Les vies secrètes du cerveau de David Eagleman

C’est une bouchée, mais pertinente, de mentionner que l’auteur est directeur de l’Initiative sur les neurosciences et le droit du Baylor College of Medicine, à l’Université de Stanford.

Au fur et à mesure que le livre progresse, il peut être considéré comme un argument pour évaluer et traiter les criminels différemment. Eagleman pense que nous devrions accorder beaucoup plus d’attention aux facteurs physiques et psychologiques qui peuvent influencer les criminels individuels, plutôt que de considérer la personne sur le quai comme venant d’un terrain de jeu égal, où tous les gens sont les mêmes. Pour étayer son argument, il passe une grande partie du livre à nous convaincre que nous sommes propulsés dans la vie par des pulsions subconscientes, nourris par une soupe de gènes et d’hormones. J’ai trouvé son argument convaincant. Surtout, ce livre est merveilleusement passionnant. C’est une sacrément bonne lecture.

Je termine avec mon tas de notes habituelles – presque toutes tirées du livre. Entrez ici à vos risques et périls. J’ai bourdonné encore plus que d’habitude. (voir spoiler)[

The power behind the throne

You gleefully say, « I just thought of something! », when in fact your brain performed an enormous amount of work before your moment of genius struck. When an idea is served up from behind the scenes, your neural circuitry has been working on it for hours or days or years, consolidating information and trying out new combinations. But you take credit without further wonderment at the vast, hidden machinery behind the scenes.

Almost the entirety of what happens in your mental life is not under your conscious control, and the truth is that it’s better this way…. When it meddles in details it doesn’t understand, the operation runs less effectively. The best way to mess up your piano piece is to concentrate on your fingers; the best way to get out of breath is to think about your breathing; the best way to miss the golf ball is to analyse your swing.

How to know if you’re a racist, a homophobe etc.

We often do not know what’s buried in the caverns of our unconscious. An example of this comes up, in its ugliest form, with racism.

Even if someone is unwilling to say they are racist, there are ways of probing what is in the unconscious brain. Imagine that you sit down in front of two buttons, and you’re asked to hit the right button whenever a positive word flashes on the screen (joy, love, happy, and so on), and the left button whenever you see a negative word (terrible, nasty, failure). Pretty straightforward. Now the task changes a bit: hit the right button whenever you see a photo of an overweight person, and the left button whenever you see a photo of a thin person. Again, pretty easy. But for the next task, things are paired up: you’re asked to hit the right button when you see either a positive world or and overweight person, and the left button whenever you see a negative word or, a thin person. In another group of trials, you do the same thing but with the pairings switched – so you now press the right button for a negative world or a thin person.

The results can be troubling. The reaction times of subject are faster when the pairings have a strong association unconsciously. For example, if overweight people are linked with a negative association in the subject’s unconscious, then the subject reacts faster to a photo of an overweight person when the response is linked to the same button as a negative word. During trials in which the opposite concepts are linked (thin with bad), subjects will take a longer time to respond, presumably because the pairing is more difficult. This experiment has been modified to measure implicit attitudes towards races, religions, homosexuality, skin tone, age, disabilities, and presidential candidates. (Greenwald, McGhee, and Schwartz, « Measuring individual differences. » )

Hunches

Often when we have hunches about things, this is due to our subconscious having worked something out before our conscious mind is aware of it. Sometimes conscious knowledge of a situation is not required for making advantageous decisions.

Consciousness as a CEO

Consciousness is the long-term planner, the CEO of the company, while most of the day-to-day operations are run by all those parts of the brain to which we have no access.

Accessing the unconscious brain.

The next time a friend laments that she cannot decide between two options, tell her the easiest way to solve her problem: flip a coin. She should specify which option belongs to heads and which to tails, and then let the coin fly. The important part is to assess her gut feeling after the coin lands. If she feels a subtle sense of relief at being « told » what to do by the coin, that’s the right choice for her. If, instead, she concludes that it’s ludicrous for her to make a decision based on a coin toss, that will cue her to choose the other option

Our conscious minds train us, then our subconscious takes over

Riding a bike, playing tennis or golf, or driving a car….at first the conscious mind teaches us how to do these things, but as we continue to do these things over and over again, the subconscious takes over.

We are pre-programmed

Nothing seems more natural than desire, but the first thing to notice is that we’re wired only for species-appropriate desire. This underscores a simple but crucial point: the brain’s circuits are designed to generate behaviour that is appropriate to our survival. Apples and eggs and potatoes taste good to us not because the shapes of their molecules are inherently wonderful, but because they’re perfect little packages of sugars and proteins…Because the foods are useful, we are engineered to find them tasty.

Consider babies. Babies at birth are not blank slates. Instead they inherit a great deal of problem-solving equipment and arrive at many problems with solutions already at hand. …. They pop into the world with neural programs specialized for reasoning about objects, physical causality, numbers, the biological world, the beliefs and motivations of other individuals, and social interactions. For example, a newborn’s brain expects faces: even when they are less than ten minutes old, babies will turn toward face-like patterns, but not to scrambled versions of the same pattern. But two and a half months, and infant will express surprise if a solid object appears to pass through another object, or if an object seems to disappear, as though by magic, from behind a screen. Infants show a difference in the way they treat animate versus inanimate objects, making the assumption that animate toys have internal states (intentions) that they cannot see….

Another example of preprogramming is the so-called mind reading system – this is the collection of mechanisms by which we use the direction and movement of other people’s eyes to infer what they want, know, and believe. For example, if someone abruptly looks over your left shoulder, you’ll immediately suppose there is something interesting going on behind you. Our gaze-reading system is fully in place in early infancy. In conditions like autism this system can be impaired. 84

Monogamy, vasopressin and the gene RS3 334.

Common sense would tell us that monogamy is a decision based on moral character, right? But this leads to the question of what constitutes « character » in the first place. Could this, too, be guided by mechanisms below the radar of consciousness?

Consider the prairie vole… Unlike other voles and other mammals more generally, prairie voles remain monogamous. The reason pivots on hormones.

When a male vole repeatedly mates with a female, a hormone called vasopressin is released in his brain. The vasopressin binds to receptors in a part of the brain called the nucleus accumbens and the binding mediates a pleasurable feeling that becomes associated with that female. This locks in the monogamy, which is known as pair-bonding. If you block this hormone, the pair bonding goes away. Amazingly, when researchers crank up the levels of vasopressin with genetic techniques, they can shift polygamous species to monogamous behaviour.

In 2008 a research team at the Karolinska Institute in Sweden examined the gene for the vasopressin receptor in 5452 men in long-term heterosexual relationships. The researchers found that a section of the gene called RS3 334 can come in variable numbers. The more copies, the weaker the effect that vasopressin in the bloodstream would have in the brain. The results were surprising in their simplicity. The number of copies correlated with the men’s pair-bonding behaviour. Men with more copies of RS3 334 scored worse on measures of pair-bonding – including measures of the strength of their relationships, perceived marital problems, and marital quality as perceived by their spouses. Those with two copies were more likely to be unmarried, and if they were married, they were more likely to have marital troubles.

This is not to say that choices and environment don’t matter – they do. But it is to say that we come into the world with different dispositions. Some men may be genetically inclined to have a single partner, while some may not.

The democratic brain

Brains are like representative democracies. They are built of multiple, over-lapping experts who weigh in and compete over different choices. As Walt Whitman correctly surmised, we are large and we harbour multitudes within us. And those multitudes are locked in chronic battle.

There is an ongoing conversation among the different factions in your brain, each competing to control the single output channel of your behaviour. As a result, you can accomplish the strange feats of arguing with yourself, cursing at yourself, and cajoling yourself to do something – feats that modern computers simply do not do. For instance when you are offered a slice of cake. Part of you wants it and part of you tries to muster the fortitude to forgo it. The final vote of the parliament determines which party controls your action. In the end you either eat the cake or you do not, but you cannot do both.

The brain is best understood as a team of rivals… In the same way that liberals and conservatives both love their country but can have acrimoniously different strategies for steering it, so too does the brain have competing factions that all believe they know the right way to solve the problem.

Re Mel Gibson and his drunken anti-Semitic tirade, we can ask whether there is such a thing as « true » colours. We have seen that behaviour is the outcome of the battle among internal systems…. A team-of-rivals brain can naturally harbour both racist and non-racist feelings. Alcohol is not a truth serum. Instead, it tends to tip the battle toward the short-term, unreflective faction – which has no more or less claim than any other faction to be the « true » one.

Neurochemistry of the brain

When the frontal lobe is compromised, people become « disinhibited », unmasking the presence of the seedier elements in the neural democracy. A common example of this disinhibited behaviour is seen in patients with frontotemporal dementia, a tragic disease in which the frontal and temporal lobes degenerate. With the loss of the brain tissue, patients lost the ability to control the hidden impulses. To the frustration of their loved ones, these patients unearth an endless variety of way to violate social norms: shoplifting in front of store managers, removing their clothes in public, running stop signs, breaking out in song at inappropriate times, eating food scraps found in public trash cans, or being physically aggressive or sexually transgressive.

For another example of changes in the brain leading to changes in behaviour, consider what has happened in the treatment of Parkinson’s disease. In 2001, families of Parkinson’s patients began to notice that when they were given a drug called pramipexole, some of them turned into pathological gamblers. For some, the new addiction reached beyond gambling to compulsive eating, alcohol consumption and hypersexuality. This was due to imbalances in the dopamine system of rewards. Lowering levels of the drug could usually get rid of these side-effects.

The more we discover about the circuitry of the brain, the less we can accuse depressives of being indulgent, or a child doing poorly at school of being unmotivated and slow. Instead we see the option of problems with the neurochemistry of the brain. Our perceptions and behaviours are controlled by inaccessible subroutines that can be easily perturbed, as seen with the frontotemporal dementia victims, and the Parkinsonian gamblers. But there’s a critical point hidden in here. Just because we’ve shifted away from the blame does not mean we have a full understanding of the biology.

Neurochemistry is incredibly complicated.

Although we know that there is a strong relationship between brain and behaviour, neuroimaging remains a crude technology, unable to meaningfully weigh in on assessments of guilt or innocence, especially on an individual basis.

In the future, problems that are now opaque will open up to examination by new techniques, and we may someday find that certain types of bad behaviour will have a meaningful biological explanation – as has happened with schizophrenia, epilepsy, depression and mania. Currently we can detect only large brain tumours, but in one hundred years we will be able to detect patterns at unimaginably small levels of the microcircuitry that correlate with behavioural problems.

The heart of the problem is that it no longer makes sense to ask, ‘To what extent was it his biology and to what extent was it him? » The question no longer makes sense because we now understand those to be the same thing.

Now, there’s a critical nuance to appreciate here. Not everyone with a brain tumour undertakes a mass shooting. Why not? As we will see, it is because genes and environment interact in unimaginably complex patterns. As a result, human behaviour will always remain unpredictable.

The main difference between teenage and adult brains is the development of the frontal lobes. The human prefrontal cortex does not fully develop until the early twenties, and this underlies the impulsive behaviour of teenagers. The frontal lobes are sometimes called the organ of socialization.

Consider someone who gets rip-roaring drunk on a Saturday night. Zombie systems which have been lurking under the surface the whole time, are no longer masked by normally functioning frontal lobe. Instead they are disinhibited, and climb onto the main stage.

Work is being done with people, using bars on a computer to exercise their frontal lobes, to give them greater self-reflection and socialization (Stephen LaConte and Pearl Chiu)

The legal system is built partially upon the premise that humans are all equal before the law. This built-in myth of human equality suggests that all people are equally capable of decision making, impulse control, and comprehending consequences. While admirable, the notion is simply not true.

Socialization

People can however be modified. The child who is scolded for shoplifting, is being socialized. We need to differentiate between those who are modifiable, such a a teenager who still needs further frontal development, and someone with frontal lobe damage, who will never develop the capacity for socialization. The latter should be incapacitated by the state in a different sort of institution.

Gene complexity

Not everyone has heard that the Human Genome Project has been, in some ways, a failure. Once we sequenced the whole code, we didn’t get hoped-for breakthrough answers about the genes that are unique to mankind; instead we discovered a massive recipe book for building the nuts and bolts of biological organisms….. Imagine going to different factories and examining the pitches and lengths of the screws used. This would tell you little about the function of the final product – say, a toaster versus a blow dryer. Both have similar elements configured into different functions.

We have to acknowledge that successive levels of reduction are doomed to tell us very little about the questions important to humans…. Most diseases are polygenetic, meaning that they result from subtle contributions from tens or even hundreds of different genes. And as science develops better techniques, we are discovering that not just the coding regions of genes matter, but also the areas in between – what used to be thought of as ‘junk’ DNA. Most diseases seem to result from a perfect storm of numerous minor changes that combine in dreadfully complex ways. 210/211

The importance of environment interacting with physical factors

Plus the contributions from the genome can really be understood only in the context of interaction with the environment. For instance many hundred of genes have been found to correlate with schizophrenia, yet one of the critical factors in developing schizophrenia seems to be the stress of being an immigrant to a new country. In studies across countries, immigrant groups who differ most in culture and appearance from the host population, carry the highest risk of developing it.

You stand an 828 percent higher chance of committing a violent crime if you carry the Y chromosome, ie if you are male; but why aren’t all males criminal? That is, only 1 percent of males are incarcerated. The answer is that knowledge of the genes alone is not sufficient to tell you much about behaviour. The way in which your body can process things like serotonin, and the environment in which you are brought up, are relevant as well.

There are genes that can predispose one to depression, but it usually takes bad life events as well, to trigger a depression.

Another example comes from the observation that smoking cannabis as a teenager increases the probability of developing psychosis as an adult. But this connection is true only for some people, and not for others. A genetic variation underlies one’s susceptibility to this. With one combination of alleles, there is a strong link between cannabis use and adult psychosis; with a different combination, the link is week.

Similarly, psychologists Angela Scarpa and Adrian Raine measured differences in brain function among people diagnosed with antisocial personality disorder – a syndrome characterized by a total disregard for the feelings and rights of others, and one that is highly prevalent among the criminal population. The researchers found that antisocial personality disorder had the highest likelihood of occurring when brain abnormalities were combined with a history of adverse environmental experiences. In other words, if you have certain problems with your brain but are raised in a good home, your might turn out okay. If your brain is fine and your home is terrible, you might still turn out fine. But if you have mild brain damage and end up with a bad home life, you’re tossing the dice for a very unlucky synergy. 215.
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