Baseline blink reflex R2 changes correlate with affective and interoceptive domains in functional movement disorders.

Functional motor disorders (FMD) are a common yet often misunderstood group of neurological conditions characterized by abnormal movements, including limb weakness, tremor, dystonia, and gait disturbances. These disorders involve disrupted sensory processing mechanism. Previous studies have shown abnormal prepulse inhibition of the blink reflex (BR) in FMD, but the baseline R2-area, reflecting brainstem excitability and cortical modulation, has not been characterized. This study investigated baseline BR R2-area in patients with FMD compared with healthy controls (HC), its associations with affective and interoceptive factors, and its diagnostic potential when combined with laser-evoked potentials (LEPs). BR responses were recorded in clinically definite patients with FMD (n = 75) and matched HC (n = 75). The R2-component was elicited by supraorbital stimulation and quantified as the area under the curve across ipsilateral, contralateral, and average responses. Associations with with behavioural and interoceptive measures were investigated. LEPs were incorporated into multivariate logistic regression models to assess diagnostic potential. Compared with HC, FMD-patients exhibited a consistent reduction in baseline R2 area. Worst depressive symptoms were associated with larger R2 areas, whereas reduced body awareness was associated with smaller responses, indicating affective and interoceptive influences on brainstem excitability. Baseline R2-metrics, particularly the ipsilateral area, contributed substantially to group discrimination, achieving 71.1% accuracy. Reduced baseline BR R2 area in FMD suggests altered brainstem excitability and possibly enhanced descending inhibition. While LEPs provided complementary information, baseline BR measures provided the strongest signal, highlighting the R2 area as a physiological signature to be integrated into multimodal diagnostic frameworks.