Take a further moment to experience your body in this quiet state. If you concentrate you can feel its inner workings. As you read these lines, can you feel the subtle movements of your tongue bobbing up and down inside your mouth? Now that your attention has been drawn towards it, can you feel the pressure of the chair you are sitting on pressing against your backside? We can be in touch with our bodies but we are more than just our bodies. We control our bodies like some skilled operator of a complex meat machine.
Figure 4: Plot of locations where individuals typically feel their ‘self’ is located (based on study by Ferrari et al., 2008. Copyright permission given)
This internal self is sometimes called the ‘homunculus’ and this little chap is a real troublemaker. The homunculus is a problem because you are left none the wiser about the location of the self. In fact, considering the homunculus reveals why the reality of the self is a problem. There can be no single individual inside your head for the simple reason that, if true, then this homunculus would require an inner self as well. You would need a ‘mini-me’ inside the ‘you’ that is inside your head. But if the ‘mini-me’ inside your head is a homunculus, then who is inside the head of mini-me and so on, and so on? This would become an infinite regression leading to no end. Like an endless series of Russian matryoshka dolls, one inside another, the homunculus simply restates the initial problem of where the self is located in the mind. This is what the philosopher Dan Dennett has called the illusion of the Cartesian Theatre after the famous French philosopher, René Descartes, who thought that each of us possess a mind that inhabits our bodies. Dennett described this like sitting in the audience inside our heads watching the world of experience unfold like a play on a stage. But who is inside the head of the person watching the play in the Cartesian Theatre? Proposing an inner self simply does not help in solving the problem of where we are inside our heads.
Are we like a factory made up of lots of autonomous little workers inside our heads carrying out all the various tasks and functions that humans can achieve? To some extent we are, in that many of the subdivisions can operate independently. But there is not a worker army of homunculi any more than there is a chief executive in charge. Rather, our minds are a multitude of different processes and decisions that are often in conflict with each other, which often can occur below our level consciousness. This is why we will need to abandon the notion of internal individuals, which is inadequate to explain the complexity of our brain, and ultimately discard the notion that there is an inner self.
Mapping the Mind Machine
If the brain is a complex machine organized into different processing subdivisions, where does this organization come from? Who sets up all the domino patterns in the first place? This question is one of the major battlegrounds in neuroscience. To what extent are we preconfigured for the world by our genes and to what extent does that configuration emerge through our interaction with the world? It’s the old ‘nature versus nurture’ issue but at the basic biological level. It all depends on what aspect of being human you are considering but even the simplest features appear to combine biology with experience.
It is quite clear that we are born with many basic neural patterns in place. Many sensory and motor areas are well specified at birth even though they have yet to reach their full adult potential.15 But babies are not just passive sponges soaking up sensation from their environment – they can also act upon the world. For example, each human newborn is equipped with a repertoire of behaviours known as reflexes that play some vital role in development. Consider the rooting reflex, triggered by gently stroking the cheek of a newborn, which makes the baby turn their head and pucker up their lips in anticipation of a tasty nipple. If a nipple (or at least something of a similar shape) is touched to the baby’s lips, this then triggers a sucking reflex. You might think that the baby has decided to feed, but the truth is that these behaviours are completely involuntary and automatic and do not require any thinking. In fact, you do not need a very sophisticated brain to execute them. Anencephalic babies, born without any cortex, can still execute sucking reflexes because these behaviours are supported by primitive neural circuitry that lies beneath the cortex. But anencephalic babies are never destined to experience what it is to be human. They do not learn. They do not get bored.16 They simply respond. They will never develop a sense of their own self. Most die within days.
In contrast to the unfortunate babies born with brain damage, healthy infants are equipped with a brain that is designed to learn about its environment and this learning starts very early. We now know that the unborn baby can learn the sound of their mother’s voice, develop a preference for the food she eats while pregnant and even remember the theme tune to the TV soap operas she watches while waiting for the big day to arrive.17 All of this proves that the brain is already functioning and storing patterns of connections that represent the outside world. This is one reason why separating the relative influence of nature from nurture is always going to be hard and contentious. When do you start measuring? From conception or from birth?
Neuroscientists argue about how much of the adult brain structure is already evident in the infant, but it is quite clear that even if much of the blueprint for brain architecture has been passed on in the genetic code we inherit, there is still considerable scope for making amendments and building extensions to the original plan. This is where the environment shapes the brain by sculpting the matrix of neuronal connectivity that generates our minds.
Plastic Brains
I once bought a ‘Grow Your Own Brain’ gimmick toy, which was basically a compressed tiny plastic foam brain that you put in water, and it eventually expands to a much greater size. It’s amusing but not really a useful teaching aid. It is true that as babies grow their brains expand, but they are not simply swelling. The human newborn baby’s brain weighs about a quarter of the weight of an adult brain but within the first year more than half of the difference in weight is made up. What may surprise you is that this weight change is not because the brain is growing more neurons. In fact, newborn babies have almost their full complement of neurons that will remain with them throughout the rest of their lives. Rather most of that weight change is due the rapid expansion of communications between the neurons.18
As you can see in Figure 5, a diagram of the cortex taken from newborns through to fifteen months old, the human brain undergoes a massive explosion in connectivity between neurons during infancy.19 For example, during peak activity, the rat pup brain is generating neuronal connections at the rate of 250,000 every second. That’s fifteen million connections every minute. We do not know how fast the process occurs in humans. If anything it may well be even faster.
Figure 5: Illustration of neurons’ increasing connectivity during development
These structural changes reflect the way that biological processes interact with the world to shape the brain to fit into its environment. Two complementary processes create this sculpting.20 First, genetic commands tell the neurons to start growing more and more connections. This creates an initial over-production of connectivity between the neurons. That’s why the diagram looks like the underground root system of weeds growing in your garden. Second, this bout of over-production is then followed by a period of pruning, where connections are lost between neurons.21 Around four out of every ten connections are lost with about 100,000 lost every second during the peak rate. This loss of connectivity is particularly interesting and at first surprising. Why would nature put in all the effort to build bridges between neurons only to knock them down almost equally as fast at a later date?