This article was published in the Dystonia Dialogue.
Excessive muscle contractions are a hallmark sign of dystonia, but the muscles are not the source of the problem. The muscles are responding to abnormal signals from the brain, which cause them to flex, and this results in dystonic movements and postures.
Research shows that the origins of dystonia lie in the complex pathways and networks of neurons that convey signals from one part of the brain to another.
There are an estimated 86 billion neurons in the human brain, making roughly 100 trillion connections. Neural pathways carry the information and instructions necessary for the brain to function. If there is a problem anywhere along a pathway, the communication between brain structures in that network breaks down. When areas of the brain responsible for movement cannot communicate properly, movement disorders such as dystonia can occur.
This explains why numerous brain structures have been implicated in dystonia: basal ganglia, cerebellum, thalamus, midbrain, cortex, and others. These brain areas are interconnected across different but often overlapping neural networks. It may even be possible that certain brain structures play greater or lesser roles in specific types of dystonia.
Researchers are painstakingly working to identify the neural pathways and networks implicated in dystonia and pin-point dysfunction within these complex connections. Once the problem areas are identified, researchers can strategize effective treatment approaches.
Last year dystonia experts met for a virtual workshop, “Defining the Role of Brain Networks in the Pathophysiology and Treatment of Dystonia.” The meeting’s distinguished Scientific Co-Chairs, Drs. Mark Hallett of National Institute of Neurological Disorders & Stroke, David Peterson of University of California, San Diego, and Kristina Simonyan of Harvard Medical School developed an intensive program to review what is known about the neural networks involved in dystonia, discuss emerging research, and identify gaps in need of future research. A manuscript from the meeting is planned for publication in the DMRF’s new scientific journal, Dystonia.
Although the exact mechanisms underlying the origins of dystonia are not fully understood, several contributing neurological problems have been identified.
A neurotransmitter is a chemical generated by one neuron to transmit an electrical signal to another neuron. Some neurotransmitters stimulate neuron activity while others suppress activity, similar to the gas and brake pedals in a car.
Dystonia is an imbalance of the neurotransmitters that control brain activity related to moving the body. When neurotransmitter levels are not normal, movement disorders occur.
Many oral medications used to treat dystonia act to restore normal neurotransmitter levels in the brain.
When signals between neurons are compromised by unbalanced neurotransmitters, this disrupts normal firing patterns. Neurons may have trouble initiating or receiving signals.
This results in a loss of connectivity in the brain, which disrupts motor pathways. Researchers are investigating whether this altered connectivity in dystonia is specific to certain brain regions or possibly more widespread beyond brain functions specific to movement.
Plasticity, or neuroplasticity, is the brain’s capacity to change over time.
The developing brain organizes itself and assigns brain functions to various regions. New neurons can be generated, creating new connections.
Neuroplasticity explains how we learn, remember, and adapt behavior.
Neuroplasticity likely plays a key role in the development of dystonia— the brain’s ability to re-organize and adapt is impaired. The brain loses its internal equilibrium. This opens the door for movements that were once mastered to be ‘re-learned’ incorrectly.
The more the nervous system ‘practices’ activating abnormal movements, the more difficult they are to unlearn.
A hallmark sign of dystonia is that the brain activates more muscles than needed to complete a movement task. For example, an individual with dystonia may pick up a pen to write and experience excessive muscle contraction in the hand and fingers, plus an overflow of involuntary movements in the arm and shoulder.
The brain loses the ability to suppress activation of muscles that are not needed to complete a voluntary movement.
By contrast, when the normal brain is planning and coordinating movements, it activates the muscles required for a task while inhibiting the surrounding muscles not needed for the task.
The Dystonia Medical Research Foundation is a 501(c)(3) non-profit organization dedicated to advancing research for improved dystonia treatments and ultimately a cure, promoting awareness, and supporting the well-being of affected individuals and families.