Most people experience a range of moods throughout the day based on interactions with their surroundings. A smile from a loved one can brighten your day. A traffic jam can sour it. Emotions, and the ability to control them, are an essential part of our lives. In people with bipolar disorder, their mood can swing wildly and uncontrollably between depression and mania. These swings can severely handicap a person’s life, affecting personal relationships, work, and even their own well-being.

Bipolar disorder is a serious brain illness that affects around four percent of people in the United States: almost two million people. Because it affects brain function, bipolar disorder disrupts a person’s behavior. The effects differ from person to person, but the main symptom is the mood swings. During depression, a person will feel hopelessness, loss of appetite, general lack of interest in activities, and suicidal thoughts. During manic periods, a person will completely shift and feel optimistic, speak quickly, become overly joyful and even aggressive, have an increased sex drive, and make irrational decisions.

Though anyone can get bipolar disorder, it commonly occurs between the ages of 18 and 35. Because the symptoms are different from person to person, doctors have categorized the illness into four types:

• Bipolar I Disorder: Manic symptoms are severe and last around seven days. A person will also suffer from weeks-long episodes of depression.
• Bipolar II Disorder: Bipolar II Disorder is not as severe at Bipolar I in that there are no full manic episodes. They still experience an elevation of depressed or manic moods.
• Bipolar Disorder Not Otherwise Specified: This version of bipolar disorder is below bipolar I and II in that a person does not experience drastic mood swings and manic episodes strong enough to be diagnosed, but still has symptoms beyond that of someone without a bipolar disorder.
• Cyclothymia: This is a mild form of bipolar disorder that lasts at least two years but is not debilitating enough to meet the requirements of bipolar disorder.

Neurotransmitters and the Brain

It is believed the origin of bipolar disorder can be traced back to the brain. But in order to understand how the brain plays a part in bipolar disorder, it is important to understand how the brain transmits information.

The forebrain is the largest part of the brain, and it is also the most intricate. The forebrain consists of the cerebrum, thalamus, hypothalamus, and the limbic system. The cerebrum is important to mental health because it holds the essential parts of our personality, including emotion, intelligence, and memory. The cerebrum is split into left and right halves known as hemispheres. The left side is believed to be the logic side, while the right side is the creative side.

Each hemisphere has a surface known as the cerebral cortex, or grey matter. Information gathered by your senses travels from the spinal cord to the cerebral cortex. This information is then transmitted to proper parts of the nervous system that help you react to a situation.

Inside the forebrain, the thalamus acts as a relay of information from the senses to the cerebral cortex. The hypothalamus deals with many automatic functions, such as appetite, sleeping, pulse, and temperature. Finally, the limbic system controls emotions, memory creation, learning, and decision-making.

Neurons are cells in the nervous system that carry information through an electrical process. They are responsible for giving the brain the necessary information to regulate the body. Inside a neuron is a neurotransmitter, which ‘excites’ a nearby neuron through electrical impulses. The space between neurons, or synapse, allows neurotransmitters to pass from neuron to neuron. This transfer of neurotransmitters allows information to move through the nervous system.

Specific neurotransmitters known as monoamines and acetylcholine are involved in the origin of bipolar disorder. It is believed mood disorders can be traced to the way a cell reacts to imbalances in neurotransmitters.

Serotonin and Depression

Serotonin is a monoamine neurotransmitter important to brain and body function. Though most serotonin can be found in the digestive system, the small portion in the brain is important to the regulation of mood, sleep, and appetite. Researchers believe a variance of serotonin in the brain can change a person’s mood, leading to depression. This happens either through a lack of serotonin, a lack of receptors for the serotonin, or even a shortage of tryptophan, the chemical that makes up serotonin.

Norepinephrine and Manic Episodes

Norepinephrine, also known as noradrenaline, is a neurotransmitter responsible for emotions, attention, sleeping, and learning. There have been studies that show increased levels of norepinephrine can trigger manic episodes in people with bipolar disorders. Because norepinephrine works with adrenaline and epinephrine to create the “fight or flight” response of the body, it is possible an excess of this neurotransmitter is related to manic episodes.

Dopamine and Bipolar Disorder

Dopamine is a neurotransmitter associated with a reward system in the brain, meaning it gives a person motivation to perform tasks. Since a lack of motivation is key to depression and bipolar disorders, researchers deduce that deficiency and excess of dopamine can lead to mental illnesses. Excess dopamine can lead to schizophrenia and mood swings.

Hippocampi and Bipolar Disorder

The hippocampus is responsible for forming new memories, including time and place. Without the hippocampus, information would never be stored. But it also plays a role in emotion.

Some research has uncovered that certain people with depression or those who have experienced extreme stress, such as the rigors of war, have a smaller than average hippocampus. There are also studies suggesting a smaller hippocampus may be inherited.

Is Bipolar Disorder Genetic?

People who have a family member with bipolar disorder are at a higher risk of developing the illness. In fact, children with a blood relative in their nuclear family with bipolar disorder are up to six times more susceptible to acquire the condition themselves.

Research is ongoing to determine which genes are responsible. Interestingly, identical twins do not always both develop the disorder. Because they share the same genes, this indicates there is more at play than just genetics.