The neuroscience behind the urge to move your restless legs
Are you not able to sit still while watching TV or at a meeting? Do you keep shaking your legs? You may have restless legs syndrome (RLS) or periodic limb movement disorder (PLMD).
(Image by Nicolas P. Rougier)
In patients with restless legs syndrome, two features can be observed during daytime hours: periodic limb movements (PLM) and voluntary leg movements. Voluntary leg movement occurs in order to get rid of unpleasant sensations and the urge to move. There is a clear division between voluntary and involuntary movements in RLS, which can be reported by patients and further evaluated by expert physicians. Notably, periodic limb movements are often visible in RLS during the day, even when the patient is subjectively symptom free during that time. Sometimes intense jerks may occur.
Symptoms of RLS usually get worse in situations of minimal physical activity, such as watching TV, attending business meetings and flying long distances. One may not notice the RLS himself until it gets stronger. When observing with a trained eye, there are many opportunities to observe PLMs in public spaces, e.g. in waiting lounges at airports and at concert halls.
Typically, symptoms of RLS occur in the evenings or at night. During the night and while asleep, periodic limb movements can be more frequent. They may range from a barely visible extension of the foot or big toe, to classic periodic limb movement with knee and hip bending, to periodic limb movement involving the arms and possibly the rest of the body. In the face-down position, a pelvic component of muscle contractions is sometimes notable. PLMs can be smooth or jerky.
A different and very specific situation is the augmentation of restless legs syndrome. Here, the urge to move sometimes becomes overwhelming and very intense. Violent movements can be observed, often involving the whole body with rocking movements. In addition, PLMs are present during the day and night.
The reason for this urge in moving legs is linked with impaired function of some nerve cells called dopaminergic neurons. These neurons secrete the neurotransmitter called dopamine and are located in a part of the brain known as striatum. The medications used to manage RLS or PLM conditions stimulate dopamine receptors in the striatum. These medications belong to the family of drugs which mimic dopamine. They are the so called dopamine receptor agonists.