Bruce Hood - The Domesticated Brain - A Pelican Introduction (Pelican Books)

Just like me

These tales of desperation for companionship reinforce a central point of this book: that the human brain evolved for social interaction and that we have become dependent on domestication for survival. Social animals do not fare well in isolation and we are the one species that spends the longest period being raised and living in groups. 6Our health deteriorates and life expectancy is shortened when we are on our own. The average person spends 80 per cent of their waking hours in the company of others and that social time is preferred to time spent alone. 7Even those who deliberately seek out isolation, such as hermits, monks and some French scientists, are not exceptions that prove the rule.

It is not enough just to have people around; we need to belong. We need to make emotional connections in order to forge and maintain those social bonds that keep us together. We do things to make others like us and refrain from doing things that make them angry. This may seem trivially obvious, until you encounter those who have lost the capacity for appropriate emotional behaviour and you realize just how critical emotions are for enabling social interactions. Various brain disorders such as dementia can disrupt emotions, making them too extreme, too flat or too inappropriate. Even those without brain disorders vary in their capacity for emotional expression. Those lacking in or unwilling to share their emotions are cold and unapproachable, whereas others who willingly express their emotions, assuming they are positive, are warm and friendly.

Sometimes others’ emotions can be infectious. Emotional contagion describes the way that others’ expressions can trigger our emotions automatically. Many of us get teary when we see others crying at weddings and funerals. Or we may collapse into a fit of the giggles when a friend does, even though we should be keeping our composure in front of others. Actors call this ‘corpsing’, probably because the worst time to giggle is when playing a corpse on stage.

Laughter and tears are two social emotions that can transmit through a group like an involuntary spasm. When we are sharing these emotions we are having a common experience that makes us feel connected to each other. We know this is innate, rather than learned, because babies will also mimic the emotions of others. They cry when they hear other babies cry or see others in distress. Charles Darwin described how his infant son William was emotionally fooled by his nurse: ‘When a few days over 6 months old, his nurse pretended to cry, and I saw that his face instantly assumed a melancholy expression, with the corners of his mouth strongly depressed.’ 8

What could possibly be the benefit of emotional contagion and why do we mimic some expressions and not others? One suggestion is that expressions evolved as adaptations to threat. Fear changes the shape of our face and raises our eyebrows, so that can make us more receptive to potential information from the world. On the other hand, disgust, where we wrinkle up our noses and close our eyes, produces the opposite profile, making us less susceptible to potentially noxious stimuli. 9Seeing or hearing someone vomit makes us gag, possibly as a warning to expel the contents of our own stomach as we both may have eaten something that is not good for us.

Our capacity for imitation is supported by brain mechanisms that form part of the so-called mirroring system – a network of brain areas that include neurons in the motor cortex that control our movements. These neurons are normally active when we are planning and executing actions. However, back in the 1990s in Parma, Italy, researchers chanced upon a discovery about motor neurons that was to change the way we think about ourselves and what controls our actions. Vittorio Gallese and colleagues had been measuring from a neuron in the premotor cortex of a rhesus macaque monkey, using a very fine electrode. 10The cell burst into activity when the monkey reached for a raisin. That was to be expected as it was a premotor neuron that initiates movements. However, the Italian researchers were astonished when the same cell also fired as the monkey watched the human researcher reach for a raisin. The monkey’s brain was registering the experimenter’s reaching; an activity that was controlled by the human brain.

The reason this is remarkable is that it used to be thought that the areas for perceiving others’ actions were different from the network for producing your own movements. Instead, the Italian researchers had discovered that around one in ten neurons in this region were ‘mirroring’ the behaviour of others. It was as if these mirror neurons in the monkey’s brain were pantomiming the actions of others. As neuroscientist Christian Keysers explained, ‘Finding a premotor neuron that responds to the sight of actions was as surprising as discovering that your television, which you thought just displayed images, had doubled all those years as a video camera that recorded everything you did.’ 11

This dual role of copying other people’s behaviour and executing your own set the scientific community alight. Direct mapping between our brain and the brains of others, by observing them, could explain why we cry at weddings, feel others’ pain, emotional contagion and all manner of social behaviours that seem to reveal the human capacity for mimicking. It was as though scientists had found a direct psychic connection between the minds of others. It was even announced that the discovery of mirror neurons was as significant to understanding the brain as the discovery of the structure of DNA was to biology; while this is an exaggeration, it captures the excitement mirror neurons generated. 12

Others were more sceptical because recording directly from neurons in the brain of a human had not been done. However, in 2010, neurosurgeon Itzhak Fried published a study 13of patients he had been treating for epilepsy. To isolate the affected brain region, he implanted electrodes to determine which areas to surgically remove – much in the same way that Wilder Penfield had done all those years earlier with his neurosurgery patients. During this procedure, the patients were fully conscious and able to take part in a study designed to establish the presence of mirror neurons once and for all. They were asked to either smile, frown, pinch their index finger and thumb together or make a whole grip with their hand. When Fried found neurons that were activated during one of these movements, the patients were then shown a video of someone else making the same types of movements. Just as in the macaque monkey, premotor neurons were activated both by making a movement and also by watching someone else perform exactly the same action – bona fide mirror neurons in humans. The real burning question is how did they get there? 14Are they simply neurons that have acquired their dual activity after years of watching others and mapping their behaviour to one’s own movements? Or are babies already prepackaged with mirror neurons, which might explain reports where newborns have been shown to copy adult facial expressions without any learning?

The ‘in’ crowd

As we read in Chapter 2, there are reasons to believe that we may be born with a rudimentary capacity for mimicking others. Infant mimicry is instinctual but the system is not simply a dumb mechanism that slavishly copies every Tom, Dick or Harry a child encounters. Rather, infants become more discerning of others, assessing whether they are friend or foe. Initially, this distinction is drawn between those that share the same interests and preferences as the baby. In a food-preference study, 15eleven-month-olds were offered the choice of crackers or cereal from two bowls. Having made their choice, they watched as two puppets came along and approached the food. For each bowl, one puppet said, ‘Hmm, yum, I like this’ and the other said, ‘Ewww, yuck, I don’t like that.’ Each puppet expressed the opposite attitude to each food. The infant was then offered the choice to select to play with one of the puppets. Four out of five infants chose the puppet that had the same food preference as him or herself, irrespective of whether it was crackers or cereal. Before they have reached their first birthday, babies are showing clear signs of preference and prejudice. Just as their brains are tuning into the faces and voices that surround them, so too are they learning to identify who is, and who is not, like them.