Altered Saccades, Blink and Pupil Responses in Functional Motor Disorder: New Insight Into Neurobiological Mechanisms

Abstract

ABSTRACT Background Functional motor disorder (FMD) is a common and disabling condition with incompletely understood pathophysiology. Eye‐tracking offers a method to objectively examine cognitive and motor control processes and their underlying neural pathways. We aimed to quantify saccade, blink, and pupil responses in FMD and healthy controls performing an interleaved pro‐/anti‐saccade task, and to investigate the relationships between oculomotor measures and motor and non‐motor symptom severity. Methods We conducted video‐based eye‐tracking in 104 patients with clinically definite FMD and 115 age‐ and sex‐matched healthy controls performing the saccade task. Patients completed questionnaires on depressive, pain‐related, dissociative, and non‐motor somatic symptoms. Clinician‐rated motor severity and centrally acting medication were recorded in FMD patients. Results Compared to controls, FMD patients showed increased anti‐saccade error rates (p < 0.001), anticipatory saccades (p ≤ 0.003), altered blink distribution (p < 0.001), and reduced pupil dilation velocity (p < 0.001). However, reduced pupil dilation velocity was not significant in the subsample of unmedicated patients. Higher anti‐saccade error rates were significantly associated with depressive symptoms, pain severity, dissociative symptoms, non‐motor somatic symptom burden, and motor severity (all p < 0.05). Conclusions We hypothesize that the altered saccade and blink responses result from altered processing in the frontal cortex and basal ganglia, which provide critical input to brainstem oculomotor control areas in FMD. These results support neurobiological models proposing altered predictive and attentional processing underlying FMD. Association between oculomotor measures and symptom severity suggests that specific cognitive abnormalities may play a role in the pathophysiology of these symptoms in FMD.