The Domesticated Brain (8 page)

Each neuron looks like a many-tentacled creature from outer space with a body from which branch thousands of receptors or
dendrites
that receive incoming signals from other neurons. When the sum of incoming nerve impulses
reaches a critical threshold, the receiving neuron then discharges its own impulse down the axon to set off another chain reaction of communication. In this way, each neuron acts like a miniature microprocessor. The patterns of nerve impulses that spread across the vast network of trillions of neural connections are the language of the brain as information is received, processed, transmitted and stored in these networks. The presentations of experiences become represented, or
representations
– neural patterns that reflect experiences and the internal computing processes our brains perform when interpreting information.

One of the more surprising discoveries about brain development is that human infants are born with almost the full complement of neurons that they will have as an adult. Yet the newborn brain weighs about a third of the adult brain. Within a year, it is about three-quarters the size of the adult brain.
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Connections form at a rate of 40,000 per second in the newborn, which is over 3 billion per day.
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Eventually, the length connecting fibres will extend to an estimated 150–180,000 km – enough wiring within an individual human brain to circumnavigate the world’s equator four times.
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In fact, the bulk of the brain is mostly connections, with the neurons squeezed into 3–4mm of the outer layer that covers the surface of the brain, called the
cortex
after the Latin word for ‘bark’.

These changes in connectivity enable the world to shape the brain by experience because experience keeps the neurons active through repeated mutual activation. This shaping process is called
plasticity
after the Greek word
plassein
, meaning ‘to mould’. Synapses between cells that are in
constant communication change in their sensitivity so that messages transfer more easily between them. At its most basic level, this is how information is stored in the brain – as changing patterns of neuronal activity. This crucial role for reciprocal neuronal activity is captured in the first of the neuroscientist’s principles of plasticity, ‘cells that fire together, wire together’.
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Most brain plasticity occurs during child development, with some areas continuing to change well into the late teenage years. The front part of the brain, associated with decision-making, does not become fully mature until the child reaches adulthood. Of course, there is plasticity in the adult brain as we constantly learn throughout our lifetime. However, connectivity in some brain systems seems to be time sensitive, requiring input much earlier in development. Remember neural activity is metabolically expensive. If neural connections are not active, then why keep them? In many ways it is similar to pruning your favourite rose bush. You cut away the weaker branches in order to allow the stronger branches to flourish.

These windows of opportunity, which are sometimes called
critical periods,
reflect the way that Nature has produced a brain that anticipates specific experiences at certain times; if these are denied or impoverished, there may be long-term impairment. This is true for the sensory systems such as vision and hearing, but as we will read in the next chapter, there appear to be critical periods for social skills as well. This loss of function due to deprivation is a second principle of plasticity, where you have to ‘use it or lose it’ when it comes to keeping neural mechanisms functional.

Core knowledge

In the same way that our brain is pre-configured to experiences before we have even had the chance to encounter the relevant sensations, some scientists believe that we are also wired to interpret the world in particular ways before we have had the chance to think about it. The speed at which babies acquire and understand aspects of the world around them before they are capable of comprehending spoken language indicates that they must be working things out fofigr themselves. As adults, we take it for granted that the world is made up of objects, spaces, dimensions, plants, animals and all manner of complex ideas that we rarely take the time to consider because we have had a lifetime of exposure to them. But how do young babies come to appreciate these concepts in the absence of language? When a baby looks around its new blurry world, what does it make of it all? Even if they are learning by themselves, how do they know what to pay attention to and what is relevant? These sorts of problems have led to the proposal that some key components of understanding the world, especially those related to the physical nature of objects, numbers and space, must be programmed into the brains of infants from birth. But how do we know what babies are thinking when they are not even capable of telling us what is on their minds? The answer comes down to showing them magic tricks.

The reason that we find magic tricks so entertaining is that they violate our expectations. When a magician makes an object vanish into thin air, we are first surprised and then set about trying to figure out how they achieved the illusion. As adults, we know that a physical law has only apparently
been violated because if we did not have that understanding, then we would not be surprised. That is why it is a trick. The same is true for babies. When they are shown magic sequences where objects appear to vanish, infants look longer. They do not applaud or gasp as an adult audience would, but they notice that something is not quite right.

This magic-trick technique, known as
violation of expectancy
, has spawned hundreds of experiments used to tap into the minds of infants who cannot tell us what they are thinking. Harvard psychologist Elizabeth Spelke has been using violation of expectancy to probe the rules infants apply when understanding the physical world.
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From very early on, infants recognize that solid objects do not pass through other solid objects, move from one position to another without appearing in between, move by themselves unless contacted and nor do they dissolve or fall apart when touched. When we say that something is ‘solid as a rock’, it is so because it obeys Spelke’s rules for physical objects. These rules do not have to be learned and for most objects that the child will encounter throughout the rest of their life, these principles will hold true, which is why they are referred to as
core knowledge
, because they are programmed into the mind from birth.

Of course, there are some exceptions to these rules, such as in the case of magnets, where an iron object will move in the absence of direct contact with another object. Soft bananas dipped in liquid nitrogen become hard as nails. These exceptions to the normal rules are enchanting because they violate our expectations of how physical objects should behave. Many toys that you find in science
museums are counter-intuitive examples that amaze and amuse precisely because they do not behave like most ordinary objects.

It’s alive!

Babies appreciate that people are also another type of object, but one with a special set of properties. For a start, people can move by themselves. If an inanimate object is left behind a screen then it should still be there unless someone has moved it. A person, on the other hand, can leave the room when you are not looking, so may not necessarily remain stationary when they are out of sight.
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Also people do not have to move in a straight line. Five-month-olds who watched a video of a box sliding across a stage and passing behind two screens were surprised if it did not reappear in the gap in between. However, they were not surprised when a person moving across the same stage did not reappear in between the screens, suggesting that the infants could draw a distinction between how a box and a person can behave when moving in between screens.

Living things also move in particular ways. Objects that are not alive tend to move in a rigid way, whereas living things have ‘biological motion’ which is much more fluid and flexible. These types of movement are processed by neurons that are tuned to directions and speed in the visual area at the back of the brain known as
MT
. Biological motion is less rigid and activates a different region which is closer to the area behind your ears that is activated by faces. This area, the
fusiform gyrus
, also registers the shape of the human body,
which suggests it might be a region that stores general information about others like us.
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When we think of others, we expect them to be a certain shape and move in a certain way. By six months of age, babies are surprised to see a female who appears to have arms growing out of her hips that swing as she walks.
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How do babies decide what is human? We know that babies like to look at other people. They prefer biological motion at birth.
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We also know they prefer the sound of the human voice and their mother’s voice in particular.
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They prefer the smell of their mother compared to the smell from another mother.
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Just about every capability of the newborn’s senses seems to be tuned into their mums.

Over time, infants gradually start paying attention to others and noticing what they are doing. When you think about it, the sheer volume of information contained in just a minute or two of a typical everyday action that an adult might perform is staggering.
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Consider the individual steps involved in making a cheese sandwich. Every sequence requires complex motor skills that must be performed in a way that is beyond the capabilities of robots. Ingredients and implements must be retrieved from various locations in the kitchen and then prepared and assembled in the correct pre-planned order. There is no point trying to butter the slice of bread after the cheese has been inserted. How do babies begin to make sense of what they see when watching others? It turns out that in just the same way that baby brains are wired to chop language up into different segments, they are programmed to observe and learn different actions. Infants as young as six months are sensitive to the statistical
regularities in action sequences and by ten to twelve months readily segment complex actions up into their constituent parts based on the flow of movements as they start and stop.
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So babies are the consummate
people persons
– they love to watch others. People are the most interesting objects to babies not only because they look and move in a particular way in complex action sequences but because they interact with them. Synchrony is critically important to establishing social interactions and babies are on the lookout for those who are tuned into them. As adults, we instinctively engage in these synchronized activities, often mimicking the baby in an attempt to capture their affections. Two-month-old infants will even treat non-living objects that act contingently as if they are alive and smile at them.
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As they build up their models of what it is to be human, they are looking for evidence for those things that are most likely to be important for their survival and becoming increasingly more sophisticated in their decisions.

Thinking objects

Babies rely on faces, biological movement and contingent interaction to draw up a list of credentials that make something worth paying attention to. Any one of these attributes may signal that something is worth watching because they are starting to draw a distinction between the living and non-living world in terms of agency. Non-living things move because some force has acted upon them, whereas agents act independently for a purpose – they have goals. They have
choices. When we understand that something has goals, we see it as intentional. We do this all the time with animals and our pets, when we give them human qualities using a cognitive bias called
anthropomorphism
, but we will even extend such ‘humanness’ to things that are clearly not alive, let alone possessed of minds.

Imagine three geometric shapes moving around a screen. A large triangle attacks a smaller triangle by banging into it and then corners a small circle inside a rectangular box. The circle moves around frantically inside the box as if trapped. The smaller triangle distracts the large triangle, allowing the circle to escape, and then closes the opening to the box, trapping the large triangle inside. The small triangle and circle rotate around each other in joy and then exit the screen. The large triangle proceeds to break up the box in a fit of rage. Hardly the script of a Hollywood blockbuster, but observers interpret this sequence as some sort of domestic dispute.
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This simple animation made by psychologists Fritz Heider and Marianne Simmel in 1944 demonstrates that humans anthropomorphize moving shapes that appear to be goal directed and generate rich interpretations consistent with social relationships. The philosopher Dan Dennett thinks that we adopt
an intentional stance
as a strategy to first look out for things that could be agents that could have consequences for us and then give them intentions.
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When something has a face, moves as if alive or behaves in a purposeful way, we think that it has a mind that may have intentions directed towards us.

Attributing agency is something that babies also do from very early on. Based on the Heider and Simmel animation,
infant psychologist Val Kuhlmeier showed infants a cartoon geometric red sphere, appearing to climb up a steep hill, that kept faltering and slipping down the slope.
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At one point, a green pyramid shape comes along and pushes the sphere up the slope until it reaches the top. To most of us, this seems to be a case where the pyramid has helped the sphere up the slope. In a second scene, the red sphere is again trying to climb up the hill but this time along comes a yellow cube that blocks the path and then pushes the sphere down the slope. The cube has hindered the sphere. Even though these are simple animations of geometric shapes, we readily see them as intentional agents. A sphere that wants to climb a hill, a pyramid that wants to help and a cube that wants to hinder.