Cortical modulation of brainstem circuits is abnormal in cervical dystonia

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.