- [Voicover] 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 prevade
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 U.S., 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 awhile.
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, 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 prefrontal 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 rewards 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 lot of 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 awhile,
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.
Individuals 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 unlikeable
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 they 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 is close to them or being angry
if they were dumped by their 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've probably internalized 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 biopsychosocial 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.