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Depression is the leading cause[br]of disability in the world.

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In the United States,

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close to 10% of adults [br]struggle with depression.

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But because it's a mental illness,

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it can be a lot harder to understand,[br]than say, high cholesterol.

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One major source of confusion is[br]the difference between having depression

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and just feeling depressed.

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Almost everyone feels down[br]from time to time.

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Getting a bad grade,

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losing a job,

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having an argument,

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even a rainy day can bring on[br]feelings of sadness.

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Sometimes there's no trigger at all.

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It just pops up out of the blue.

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Then circumstances change,

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and those sad feelings disappear.

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Clinical depression is different.

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It's a medical disorder,

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and it won't go away [br]just because you want it to.

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It lingers for at least [br]two consecutive weeks,

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and significantly interferes [br]with one's ability to work,

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play,

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or love.

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Depression can have a lot[br]of different symptoms:

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a low mood,

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loss of interest in things[br]you'd normally enjoy,

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changes in appetite,

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feeling worthless or excessively guilty,

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sleeping either too much or too little,

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poor concentration,

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restlessness or slowness,

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loss of energy,

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or recurrent thoughts of suicide.

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If you have at least five[br]of those symptoms,

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according to psychiatric guidelines,

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you qualify for a diagnosis of depression.

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And it's not just behavioral symptoms.

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Depression has physical manifestations[br]inside the brain.

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First of all,

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there are changes that could be seen[br]with the naked eye

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and x-ray vision.

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These include smaller frontal lobes[br]ad hippocampal volumes.

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On a more microscale,

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depression is associated [br]with a few things:

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the abnormal transmission or depletion[br]of certain neurotransmitters,

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especially serotonin, norepinephrine,[br]and dopamine,

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blunted circadian rhythms,

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or specific changes in the REM[br]and slow-wave parts of your sleep cycle,

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and hormone abnormalities,

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such as high cortisol and deregulation[br]of thyroid hormones.

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But neuroscientists still don't have[br]a complete picture

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of what causes depression.

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It seems to have to do with a complex[br]interaction between genes and environment,

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but we don't have a diagnostic tool

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that can accurately predict where[br]or when it will show up.

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And because depression symptoms[br]are intangible,

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it's hard to know who might look fine[br]but is actually struggling.

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According to the National Institute[br]of Mental Health,

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it takes the average person[br]suffering with a mental illness

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over ten years to ask for help.

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But there are very effective treatments.

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Medications and therapy compliment[br]each other to boost brain chemicals.

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In extreme cases,[br]electroconvulsive therapy,

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which is like a controlled seizure[br]in the patient's brain,

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is also very helpful.

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Other promising treatments,

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like transcranial magnetic stimulation,

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are being investigated, too.

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So, if you know someone [br]struggling with depression,

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encourage them gently to seek out[br]some of these options.

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You might even offer to help[br]with specific tasks,

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like looking up therapists in the area,

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or making a list of questions[br]to ask a doctor.

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To someone with depression,

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these first steps can seem insurmountable.

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If they feel guilty or ashamed,

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point out that depression [br]is a medical condition,

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just like asthma or diabetes.

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It's not a weakness [br]or a personality trait,

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and they shouldn't expect themselves[br]to just get over it

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anymore than they could will themselves[br]to get over a broken arm.

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If you haven't experienced [br]depression yourself,

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avoid comparing it to times[br]you've felt down.

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Comparing what they're experiencing[br]to normal, temporary feelings of sadness

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can make them feel guilty for struggling.

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Even just talking about [br]depression openly can help.

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For example, research shows that asking[br]someone about suicidal thoughts

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actually reduces their suicide risk.

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Open conversations about mental illness[br]help erode stigma

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and make it easier [br]for people to ask for help.

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And the more patients seek treatment,

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the more scientists will learn[br]about depression,

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and the better the treatments will get.