Trunk bradykinesia and foveation delays during whole-body turns in spasmodic torticollis

Abstract

We have investigated how the abnormal head posture and motility in spasmodic torticollis interferes with ecological movements such as combined eye-to-foot whole-body reorientations to visual targets. Eight mildly affected patients and 10 controls voluntarily rotated eyes and body in response to illuminated targets of eccentricities up to ±180°. The experimental protocol allowed separate evaluation of the effects of target location, visibility and predictability on movement parameters. Patients’ latencies of eye, head, trunk and foot motion were prolonged but showed a normal modification pattern when target location was predictable. Peak head-on-trunk displacement and velocity were reduced both ipsi- and contralaterally with respect to the direction of torticollis. Surprisingly, peak trunk velocity was also reduced, even more than in previously studied patients with Parkinson’s disease. As a consequence, patients made short, hypometric gaze saccades and only exceptionally foveated initially nonvisible targets with a single large gaze shift (4 % of predictable trials as opposed to 30 % in controls). Foveation of distant targets was massively delayed by more than half a second on average. Spontaneous dystonic head movements did not interfere with the execution of voluntary gaze shifts. The results show that neck dystonia does not arise from gaze (head-eye) motor centres but the eye-to-foot turning synergy is seriously compromised. For the first time we identify significant ‘secondary’ complications of torticollis such as trunk bradykinesia and foveation delays, likely to cause additional disability in patients. Eye movements per se are intact and compensate for the reduced head/trunk performance in an adaptive manner.

Fast gaze reorientations by combined movements of the eye, head, trunk and lower extremities

“…Multiple-step gaze shifts were characterized by significantly low head-in-space velocity. High head-in-space velocity during task execution thus increases the probability of eliciting single-step gaze shifts and quickly acquiring a predetermined direction of the visual axis, as hypothesized in previous studies (Anastasopoulos et al 2009 , 2011 , 2013 ). The slower, multiple-step gaze shift pattern, incorporating sections of VOR mediated gaze stability, looks suitable for visually scanning the environment during lower velocity roaming head movements.…”

“…It has been suggested that the higher the head-in-space velocity during this task, the more likely that a single-step gaze shift pattern will be elicited (Anastasopoulos et al 2009 ). For example, patients with Parkinson’s disease and spasmodic torticollis generate accurate single-step gaze displacements to large target eccentricities less frequently than normal subjects, most likely because of the low head-in-space velocity which they can attain (Anastasopoulos et al 2011 , 2013 ), but this improves after deep brain stimulation treatment (Lohnes and Earhart 2012 ). However, the question of whether increasing head (and other body segments) velocity during whole-body gaze transfers will result in a higher proportion of single-step gaze shifts has never been directly investigated.…”

Disruption in cerebellar and basal ganglia networks during a visuospatial task in cervical dystonia

“…First, eye movements were not measured during the task execution, even though this factor might be of significance. This decision was based on the results of previous studies showing that the ocular reflexes and eye movements per se were intact in CD patients. In addition, involuntary head movements of small amplitude could have influenced the results.…”

Sensorimotor Control in Dystonia

“…Oculomotor control is impaired in dystonia, including saccade control and saccadic adaptation [50,51]. Patients show nystagmic step-patterns of gaze while transitioning from central fixation points to lateral targets during turning movements, as opposed to single-step saccades in controls.…”