What is straight ahead to a patient with torticollis?

Abstract

Vestibular and neck proprioceptive signals are known to be used in judging the locations of objects in space and relative to the body. Given that these signals are asymmetric in patients with spasmodic torticollis, one would expect such patients to have abnormal spatial perception. We tested this idea by measuring patients' perception of visual straight ahead (VSA) under various conditions: with the body in its primary position, i.e. with the head and trunk as closely aligned as possible, and after well defined passive rotations of the head and/or trunk. In the primary body position, patients' VSA direction showed considerable variations which were similar, however, to those of normal subjects; it was independent of torticollis direction, of the head torque it produced, and of the weak spontaneous nystagmus recorded in seven of the 10 patients. After whole-body rotations, i.e. where head and trunk underwent the same motion, the VSA was shifted in both patients and normal subjects, and in both groups the shift was symmetrical after rotations to the right or left. After motions where the trunk rotated under the stationary head (neck proprioceptive stimulation) or the head on the stationary trunk (combined vestibular and neck stimulus), the VSAs of normal subjects coincided rather well with their head midsagittal planes, whereas the VSAs of patients were shifted considerably towards the trunk, again in a symmetrical way. We suggest two mechanisms to explain the findings in patients: (i) a central compensation which restores symmetry of the afferent inflow in the patients (unlike the motor efference); (ii) shifting of the reference for the VSA from the head towards the trunk, because the trunk is a more reliable egocentric reference than the head in the patients. Our findings do not support the assumption that asymmetries in afferent inflow are responsible for the asymmetry of motor output in spasmodic torticollis.

Keeping Your Head On Target

“…2). These results are consistent with prior studies showing the importance of proprioceptive feedback for head control (Smetanin et al, 1993;Anastasopoulos et al, 1998;Bove et al, 2004Bove et al, , 2007Malmström et al, 2009). There are several reasons the head integrator may depend on proprioception.…”

“…Most healthy subjects show subtle end-gaze nystagmus in the dark, a phenomenon attributed to an imperfect ocular integrator and its reliance on visual feedback (Jürgens et al, 1981;Pastor et al, 1994;Abadi and Scallan, 2001; Leigh and Zee, 2006). Patients with cerebellar disease and monkeys with lesions of the cerebellum show enhanced gaze-evoked nystagmus (Zee et al, 1980(Zee et al, , 1981.…”

“…Disruption of inputs from the vestibular nuclei may reflect the subtle vestibular abnormalities reported in CD (Münchau and Bronstein, 2001;Münchau et al, 2001). Finally, several studies suggest that the pathogenesis of CD includes abnormal proprioception from neck muscles (Lekhel et al, 1997;Anastasopoulos et al, 1998;Karnath et al, 2000;Bove et al, 2004), which also projects to the interstitial nucleus of Cajal. Thus, the concept of dysfunction of a neural integrator for head position involving the INC and nearby regions accommodates results from many apparently unrelated prior studies of CD, and provides an experimental model for future studies.…”

Posturographic Findings in Patients with Idiopathic Cervical Dystonia before and after Local Injections with Botulinum Toxin

“…In addition, studies of visuospatial perception in patients with spasmodic torticollis [24]reported similar findings: measuring the patients’ visual perception under various conditions (with the body in its primary position and after passive rotations of the head and/or trunk) revealed symmetrical results independent of the direction of the torticollis. Accordingly, the authors concluded that it is unlikely that asymmetries in afferent inflow are responsible for the asymmetry of motor output in spasmodic torticollis.…”

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

“…Instead, they set the line to upright, on average, i. e. parallel to the midsagittal plane of their trunks [2]. Similarly, in a previous study in which we tested the subjective visual straight ahead (VSA) after rotations of the head and trunk, ST patients referenced it to their trunks, unlike normal subjects who use a head-centric frame of reference [3]. One could conclude that these findings reveal a direct correlate for an erroneous proprioceptive head-on-trunk signal.…”