piling atop one another. And we also catch the brain in the act of showing you that your consciousness is just the tip of the iceberg.
Your consciousness is, roughly, what you are aware of going on in your own head. The sound of these words being read, internally. The sight of the font on the page. But we are barely aware of the extraordinary number of processes our brain is doing simultaneously. Occasionally, like hitting the wrong note, we catch a glimpse.
When singing, it’s a fair bet your consciousness is focussed on belting out those notes. But for you to know you hit the wrong note, here’s the bare minimum of what else must be happening in your brain, all at the same time. Your brain is hearing the sound you are producing. It is holding a memory of what the note should be. It is computing the difference between the sound it is hearing and the memory it is holding. And it signals that difference to you via dopamine neurons. The result of all this hidden machination is your smarter subconscious brain tapping you on the consciousness and saying “Oi, doofus, you made a mistake”. And you catch a glimpse of the extraordinary machinery hidden below the conscious surface.
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(*) Wait, hold up: Birds have dopamine neurons too? Yes. As far as we can tell, every animal has. All vertebrates have dopamine neurons. Invertebrates have dopamine, or something very similar doing the same job. Bees have octopamine, for example, with which they appear to signal a prediction error. But remember that not all dopamine is for signalling prediction errors: there is dopamine inside your retina, for example, where it is emphatically not signalling a prediction error.