Blondiaux, Florence
[UCL]
Lebrun, Louisien
[UCL]
Hanseeuw, Bernard
[UCL]
Crevecoeur, Frédéric
[UCL]
Essential Tremor (ET), one of the most common movement disorders, is characterized by involuntary oscillations of the limbs, mainly during movement. Although its origin remains unclear, there is a consensus on a neurogenic cause originating from a dysfunction of the cerebello-thalamo-cortical loop. A recent neuroimaging study reported reduced connectivity between the cerebellum and other brain regions, providing additional evidence for an implication of cerebellum in the generation of the tremor. To gain further insight into whether cerebellar functions are altered in ET, we sought to investigate the performances of patients affected by ET in a saccadic adaptation task, which is known to rest on the integrity of the cerebellum. We hypothesized that if the tremor is linked to cerebellar deficits, then a deficit in saccadic adaptation could be observed. We recruited 33 participants (18 ET patients (13 F) and 15 healthy aged-matched controls (9 F)) to perform a standard saccadic-adaptation task. They were first assessed with standard clinical evaluation (Fahn-Tolosa-Marin tremor rating scale) to confirm their inclusion in the study. During the task, a visual target presented laterally (eccentricity: 20 degrees) jumped vertically during the saccade (5 degrees). The target shift was typically not perceived but it resulted in a final error in the vertical direction that participants learned to anticipate with practice. After adaptation, the final position of the saccade became closer to the goal target after the jump. Participants performed a series of 5 blocks of 60 saccades. The protocol included oblique and horizontal saccades without any jump for control analyses (60 trials in total). There was no significant difference between the two groups during the baseline trials. Regarding the adaptation trials, ET patients showed reduced adaptation captured by the extent of vertical component of the saccade and by the peak vertical velocity of partially adapted saccades. Mixed models analysis of these two parameters revealed strong interaction between groups and the trial indices, revealing slower adaptation for the ET group (p < 0.001). The curvature of saccades from ET patients after adaptation also differed from the control group, showing an adaptation mainly towards the end of the saccade, in contrast with the control group who showed more gradual change in saccade curvature within each movement. These results show impairments in saccadic adaptation, for which no effect of the tremor itself was expected. Indeed, participants did not exhibit any nystagmus or eye oscillation, and their behaviour during fixation prior to saccades was similar to the control group. We suggest that these results support the hypothesis of a cerebellar origin of ET and could represent a new quantitative behavioural marker of the disorder.


Bibliographic reference |
Blondiaux, Florence ; Lebrun, Louisien ; Hanseeuw, Bernard ; Crevecoeur, Frédéric. Impact of essential tremor on saccadic adaptation.Neural Control of Movement (Virtual, du 21/04/2021 au 23/04/2021). |
Permanent URL |
http://hdl.handle.net/2078.1/285109 |