(11 min read)
A brief tour of the brain
It feels rather trite to describe the brain as ‘astonishing, remarkable and prodigious’ (and all the other ‘phenomenal’-like adjectives), but it’s true.
It is an incredibly complex organ, more sophisticated than any machine ever invented, capable of processing information at 120 miles per hour. It never switches off.
It is around 60% fat, making it the fattiest organ in the body (and why omega-3s and omega-6s are so good for brain health). It uses about 20% of the oxygen in the body – up to 50% if you’re working hard. Each minute, enough blood to overwhelm a wine bottle flows through it.
It is also about 75% water. Dehydration – even just 2% – and a loss of sodium and electrolytes can have a significant negative effects on its ability to pay attention and recall memory.
It has around 86 billion nerve cells, or neurons, which is around the same number of stars in the milky way. Within the brain are several different structures who all interact to produce a personalised version of reality that we take for granted.
Brains can’t feel pain. The covering can, but not the brain itself. Which is why patients undergoing brain surgery are often only anesthetised during the cutting of the skull; they are woken to act as partner in brain surgery, responding to stimulation of brain regions and thus directing the surgeon’s course.
When we’re awake, the brain generates enough watts of electricity to power a small light bulb. It can send messages to your arms and legs at speeds of up to 260 miles an hour.
The average person has between 12,000- and 60,000 thoughts per day: the vast majority of them are the same as the day before (95%) and around 80% of these thoughts are negative.
And we all walk round with one of these super-computers in our skulls…
Meet your brain!
Let’s assume that you now appreciate the biological mastery of the brain. Here is a grossly oversimplified tour of the main structures:
If you opened up the skull, you’d see the cortex (from the Latin word for ‘bark’ or ‘covering’). It’s the wrinkled, walnutty outer part that we’re familiar with. From an evolutionary perspective it’s the youngest part and contains the bits that develop last, in late adolescence, which is why it’s sometimes also called the ‘neocortex’. And why teenagers are utterly bonkers some of the time.
The cortex is known as ‘grey matter’, because that’s the colour of the neuron cell’s body. White matter is white on account of the fatty insulation around the nerves. (Actually, brain parts don’t really look white or grey until it is pickled. When alive, the brain’s grey matter looks pinkish, and the white matter rather grey).
Under this cortex rind sits the rest of the cerebrum.
It’s the seat of intellectual activities; where all the things that make us distinctly human happen. Reasoning, self-awareness, memory, self-control and so on. Its split into two halves, connected by an information superhighway called the corpus callosum. Despite looking like mirror images of each other, the two sides are different. No one really knows, yet, why nearly all the signals travelling between the brain in body cross over on their way through. This means the left half primarily controls the right side of the body, and vice versa.
The frontal lobes of the cerebrum allow us to make future plans and reason (or argue) with someone. They act as short-term storage sites, keeping one idea on hold whilst others are considered. At the back of the frontal lobes is the motor area, helping to control movement. Broca’s area, on the front left lobe allows thoughts to be changed into words.
Behind the frontal lobes are the parietal lobes, which convert aromas, tastes and textures into electrochemical signals that the brain interprets as ‘delicious’ or ‘revolting’. Near here are the primary sensory areas, which receive all the information about the world – temperature, touch, taste, movement – sent from the body. It’s also where reading and mathematics happens. As you read this, the occipital lobes at the back of the brain are at work, processing letter images from the eyes and linking it to your memory of what they mean.
The temporal lobes, located unsurprisingly where the temples are, receive and process information from the ears. Not only that, but it’s here that your unique taste in music resides. Memories are also integrated with sensations of taste, sound, sight and touch. The underside of the temporal lobe plays a vital role in making and retrieving memories.
Deep brain structures
Below the cerebrum lie deep brain structures. These liaise between the spinal cord and the cerebrum. Each of these also has a partner, mirrored on each side of the brain.
The hypothalamus, a pearl-sized structure, directs a host of important functions, including waking you up in the morning, getting adrenaline flowing and communicating thirst and hunger. It controls the molecules that make us feel excited, angry or happy. Quite a lot for something so small. Above the hypothalamus is the thalamus, a sorting room for information flowing both ways between the spinal cord and cerebrum.
The hippocampus is so called because it closely resembles a seahorse (and the ancient Greek word for seahorse is, in fact, ‘hippocampus’). The hippocampus features a great deal in anything related to educational neuroscience, learning or memory, because acts as a memory indexer. It sends memories out to the correct parts of the cerebrum and retrieves them when necessary. The basal ganglia surround the thalamus in little clusters. They initiate and integrate movements; when they are diseased by Parkinson’s it causes shakiness, and a stiff, shuffling walk.
The midbrain lies at the top of the brainstem. It’s a small part of the brain, yet crucial. It controls some reflex actions and is part of the circuit used to control voluntary movements, such as those of the eye.
Finally, the hindbrain. This includes the upper part of the spinal cord, the brain stem. It controls vital functions like breathing and heart rate. The wrinkled ball of tissue hanging off the back of the brain is the cerebellum. This coordinates movements – it allows you to hit a tennis ball or play the piano.
The connectome
A different, but helpful model when considering the brain is the connectome. It’s a term that has only been around for the last decade or so because it’s a recent feat of scientific progress. It is the complete map of all the neural connections in a brain. It’s a bit like the flight route maps in the back of aeroplane magazines (ah, in those pre-pandemic days).
If you map the bundles of nerve fibres carrying information through the brain, you can see clearly that there are ‘hubs’ or ‘nodes’ in the network that have the strongest connections or the highest frequency of links with other nodes. These are the London Heathrows and Dubais, with more flights and more intercontinental flights than other airports.
Each person’s connectome is slightly different, but there are patterns that ‘typical’ brains share. Being able to map the brain networks of these healthy individuals has put scientists in a much stronger position to recognise how brain network organisation is different for people with psychiatric disorders. The connectomes of people with Schizophrenia for example are different – on average, their brain network hubs are less strongly connected. Rather than flying direct from London Heathrow to Delhi, for example, you’d have to fly via lots of smaller airports to get there.
Being human.
Forgive me now for going a bit weird on you (I’ll be brief). But I think it’s really important to appreciate that the brain doesn’t just sit passively inside your skull – it sits in a series of interactions. Interactions between and within the brain’s different structures; between the body and the brain, and between the body and the world.
This is perception – how the brain makes meaning from the interactions this body has in this world.
We don’t see reality. This isn’t a segue into a post-modern relativist strangeness, it’s the truth. As world-renowned neuroscientist Beau Lotto says, There is a physical world. It’s just that we don’t ‘see’ it. Red doesn’t exist, the note ‘C’ doesn’t exist. These are all things inside our heads that we project out into the world.
Our remarkable capacity for learning is what sets us humans apart from other animals. How we learn and the environment in which we learn alters how our genes express themselves, not only in our bodies but in the next generation. Mind-blowing! At least I think so.
And this is a segue onto the next question, which answers: What is learning? Give me the basics!