Our thoughts, feelings and behaviour do not occur in disembodied space – they occur in our bodies. This chapter investigates four big questions about the relationship between mind and body:

• Can we locate our feelings in the brain?

• How does our mental wellbeing affect the rest of our body?

• How in turn does our body affect our mental wellbeing?

• How do our genes affect our mental wellbeing?

Feelings and the Brain

Neuroscience is still in its infancy. But we can already locate areas in the brain where people experience their mental wellbeing and their distress. The method is to ask many people how they feel and then to correlate their answers with the electrical activity in different parts of their brains. The best method of measuring electrical activity in different parts of the brain is by functional Magnetic Resonance Imaging (fMRI).Footnote ¹ Using fMRI, significant correlations have been found between measures of wellbeing and electrical activity in a number of different brain areas. For example, Richard Davidson and his colleagues at the University of Wisconsin have found a strong relationship with activity in the ventral striatum (and within it the nucleus accumbens).Footnote ² The relationship holds both over time for the same person (as when a mother is shown a picture of her child) and also, more importantly, across people. Thus people with higher sustained activity in the ventral striatum report higher psychological wellbeing (see Figure 5.1). Their adrenal glands also produce less cortisol – another positive sign of wellbeing (see below).

Figure 5.1 Sustained activation of the ventral striatum predicts psychological wellbeing

Source: Heller et al. (Reference Heller, Johnstone, Light, Peterson, Kolden, Kalin and Davidson2013)

The ventral striatum is a subcortical area that humans share with other mammals. But neuroscientists have also found correlation between wellbeing and activity in different parts of the pre-frontal cortex (including the ventro-medial and the dorsolateral).Footnote ³ Researchers have also identified a Default Mode Network in the brain that takes over when nothing much else is going on. It is focused on the self, and people where the network is more active report themselves to be less happy.Footnote ⁴

So there are objective measurements that correlate with reports of subjective experience, and this confirms that there is some objective information content in the reports of subjective wellbeing. But our understanding of the neural correlates of wellbeing is still quite partial.

More advanced is the neuroscience of pain. The main area where people feel distress when they are in pain is the anterior cingulate cortex (ACC), which is another subcortical area. Physical pain has two components – the ‘sensory’ aspect and the ‘emotional’ aspect. The sensory aspect informs us where the pain comes from (back, leg etc.) and its nature (e.g., pulsating, continuous, hot, cold), and it is recorded in the somatosensory cortex. But the emotional distress felt as part of the pain is located in the ACC.Footnote ⁵

So too, is the emotional distress resulting from social pain.Footnote ⁶ So it is not surprising that the pain-killing drug paracetamol (Tylenol in the United States) has the same dulling effect on the experience of both physical pain and social pain. In each case, the drug is moderating the electrical activity in the same part of the ACC.

So we already know something about where our conscious feelings of wellbeing and pain are experienced. But how does our mental life affect the rest of our body?

How the Mind Affects the Body

The clearest effect of the mind on the body is its effect on longevity. In September 1932, the mother superior of the American School Sisters of Notre Dame decided that all new nuns should be asked to write an autobiographical sketch. These sketches were kept, and much later psychologists independently rated them by the amount of positive feeling they revealed. These ratings were then compared with how long each nun lived. Remarkably, the amount of positive feeling that a nun revealed in her twenties was an excellent predictor of how long she would live. Of the nuns who were still alive in 1991, only 21% of the most cheerful quarter died in the following nine years, compared with 55% of the least cheerful quarter of the nuns.Footnote ⁷ This shows how happiness can increase a person’s length of life.

More recently, a random sample of English adults over 50 were asked questions about their happiness, and they were also asked whether they had been diagnosed with any long-term physical illness, such as heart disease, lung disease, cancer, diabetes or stroke.Footnote ⁸ They were followed for nine years to see if they died. The crude results are shown in Figure 5.1. The least happy third of them were three times more likely to die than the happiest third. And, even when controlling for all their initial physical illnesses, the least happy third were still some 50% more likely to die. Another study traced everybody in a Norwegian county over a six-year period. At the beginning, they were all diagnosed for their mental state and also asked other questions, such as whether they smoked cigarettes. Over the next six years, it turned out that diagnosed depression was as powerful a predictor of mortality as smoking was (Figure 5.2).Footnote ⁹

Figure 5.2 Percentage dying over the next nine years (People originally aged 50 and over)

Source: Andrew Steptoe. See also Steptoe and Wardle (Reference Steptoe, Hamer and Chida2012)

What explains this effect of mood upon physical health? The clearest channel is through the effects of stress. The body has a mechanism that responds to stress in a similar way whether the stress is physical or mental. This is sometimes called the ‘fight or flight’ response: our heart rate, blood pressure and breathing rate increase; we sweat more and our mouths go dry.

This response begins in the brain, which is linked to the rest of the body by two main sets of nerves. One set includes the sensory nerves and the motor nerves, which give conscious instructions to our limbs about what to do. But the other set is the ‘autonomic nervous system’, which is largely outside our conscious control and regulates the workings of all our internal organs.

The autonomic system has two main branches: the sympathetic and the para-sympathetic. It is the sympathetic nervous system that initiates the fight or flight response. It immediately instructs the adrenal gland to produce what Britons call adrenaline and Americans call epinephrine. This is a hormone (Greek for messenger) that enters the bloodstream and galvanises the whole body for action. It also mobilises the immune system to produce pro-inflammatory cytokines in case they are needed to handle possible infections. The parasympathetic nervous system, in contrast, calms the body. When it is active, the body’s organs become less active. For example, in meditation or breathing exercises the vagus nerve is active in reducing the heart rate. But, so long as stress is maintained, it is the sympathetic system that is most active.

At the same time, a second hormone is produced in another part of the adrenal gland: cortisol. A message goes from the brain’s hypothalamus to the pituitary gland to the adrenal gland, which releases cortisol into the bloodstream, and this then stimulates the muscles by releasing their store of glucose.

The stress response is totally functional when the stress is brief. But when the stress is persistent, it can lead to over-activity of the immune system (especially of C-reactive protein and IL6) and to persistent inflammation around the body, which eventually reduces life expectancy.Footnote ¹⁰ It also leads to more fibrinogen in the blood – intended to cause blood clots in a wound but unwanted in the longer term. In Western countries the most common sources of prolonged stress are psychological, and increased inflammation has been observed as a result of marital conflict, caring for demented relatives, social isolation, social disadvantage and depression.Footnote ¹¹

Another cause of stress with long-lasting effects is child abuse. One study followed children born in Dunedin, New Zealand. Those who had been abused in the first ten years of life had increased markers of inflammation twenty years later.Footnote ¹² These findings on child abuse are confirmed in a meta-analysis of many comparable studies.Footnote ¹³ By contrast, optimism and purpose in life protect against coronary heart disease and stroke.Footnote ¹⁴

Perhaps the simplest evidence of the effect of mind on body comes from a simple experiment. In it people were given a small experimental wound. Those who were depressed or anxious took the longest to recover.Footnote ¹⁵ In another experiment, people were given injections, and people in the greatest psychological distress developed the fewest antibodies.Footnote ¹⁶ Since we can affect the mind by psychological intervention, we can also affect the body that way. For example, mindfulness meditation reduces the level of pro-inflammatory cytokines.Footnote ¹⁷ It also increases the production of telomerase, which increases life-expectancy.Footnote ¹⁸

Perhaps the most striking effect of the mind on the body is the placebo effect. For many diseases, up to 30% of people given a placebo pill (with no active ingredient) will recover.Footnote ¹⁹ People recover because they believe that they will.

So the mind has profound effects on the body. These are a major part of how our wellbeing is generated, and the different chemicals involved provide useful biomarkers of how our wellbeing is developing.

How the Body Can Affect the Mind

But there is also a stream of causation going in the opposite direction – from our body to our wellbeing. Bodily events can alter our mental state. Healthy living is vital for our mental wellbeing and this means plenty of exercise, enough sleep and good sense in drinking and eating.Footnote ²⁰ Equally, physical illness and dementia reduce our wellbeing.

But one of the clearest examples of the effect of the body on the mind is the power of drugs, be they recreational or psychiatric. These work by affecting the operation of chemical ‘neurotransmitters’, which are crucial to the working of the brain. The brain consists of about 100 billion brain cells or neurons, and each neuron is connected to thousands of other neurons. Messages travel round the brain one neuron at a time. When that neuron ‘fires’, an electrochemical impulse travels from one end of the neuron to the other. But then it reaches a gap between that neuron and the next neuron. This gap is called a ‘synapse’ and the message is carried across the gap from the sending neuron to the receiving neuron by a chemical neurotransmitter.Footnote ²¹

So the different circuits in the brain are operated by different neurotransmitters:

• Serotonin produces a good mood.

• Dopamine and acetylcholine are neurotransmitters that stimulate (and can heighten) mental activity. (A ‘high’ feeling is generally associated with a rush of dopamine).

• GABA (gamma aminobutyric acid) and endocannabinoids reduce mental activity.

• Endorphins reduce pain.

Drugs affect the operation of a neurotransmitter. Some stimulate production of a neurotransmitter, others reduce its production, while others bind to the same receptors as some neurotransmitters and thus have a similar effect as the neurotransmitter that they mimic. Table 5.1 shows how the main recreational drugs alter our mental state, through the way in which they alter the operation of the neurotransmitters. Unfortunately, all these drugs can be addictive.Footnote ²²

There are, however, other drugs that can make people feel better: psychiatric drugs. These are generally less addictive. Table 5.2 shows some of the psychiatric drugs recommended for different psychiatric conditions. Take one example, Prozac. This is a psychiatric drug that increases the flow of serotonin and thus activity in the circuits that it serves. It does this by inhibiting the reuptake of serotonin, thus increasing the supply of serotonin and improving mood. In other words, it is a selective serotonin-reuptake inhibitor (SSRI). In many depressed patients, Prozac improves mood. Clearly dopamine is a tricky neurotransmitter: increasing it can be stimulating, but an excess of dopamine leads to schizophrenia (and a deficiency of dopamine to Parkinson’s disease). Like psychological therapy, psychiatric drugs do not always work. They are, however, strongly recommended for severe depression, where they achieve 50% recovery rates. But they have no effects on relapse unless they continue to be taken.

A key fact about the brain is the ease with which it can be altered by experienceFootnote ²³ – in other words, there is a high level of ‘neuroplasticity’. Blind people use part of their visual cortex to hear. And London taxi drivers have to remember so many streets and routes that they develop abnormally large hippocampal areas in their brains.Footnote ²⁴ There are many places in this book where we shall report the effect of wellbeing interventions on brain activity.

How Our Genes Affect Our Wellbeing

The one part of our body that never changes is our genes. They were determined at the moment of our conception and, apart from mutations, we keep the same genes throughout our life. The same genes are present in the nucleus of nearly every cell in our body. It is the continuity in our genes that explains much of the continuity in our personality, our appearance and our behaviour over our life.

But how do we know this, and how far do differences in our genes explain the differences in wellbeing in the population? To explore these questions, we shall proceed this way.

1. (1) We shall examine twins and show that identical twins (with the same genes) are much more similar to each other in wellbeing than non-identical twins are (with many different genes).

2. (2) We shall look at adopted children and show that they still resemble their biological parents in many ways.

3. (3) We shall show that the genes and the environment do not have independent effects on our wellbeing – they interact. Therefore, it is not possible to say in any meaningful way how much of the spread of wellbeing is due to differences in genes and how much to differences in environment.

4. (4) We shall describe the pioneering search for the specific genes that affect wellbeing.

5. (5) Finally, we shall examine the inter-relation between genes, personality and wellbeing.

Evidence from twins

To see that genes matter we have only to look at the following data on Norwegian middle-aged, same-sex twins (see Table 5.3). Some of the twins are identical: both come from the same egg. They therefore have the same genes and look more-or-less identical. The other sets of twins are non-identical: each twin comes from a separate egg. So half her genes are the same as her co-twin’s but half are different (just as is the case with any other pair of siblings).Footnote ²⁵ And what a difference that makes! As Table 5.3 shows, if the twins are identical, their life satisfaction is fairly similar (with a correlation across the 2 twins of 0.31). But if the twins are non-identical, their enjoyment of life is much less similar (with an across-twin correlation of only 0.15).

Table 5.3 Correlation in life satisfaction between each twin and his/her co-twin (Norwegian adults in mid-life)

Identical twins	0.31
Non-identical twins	0.15
Difference	0.16

Source: Roysamb et al. (Reference Røysamb, Nes, Diener, Oishi and Tay2018)

What could account for this difference? Clearly it must be because the identical twins have genes that are more similar. Even though both sets of twins were raised together, their final wellbeing was very different. This suggests that the family environment has a smaller influence than many people suppose.

Countless twin studies testify to the effect of our genes not only on our wellbeing but also on our mental health. For example, if you are bipolar and you are an identical twin, then the chance that your co-twin is also bipolar is 55%. (That is the degree of ‘concordance’.) But, if your co-twin is not identical, the chance is only 7%.Footnote ²⁶ Thus if someone has bipolar disorder, the risk to the co-twin is a huge 48 points higher (55%–7%) if the co-twin is identical rather than non-identical. Figure 5.3 gives comparable numbers for many other types of mental illness. In every case, the difference is substantial. That is an astonishing testimony to the power of genes.

Figure 5.3 Difference between identical and non-identical twins in the concordance between twin and co-twin

Note: For each condition, we calculate the concordance for identical same-sex twins and for non-identical same-sex twins and report the difference. For OCD, alcoholism and all childhood conditions except autism, we give the difference in co-twins’ correlation (on a continuous measure). For rare binary conditions, the concordance and the correlation are very similar

Source: Plomin et al. (Reference Plomin, DeFries, McClearn and McGuffin2013) pp. 245, 249, 251, 252, 259, 265, 290

Heritability

A natural question now is to ask What fraction of the variance of wellbeing across individuals is due to the genes?Footnote ³⁰ In other words, what is the heritability of wellbeing? Questions on heritability are usually answered using some strong assumptions, which we will question later.

We assume an additive model with (in its simplest form) two components – G for the genetic component and E for the environmental component. Thus wellbeing (W) is determined by W = G + E. It follows that the variance of wellbeing equals the variance of the genetic component plus the variance of the environmental component plus twice the covariance of the genetic component and the environmental component:

$\mathrm{Var}\left(W\right)=\mathrm{Var}\left(G\right)+\mathrm{Var}\left(E\right)+2\mathrm{Cov}\left(G,E\right)$

Crucially, in behavioural genetics this covariance is considered to be due to the genes. But in truth, it can be as much due to the environment as to the genes. For while it is certainly true that people with good genes are skilful at finding good environments, it is equally true that in most societies good environments are more receptive to people with good genes.Footnote ³¹ So the first arbitrary assumption in behavioural genetics is that individual outcomes related to genes are caused by genes. The second arbitrary assumption (to which we shall return) is that there are no gene-environment interactions.Footnote ³²

But if we wish away these two problems, we can show that the heritability of a trait (like wellbeing) equals twice the difference between the correlation of the trait across identical twins and its correlation across non-identical twins.Footnote ³³ So if we use the numbers in Table 5.1, the heritability of life satisfaction is 2 (0.31−0.15) = 32%. This is a typical estimate of the heritability of life satisfaction obtained from twin studies worldwide.Footnote ³⁴

Personality and Wellbeing

As we have seen, an important way in which genes affect our wellbeing is through our mental health. But a more general way is through all aspects of our personality. Psychologists find that much of the variation in character that we experience in those we encounter can be described by five dimensions. These are Openness, Conscientiousness, Extroversion, Agreeableness and Neuroticism (which spell OCEAN). Some of these dimensions appear to be poorly correlated with our life satisfaction. But two are highly correlated with life satisfaction. These are neuroticism (as you might expect from our earlier analysis) but also extroversion. So, if we revert to the mid-life Norwegian twins we discussed at the beginning of the chapter, personality overall explains about a third of the variance in wellbeing. And personality itself is partly determined by our genes (see Table 5.5). So a significant part of the heritability of wellbeing comes from the heritability of personality.

This said, it is crucially important to recognise that personality (like wellbeing) varies substantially over the life course. Not only do we on average become more conscientious, agreeable and emotionally balanced over time, but we also become less open and less extrovert. And we also change a lot relative to our contemporaries – due to differences in how life treats us.Footnote ⁴³ Genes are important, but from now on we concentrate on the effect of what policy-makers can affect – namely our experience of the environment in which we live.

Conclusions

1. (1) Self-reported wellbeing is correlated with activity in a number of brain areas. The sensation of pain is most clearly experienced in the anterior cingulate cortex (ACC), which registers both physical pain and social pain.

2. (2) The mind affects the body. Wellbeing predicts mortality as well as smoking does. Prolonged psychological stress leads to excessive production of adrenaline/epinephrine and cortisol, over-activity of the immune system and excessive inflammation in the body. Mindfulness meditation reduces these effects and increases life-expectancy.

3. (3) The body affects the mind. The most obvious effects are those of drugs, recreational and psychiatric.

4. (4) Genes have important effects on our wellbeing. We know this in two ways.

   • Identical twins (who have identical genes) are much more similar to each other in their wellbeing than are non-identical twins (who share only 50% of their genes).

   • Adopted children are more similar in mental health to their biological parents than to the parents who raised them.

     • It is important that parents and professionals realise the importance of these genetic effects and do not automatically blame parents’ behaviour for the problems of their children.

5. (5) It is, however, not possible to neatly separate the effects of the genes and the environment for two reasons:

   • Genes and environment often interact in their effects on wellbeing.

   • Genes and the environment are correlated, and there is no simple way to apportion that part of the variance of wellbeing that comes from the covariance of genes and the environment.

And we should never assume that, because a problem is partly genetic in origin, it cannot be treated as effectively as one that is primarily environmental.Footnote ⁴⁴

This completes our review of some basic processes common to all humans – our behaviours, thinking styles, physical processes and genes. It is time to turn to the impact on us of specific features of our experience.