Implicit motor imagery using laterality recognition in functional movement disorders

Functional movement disorder (FMD) presents as disabling motor symptoms that cannot be explained by organic processes. Despite the lack of lesion or known central nervous system dysfunction, distortion in sensorimotor processing in movement generation and execution is often observed. A person's capacity to judge laterality of a body part requires processing of sensorimotor information. This prospective observational study compared reaction time (RT) and accuracy (ACC) of hand laterality recognition between 30 people diagnosed with FMD and 30 age-matched healthy control participants. The association of RT and ACC with severity of FMD as measured by the Simplified Functional Movement Disorders Rating Scale (SFMDRS) was also explored. RT was on average 0.6 s slower (95% CI 0.4 - 0.8 s, p < 0.001) in patients with FMD (mean 2.2 s, standard deviation (SD) 0.5) than controls (mean 1.7 s, SD 0.3). ACC was on average 8.9% lower (95% CI -15.7 - -2.2, p = 0.01) in patients with FMD (mean 79.6%, SD 16.6) than controls (mean 88.5%, SD 8.1). When adjusted for SFMDRS using robust regression, RT was 0.3 s slower (95% CI 0.01 - 0.5, p = 0.04) in cases than in controls, but ACC was no longer different between groups. There was a moderate negative correlation between RT and ACC in FMD patients (ρ -0.58, p < 0.001 but not in controls (ρ -0.26, p = 0.17). People with FMD had significantly slower RT and lower ACC compared to the control group. These results provide new insights into underlying sensorimotor processing deficits in those with FMD.