What does a thought look like?

Neuroscience Explained

I’m often surprised to find that I have a brain. Yes, I’m sure the witty amongst you readers will be quick to corroborate this (goodness knows there’s no shortage of evidence throughout my life so far to confirm this sketchy awareness!) but on this occasion I don’t mean it quite like that. In this instance I’m talking literally, physically. I’m often surprised by the bizarre reality that crammed away inside my head is a folded, squidgy lump of jelly that effectively is me. It runs the show that is Rebecca Casterton, so quietly and efficiently that I forget it’s even there.

I remember the first time I ever held an actual human brain in my hands. My initial thought was: ‘wow, I’ve got one of these!’ At present, none of us will ever consciously lay eyes on our own brains in the flesh, but we all have a notion of what a brain looks like. This still doesn’t quite prepare you for the feeling of the tangible weight of one in your hands (and it was surprisingly heavier than whatever expectation I’d had). As a scientist you’re supposed to be impartial and unsentimental when it comes to things like this; but when you pause to think about it, as I did, brain-in-hand, there’s something inescapably odd about the whole situation. Initially I couldn’t help acknowledging that here I was prodding and poking what used to be the very essence of a person: what made them…them. Brains just aren’t the same as hearts or lungs or kidneys, are they? I was struck by the realisation of the fact that in my hands I was squishing something that hadn’t just kept someone running but had once made a person have thoughts: perhaps made them rubbish at maths, adore tomato ketchup on everything but hate the smell of fish, made them terrified of heights, loathe rap music but unashamedly love singing along to Michael Bublé.

Since this surreal experience I’ve pondered our out-of-sight-out-of-mind relationship with our brains. It’s amazing really: as you go about your day-to-day life how often can you say you ever give a second thought to what’s going on inside your head? What does a thinking brain look like? Forget neuro-imaging and all it’s pretty, light-up pictures for a moment. What does a real working brain look like? What does your brain look like right now? What does a thought look like?

While the same question would be utterly meaningless when posed to, say, the completely blind star-nosed mole; as humans our visual sense plays an enormous part in how we perceive the world, and so trying to visually grasp concepts like this is something we place great importance on, and influences the way we ask questions about the world.

Most people – even with a bare minimum of scientific knowledge and only a passing familiarity with ‘Frankenstein’ – are aware to some extent that brain activity vaguely has something to do with electricity. Even when sitting still doing absolutely nothing the millions of neurons in your brain are firing off signals – called action potentials – in a fever of electrical activity. There’s never a dull moment in the brain: it’s the cerebral city that never sleeps, and yet we never physically feel a fizzing hive of electrical activity buzzing in our heads, not even a mild tingling. We might have to occasionally dodge the triumphant arm-flailing of someone who’s just had a ‘eureka’ moment, but never a wild whizz-bang of sparks bursting out of their eyes or ears as testament to their power of thought.

I suspect (and if you happen to be a neurosurgeon feel free to call me out on this) that when looked at as a whole, the working brain doesn’t look very exciting at all. It probably just looks like a pink, slimy lump of jelly; maybe it pulsates or squelches a very tiny bit from all the blood rushing through it but apart from that it just…sits there. If you knew nothing about it, you’d never suspect it of being the most complex thing in the known universe. We can’t see flashes of ‘thoughts’ shooting and crackling around it. It doesn’t literally spark and light up the way it appears to in brain scans.

To see the closest approximation to ‘seeing’ a thought that we’ve reached so far – watching an action potential in action – we have to zoom in to the microscopic level of individual neurons, as you can see below. At the moment, this is the closest physical grasp on what a ‘thought’ is that we have, and while it isn’t wrong it is still a pretty sweeping generalisation. Certainly, every thought or action that stems from your brain involves an action potential: a spark of electricity that causes chemicals to move from one neuron to another. But how do we distinguish an action potential that’s contributing to scratching your nose, and an action potential that might possess you to you think ‘gosh, isn’t Johnny Depp an attractive chap’ or ‘what is the point of my existence’ or ‘oh dear, I think I’ve left the oven on’.

Image: Biosciences Imaging Gp, Soton. From Wellcome Images.

Today numerous research relating to ‘reading’ our thoughts is on-going, though don’t get too carried away: mind-reading is still well in the realms of science fiction. However, several experiments have certainly caused us to reconsider the knowledge we have of how our neurons work together to make the whole mysterious entity that is the brain. Take the ‘Jennifer Aniston neuron’ phenomenon for instance. Yes, you heard me right: Jennifer Aniston, that very one – actress, and now unknowingly the basis of a neuroscience experiment.

In the 1960s the concept of ‘grandmother neurons’ was suggested: that some neurons are hyper-specific and fire signals only when they encounter a certain thing that you come across frequently. Basically, neuroscientists argued that you might have a single neuron whose main role is to become active when you see, for instance, your grandmother – allowing you to ascertain that the woman in front of you is your dear old grandmother and not, in fact, Boris Johnson. At the time this idea was dismissed as laughably simplistic – which it is – but more recent experiments have suggested that there might be something in developing this idea. One study, where epileptic volunteers had 100 electrodes implanted in their brains to measure neuron activity, potentially identified single neurons which fire in response to only certain images in the range of famous people, places and food shown to them. After an initial test to identify the neurons which particularly responded to certain images (in the case of one woman, a picture of Jennifer Aniston) the subject was shown more pictures but this time with multiple images of the neuron’s ‘trigger’ (Jennifer Aniston’s face) thrown in. In this second test the ‘Jennifer Aniston neuron’ was seen to be active only when Jennifer Aniston appeared on screen. Interestingly, in one participant the ‘Jennifer Aniston neuron’ also fired in response to pictures of other ‘Friends’ cast members, hinting at the conceptual nature of our thoughts and the linked way in which we store and remember things.

So, do we all have a neuron dedicated purely to the concept of Jennifer Aniston? Tickling as this idea is, and despite the sheer number of neurons we have (there are more neurons in one head alone than there are people on this planet) this is unlikely. But, experiments like this do highlight the notion of our brains being a network, and today neuroimaging is starting to place emphasis on this by using new techniques to map pathways of different neuron sequences (e.g. the ‘Brainbow’ technique, see below) rather than isolating ‘regions’ of the brain. And all of this is taking us one step closer to being able to really see the stuff that thoughts are made of…even if it seems like that might be Jennifer Aniston.

While it might look like a piece of modern art, the ‘Brainbow’ technique maps and traces brain cell connections using more than 100 different colours. Pretty and useful.
Image: Jean Livet, Joshua R. Sanes and Jeff Lichtman, Harvard Universtiy. From BrainFacts.org

 More on the ‘Jennifer Aniston neuron’ if you’re interested.

And here’s the actual research paper it came from – http://www.nature.com/nature/journal/v435/n7045/full/nature03687.html