How Brain Chemicals Can Contribute to Bipolar I and Bipolar II

Bipolar disorder is not caused by one single brain chemical. It appears to involve changes in the brain systems that control mood, energy, reward, sleep, stress and emotional control.

The main chemicals involved include:

• Dopamine
• Norepinephrine
• Serotonin
• Glutamate
• GABA The important point is that these systems can become too active at some times and too quiet at others.

That helps explain why bipolar disorder can involve both high-energy mood states and depressive mood states

Dopamine — Motivation, Reward and Drive

Dopamine helps regulate:

• Motivation
• Reward
• Pleasure
• Energy
• Goal-directed behaviour
• Attention During mania or hypomania, dopamine-related reward systems may become overly active.

This can contribute to:

• High energy
• Increased confidence
• Increased activity
• Reduced need for sleep
• Rapid pursuit of ideas or rewards
• Impulsive decisions A simple way to think about it:

1. Reward system becomes too active
2. Everything can feel unusually important, exciting or achievable

In bipolar depression, dopamine-related activity may move in the opposite direction.

This can contribute to:

• Low motivation
• Loss of pleasure
• Low energy
• Difficulty getting started

Dopamine in the Reward System

The striatum and related reward circuits help decide: “Is this worth doing?”

During mania:

1. Dopamine reward signaling may become too strong
2. Rewards feel unusually attractive
3. Risk-taking and impulsive behaviour may increase

During depression:

1. Reward signaling may become weaker
2. Things that were once enjoyable may no longer feel rewarding

Norepinephrine — Energy and Alertness

Norepinephrine helps regulate:

• Energy
• Wakefulness
• Attention
• Stress responses
• Mental speed During mania or hypomania, norepinephrine-related systems may become more active.

This may contribute to:

• High energy
• Reduced need for sleep
• Racing thoughts
• Restlessness
• Increased alertness During bipolar depression, norepinephrine activity may be less effective in some brain circuits.

This may contribute to:

• Fatigue
• Low energy
• Poor concentration
• Mental slowing So, the same system can behave differently depending on the mood state.

Serotonin — Mood and Emotional Control

Serotonin helps regulate:

• Mood
• Anxiety
• Sleep
• Impulse control
• Emotional stability Poor serotonin regulation may make mood less stable.

During depression, this may contribute to:

• Low mood
• Anxiety
• Negative thinking
• Sleep problems During mania, serotonin may not provide enough control over highly active dopamine and norepinephrine systems.

The result can be: Less emotional restraint and greater impulsivity

This is one reason bipolar disorder is better thought of as a problem of balance between several brain systems, rather than simply “low serotonin.”

Glutamate — The Brain’s Accelerator

Glutamate is the brain’s main activating chemical.

It helps with:

• Learning
• Memory
• Brain activity
• Communication between nerve cells During mania, some brain circuits may become overly activated.

A simple way to think about this is: Too much accelerator

This may contribute to:

• Racing thoughts
• Rapid speech
• Increased activity
• Difficulty slowing down
• Reduced sleep Glutamate dysregulation may also play a role in bipolar depression, but the pattern is complex and can vary between brain regions and mood states.

GABA — The Brain’s Brake

GABA helps calm excessive brain activity.

Think of: Glutamate as the accelerator and: GABA as the brake

If calming GABA activity is not strong enough during a manic state:

1. Brain activity rises
2. Thoughts and behaviour become harder to slow
3. Manic symptoms may intensify

A healthy brain needs the right balance between:

Excitation

and:

Calming control

What Happens in the Prefrontal Cortex?

The prefrontal cortex helps with:

• Judgment
• Planning
• Impulse control
• Decision-making
• Emotional regulation During mania, highly active reward and emotional systems may overpower the prefrontal cortex.

This can lead to:

• Poor judgment
• Risk-taking
• Impulsive spending
• Starting many projects
• Difficulty recognizing consequences A simple way to think about it:

1. Reward and energy systems become very strong
2. The brain's “manager” has more difficulty applying the brakes

What Happens in the Amygdala?

The amygdala helps process:

• Emotions
• Stress
• Threat
• Emotional importance In bipolar disorder, the amygdala may respond too strongly or unpredictably.

This can contribute to:

• Irritability
• Intense emotions
• Anxiety
• Rapid emotional reactions During depression, this system may also become overly focused on negative emotional information.

What Happens to Sleep and the Body Clock?

Sleep is especially important in bipolar disorder.

The brain has internal systems that control sleep and wake cycles

When these rhythms become disrupted:

1. Less sleep
2. Dopamine, norepinephrine and other activating systems may become more active
3. Mania or hypomania may be triggered or worsened

This is why changes in sleep can sometimes be an early warning sign of an approaching mood episode.

Bipolar I and Bipolar II — What Is the Difference?

The underlying brain systems overlap greatly.

The main difference is the severity of the elevated mood state.

Bipolar I

Bipolar I include episodes of: Mania

Mania can involve:

• Very high or irritable mood
• Major increase in energy
• Very little need for sleep
• Racing thoughts
• Impulsive behaviour
• Poor judgment
• Sometimes psychosis A simplified biological picture is activating and reward systems become strongly dysregulated

particularly dopamine, norepinephrine and excitatory brain circuits.

Bipolar II

Bipolar II includes: Hypomania and Major depressive episodes

Hypomania involves many of the same changes as mania, but they are less severe and do not reach the level of full mania.

People with Bipolar II can still experience very significant depression.

A simplified picture is:

1. Periods of increased reward, energy and activation
2. Hypomania

followed at other times by:

1. Reduced reward, motivation and energy
2. Depression

Why Can Someone Move from Mania to Depression?

Bipolar disorder involves systems that help regulate mood within a healthy range.

Normally: Energy and reward increase when needed and then return toward normal

In bipolar disorder, these regulating systems may be less stable.

A simplified pattern is:

1. Dopamine + norepinephrine + glutamate activity rises
2. Mania or hypomania

then later:

1. Reward and energy systems become less active
2. Depression

The biology is much more complicated than a simple chemical rise and fall, but this helps explain why bipolar disorder involves changes in brain regulation rather than one permanently high or low chemical.

A Simple Overview

Brain chemical	Main role	During mania/hypomania	During depression
Dopamine	Reward, motivation, drive	Reward and motivation may become excessive	Motivation and pleasure may decrease
Norepinephrine	Energy and alertness	High energy, alertness, reduced sleep	Fatigue and poor concentration
Serotonin	Mood and emotional control	Reduced control of mood and impulses may contribute	Low mood and anxiety may become prominent
Glutamate	Activates brain circuits	Circuits may become overly active	Regulation may also be disturbed
GABA	Calms brain activity	Braking may be insufficient	Balance with glutamate may remain disturbed

The Simple Explanation

Bipolar disorder can be thought of as a problem with the brain’s:

• Mood control
• Energy control
• Reward system
• Brain braking system During mania or hypomania:

1. Dopamine, norepinephrine and activating brain systems may become too strong
2. High energy, little sleep, rapid thinking and increased reward-seeking

During depression:

1. Reward, motivation and energy systems may become less active
2. Low mood, fatigue, reduced motivation and loss of pleasure

The difference between Bipolar I and Bipolar II is mainly how severe the elevated mood episode becomes: Bipolar I involves mania, while Bipolar II involves hypomania together with major depression.

It is therefore more accurate to describe bipolar disorder as dysregulation of several brain chemicals and brain circuits over time, rather than simply having too much or too little of one neurotransmitter.