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  • With over 350 million people affected by depression worldwide, it's no doubt an incredibly real and serious issue.

  • But, what exactly is going on inside of a depressed person?

  • Is there a biological basis for these intense feelings of sadness?

  • In the past, depression was often described as simply a "chemical imbalance" in the brain.

  • Specifically, scientists believed that a lack of the neurotransmitter, serotonin, was to blame, which is often referred to as the "feel good" chemical.

  • 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.

  • But while chemicals most certainly are involved, this view doesn't really capture just how complex depression is.

  • In recent years, scientists began to notice that the brain cell growth and connections may actually play a larger role.

  • When we look at the brain of a depressed person, studies show that the hippocampus tends to be much smaller than average.

  • Other areas of the brain are also physically affected, but this region in particular controls memory and emotion.

  • And the longer a person has been depressed, the smaller the hippocampus becomes.

  • The cells and networks literally deteriorate.

  • It turns out that stress may actually be a main trigger in the decrease of new neurons in this area of the brain.

  • In fact, studies have shown that when this region of the brain is regenerated and new neurons are stimulated, mood improves.

  • Interestingly, many modern drugs, including those which affect serotonin levels, have an indirect effect on the growth of brain cells.

  • This is likely why serotonin-based drugs seem to help some patients - but not for the reasons we once thought.

  • Instead, they promote the release of other chemicals, which ultimately stimulate neurogenesis, or the growth of new neurons.

  • Knowing this, some scientists now believe focus should be on drugs which directly affect neurogenesis.

  • But while your neurons and chemicals may be the direct influencers, many genetic factors have been discovered as well.

  • One particular study found that a variation in the serotonin transporter gene leaves individuals more vulnerable to depression.

  • Every individual has two copies of the gene - one from each parent.

  • And this gene can either be short or long.

  • After tracking 800 young adults over 5 years,

  • 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.

  • On the other hand, those with two "long" genes were much less likely to become depressed with similar life stress.

  • Many other genes have been identified which increase the likelihood of depression, too.

  • And it makes sense when you consider that depression and bipolar disorder both run in families.

  • Studies of identical twins show that if one has bipolar disorder, the other has a 60-80% chance of developing it, too.

  • 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.

  • It's important to remember that depression is a disease with a biological basis, along with psychological and social implications.

  • It's not simply a weakness that somebody should get over, or even something that we have a say in.

  • 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.

  • But, is depression only a human phenomenon?

  • We look into the question "Do Dogs Get Depressed?" in our latest AsapTHOUGHT video,

  • and discover the many studies done to understand depression among other species, including your pets at home.

  • You can click the link in the description for that video.

  • You can also check out the bookAnimal Madnessby Laurel Braitman which touches on the subject.

  • In fact, you can get it for free from our friends at Audible by going to

  • Audible is the leading provider of audiobooks with over 150,000 downloadable titles across all types of literature.

  • You can download this audio book or another of your choice, for free, at

  • And with a subscription you get one free book a month!

  • Special thanks Audible for making these videos possible!

  • If you think you're suffering from depression, we have included some resources and more information in the description.

  • And subscribe for more weekly science videos!

With over 350 million people affected by depression worldwide, it's no doubt an incredibly real and serious issue.

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