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Depression Defined

By Saina Suhag


  • Depression is a neurological disease related to various negative emotions.

  • Emotions are a crucial part of human life but feeling sad or depressed once in a while is not considered depression. Depression is more than just feeling sad or numb. It is a continuous feeling of negative emotions that isn't just the blues.

  • This illness is closely related to losing interest in activities one enjoyed doing and a sense of always being tired and lethargic. Moreover, depression is a clinical illness that is, fortunately, treatable.


Symptoms of Depression

  • Anhedonia: One of the most common symptoms of depression is Anhedonia, which is a loss of interest in things one used to enjoy. Examples include avoiding fun activities and people friends, a music lover not enjoying their favorite song and, a cricket fan not excited when their team wins, etc. It is not only a symptom of depression but also various other mental illnesses.

  • Concentration Problems: One might not be able to concentrate or focus on several activities. This also includes memory loss.

  • Changes in Sleeping Pattern: Depression and sleep are closely linked. People with depression may not fall asleep at night or have excessive sleep during the daytime. For example- insomnia, hypersomnia etc.

  • Appetite: A huge possibility of sudden weight gain or weight loss. A person might suffer from "loss of appetite" and others from "increase in appetite".

  • Irritation and Mood Swings: This is associated with feeling restless or impatient and losing your tolerance even when the slightest thing doesn't go your way.

  • Feeling Tired: A continuous feeling of tiredness and lethargy. Even the smallest tasks like doing the laundry or putting up decorations can feel overwhelming.


Biological Basis of Depression

Amygdala: This part of the brain is closely associated with depression. It is a part of the limbic system and plays a crucial role in regulating emotions such as fear and stress. Amygdala is overactive in people with depression. It is the site where abnormalities in emotional stimuli have been recognized in various aspects like sleep and metabolism. Feeling anxious, stressed and behaviors of social isolation are symptoms of the overactive amygdala. In addition, an overactive amygdala causes negative emotions towards the world and self. What activates the amygdala? Simply, the amygdala is activated by fear-inducing images. The feeling of being scared or threatened activates the amygdala and causes to release of stress hormones. These hormones, as a result, generate emotions like anxiety, fear and aggression.

Hippocampus: The hippocampus is the part of the brain responsible for learning and making new memories. It is confirmed by scientific research that the hippocampus is smaller in people with depression. Studies showed that people with a smaller hippocampus faced difficulty in engaging with long-term memories. More importantly, they faced problems in connecting emotions to memories. A damaged hippocampus can lead to loss of memory and the ability of the person to make new memories. What can damage the hippocampus? Factors like trauma, brain tumors, drug withdrawal, exposure to chronic stress and Alzheimer's disease can lead to the damage of the hippocampus.

Thalamus: The thalamus is responsible for carrying sensory impulses from various parts of the body to the cerebral cortex. The sensations are passed onto the cerebral cortex for the interpretation of touch, temperature or pain. Furthermore, the thalamus links sensory information to good or bad emotions. People with depression have a greater number of nerve cells in the thalamus region. Damage in the thalamus can lead to bipolar disorder that causes extreme mood swings.

One could suffer from severe depression and the other from overwhelming happiness, energy, excitement, etc. What can damage the thalamus? Blockage in an artery of the brain can damage the thalamus. In addition, leakage of the blood vessel causing Hemorrhagic strokes is also something that can damage the thalamus severely.


Hormones Involved in Depression

Serotonin: Serotonin is a "feeling good" hormone that fills our mood with well-being and happiness. A low level of serotonin may cause various symptoms of depression like- sleep trouble, anxiety, irritability, low self-esteem etc. Very low level of serotonin can weaken nerve signals and cause problems in the nervous system. Research shows that caffeine can reduce serotonin in the brain.

Norepinephrine: Norepinephrine plays a role in several functions, which includes a person's ability to concentrate, memory, attention and energy levels. Too much norepinephrine can generate very happy emotions but can also cause panic attacks, hyperactivity and excessive sweating. On the other hand, low levels of this hormone can cause attention deficit hyperactivity disorder (ADHD), lack of concentration and depression. A low level of norepinephrine is closely linked to anxiety, sleeping problems and migraine as well.



Moret, C., & Briley, M. (2011, May 31). The importance of norepinephrine in depression. Neuropsychiatric disease and treatment.

Scaccia, A. (2020, August 19). Serotonin: Functions, Normal Range, Side Effects, and More. Healthline.


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