13 fascinating facts about the brain from leading neuroscientists
By April Cashin-Garbutt
Over the past year I have had the privilege to interview world-leading neuroscientists who have visited the Sainsbury Wellcome Centre. As part of Brain Awareness Week 2019, I wanted to share some of their favourite neuroscience facts.
1. Even when we don’t have free will, our brains make-up stories implying that we do
“Neuroscientists who study human patients have shown that if you stimulate a part of the motor area to generate a certain behaviour, the person will come up with a story about why they had volition to do that action.
I don't know if we have free will or not, but I think that as you start to see more and more examples like that of situations where clearly their free will did not generate their action, but their brain nevertheless, for consistency, makes up a reason that it did.” James Fitzgerald, Group Leader, Janelia Research Campus
2. Neuroscientists can read a rat’s imagination
“The hippocampus is long known to store memories and represent space, but recent evidence suggests that it also supports imagination. When this mental simulation mode is on, you can read out what a rat might be imagining from its neural activity.” Adam Kepecs, Professor and Chair of Neuroscience Program at Cold Spring Harbor Laboratory
3. Over half the neurons in your brain only have four inputs
“Granule cells, which are one of the simplest cells in the cerebellum, make up over half the neurons in your brain!
Granule cells are very small and only have four dendrites with only have one synapse each. This means that granule cells receive only four excitatory bits of information in total, so they must be doing some simple integration, yet they make up half the neurons in your brain so they must be very important substrate for something.
What granule cells are actually doing is unknown because although they are small and simple, they are very hard to record from. The Margrie lab at the Sainsbury Wellcome Centre have done some the only recordings of these cells.” Dr Adam Hantman, Group Leader, Janelia Research Campus
4. Elephants have evolved huge brain regions to control their trunks
“People say elephants have the biggest brains and the most number of cells and the reason is they have a huge (even more disproportionate than humans) amount of granule cells in their cerebellum. I think part of the reason is that elephants have to be able to control their trunks which are incredibly complex with many different muscles.” Professor Javier Medina, Baylor College of Medicine (Houston)
5. Zebrafish can regenerate their spinal cord
“The amazing thing with zebrafish, and most amphibians and fish, is that if you cut their spinal cord and then leave the animal by itself, within at most a week, the whole spinal cord regenerates itself and the fish will just swim away.” Dr Tuan Bui, Associate Professor in the Department of Biology at the University of Ottawa
6. Most of your neurons live with you all your life
“The neurons you're born with are mostly the neurons you have when you die, so these cells live with you your entire life. Throughout your lifetime, these brain cells accrue genetic mutations and in an adult individual it is thought that the genomes of seemingly all neurons in the brain are unique.” Dr Randall Platt, ETH Zurich
7. Your brain makes sure the world doesn’t look upside down
“In the early days of neuroscience, when scientists discovered that in addition to focusing images, the lens in the eyeball also flips images upside down relative to the world. A big open question for a while was how does your brain flip it right side up again? Why doesn't the world look upside down, if it's in your eyeball upside down?
Eventually people realised that the brain doesn't need to flip it upside down again, once it gets into the brain, you don't really have absolute coordinates anymore. If something is at the bottom of your visual cortex, that doesn't correspond to it actually being low in the world. The brain only cares about relative coordinates now, once you've put it into neural space.
This was a philosophical breakthrough for neuroscience: the coordinates of the brain were more untethered from the coordinates of the world than seems intuitive at first. I think this is just a really good metaphor for the hard problem of neuroscience in general, which is that representations in the brain are not beholden to representations in the world in any very clean and easy to characterise way.
As long as the brain can piece things back together in order to construct behaviour, it can rip it up, fold it, and do all sorts of weird things with the representation. It just needs to be able to project it onto the correct behaviour in the end. That's one of the reasons I think representation learning is so important, because it gives us some context for understanding, what should a good representation look like? We can constrain these untethered models of representations in the brain by thinking, "What should these be good for," and "What would I do if I were a brain?" (which is a funny question, because we are).” Kim Stachenfeld, PhD, Research Scientist, DeepMind
8. The brain needs to forget in order to function properly
“People tend to think of forgetting as being a pathology, but forgetting is adaptive as it is not good to remember every single thing that happened to you.
There are people that have these amazing episodic memories, but they tend to lose the ability to extract general principles of this memory. They see the trees, and not the forest, basically. And so it is not a good thing to remember every single detail.” Professor Sheena Josselyn, Neurosciences & Mental Health program at The Hospital for Sick Children (SickKids)
9. A split-brain may result in split consciousness
“There was an experiment in the '60s on the phenomenon called ‘split brain’, which is a result of the corpus callosum that connects the two hemispheres being severed. In this condition, there are two separate cognitions in the same individual.
In this experiment different pictures are shown to the right and left parts of the visual field of the patients. When asked what they see, individuals report what they saw in the right part of the visual field, because this information is processed by the left hemisphere, which is associated with speech.
If you ask the patient to choose the object they see using their left hand, they will choose the object that was presented at the left part of their visual field, as that information goes to the right hemisphere that controls the left hand. Thus, it seems like there are two different consciousnesses in the same individual.
The term ‘individual’ means that it cannot be divided and I find it amazing that one can use modern techniques to answer questions that people asked themselves thousands of years ago.” Dr Alon Rubin, Weizmann Institute of Science
10. Hemineglect in stroke patients affects memory too
“Patients who have a stroke, or for some reason suffer damage to their parietal lobe, will experience this weird phenomenon called hemineglect, where they don’t pay attention to the left half of their visual field. For example, maybe they won’t shave one half of their face. If you ask them to draw a flower, they’ll only draw the petals on one side. They'll only eat the food off one half of the plate.
The strangest thing about hemineglect is that it affects memory too. In a previous study, they found a unique population of patients who were suffering from hemineglect and had also spent a lot of time in Milan. They asked the patients to imagine themselves standing in the centre of a major plaza in Milan facing North and try to recall as many stores and streets around the square as they could, and the patients only remembered stores and streets on the right side. Then they asked them to imagine facing south and they remembered the opposite streets and stores.
Based on things we know about visual imagery and memory, this actually makes a decent amount of sense, but it’s still super bizarre to me. We know that visual imagery uses a lot of the same machinery as normal vision, for example, if you are imagining looking at something, it activates your visual cortex in a lot of ways similar to if you are actually looking at something. Which makes sense, if you've got the machinery, why reinvent the vision wheel?
We also now believe that memories are probably arranged in a structured way that takes spatial organization into account. Episodic memory is probably organised in this cognitive map. So the fact that recall had this spatial organisation that could be affected by attention now makes more sense.” Kim Stachenfeld, PhD, Research Scientist, DeepMind
11. Certain interneurons are as metabolically active as heart cells
“Once upon a time, if you wanted to tell whether somebody had had a heart attack, you would do a blood test to look at the ratio of LDH (lactate dehydrogenase A-B) in their bloodstream. In most muscle and blood you have much more of one isoform than the other, the exception is the heart, where the ratio is flipped to support higher levels of metabolism. This signature was something that you'd associate with heart muscle and was detectable in the blood during a heart attack.
But it turns out that there is another cell type, in which the LDH A-B ratio is flipped and that's the cortical fast spiking interneuron. These cells are very metabolically active, and they're so specialised that if you look at their metabolic profile, they don't look like neurons, they look like the heart, as they are hugely active all the time. They express a special subunit of the electron transport gene that was previously thought to be only present in the heart.
We have studied these interneurons a lot but not from the perspective of understanding what compromises they've made for metabolic efficiency. We do know that their dysregulation is linked to schizophrenia and auditory hallucinations. They clearly must be very important as the body is willing to pay such a metabolically expensive cost because what they're doing is so valuable.” Andrea Hasenstaub, PhD, Assistant Professor in the Coleman Memorial Laboratories in the Department of Otolaryngology-Head and Neck Surgery (OHNS) at the University of California, San Francisco
12. Abstract cognition in the brain has a material essence
“The discovery of place cells in the brain opened up a completely new way of thinking as it shows there is a physical, tangible reality to cognitive aspects. This is the first evidence that there is a material essence of a very abstract cognitive aspect of our brain function and this to me still remains the most significant scientific discovery in neuroscience to date.” Dr Marco Tripodi, MRC Laboratory of Molecular biology (LMB)
13. Even voluntary behaviour is implicitly regulated by the brain
“Studying Parkinson's disease really highlights how much implicit regulation of our behaviour is core to what feels like normal voluntary behaviour.
It is straightforward for us to think about how your mind can be wonderfully intact, and yet incapable of executing actions and I think we are comfortable thinking about that, in terms of the peripheral nervous system.
However, for diseases like Huntington's disease, or tic disorders, or Parkinson's disease, the idea that there is still so much implicit control over our behaviour in central brain structures, and so intimately tied into what we think of as explicit, voluntary, deliberative control over our behaviour.
If you're hungry, and you really want lunch, you'll walk faster to lunch. It doesn't seem like that is core to what voluntary behaviour is, but in some respects, I think that that capacity to regulate behaviours like that is actually core to what voluntary behaviour is.
In part, that is partially because implicit circuits are doing all of this work that you don't really have to think about. It's doing all of this good regulation of behaviour that sort of makes everything smooth, and fluid, and sort of well adapted to the environment, but maybe, it isn't always worth our explicit deliberation.
As far as we can tell, for some 500 million years we've basically kept the same circuit doing that. The basal ganglia has just scaled, essentially linearly, with the size of our brain. There has been incredible diversification over that time, from this tiny little thing called the pallium, which is the beginnings of the cortex, through the massive neocortex of primates, and yet the basal ganglia is there, critical to all of that.” Dr Josh Dudman, Group Leader, Janelia Research Campus