At first sight, the human brain is rather unappealing. After it has been chemically prepared for dissection, it resembles a large split walnut with the rubbery consistency of a firm mushroom. Like a walnut, it is obviously shaped in two halves but beyond that, much of the structures are relatively indistinct. And yet we know that this small lump of tissue is somehow responsible for the most amazing experiences we can ever have in the universe – human thoughts and behaviours. How does this wondrous organ produce them?
The Matrix That Is Your Mind
In the science fiction classic, The Matrix, our hero, computer hacker ‘Neo’, played by Keanu Reeves, discovers that his reality is not real. He thinks he is living in the United States in the year 1999 but, in fact, he is living in a post-apocalyptic future world hundreds of years later where humans have been battling intelligent machines. His mundane daily reality is actually a computer program called the Matrix that is fed directly into his brain and the brains of other enslaved humans who are imprisoned in pods and harvested for their bioelectrical energy by the intelligent machines. But because all experience is so faithfully simulated, the humans are blissfully unaware of their true fate.
This plot may sound too fantastic to believe, but the movie is not that far off the mark when it comes to understanding the nature of the human mind. Of course, we are not enslaved humans controlled by machines, but there again, how would one ever know? These are entertaining suppositions, and all students of the mind should watch the movie, but one thing is clear: each of us really does have a matrix in our brain. This is because our brains are constructing simulations or stories to make sense of our experiences because as we have no direct contact with reality. This does not mean that the world does not really exist. It does exist but our brains have evolved to process only those aspects of the external world that are useful. We only sense what we are capable of detecting through our nervous system.
We process the outside world through our nervous system in order to create a model of reality in our brains. And just like The Matrix, not everything is what it seems. We all know the power of visual illusions to trick the mind into perceiving things incorrectly, but the most powerful illusion is the sense that we exist inside our heads as an integrated, coherent individual or self. As a self, we feel that we occupy our bodies. On an intellectual level, most of us understand that we need our brains, but few of us think that everything that makes us who we are can be reduced down to a lump of tissue. Most of us think that we are not simply our brain. In fact, we are our brains, but the brain itself is surprisingly dependent on the world it processes and, when it comes to generating the self, the role of others is paramount in shaping us.
Brain Reductionism
Some people get awfully upset with statements such as ‘we are our brains’ – as if this reduces or demeans the experience of life by making it material. Others point out that brains need bodies and so the two are inextricably linked. Still, others point out that brains exist in bodies that exist in environments and so it is illogical to reduce experience down to the brain. All of these objections are valid but ultimately we need to start taking a stand on how we think these all work together. The brain seems the most obvious place to start. We can change environments and replace most body parts, but our brain is pretty fundamental to who we are. And who we are includes a sense of self. That said, understanding where the sense of self comes from ultimately needs to involve the consideration of bodies and environments that shape the self.
Back in the dissection suite, it was the brain that had our full attention. This was no ordinary piece of the body. This was more than tissue. Somehow, each brain yielded the agony, the ecstasy, the confusion, the sadness, the curiosity, the disappointment and every other mental state that makes us human. Each brain harboured memories, creativity and, maybe, some madness. It is the brain that catches the ball, scores the goal, flirts with strangers or decides to invade Poland. Each brain that we held in our hands that afternoon in the dissection suite had experienced a lifetime of such thoughts, feelings and actions. Each brain had once been someone who had loved, someone who had told a joke, someone who had charmed, someone who had sex and ultimately someone who had contemplated their own death and decided they would donate their body to medical science when they were gone. Holding another’s brain in your hands for the first time is the closest to a spiritual experience I have ever had. It makes you feel humble and mortal at the same time.
Once you have overcome the emotional shock, you are then struck by the absolute wonder of this organ – especially if you have an appreciation of what an amazing thing the human brain is. Although you cannot see them with the naked eye, packed inside this lump of tissue are an estimated 170 billion cells.1 There are many different types of cells but for our purposes, the nerve cell or ‘neuron’ is the basic building block of the circuits of the brain that do all the really clever stuff. There are an estimated eighty-six to one hundred billion of these neurons – the elements of the microcircuitry that create all of our mental life. There are three major types of neurons. Sensory neurons respond to information picked from the environment through our senses. Motor neurons relay information that controls our movement outputs. But it is the third class of neuron that makes up the majority – the interneurons, which connect the input and the output of the brain into an internal network where all the really clever stuff happens. It is this internal network that stores information and performs all the operations that we recognize as higher thought processes. By themselves, neurons are not particularly clever. When not active, they idle along occasionally discharging an electrical impulse like a Geiger counter that picks up background radiation. When they receive a combined jolt of incoming activity from other neurons, they burst into activity like a machine-gun, sending cascading impulses out to others. How can these two states of relative inactivity and a frenzy of firing create the processing power and intricacy of the human mind?
The answer is that if you have enough of them connected together, this collection of interconnected neurons can produce surprising complexity. Like the legions of soldier ants in a colony, or thousands of termites in one of those amazing earth mounds, complexity can emerge if you have enough simple elements communicating with each other. This was discovered in 1948 by Claude Shannon,2 a mathematician working at Bell Laboratories in the United States on the problem of sending large amounts of data over the telephone. He proved that any pattern, no matter how complicated, could be broken down into a series of on and off states distributed across a network. Shannon’s ‘information theory’, as it became known, was not a dusty theoretical notion, but rather it was a practical application that revolutionized the communications industry and gave birth to the computer age. He showed that if you connect up a large number of simple switches that could be either ‘on’ or ‘off’, then you can create a binary code,3 which is the communication platform for all digital systems that control everything from an iPod to the orbiting International Space Station. This binary code is the foundation for every modern computer language. It is also the same principle operating in every living organism that has a nervous system.
The neurons communicate with each other by sending electrochemical signals through connecting fibres. A typical neuron has lots of fibres connecting with local neurons next to it but also has a long-distance fibre called an axon that connects with groups of neurons much further away. It’s like having a bunch of friends you talk to regularly in your neighbourhood but also a really good connection with a group of friends who live abroad. The neurons are jam-packed into a 3-4 mm thick layer on the outer surface of the brain, known as the cortex (from the Latin for ‘bark’). The cortex is of particular interest because most of the higher functions that make us so human appear to rely on what’s going in this tiny sliver of tissue. The cortex is also what gives the human brain its peculiar appearance of a giant walnut with many crevices.4 The human brain is 3,000 times larger than that of the mouse but our cortex is only three times thicker 5 because of the folding. Think about trying to cram a large kitchen sponge into a smaller bottle. You have to scrunch it up to make it fit. It’s the same with the human brain. Its folded structure is nature’s engineering solution to cram as much brain into a typical skull as possible without humans evolving heads the size of beach balls to accommodate the same cortical surface area. Ask any mother during delivery: she will probably tell you politely that it’s bad enough giving birth to a normal-sized head without it being any larger!