فهم الاكتئاب: أسباب بيولوجية وتأثير الدماغ والوراثة

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 believe 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 study 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 increased 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 to 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's a huge list of other variables that studies

suggest may come into 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 ASAP thought 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 book Animal Madness by Laurel Breitman, which touches on the

subject. In fact, you can get it for free from our friends at Audible by going to audible.com/asap.

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

literature. You can download this audiobook or another of your choice for free at audible.com/asap.

And with a subscription, you get one free book a month. Special thanks to Audible for making these videos

possible. If you think you're suffering from depression, we've included some resources and more information in the

description. And subscribe for more weekly science videos.