A Reflection on Motor Overflow, Mirror Phenomena, Synkinesia and Entrainment

Abstract

In patients with movement disorders, voluntary movements can sometimes be accompanied by unintentional muscle contractions in other body regions. In this review, we discuss clinical and pathophysiological aspects of several motor phenomena including mirror movements, dystonic overflow, synkinesia, entrainment and mirror dystonia, focusing on their similarities and differences. These phenomena share some common clinical and pathophysiological features, which often leads to confusion in their definition. However, they differ in several aspects, such as the body part showing the undesired movement, the type of this movement (identical or not to the intentional movement), the underlying neurological condition, and the role of primary motor areas, descending pathways and inhibitory circuits involved, suggesting that these are distinct phenomena. We summarize the main features of these fascinating clinical signs aiming to improve the clinical recognition and standardize the terminology in research studies. We also suggest that the term “mirror dystonia” may be not appropriate to describe this peculiar phenomenon which may be closer to dystonic overflow rather than to the classical mirror movements.

Boundaries of task-specificity: bimanual finger dexterity is reduced in musician’s dystonia

“…Our results flag certain difficulties with the name task-specific as we found a bilateral reduction in finger individuation in a related but distinct task to musical performance. Specifically, we have found upregulated mirror movements ( voluntary unilateral movement of a limb that cause involuntary movement or mirroring of the homologous muscles of the opposite limb), a phenomena that more commonly associated with other congenital and acquired disorders such as idiopathic Parkinson’s disease and Huntington’s disease 9 , 17 . Indeed, whether the motor deficit is task-specific or not depends on the type of information or measure used to assess this (Fig.…”

“…Additionally when task-specific dystonia affects the hand, some patients show mirror dystonia , defined as involuntary movements resembling dystonia in the symptomatic hand that occur when the contralateral, asymptomatic hand moves 11 . This is distinct to mirror movements, unintentional movements of one side of the body that mirror intentional movements on the opposite side and though not classically associated with task-specific dystonia, can be seen in people with dystonia in general 9 . In the task-specific context (e.g.…”