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A Journey Into the Human Brain – Everything You Need to Know
The brain is the seat of our subjective experience. Without a brain, we wouldn’t be conscious of the world around us. This is what makes us “us” and what allows us to move, think, feel, and plan.
And yet we have very little idea about how the thing works. How can we optimize our brains if we don’t have a model of how they should work?
See also: Cognitive Training – Is Brain Training Effective for Sports, Productivity, and General Performance?
While no complete model of the brain exists, and although scientists are still a long way from understanding its ins and outs, there are still a lot of incredible things to learn. Not least some new discoveries and ideas that completely change the way we think about our grey matter. So keep watching to get a better picture of just what’s going on inside your head, and how to get the most from it.
The Connectome
At its simplest level, the brain works a little like a mind map. Our grey matter is made up from roughly 86 billion neurons (neurons being brain cells). There are over 100 trillion connections between these neurons, which are known as synapses. The average neuron has a whopping 7,000 connections to other neurons.
This huge network, which we can liken to a mind-map or spiderweb, is unique to every single person and is sometimes referred to as a “connectome.”
Neurons are composed of a cell body, soma, with sprouting dendrites and axons. Dendrites look like tendrils that reach out across the brain in order to connect with other neurons. The axons, meanwhile, are the “tails” that protrude from the cells.
The connections (synapses) between neurons can be localized but in some cases connections can span large portions of the brain. Axons can be up to one meter long!
Synapses and Action Potentials
Synapses take the form of small gaps across which signals can travel. Signals, meanwhile, are in fact electrical impulses. When a neuron “fires,” which is known as an action potential, an electrical impulse will travel down the axon to the synaptic terminal at the end. This is the “output port” where the electrical impulse will then jump across to stimulate the dendrites of other neurons.
Action potentials are binary. That is to say, a neuron is either firing or not and there are no gradations of intensity. When a neuron receives enough stimulation from incoming dendrites to raise it above a certain threshold, it will then fire and carry that signal onwards. In some cases, input from one neuron may be enough to cause this. In other cases, multiple inputs will be required to depolarize the neuron. Most neurons have a “resting potential” of around -60mV and a threshold potentiation of around -50mV and -55mV, though this can vary.
There is then a brief cool-off period before the neuron can fire again.
How We Experience the World
This electrical activity is what gives rise to our subjective experience of the world.
When a neuron fires, it will correlate with an experience or action. For instance, there are specific neurons that correlate to points within our visual field. If you artificially stimulate these neurons with an electrode (which can actually be achieved during open-brain surgery), you see points of light appear like pixels on a monitor. Other neurons correspond with motor units that cause twitches within muscles.
Other neurons still, combine to represent our memories, ideas, and experiences. For example, there will be a group of neurons that represent friends, or concepts like freedom. Because of the interconnected nature of neurons, activity in one area will bring to mind related concepts and ideas – giving rise to our train of thought.
This alone raises some interesting questions. If you were to surgically remove the right neurons, could you completely destroy someone’s memory of a specific person? How many neurons would it take? This line of reasoning is sometimes referred to as the “grandmother cell” or “Jennifer Aniston neuron.”
We know, for example, that brain damage can in some cases result in some shockingly-specific memory deficits. For example, there are recorded examples of people losing the names of vegetables!
Understanding
When a neuron fires in the occipital lobe (visual cortex), it is easy to understand how this directly connects to the eye and creates a solid experience.
But how do we “experience” something like the feeling of walking through the woods? Or the number 7? Or loneliness?
One leading theory that I particularly like, is that of “embodied cognition.” This theory suggests that all our experiences ultimately relate back to physical experiences and interactions with the world. Our thoughts would be too abstract to mean anything without a grounded experience in the real world. When someone tells you a story about walking through the woods, you only understand this by utilizing the neurons that would fire if you were walking through the woods yourself. Abstract quantities, like numbers, ultimately must also relate back to physical experiences.
See also: What is Embodied Cognition? How You Think With Your Body
Brain Areas
While the brain might look like one giant web, the truth is that it is more organized than that. Generally, neurons are grouped by function. Thus we have a “visual cortex” and an “auditory cortex” which handle precisely what you would expect. More abstract functions like forward planning and emotion are largely handled by the hippocampus and amygdala, for example.
The brain can also be roughly divided into three larger components: the forebrain (which is responsible for our higher reasoning and is thought to have evolved most recently), the midbrain (which is the smallest part of the brain and thought to act as a relay area for auditory and visual information), and the hindbrain (which is the “primary brain”). Discounting the cerebellum (meaning “little brain”), which helps us coordinate movement and may play an important role in our ability to predict outcomes, the hindbrain and midbrain are generally grouped together as the “brain stem.” This part of the brain is responsible for many of our most basic functions, such as breathing and digestion. Most of this occurs largely unconsciously.
We can also divide the brain down the middle into two halves, called “hemispheres.” These two halves are connected by a thick bundle of nerves called the “corpus callosum.”
Brain Activity
But lest you think that the brain is neatly organised into predictable components, the truth is far more complex. Many functions rely on the interactions of multiple brain regions at once.
See also: What is Dynamic Functional Connectivity? Implications for Performance and More
As well as looking at individual brain regions, neuroscientists are also interested in common patterns of activity throughout the brain. These include the likes of the “default mode network” – a network of regions that work together during daydreaming; and the “salience network” – which correlates with focus and attention. This is “functional connectivity.” But even this is overly simplistic. More recent approaches use “dynamic functional connectivity” to look at how different brain regions interact over time. Activity in one area might mean something different if it immediately follows activity from another area!
Not only that, but in non-typical development it is possible for functions to migrate to entirely different parts of the brain! As in the case of people who undergo hemispherectomies (losing half of the brain) and still retain a shocking amount of functionality.
Brainwaves
Inside your brain at any given time, there will be countless neurons firing in different regions of the brain. This activity is what can be detected via an EEG (electroencephalogram) and is where we get “brainwaves” from. Contrary to popular belief, however, we do not experience a single type of brainwave at any given time. One part of your brain may be in theta, while another is in alpha! When someone tells you your brain is in an theta state, they’re really talking about the average activity across the entire brain. This only tells a very small part of the story!
See also: How Optimal Brainwaves Can Correlate With Productivity, Athletic Performance and Creativity
This is, possibly, where the misconception that we only use “part of our brain” comes from. In truth, we only use part of our brains at any given time. This is exactly as we would want it: too much activity across the entire brain could result in a cascade of uncontrolled electrical activity, which is what happens in a seizure. The brain must be modelled to perfectly manage the amount of activity so as to eek out optimal activity, without triggering a neuronal avalanche – dancing on a knife-edge. This is called the “critical brain hypothesis.”
Overactivity in specific areas of the brain can also cause issues like OCD or anxiety, whereas inactivity may correlate with feelings of malaise or drowsiness.
The Analogue Brain
Thus, an important job for the brain is to careful manage these levels of activity. There are numerous mechanisms in place to accomplish this.
One such mechanism is smart organisation. Increasingly, researchers are viewing the brain as a math problem and attempting to model the kinds of networks that would allow for complex thought. It has been suggested that this organisation is akin to a small world topology, meaning that neurons can connect across great distances using the minimal number of connections.
Physically, this is partly made possible by the sulci and gyri (grooves and bulges) on the surface of the brain. This wrinkled appearance helps us fit more brain into our skulls, but also provides handy little shortcuts – like wormholes – to connect disparate neurons.
More fundamental are neurotransmitters. Neurotransmitters are chemicals that are released in the brain via various mechanisms and modulate the activity of neurons. Many neurotransmitters are stored at the ends of axons (synaptic terminals), located at the “synaptic knobs” and contained within little sacs called “vesicles.” During an action potential, these chemicals are released and will thus affect the “post synaptic neurons” – those neurons on the receiving end of the synaptic gap.
Neurotransmitters include the likes of dopamine, norepinephrine, serotonin, and GABA. Each of these can be placed into one of two categories: excitatory neurotransmitters that increase activity and make neurons more likely to fire, and inhibitory neurotransmitters that decrease activity and firing. Hormones can also act like neurotransmitters in some cases.
The Unbelievable Complexity of Neurotransmitters
As ever, neurotransmitters are more complicated than they are often given credit for. Your brain is constantly awash with a cocktail of different neurochemicals – you don’t simply produce more serotonin and feel better! Neurotransmitters also need to interact with receptors in order to have a direct effect on a specific neuron. If a neuron doesn’t have a receptor for that specific neurotransmitter, it will have no effect. Certain brain regions are more receptive to specific neurotransmitters and may have unique reactions.
Neurotransmitters also have countless different roles within the brain and body. For example, cortisol is often described as the “stress hormone.” However, it is far more complex than that. Cortisol also modulates hunger, it helps us to wake up, and it increases focus. Cortisol also affects the way that fat is stored and the effect of testosterone.
Likewise, serotonin is the “feel good hormone” but it is also inhibitory and thus can incur drowsiness. This is especially true as serotonin converts to melatonin and makes us sleepy. Serotonin once again has an effect on hunger. And in one study, researchers found that delivering small electric shocks to the paws of mice would trigger the release of serotonin in brain regions associated with depression.
Short Term Plasticity
Likewise, short-term plasticity shows us how the activity of neurons is altered in the short term. For example, short term depression occurs when specific neurotransmitter vesicles are depleted. This results in a connection that is less likely to fire. Short term synaptic facilitation, meanwhile, occurs when a build-up of Ca2+ concentration, among other factors, makes a synapse more active.
Temporarily increasing and decreasing sensitivity at specific points in the network can drastically alter the flow of information through the brain, and should be a critical component of any attempt to model neuronal activity.
See also: Priming: Warm Ups for the Brain
For all these reasons, simply ingesting supplements to increase one neurotransmitter or other is not an effective way to increase cognitive performance. As I’ve said many times: it’s akin to trying to fix a watch with a sledgehammer.
And over time, the brain can upregulate or downregulate specific neurotransmitter receptors in response to an overabundance or lack of particular chemicals. This is how users develop tolerances and addictions to mind-altering substances.
Instead, we should focus on proper nutrition to ensure the brain is able to synthesize all the neurotransmitters it needs – along with a balanced lifestyle that helps us to achieve the necessary balance. The aim is to build a brain that can transition seamlessly from one “state” to another, as the environment dictates.
Dendritic Computation and Glial Cells
Further complicating matters is dendritic computation. This refers to the ability of the dendrites themselves to carry out basic maths. This occurs through a number of processes, including the use of membranous “spines” that protrude from the dendrites like branches and form compartments. These spines can connect to individual axons and act like filters (by offering additional resistance) as well as spacing apart different signals to introduce a temporal element.
This way, dendrites themselves are able to alter the effect of an incoming signal and even carry out rudimentary logical operations such as AND, OR, and XOR. Far from inert input nodes (as they were described by the old “point neuron hypothesis” of the brain), they act much close to the complex switches found in microchips.
Then there are the glial cells. Whereas your grey matter is made from neurotransmitters, glial cells are the “white matter” that actually make up 85% of the brain. These cells play a number of key supporting roles, supplying the neurons with nutrients and cleaning up by-products. However, we now think that the glial cells may also play important roles in enabling action potentials and determining which cells fire and which do not.
There are numerous different types of glial cells, such as oligodendrocytes, astrocytes, and microglia. There are even “gliotransmitters” which are neurotransmitters that interact specifically with certain glial cells.
And to think that most models of the human brain don’t even include glial cells, simply because we don’t know enough about them! The brain truly is a mystery to us.
The Dynamic Brain
So far, we have painted a picture of a static brain. Such a brain would be largely useless, however.
To survive, we must be able to adapt to our surroundings and change our behavior and approaches. To this end, the brain is plastic and malleable: constantly transforming and changing shape in response to inputs. This is brain plasticity, or neuroplasticity.
Through neuroplasticity, we are able to grow new connections between neurons, strengthen the existing connections that we use most often (long-term potentiation), cull those synapses we don’t need, and even birth entirely new neurons. This activity is more prolific in some parts of the brain than in others.
The defining rule of neuroplasticity is often described as “neurons that fire together, wire together.” That is to say that if two neurons are repeatedly active simultaneously, they will reach out over time and form a connection. This is how habits can form and it’s why association works the way it does. And likewise, “neurons that fire apart, wire apart.”
This simple rule can give rise to shocking organization through the brain. For example, the motor cortices of the brain are often remarked upon for being organised in a way that represents the shape of the body: with the neurons for the hands being located near the neurons for the arms, etc. But given some thought, this makes sense: after all, we are most likely to move in that order. We rarely move our hands without moving our arms! And the same goes for the foot and leg, leg and hip, hip and stomach.
Increasing Plasticity
We can tap into this amazing plasticity to learn any new skill. However, it can also be a negative force. For example, one of the reasons that we find it so hard to move our toes individually, is that they are so often welded together in our shoes. This literally “fuses” the neural maps for the toes together, such that we can’t move one toe without triggering movement in the neighboring toes.
Neurotrophic factors are chemicals that support the growth and help of both developing and mature neurons. These include the likes of brain-derived neurotrophic factor, and nerve growth factor.
Our brains are most plastic when we are young and typically become less plastic as we age. However, there are many things we can do to slow the loss of this plasticity – such as exercising and gaining new experiences into old age.
***
And with that, you have a basic understanding of the human brain! Of course, there’s plenty more to learn and even more that we don’t yet know! But with these fundamentals, you should have some concept of what’s going on inside your noggin. As a result, you should hopefully be able to devise some strategies for optimization.
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The images you make is sick! Calm and mysterious vibes.
Glad I found your site.
Adrián