Elsevier

Neuroscience Letters

Volume 677, 11 June 2018, Pages 84-87
Neuroscience Letters

Research article
Cortical modulation of brainstem circuits is abnormal in cervical dystonia

https://doi.org/10.1016/j.neulet.2018.04.047Get rights and content

Highlights

  • The normal enhancement of hand-evoked blink reflex in the peripersonal space was lost in cervical dystonia.

  • The reduction of reflex magnitude in peripersonal space was observed in cervical dystonia with sensory trick.

  • No change of reflex magnitude in the peripersonal space was observed in cervical dystonia without sensory trick.

Abstract

Objective

In healthy subjects, magnitude of hand-evoked blink reflex (BR) is increased if the stimulated hand is positioned in the peripersonal space. Here, we aimed to investigate the modulation of hand-evoked BR in peripersonal space to understand alterations of cortical modulations of subcortical structures in cervical dystonia.

Patients and method

We recruited 23 patients with idiopathic cervical dystonia and 21 healthy subjects, all of whom had hand-evoked BR. The reflex was recorded while stimulated hand was close to face (‘peripersonal space) and far away from face (extrapersonal space). Comparisons were done between two conditions in each group.

Results

In extrapersonal space, magnitude of the reflex was bigger in patients compared to healthy subjects. In peripersonal space, magnitude of the reflex was increased in healthy subjects whereas it was reduced in patients. Comparisons of patients with and without sensory trick disclosed reflex magnitude was reduced in peripersonal space in patients with sensory trick whereas it did not change between two conditions in patients without sensory trick.

Discussion

Enhancement of hand-evoked BR is a normal phenomenon that provides evidence for top-down modulation of its neural circuitry. In cervical dystonia, the normal modulation is lost which suggests abnormal modulatory effect of higher-order centers upon brainstem circuits. The pattern of alteration also differs if there is no sensory trick.

Introduction

Blink reflex (BR) is a protective response for eyes and is obtained after different kinds of stimuli, such as trigeminal supraorbital branch stimulation or median nerve stimulation at wrist (hand-evoked BR) [1]. The generator of the hand-evoked BR is localized in brainstem [2,3], however, it is assumed to be under the control of top-down modulation. Sambo et al. [4,5] previously showed the enhancement of hand-evoked BR in the peripersonal space of face and they attributed the hand-evoked BR changes in the nearby environment to the tonic top-down modulation exerted by association areas such as the premotor cortex and ventral intraparietal area.

Cervical dystonia leads to abnormal contraction of the muscles of the neck and, sometimes, the shoulders. Decreased inhibition, sensory dysfunction, and abnormal plasticity are common pathophysiological factors in all types of dystonia [6]. Increased excitability of brainstem reflexes is known in cervical dystonia and is indicative of increased brainstem interneuron excitability [7,8].

Here, we aimed to investigate changes of hand-evoked BR in peripersonal space to understand cortical contribution in pathophysiology of cervical dystonia. We first tested hand-evoked BR in a group of cervical dystonia patients in comparison to healthy subjects. Second, we compared hand-evoked BR findings in peripersonal space and extrapersonal space of face. This investigation will also provide to examine the differences in top-down modulation of hand-evoked BR in patients with cervical dystonia exhibiting and not exhibiting sensory trick.

Section snippets

Patients

We recruited 30 consecutive patients who were seen in our movement disorders outpatient clinic with a diagnosis of idiopathic cervical dystonia. However, seven patients with cervical dystonia did not have hand-evoked BR at baseline. Therefore, they were excluded from the study and 23 patients (15 women, 65.2%, mean age: 41.5 ± 11.2) were included. The study also excluded patients who had involuntary contractions of the facial muscles and those who had their facial muscles treated with botulinum

Results

Between-group analysis of hand-evoked BR parameters in the extrapersonal space showed mean latencies of hand-evoked BR were similar between groups of patients and healthy subjects (p = 0.217) whereas amplitude and AUC were significantly high in patients with cervical dystonia (p=0.009 and 0.023, respectively, t-test for independent samples).

In-group analysis (peripersonal space vs. extrapersonal space) among healthy subjects disclosed there was a trend for a higher hand-evoked BR amplitude

Discussion

The major findings in this study were as follows: i. the normal enhancement of hand-evoked BR in the peripersonal space of face was lost in cervical dystonia; ii. the reduction of hand-evoked BR magnitude in peripersonal space was also observed in cervical dystonia patients exhibiting sensory trick; iii. no change of hand-evoked BR magnitude in the peripersonal space was observed in cervical dystonia patients without sensory trick.

In cervical dystonia and other kinds of dystonia, there exists a

Funding sources

None.

Conflicts of interest

None of the authors have potential conflicts of interest to be disclosed.

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      People with migraine demonstrated a greater overall hand blink reflex than controls, especially if they were experiencing a headache at the time of testing (Ayas et al., 2020), although the typical spatial modulation was not found. People with cervical dystonia also showed a greater hand blink response than controls and an inversion of the normal spatial modulation (Öztürk et al., 2018). Taken together, these findings suggest that there is abnormal higher-order cortical modulation of the brainstem reflex in dystonia, headache/orofacial pain, and neuropathic pain.

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