Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia

Abstract

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Bringing order to higher order motor disorders

“…Acquired MM are seen cerebral palsy [74], particularly when uninjured hemisphere control movements of both sides (Video 16). Of interest for adult neurologist, MM are present in asymmetric neurodegenerative diseases such as Parkinson's disease (Video 17) , corticobasal degeneration [73] (Video 18), but also in Huntington disease [77], motor neuron disease [78], essential tremor [79] and Friedreich ataxia [80]. As mirroring accompanies various neurological diseases, as well as schizophrenia [81], MM may be considered as an unspecific, soft neurological sign, that nevertheless points toward deficient brain inhibition.…”