What is Parkinson’s disease and how does Parkinson’s affect the brain? 

Parkinson’s disease is a progressive neurological condition that primarily affects movement, although it also involves various non motor symptoms. It is characterized by the gradual loss of specific nerve cells in the brain, leading to a reduction in essential chemical messengers. While it is often associated with visible tremors, the underlying biological changes affect a wide range of bodily functions, from balance and coordination to mood and sleep. Understanding how the disease alters brain chemistry is fundamental to managing the condition and improving the quality of life for those affected. 

What we will discuss in this article 

• The biological definition of Parkinson’s disease as a neurodegenerative disorder 

• The specific role of the substantia nigra and dopamine production 

• How the loss of nerve cells disrupts motor signalling in the brain 

• The impact of Alpha synuclein proteins and Lewy bodies on brain health 

• Common motor and non motor symptoms resulting from brain changes 

• The psychological and emotional effects of neurological degeneration 

• Emergency guidance for acute neurological changes 

The role of the substantia nigra 

The primary site of change in a brain affected by Parkinson’s is a small area in the midbrain called the substantia nigra. 

This region is responsible for producing dopamine, a vital neurotransmitter that acts as a chemical messenger between the brain and the rest of the body. In a healthy brain, dopamine signals are sent to the striatum to coordinate smooth, purposeful muscle movements. In Parkinson’s disease, the nerve cells in the substantia nigra begin to die off. By the time the first physical symptoms appear, a significant percentage of these dopamine producing cells have already been lost. 

Dopamine and motor control 

Dopamine is essential for the brain to control how and when the body moves. 

When dopamine levels decrease, the brain can no longer send effective instructions to the muscles. This disruption leads to the four primary motor symptoms of the condition: 

1. Tremor: Often starting in one hand or foot, usually occurring when the limb is at rest. 

2. Bradykinesia: A general slowness of movement that can make daily tasks like dressing or walking difficult. 

3. Rigidity: Muscle stiffness and tension that can limit the range of motion and cause pain. 

4. Postural instability: Problems with balance and coordination that increase the risk of falls. 

Alpha synuclein and Lewy bodies 

While the loss of dopamine is a central feature, the disease also involves the abnormal buildup of proteins within the remaining brain cells. 

A protein called alpha synuclein begins to misfold and clump together, forming microscopic deposits known as Lewy bodies. These deposits are a hallmark of the disease and are thought to interfere with normal cellular function, eventually leading to cell death. As these Lewy bodies spread to different parts of the brain, they can affect areas responsible for functions beyond movement, such as the cerebral cortex, which governs thought and memory. 

Beyond movement: Non motor impacts 

The neurodegeneration is not limited to dopamine. Other neurotransmitters like serotonin and norepinephrine are also affected. This explains why many patients experience non motor symptoms long before physical tremors begin. 

These can include: 

• Mood Disorders: Depression and anxiety are very common due to changes in brain chemistry. 

• Sleep Disturbances: Changes in the brainstem can lead to insomnia or vivid dreaming. 

• Cognitive Changes: Difficulties with planning, attention, and in later stages, memory. 

• Autonomic Dysfunction: Problems with blood pressure regulation and digestion. 

Comparison of brain changes in Parkinson’s 

Brain Feature	Normal Function	Change in Parkinson’s
Dopamine Levels	High: Smooth movement	Low: Jerky or slow movement
Substantia Nigra	Pigmented and dense with cells	Loss of pigmentation and cells
Alpha synuclein	Distributed normally	Clumped into Lewy bodies
Motor Signalling	Fast and coordinated	Disrupted and delayed
Non motor Signals	Balanced mood and sleep	Imbalanced: Anxiety or insomnia

Emergency guidance 

While Parkinson’s is a slow, progressive condition, certain acute changes in brain function require immediate medical assessment to rule out complications or other neurological events. 

If you experience sudden and severe neurological changes, call 999 immediately. 

Seek urgent medical help if you notice: 

• Sudden confusion, hallucinations, or a rapid change in mental state 

• A sudden inability to move or a severe freezing episode that prevents safety 

• Signs of a stroke such as facial drooping or sudden weakness on one side 

• A severe fall resulting in a head injury or suspected fracture 

• Uncontrolled, violent movements (dyskinesia) that cause physical distress 

To summarise 

Parkinson’s disease is defined by the progressive loss of dopamine producing cells in the substantia nigra and the accumulation of Lewy bodies throughout the brain. This loss of dopamine disrupts the brain ability to coordinate movement, leading to tremors, stiffness, and slowness. However, because the disease affects multiple neurotransmitters and brain regions, it also has a profound impact on mood, sleep, and cognition. Understanding that these symptoms are the result of physical changes in the brain is essential for developing a holistic treatment plan that addresses both the motor and psychological aspects of the condition. 

Authority Snapshot 

This article was reviewed by Dr. Rebecca Fernandez, a physician with an MBBS and extensive experience in internal medicine, surgery, and psychiatry. Dr. Fernandez specializes in the integration of clinical care with mental health support, applying evidence based approaches to help patients manage the complex emotional and physical challenges of neurological conditions. Her background in intensive care and patient assessment ensures a comprehensive understanding of how degenerative diseases impact overall well being.