For decades, people believed depression was simply the result of brain chemical deficiency. We thought decreased levels of serotonin, norepinephrine, and dopamine caused the condition. Still, to date, mainstream therapy uses antidepressants that target these brain chemicals.
We now know that there is more that happens to the brain during depression. Thanks to advanced imaging techniques like MRIs and CT scans, researchers found many changes occur in the brain. Let’s have a look at what we know so far, based on previous and recent studies.
The Chemistry of Depression
The neurotransmitter imbalance theory is the reason why doctors prescribe antidepressants. For example, selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressant. They target serotonin levels.
Other classes of antidepressants aim to improve two neurotransmitters. These include serotonin and norepinephrine reuptake inhibitors (SNRIs) and norepinephrine and dopamine reuptake inhibitors (NDRIs).
Older generation antidepressants like MAO inhibitors target the same neurotransmitters. However, they work through a different mechanism.
Only 50%-70% of people with depression taking antidepressants get a mood lift. Other neurotransmitters like histamine, glutamate, and GABA are out of balance during depression. The condition could be due to excess histamine, excess glutamate, and/or low GABA levels. From this, scientists explored other reasons why depression develops.
Inflammation in the Brain and Body
The brain inflammation (neuroinflammation) theory is gaining more and more attention. This is because more well-designed studies reveal that brain inflammation is a key player in depression.
Studies found various inflammatory molecules both in the brain and body during acute phases of depression. Furthermore, chronic inflammation could be the reason brain neurotransmitters go off balance. Certain brain circuits become impaired and people do not respond to antidepressants.
The depressed brain is on fire. According to a study featured in the JAMA Psychiatry, people with clinical depression had 30% more inflammation in their brain. The inflammation was more severe among those who had the most severe depression.
This underlying inflammation may explain why autoimmune diseases associate with high depression rates.
The Brain Degenerates, Shrinks, and Lacks Oxygen
Advanced imaging found special areas of the brain shrink in depressed people. Affected parts of the brain may include the hippocampus, thalamus, amygdala, and prefrontal and frontal lobes.
Researchers suggest the amount of brain shrinkage depends on the severity and the length of depressive episodes. These findings are important because the hippocampus connects to memory. This could explain why depression associates with memory impairment. The prefrontal cortex helps execute function and attention, which depression can alter. The amygdala plays an essential role in mood and emotion regulation.
The brain also suffers from degeneration. Studies found that there are smaller amounts of myelin, a protective sheath surrounding nerve fibers, in some areas of the brain during depression. Further research will evaluate the role of myelin in emotions, behavior, and cognition. Currently, researchers recognize myelin for its role in increasing the speed of electrical impulses and signals throughout the nervous system.
The depressed brain also doesn’t get enough oxygen. Perhaps, it’s because depression and anxiety affect our breathing. Some studies show that oxygen therapy in the form of hyperbaric oxygen treatments helps improve depression. One study found hyperbaric oxygen therapy has similar effects to psychotherapy in improving symptoms of depression and anxiety.
Is Depression Type 3 Diabetes?
You’re probably familiar with type 1 and type 2 diabetes. But did you know there is type 3 diabetes? Type 3 diabetes is insulin resistance in the brain. It’s a form of diabetes that selectively involves the brain, originally described in Alzheimer’s disease. It does share some similarities with type 1 and 2 diabetes.
According to studies, there is evidence of insulin signaling to brain mechanisms related to depression. Furthermore, insulin resistance, which is a hallmark of type 2 diabetes, may develop in the brains of those with depression. We need more research as it is unclear if brain inflammation creates imbalances in the brain glucose metabolism or the other way around.
Some studies found that a low-carb diet, like a ketogenic diet, may help improve symptoms of depression and stabilize mood.
Effects on the Second Brain
We consider the gut as the second brain since it’s home to the enteric nervous system (ENS). 100 million neurons make up the ENS, which means it has more neurons than the spinal cord.
The gut communicates with the brain via the gut-brain axis. Researchers found depression correlates with digestion impairments. It makes sense because there is a connection between the two systems. Furthermore, depression is associated with gut flora imbalances. Friendly bacteria from the intestines (gut flora) play a key role in regulating mood. An extensive review of studies found probiotics, which improve gut flora, showed a significant reduction in depression.
There are things you can use in addition to antidepressants and psychotherapy. Choosing a low-carb diet and probiotic supplements can help with brain insulin resistance. It can also improve gut flora.
Regular exercise can bring more oxygen to the brain. This then raises serotonin, dopamine, and norepinephrine naturally. Finally, a good night’s sleep and a healthy lifestyle help reduce brain inflammation.