Patients with functional upper‑limb tremor showed significantly faster split‑belt gait adaptation and faster washout than matched controls, implying enhanced sensorimotor adaptation and altered integration of priors and sensory feedback.

While not directly actionable for Parkinson's therapeutics, the contrasting accelerated adaptation phenotype versus the slowed adaptation seen in PD can help parse circuit/computational differences in sensorimotor integration, informing biomarkers or differential-diagnosis strategies rather than…

BACKGROUND: Functional neurological disorders (FNDs) are common, disabling conditions that are genuinely experienced and arise from functional rather than structural abnormalities. Although theoretical frameworks implicate aberrant integration of prior expectations and sensory input, empirical evidence is limited, and it remains unclear whether such alterations reflect symptom-specific deficits or broader trait characteristics. OBJECTIVE: To determine whether individuals with functional tremor exhibit altered integration of prior expectations and sensory input, by comparing their rate of adaptation to a split-belt gait perturbation with that of healthy controls. METHODS: We examined split-belt treadmill adaptation-a paradigm inducing mismatch between predicted and actual sensory feedback-in patients with functional upper-limb tremor and age-matched healthy control subjects. Fifteen patients and 15 control subjects were recruited; three patients were excluded postenrolment because of the presence of functional gait features resulting in an inability to walk unsupported. Participants completed fast and slow tied-belt baseline walking, 7 minutes of split-belt adaptation, and 4 minutes of washout (ie, slow tied-belt walking). Adaptation and washout of step length asymmetry were quantified using single-exponential fits. RESULTS: Baseline spatiotemporal gait parameters did not differ between groups. Patients with functional tremor adapted step length asymmetry significantly faster than control subjects (26.7 ± 24.9 seconds vs. 100.6 ± 82.2 seconds; P = 0.006) and showed faster adaptation when returning to tied-belt modus (4.1 ± 5.9 seconds vs. 12.2 ± 11.3 seconds; P = 0.033). CONCLUSIONS: These findings indicate that individuals with functional tremor exhibit enhanced adaptation to novel sensorimotor contexts, contrasting with slowed adaptation reported in other neurological populations such as Parkinson's disease. Because this study included people with upper-limb functional tremor, accelerated adaptation may reflect a predisposing trait of FND rather than a symptom-specific or task-dependent phenomenon. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.