title: Does dystonic muscle activity affect sense of effort in cervical dystonia?
abstract: BACKGROUND
  Focal dystonia has been associated with deficient processing of sense of effort cues. However, corresponding studies are lacking in cervical dystonia (CD). We hypothesized that dystonic muscle activity would perturb neck force control based on sense of effort cues.
  
  
  METHODS
  Neck extension force control was investigated in 18 CD patients with different clinical features (7 with and 11 without retrocollis) and in 19 control subjects. Subjects performed force-matching and force-maintaining tasks at 5% and 20% of maximum voluntary contraction (MVC). Three task conditions were tested: i) with visual force feedback, ii) without visual feedback (requiring use of sense of effort), iii) without visual feedback, but with neck extensor muscle vibration (modifying muscle afferent cues). Trapezius muscle activity was recorded using electromyography (EMG).
  
  
  RESULTS
  CD patients did not differ in task performance from healthy subjects when using visual feedback (ANOVA, p>0.7). In contrast, when relying on sense of effort cues (without visual feedback, 5% MVC), force control was impaired in patients without retrocollis (p = 0.006), but not in patients with retrocollis (p>0.2). Compared to controls, muscle vibration without visual feedback significantly affected performance in patients with retrocollis (p<0.001), but not in patients without retrocollis. Extensor EMG during rest, included as covariate in ANOVA, explained these group differences.
  
  
  CONCLUSIONS
  This study shows that muscle afferent feedback biases sense of effort cues when controlling neck forces in patients with CD. The bias acts on peripheral or central sense of effort cues depending on whether the task involves dystonic muscles. This may explain why patients with retrocollis more accurately matched isometric neck extension forces. This highlights the need to consider clinical features (pattern of dystonic muscles) when evaluating sensorimotor integration in CD.
authors.affiliation: FR3636, CNRS / Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Loïc
authors.initials: L
authors.lastname: Carment
authors.affiliation: FR3636, CNRS / Université Paris Descartes, Sorbonne Paris Cité, Paris, France.|Université Paris Diderot, Sorbonne Paris Cité, Paris, France.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Maier
authors.affiliation: Service de Neurologie, Fondation OPH de Rothschild, Paris, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Sangla
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, INSERM U894, Paris, France.|Service de Neurologie et Unité Neurovasculaire, Hôpital Sainte-Anne, Paris, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Guiraud
authors.affiliation: UMR 7287, CNRS Aix Marseille Université, Institut des Sciences du Mouvement, Marseille, France.
authors.forename: Serge
authors.initials: S
authors.lastname: Mesure
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR S 1127, Paris, France.|AP-HP, Hôpital de la Pitié Salpêtrière, Département de Neurologie, Paris, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Vidailhet
authors.affiliation: FR3636, CNRS / Université Paris Descartes, Sorbonne Paris Cité, Paris, France.|Centre de Psychiatrie et Neurosciences, Inserm U894, Paris, France.
authors.forename: Påvel G
authors.initials: PG
authors.lastname: Lindberg
authors.affiliation: Service de Neurologie, Fondation OPH de Rothschild, Paris, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bleton
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D004421:Dystonia / Q000503:physiopathology*; D004576:Electromyography / Q000379:methods; D056228:Feedback, Sensory / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology; D009334:Neck Muscles / Q000503:physiopathology*; D014103:Torticollis / Q000503:physiopathology*; D014732:Vibration