Idiopathic spasmodic torticollis is not associated with abnormal kinesthetic perception from neck proprioceptive and vestibular afferences

Abstract

Proceeding from recent evidence for a sensory involvement in the pathophysiology of idiopathic spasmodic torticollis (ST), we asked whether the abnormal head posture of these patients is associated with distortions of their internal spatial reference frames due to abnormal processing of neck proprioceptive and/or vestibular input. Twelve ST patients were instructed to estimate, by adjusting a light pointer in the dark, their head and trunk mid-sagittal directions (as representatives of ego-centric references) and to reproduce a remembered target location in space (space centric reference). They did so before and after horizontal head and trunk rotations, which evoked isolated or combined vestibular and/or neck stimulation. In ST patients, unlike in normal controls, pre-stimulus estimates of the head and trunk mid-sagittal directions (baselines) showed a pronounced across-subjects variability, with essentially normal mean values. Their post-stimulus estimates in all tasks, after correction for the individual baseline errors, were normal with respect to both amplitude and variability, independent of stimulus direction, modality and rotation dynamics. Our findings suggest that ST patients have a rather inaccurate knowledge of their head posture, but can effectively use neck proprioceptive input and vestibular cues when estimating head and trunk displacements in ego-centric and space centric spatial orientation tasks. We propose that an offset of a non-sensory set point signal in the neck proprioceptive loop for head-on-trunk control may be responsible for the pathological head deviation in ST.

Interactions between voluntary head control and neck proprioceptive reflexes in cervical dystonia

“…Our experimental findings argue thus in favor of a (yet unidentified) common link in the cascade of processes generating the observed sensorimotor impairments and the abnormal head posture. They exclude the involvement of sensory biases, in line with previous observations from perceptual studies [6].…”

“…the geste antagoniste). Perception of the size and direction of passive bodysegment motion is normal [5,6], yet the illusory perception of joint movement produced by muscle vibration appears to be abnormal in CD [5,7,8]. Also, tactile, visuo-tactile temporal discrimination [9] and spatial somaesthetic discrimination [10] are impaired in CD.…”

The role of spinal manipulation in addressing disordered sensorimotor integration and altered motor control

“…Other groups have also demonstrated that there is a shift in the gain of the sensory signals, i.e. a central re-weighting of proprioceptive input, in patients with spasmodic torticollis (Anastasopoulos et al, 2003) and low back pain patients (Brumagne et al, 2004). …”

Disturbed egocentric space representation in cervical dystonia

“…Sensory systems have been implicated recently in CD or other dystonic syndromes 7–9. Studies using natural neck proprioceptive stimulation (head rotation relative to the trunk) have confirmed that, in humans, neck afferents are important in perceiving not only head posture but also motion and localization of visual objects 10–14.…”