Fingerprint of Essential Tremor in motor control

The pathophysiology of Essential Tremor (ET), the most common movement disorder, is not well understood. Evidence points towards an implication of the cerebellum in the generation of movement oscillations. Recent theoretical work showed, on the other hand, that oscillations could arise from an erroneous estimation of transmission delays, inherent to the conduction of neural signals. This process of sensory delay estimation is often assigned to the cerebellum. These two findings prompted us to investigate the fingerprint of Essential Tremor on motor adaptation, a task known to involve the cerebellum and which depends on delayed sensory feedback. We performed two motor adaptation tasks, focusing on saccadic and upper limbs movements, with a group of ET patients and a group of aged-matched controls. Patients with ET appears to have limited abilities to adapt their movements in response to perturbations, and this impairment was correlated with the intensity of the tremor. This motor adaptation impairment could be a new behavioral marker of the disorder and could bring novel possibilities for diagnosis, including a quantitative way to assess the patient's disorder, and new perspectives for rehabilitation. Further research is needed to validate these findings. However, the encouraging results obtained with the two experiments will pave the way for further investigations in the field, particularly on tasks involving the sensory feedback loop, which is suspected to play a major role in the generation of Essential Tremor.