Читать книгу Emotional Rollercoaster: A Journey Through the Science of Feelings - Claudia Hammond - Страница 21

Traditionally, an expert’s answer to this question depends on the theoretical background in which they are working. One of the most plausible explanations and one that we can all relate to, is that social factors play a large part. It wouldn’t be surprising for depression to be present in a tough life where lots of things go wrong. A landmark study conducted in the seventies by two British sociologists George W. Brown and Tirril Harris, found that the biggest risk factors for depression in women were caring for three children under the age of five, with no family or friends in whom to confide, and having lost a mother before the age of eleven.

However, your chances of getting depressed might have been set in stone long before adulthood, even before birth. If one of your parents or siblings suffers from clinical depression it makes the likelihood of you becoming depressed between one-and-a-half and three times more likely. This doesn’t prove that depression is simply a genetic condition. Instead you might learn from a parent or sibling that depression is the best way to respond when things are going badly. A different person might turn to violence or alcohol abuse instead. Twin studies are the standard way of separating the influence of genetics from the effect of life experiences – in other words nature and nurture. The theory is that if identical twins are brought up separately then any differences between them must be down to the environment rather than genetics, because both twins have the same genes. If one identical twin develops depression there’s almost a fifty-fifty chance that the other twin will too, indicating a role for both genetics and life experiences. However, it’s not simply the case that there is one gene which predisposes you to depression, or not as far as we know. For some reason various genes seem to be implicated.

Other researchers believe that to get to the root of depression we should study chemical changes in the brain. However, this need not rule out the influence of the environment. The work on serotonin is a good example of how all these factors can work together. Studies of monkeys in the early 1990s demonstrated that the dominant members of the group had higher serotonin levels, but that these levels weren’t permanent. If a monkey was removed from the group by the experimenters its serotonin levels fell. The same thing could happen in humans. You lose your job, which affects your feelings about your status, which causes your serotonin levels to fall, with the result that you feel sad. Low serotonin levels tend to have different effects on men and women; women are more likely to become depressed while there’s some evidence that low serotonin levels in men lead to aggression. In the monkey studies it was found that after the dominant monkey had been removed, the serotonin levels of whichever monkey took its place would rise. Interestingly, if a monkey’s serotonin levels were artificially boosted, the monkey appeared to show an improvement in social skills and began rising through the group and, provided the dominant male was absent, could even take his place. If their levels were artificially lowered they would lose status.

Trying this out on people, Alyson Bond gave them SSRIs for four weeks and then gave them various games to play as well as asking their flatmates to report back on any changes they might have noticed while living with them. During the games the people on SSRIs made more eye contact while they were speaking and less while the other person spoke – a sign of dominance. They also became more cooperative during the game, while their flatmates reported them to be less submissive than they used to be. This suggests that high levels of serotonin increased both their dominance and made them more cooperative. Although these two results might sound contradictory, in fact this fits in with the pattern seen in monkeys. Those of high status aren’t necessarily more aggressive, but they are better at getting on with other monkeys.

So it appears that success can boost serotonin levels and high serotonin levels can lead to success, possibly through getting on with other people better, which might seem somewhat unfair. Those who are already happy and have high serotonin levels are likely to continue to succeed in society and remain happy, while those with lower levels – the very people for whom success could make a big difference – get left behind and their levels remain low. Most of the work in this area involves animals and so it can’t be guaranteed that the same effects would be seen in humans. However, a study conducted in Pittsburgh in 2000 found that the people with lower socio-economic status have a blunted response to a particular drug, which in turn suggests that they have a low turnover of serotonin. Since people with lower socioeconomic status are known on average to experience a greater number of stressful life events and to be exposed to more episodes of physical and psychological violence, the researchers speculate that these negative experiences could be altering the brain in such a way that the turnover of serotonin is reduced long-term.

This illustrates that the search for chemical explanations does not rule out the role that life events can play in the way we feel. Our mood is not predicted solely by the quantities of certain chemicals in our brain. Changes in these chemicals might simply be a reflection of influences from outside, so when things go wrong in life the balance of chemicals can shift. Early experiences could even play a part by affecting the way in which the brain copes with changes in neurotransmitter levels.

Earlier in this chapter the stress hormone Cortisol was mentioned. If it is the case that some depressed people have a problem with the system regulating Cortisol, then as with serotonin function the same question remains: why has the system gone wrong in those particular people? They might have been born with a predisposition to release excess Cortisol, or once again their experiences might actually alter the system. Charles Nemeroff from Emory University, Atlanta, has found that newborn rats who were separated from their mothers for ten out of the first twenty-one days of life, grew up with increased levels of the hormone. This suggests that early negative experiences might rewire the brain in terms of its response to stress. This hypothesis is based on animal studies, so is not entirely conclusive, but Nemeroff might have finally hit on a biochemical explanation for how bad childhood experiences could link to depression in adulthood.

Not everyone believes that Cortisol or serotonin holds the chemical answers to depression. There is a new theory, admittedly very much in its infancy, that the immune system could be involved. The idea is that people with problems with the immune system respond in one of two ways – either they develop an auto-immune disease or they become depressed. Women are more prone to both of these conditions. It is even possible that drugs like SSRIs are acting not only on serotonin but on the immune system and the Cortisol system in addition, which could explain why the drugs take several weeks to have an effect.

Again, these chemical changes in the brain could sometimes be a response to the outside world, rather than the brain spontaneously malfunctioning by itself. It’s arguable that we should no longer consider the physiological and the social to be separate. They affect each other, which would explain why drug treatments and talking therapies – which couldn’t be more different from each other – can both relieve depression.