There are two great wonders of creation. The first is the existence of stars, planets and life itself. The second is the existence of minds, able to appreciate the first great wonder.
Every one of us has a mind. It enables us to perceive the world, to experience our own thoughts and feelings, and to direct our actions. But where do minds come from, how do they work and why do we have them? Could a mind ever understand itself?
Millions of words have been written, by psychologists, biologists, neuroscientists and many other ‘-ists’, on the origins and workings of the mind. Even so, what we don’t know is much greater than what we do know. In this chapter we review some basic facts about the mind, as a foundation for discussions in the rest of the book.
Neither the egg that becomes a person, nor the sperm that fertilises it, has a mind. A proto-mind, something that one day will develop into a mind, appears in the womb, as part of the amazing process of embryonic development. Nine months later, a new baby emerges. She is aware. She feels. She moves.
She knows almost nothing. She has the ability to learn almost anything.
To begin with, a baby is helpless. She can breathe, suck, swallow, cry, express waste and wiggle. A baby’s most important task is to communicate with the adult, normally her mother, that will keep her alive. Instinctively, a baby cries when she is hungry or uncomfortable.
A baby’s senses are flooded with sights, sounds and smells that she cannot understand. Mother’s voice and face are amongst the earliest things from the outside world to have meaning inside a baby’s mind – to these, she may react with a smile.
Gradually, a baby starts to make sense of the world around her. Through trial and error, she learns to move with purpose. Holding, tasting and shaking a toy rattle allows the sight, sound and feel of that rattle to combine inside a baby’s mind, as a mental representation of the physical object. Bit by bit, a baby builds a mental model of the physical world into which she was born.
As she grows, she learns to communicate in ways other than crying. The acquisition of language is critical. Now she can access the mental world of other people.
For humans in particular, the physical world is relatively unimportant. Fewer than 20% of the 100 most used English nouns refer to concrete objects, like trees and rocks, the rest identifying abstract concepts1.
Imagine that we developed the ability to communicate telepathically with tigers. Conversing with a tiger about its world, we would discover that most tiger nouns refer to concrete objects. A tiger’s ability to survive and prosper, depends completely upon its interactions with the environment. Through smell, sight and hearing the tiger hunts prey, finds water, fights rivals, finds a mate and rears its young. The tiger’s vocabulary would be rich in words to label plants, animals and smells in its natural habitat. The tiger would also have words for feelings, like hunger, thirst, anger and fear, but these would be the minority.
Our mental world is very different from a tiger’s, because humanity is a social species. We live in groups, where cooperation is critical to survival. We evolved to focus more on interactions with other people, than on interactions with the natural world. Crucially, the development of language gave us the ability to share and develop abstract concepts.
Humans do not cooperate like ants, where each creature’s behaviour is an automated response to pheromones released by other ants. Nor do we cooperate as a rigid military hierarchy, with everybody automatically obeying instructions handed down from an all-controlling mind at the top. The way humans work together is by creating shared stories, or myths2. Each person operates autonomously, guided by the rules implicit in the stories. The objective truth of these stories is unimportant. What matters is that they enable beneficial collaboration, across the group of people who believe in them.
Our hunter-gatherer ancestors used stories to help each person understand their roles (gathering nuts and fruit, hunting animals, caring for children, lighting fires, weaving baskets) and what to expect from others. Language enabled groups to remain effective as they grew larger. Chimpanzee troops, for example, rely upon each animal knowing every other animal in the troop. This puts a limit on group size: a Chimpanzee’s brain can only manage about 150 relationships, before the cognitive load becomes too great, and groups tend to split once they exceed this size3. Because of our shared stories, humans can cooperate effectively with complete strangers, enabling much larger groups to develop.
Language enabled an explosion in the number and diversity of humanity’s stories. Something completely new appeared upon the Earth: culture.
Finding food and shelter, and avoiding predators, dominated the concerns of early humans. But as we became more successful, and our numbers grew, we had more time to develop and embellish our stories. Today, most of our culture is unconcerned with the basics of survival – how to find food and stay alive in the natural world. Instead, humanity is obsessed with itself. Culture is all about what humans think of each other, and the things they create, with few remnants from those times when we were just one amongst many species, struggling to survive on the plains of Africa.
We have come a long way. How would you explain Christmas to a tiger?
Let’s return to our baby, now a child. As she grows, she learns more and more about the culture into which she is born. She improves her motor skills, gaining more control over her body. There is also a gradual shift in how she views the relationship between her and the world around her.
A new born baby is completely self-centred. She cares only that her needs are met as soon as possible. There is nothing else, just her requirements and having them satisfied.
As the parent of any toddler will tell you, one of the great challenges for a growing child is learning to deal with a world that does not exist solely for their benefit.
The first problem is the physical environment, which turns out to be full of hazards. Falling over on a hard surface is painful. Hot things burn. Sharp things cut. Gradually, our child learns how to interact with the physical world without getting hurt.
Dealing with other people, who have their own agenda, is even more challenging. Since humans live through cooperation, learning how to interact with others is vital. An especially important skill is seeing the world from another person’s perspective: empathy. Without the ability to imagine what another person sees, thinks and feels, useful social interaction is difficult.
As the child becomes an adult, another step is required – something beyond empathy. It is not sufficient to be able to see things from another person’s perspective. She must also appear to be reasonable and objective: to value that other person’s viewpoint almost as much as she values her own.
The ability to interpret the feelings of others is innate4. However, reasonableness and objectivity are probably acquired through culture. Different communities have different expectations. In a hierarchical society, people in a higher echelon might not be expected to be reasonable regarding the priorities of people from a lower echelon. Nationalists may be unreasonable regarding the needs of people of other nations.
This ability to be objective eventually led to a revolution in human society, an upheaval so cataclysmic as to have consequences for all life on Earth. Scientific thinking began in ancient Greece, India and China, was nurtured in the Middle East, and later spread to Europe. In the 15th century, the invention of the printing press initiated a great transformation, enabling new ideas to spread, and connecting intellectuals across Europe. These free thinkers valued reason and objectivity above tradition, ushering in the Scientific Revolution5 and the Age of Enlightenment6.
Science requires that we doubt not only our own opinions, but all opinions! It aspires to view the world without preconception or prejudice: with true independence. Science assumes that there exists an objective truth, unaffected by human beliefs, that can be verified using carefully controlled, repeatable experiments.
Of course, science is conducted by scientists who are as human as the rest of us. It is difficult for a person to step outside themselves, to understand how their human-centric perspective misrepresents reality. The scientific approach does not come naturally to an organism that evolved to put itself at the centre of everything, in the struggle to survive and pass on its genes. Perhaps this is why science only flourished in the last 500 years, although we have had civilisations for several thousand years.
Science is another component of human culture, our collection of shared stories. However, the practical successes of science seem to confirm its prime assumption: that there is a verifiable, objective truth, that is independent of human perspectives.
We should examine what science can tell us about our own minds.
René Descartes, a 17th century philosopher and scientist, made two important contributions to our view of the mind.
Descartes began by doubting everything. How can we be sure that the things we see and touch are real? Perhaps they are illusions, and don’t actually exist? Descartes even considered the possibility that he himself did not exist! But then he reasoned that the one thing of which he could be certain was that he was thinking – that could not be doubted. He would not be able to think if he did not exist. Thus: ‘I think, therefore I am’.
Descartes’ awareness of his thoughts convinces him of his own existence. Those thoughts were more real to him than the ‘real’ world outside his mind. This is consistent with his other major contribution: Cartesian dualism7.
Descartes proposed that the body and the mind are separate and, in particular, that the body has a physical presence, but the mind does not. The mind is pure thought.
This view of the mind is intuitively attractive. It certainly feels like my private thoughts and feelings are quite separate from the physical world ‘out there’. It is also consistent with each of us having an immortal soul, a tenet of many religions. The idea that the mind is non-physical, separate from the body, has prevailed for hundreds of years. It’s likely that most people still think of the mind in this way.
However, we know that functions of the mind are closely associated with the brain: 1,500 grams of blancmange-like organic matter, inside every human skull. Ancient Egyptians knew that injuries to the head could cause paralysis in other parts of the body8. In the 19th century, scientists started identifying where mental functions were located by examining patients with damage to specific areas of the brain9,10. For example, a person with damage to Broca’s area11 normally loses the ability to speak. Damage to the visual cortex can make a person blind, even though their eyes are unaffected12.
Today, brain scanning technology13 enables neuroscientists to observe where brain activity is located and how this relates to what people are sensing, thinking and doing at the time. Using implanted electrodes, one team found a particular brain cell that became active only when the subject saw pictures, or the written name, of the actress Halle Berry14!
What does all this tell us about the idea of a non-physical mind?
If the mind is non-physical, then how does it interact with the physical world? When I move my arm, muscle contractions are triggered by the release of a chemical (acetylcholine) from nerve cells15 in response to electrochemical signals originating in my brain. There is a physical chain of causation leading from the key area in my brain, the motor cortex, to the muscles in my arm. If my mind commanded the arm movement then, somewhere, there must be a link between my mind and my brain. But if the mind is non-physical, if it has no physical presence, then how can it drive activity in a physical brain?
Thinking about how we sense the world around us, we face a similar puzzle. How can we transfer visual signals in the brain to the mind?
If the mind is non-physical, then we must assume there is something magical that connects the mind to the brain, to drive movement and to sense the world around us.
It is much simpler to consider the mind and the brain to be one and the same.
Perhaps more accurately, we can view the mind as the set of processes being executed by the brain. This interpretation accepts that there is nothing magical or mysterious about the mind. It acknowledges that the mind, which depends completely upon the brain for its existence, is an abstract representation of what the brain does.
This set of processes, the mind, is our way of describing what the brain does. It is a story we create, to explain what the brain is doing. Because it is our story, the mind exists only in our minds.
This is rather like using ‘home’ and ‘house’ as alternative words for the same building. ‘Home’ emphasises what the building means to us, while ‘house’ emphasises its physicality. We, sitting inside, see a home. Strangers, viewing from the outside, see a house. I, inside my head, perceive my mind. A neuroscientist, looking in from the outside, sees a brain. Mind and brain are two words describing the same physical object, seen from very different perspectives.
Whenever we explicitly distinguish between the mental and the physical, we are probably misleading ourselves. Saying that something is ‘only in the mind’ makes it no less physical, and no less real. Psychologists and neurologists study the same phenomena, but they focus on different aspects.
But why do we have brains, and how do they work?
Fundamentally, we have brains so that we can move. Consider the life cycle of a sea squirt. The sea squirt larva swims until it finds a hard surface, to which it attaches itself permanently. Never having to swim again, it proceeds to digest most of its brain. (A joke in academia is that this mirrors what happens when a professor secures tenure.)
Human brains do many things, but they only have impact because they trigger movement.
The first creatures able to move their own bodies, similar to today’s jellyfish, appeared in the seas at least 500 million years ago16. As well as nerve cells (neurons) driving movement, by causing muscle fibres to contract, these creatures had sensory neurons, reacting to the presence of particular chemicals for example17.
As creatures evolved, they developed larger, more complex nervous systems. These included clusters of neurons that performed a signalling role: transferring signals from sensory neurons, that receive information about the local environment, to motor neurons that trigger movement. Intermediate neuron clusters could also manipulate and modify the sensory information, to produce more sophisticated movements in response. The first brains had appeared.
Evolutionary pressure, through natural selection, favours anything that improves an organism’s chances of surviving and propagating its genes. By using sensory information to direct movement, brains helped their owners to find food and avoid danger. Critical activities undertaken by animals, where the brain plays a key role, are feeding, fighting, fleeing and procreating – sometimes referred to as the four Fs.
The purpose of a brain is to use information about the local environment, provided by the senses (e.g. the smell of food), together with information about the internal state of the animal (e.g. hunger), to determine and control the animal’s actions (e.g. eating).
Intelligence is a measure of how well a brain performs this function.
A significant development was the ability to learn. Even the humble fruit fly, with a brain the size of a poppy seed, can learn to associate a particular smell with a food reward, and thereafter become more attracted to that smell18. This requires the brain to retain internal information – memory – that is used, together with sensory input, to determine future actions.
The brain of a fruit fly contains on the order of 100,000 neurons. The human brain contains approximately 100 billion neurons19. Each neuron has a complex tree-like shape, enabling it to connect with many other neurons at locations called synapses. It is estimated that the human brain contains over 100 trillion of these synapses20, with a typical neuron having thousands of synaptic connections to other neurons.
Visualising large numbers (billions and trillions) is difficult, so consider a counting analogy. At a rate of one per second, it would require about a day to count all the neurons in a fruit fly brain. It would take 3,000 years to count all the neurons in a human brain, and 3 million years to count all the synapses.
It is helpful to understand in more detail how brains work, especially for Part II of the book where we will compare brains to computers.
Any complex living organism, including its brain, is composed of cells. Neurons are brain cells that actively process and transmit information. Most cells die and are replaced many times during an organism’s lifetime, but neurons survive for decades. The brain contains thousands of different types of neuron, performing various roles21.
All life operates in a constant state of flux. A living organism, like a bicycle, remains stable only through perpetual motion. Even inside a neuron, biochemical pathways are continually converting chemicals into other chemicals, and changing the form of the cell.
Inside the cell wall (membrane) of a neuron, the electric potential is normally lower than it is outside the cell, in the space between neurons. This is called the resting potential for the neuron.
The cell membrane acts as a barrier, preventing substances from passing into or out of the cell. However, at some locations, called ion channels, specific molecules are allowed to pass through the membrane under the right circumstances. The presence of a substance called a neurotransmitter, immediately outside the cell membrane, can cause some ion channels to open and allow electrically charged molecules (ions) to pass through the membrane. This changes the electric potential inside the neuron. If the neuron’s electric potential rises above a critical threshold, then this causes other ion channels to open and there is a runaway reaction. The electric potential inside the neuron rises rapidly, peaks, and then falls rapidly to below resting potential before finally returning to resting potential. This whole process, called an action potential22, is driven by the opening and closing of various ion channels. An action potential typically occurs within one thousandth of a second.
The action potential causes the neuron to release neurotransmitters through the cell membrane. These neurotransmitters act as a signal to neighbouring neurons, changing their electric potential as described above, and triggering some of them also to undergo action potentials. Neurotransmitter release and the associated signalling takes place at synapses, the neuron-neuron connections mentioned above.
Much of the brain’s information processing consists of neurons undergoing action potentials (firing) and thereby signalling to neighbouring neurons via neurotransmitters, triggering some of those neurons to fire in turn and continue the process. This electrochemical chain reaction is happening inside your head, 24 hours a day, every day.
One of the major challenges for neuroscience is deciphering the neural code: relating details of neural activity, this cacophony of firing neurons, to what the brain (or mind) is thinking and doing. This has been compared to deducing what a computer is doing by observing the flow of electricity in the silicon chips23.
Understanding how a brain works might be especially difficult because it has evolved - it was not designed by an engineer. From evolution’s perspective, the brain is a black box: provided sensory inputs are processed to produce outputs that promote the survival of the brain’s owner, how it works inside is unimportant. It is possible to view the brain as an enormously complicated, intricate mess, formed as a result of millions of random changes that each turned out to be beneficial.
We now have a relatively good high-level map of the human brain, identifying what functions are performed in each region24,25. This is rather like having a map of a country, where only regions and major towns are shown. Ideally, we would like to have a map that includes every road in the country. In neuroscience, this would be the connectome, or wiring diagram, of the brain. The connectome shows all neuron-neuron connections (synapses), identifying every single neuron and all of the synapses connecting it to other neurons.
Neuroscientists have obtained the connectome for the nematode worm Caenorhabditis elegans26, which has only 302 neurons. The connectome for a substantial region of the fruit fly brain, covering 25,000 neurons and 20 million synapses, was published in January 202027, the result of several years’ effort from dozens of scientists. Work is underway to obtain the connectome for a mouse brain28, about 75 million neurons, which is a huge challenge. It will be a long time before we obtain the connectome for a human brain.
It is tempting to hope that, once we have the full connectome for a brain, this gives us a good understanding of how that brain functions. We could create a connectome model, that represents the brain as an interconnected array of neurons, each of which fires according to well defined rules. Unfortunately, it’s not that simple.
Neurons don’t necessarily affect only those neurons with which they share synaptic connections. A neuron may release other chemicals, called neuromodulators, that influence a group of neurons, including many not sharing a synapse with the original neuron. Each neuron’s behaviour may be determined by multiple neurotransmitters and neuromodulators, local concentrations of which are continually changing. There are hundreds of different chemicals (neurotransmitters and neuromodulators) that perform signalling tasks and affect neuron activity29.
Looking inside each neuron, the picture becomes even more complex. There are many hundreds of different ion channel types30, controlling the transfer of chemicals and electric charge into and out of neurons, and these ion channels can change in number and location. A neuron contains thousands of different chemicals, with continual turnover as biochemical processes convert chemicals into other chemicals, and these chemicals determine how the neuron behaves and signals to other neurons. The extended, complex shape of a neuron means that chemical concentrations and electric potential can vary considerably from place to place within each neuron31, also changing how the neuron behaves.
The synaptic connections between neurons are also continually changing: new synapses appear and strengthen while others weaken and disappear32.
Around the world, hundreds of thousands of neuroscientists have been working to understand these processes. The field has grown rapidly. It is estimated that 37,000 neuroscience papers were published in 2015, compared to 27,000 papers in 200633. There has been progress, but we still have a very limited understanding of how brains work.
For science, there is no greater challenge than understanding the brain. It is scientists’ Mount Everest: we have established base camp, and we are gazing in awe at the intimidating slopes of the Khumbu icefall.
Let’s conclude with the two key messages from this chapter.
Firstly, the mind is an abstract representation of what the brain does, and it depends completely upon the brain for its existence. Our cultural legacy has been to view the mind as ethereal, something magical that is separate from the body and the brain. The best way to correct that misconception is to consider the mind and the brain to be the same thing, viewed from two different perspectives.
Secondly, the brain is an unimaginably complex organ that we are only just beginning to understand. We know enough to confirm that mental functions, our thoughts and feelings, are located in the brain. But we are a long way from comprehending how the brain works.