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Depression and major depressive disorder
- [Instructor] Major depressive disorder, which is sometimes just referred to as depression, is characterized by prolonged helplessness and discouragement about the future. Individuals with this disorder have low self-esteem and very powerful feelings of worthlessness. They also lack the energy to do the things that they used to enjoy, much less the things that they have to do or the things that they don't enjoy. They tend to feel socially isolated and have trouble focusing on important tasks and have trouble making decisions. And this low mood tends to pervade all aspects of their life. There are a number of physical symptoms that also go along with depression. Lethargy, so feeling fatigued. Individuals with depression also tend to show fluctuations in weight, so either a lot of weight gain or a lot of weight loss. And they might also have trouble sleeping or they might sleep too much. And I think that these physical symptoms are often ignored because in Western cultures like in the US, we tend to think about depression in terms of moods or in terms of emotional states. But for individuals in some Eastern cultures, especially cultures where it might be seen as inappropriate to delve into or talk about feelings and emotions, people in these cultures tend to think about depression and experience depression in terms of these bodily symptoms. And so, it's really important that these aren't discounted. Depression or depressive symptoms are the number one reason people seek out mental health services. And because of this, some people have taken to calling it the common cold of psychological disorders. And I like that term for some reasons and I dislike it for others. What I like about it is that it captures how pervasive this disorder is. It is estimated that 13% of men and 22% of women worldwide could meet the criteria for depression at least once in their lives. And one study has shown that as high as 31% of college students might experience this disorder, and these are really high numbers. And so, in that way, I think that this term is appropriate. However, I think that the term common cold doesn't really capture the seriousness of this disorder, because depression isn't just feeling down once in a while and it's not feeling sadness or grief at appropriate times, which is just a normal part of life. And I think that this term kind of minimizes that part of the disorder. Depression can be triggered by a life event, like a loss or a breakup, but it doesn't have to be. It also doesn't usually appear alone. It is actually really common for individuals with depression to have other disorders, such as anxiety disorders. And I've been writing in this blue color to kind of signify depression, but I'm kind of getting bored with it now, so let me switch it up. So, there are a number of factors that may be involved in depression, and I'm going to split them up into three categories: biological factors, psychological factors, and sociocultural or environmental factors, and let me take a minute to get all of that down. All right. First of all, we know from family and twin studies that there's a genetic component to depression. And we also know from studies that use functional imaging that individuals with depression show a decreased activation in the pre-frontal cortex. And this could be associated with the problems with decision-making that people with depression tend to have, as well as their difficulties in generating actions. Researchers have also found lower levels of activity in the reward circuitry in the brain, and this could help to explain why individuals with depression might not find enjoyment in the actions that they once found pleasurable. Depression has also been associated with certain neurotransmitters and neurotransmitter regulation, and I'll abbreviate that here by writing NT for neurotransmitter. Research has suggested that individuals with depression might have fewer receptors for serotonin and norepinephrine. And I think that all of this research is amazing. I think that it's really important. And it's also really compelling in a way that research findings that include neuroscience typically are. But with that said, I really want to caution you against oversimplifying these biological factors. To give an example about why I'm saying this, I wanna talk about the relationship between a certain serotonin transporter gene and depression, and this gene is known as 5-HTTLPR, and I'll write that down, and a lotta findings have shown that this gene is involved in depression. But in actuality, it is only associated with depression if the individual with the gene is in a stressful environment. But the story doesn't actually end there, it's actually even more complicated because it turns out that if an individual with this genetic feature is placed in a warm and positive environment, they actually show a decreased risk for depression. And this is something that we don't totally understand yet. We're still trying to figure out why this might be the case. But importantly, I think that this really shows us how complicated biological factors can be. Let's move on to some psychological factors that might influence depression. One theory is based on the concept of learned helplessness, and this theory supposes that if an individual is exposed to aversive situations over and over again, without any power to change or control them, they might begin to feel powerless in a way that might lead to depression. So, if someone is exposed to prolonged stress due to family life or bullying or some other cause that they don't have control over, their helplessness could spiral out of control. And they might stop trying to change their situation because they perceive it to be completely helpless. And that's a behavioral theory or way of thinking about depression, but there are cognitive theories about it as well. And these theories tend to focus on thoughts or beliefs that, with repetition, could trigger depression. And while it's true that everyone has negative or self-destructive thoughts every once in a while, generally we are able to step back from them and we're able to realize that what we're thinking isn't completely logical. But sometimes people can get trapped in these thought patterns and they might put too much emphasis on negative thoughts and actions and experiences. And when they ruminate on these things, when they turn them over and over in their minds, it's possible that these cognitive distortions might lead to depression. Another cognitive theory about depression focuses on the concept of attribution or explanatory style. Now, as we go about our daily lives, we naturally try to understand and explain the events that go on around us. And when we do this, we can either attribute the things we see to internal or external causes. So, is it something that I did or is it something that happened because of something that is completely out of my control? Did I get a bad grade on a test because I didn't study? That would be an internal cause. Or did I get a bad grade because the teacher made a really unfair test, which would be an external cause. Individual with depression tend to attribute negative experiences to internal causes. So, maybe they'll think that a friend didn't call or text back because they are unlikable or unlovable, and not because they were at the movies with their family and maybe their phone was off. In addition to this, they tend to see negative experiences as being stable, so they think that they'll continue to happen in the future. And I also tend to think that they're global, so they might assume that one friend not calling them back somehow signifies that none of their friends like them. And together, these things, these internal attributions, these stable attributions and global attributions, these things form a pessimistic attributional style, and it might make certain individuals particularly vulnerable to depression. And there are many other psychological theories about depression, things that have to do with coping style or self-esteem. But it can actually be hard to know whether these things cause depression or if they are the result of it. So, does a pessimistic attributional style lead to depression or do people with depression tend to have a pessimistic attributional style? It isn't always clear. Environmental and sociocultural factors can also have a strong influence on depression. Having a friend or partner or roommate with depression can actually increase the likelihood that individuals around them will also develop depression. And although we don't know exactly why that is, some researchers suggest that it might have to do with co-rumination, where friends talk about problems and negative events. But instead of discussing how to solve them, they focus on the negative emotions and dwell on future problems and occurrences. And on some level, this is kind of normal. It is perfectly normal for close friends to take on some of the negative feelings of the other, like being sad when they lose someone who was close to them or being angry if they were dumped by there partner. This is just natural empathy. But the same empathy that allows us to comfort our friends when they're in distress might also be the reason that depression seems to spread. We also know that individuals with a low socioeconomic status, especially those living in poverty, are more likely to develop depression, as are those who are struggling to keep a job or have just lost a job. And there are other environmental factors as well. Social isolation, child abuse, even prejudice have all been implicated in causing depression. And let's think about this in terms of prejudice. If someone grows up in a household that has negative feelings about homosexuality, and if they grow up and begin to have same-sex attractions, they probably internalize the prejudice after years of hearing it, and this could lead to depression. All right, so stepping back for a second, we said that we had biological factors, psychological factors, and sociocultural and environmental factors. And when we put all of these things together, we get what is referred to as a biopsychoscial model of depression. And this theory acknowledges that all of these factors play a role. So, some people are genetically predisposed to the condition, but it only comes about if the situation is right or if we develop certain patterns of thinking.