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With over 350 million people affected by depression worldwide, it's no doubt an incredibly real and serious issue.
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But, what exactly is going on inside of a depressed person?
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Is there a biological basis for these intense feelings of sadness?
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In the past, depression was often described as simply a "chemical imbalance" in the brain.
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Specifically, scientists believed that a lack of the neurotransmitter, serotonin, was to blame, which is often referred to as the "feel good" chemical.
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However, the only real evidence for this was that when some depressed people were prescribed drugs which increased serotonin levels, it helped alleviate their symptoms.
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But while chemicals most certainly are involved, this view doesn't really capture just how complex depression is.
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In recent years, scientists began to notice that the brain cell growth and connections may actually play a larger role.
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When we look at the brain of a depressed person, studies show that the hippocampus tends to be much smaller than average.
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Other areas of the brain are also physically affected, but this region in particular controls memory and emotion.
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And the longer a person has been depressed, the smaller the hippocampus becomes.
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The cells and networks literally deteriorate.
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It turns out that stress may actually be a main trigger in the decrease of new neurons in this area of the brain.
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In fact, studies have shown that when this region of the brain is regenerated and new neurons are stimulated, mood improves.
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Interestingly, many modern drugs, including those which affect serotonin levels, have an indirect effect on the growth of brain cells.
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This is likely why serotonin-based drugs seem to help some patients - but not for the reasons we once thought.
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Instead, they promote the release of other chemicals, which ultimately stimulate neurogenesis, or the growth of new neurons.
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Knowing this, some scientists now believe focus should be on drugs which directly affect neurogenesis.
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But while your neurons and chemicals may be the direct influencers, many genetic factors have been discovered as well.
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One particular study found that a variation in the serotonin transporter gene leaves individuals more vulnerable to depression.
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Every individual has two copies of the gene - one from each parent.
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And this gene can either be short or long.
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After tracking 800 young adults over 5 years,
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the studies revealed that 33% of individuals with one short version became depressed after stressful life events and people with two short genes fared even worse.
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On the other hand, those with two "long" genes were much less likely to become depressed with similar life stress.
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Many other genes have been identified which increase the likelihood of depression, too.
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And it makes sense when you consider that depression and bipolar disorder both run in families.
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Studies of identical twins show that if one has bipolar disorder, the other has a 60-80% chance of developing it, too.
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So while the true cause or causes of depression have yet to be pinned down precisely, and trust us, there is a HUGE list of other variables that studies suggest may come in to play.
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It's important to remember that depression is a disease with a biological basis, along with psychological and social implications.
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It's not simply a weakness that somebody should get over, or even something that we have a say in.
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And just like heart disease, or cancer, shedding light onto the subject is of the utmost importance, in order to bring funding and proper research.
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But, is depression only a human phenomenon?
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We look into the question "Do Dogs Get Depressed?" in our latest AsapTHOUGHT video,
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and discover the many studies done to understand depression among other species, including your pets at home.
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You can click the link in the description for that video.
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You can also check out the book “Animal Madness” by Laurel Braitman which touches on the subject.
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In fact, you can get it for free from our friends at Audible by going to audible.com/asap.
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Audible is the leading provider of audiobooks with over 150,000 downloadable titles across all types of literature.
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You can download this audio book or another of your choice, for free, at audible.com/asap.
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And with a subscription you get one free book a month!
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Special thanks Audible for making these videos possible!
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If you think you're suffering from depression, we have included some resources and more information in the description.
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And subscribe for more weekly science videos!