Congenital Mirror Movements and the Impact on the Somatosensory System

Abstract

Congenital mirror movements (CMM) is a rare neurological condition in which affected individuals have difficulty with performing solely unimanual movements; the opposite hand symmetrically mimics the actions of the volitional hand. This phenomenon is thought to occur due to robust ipsilateral corticospinal tracts. Although the motor aspects of CMM have been well documented, the somatosensory system has largely been dismissed as normal (Cohen et al., 1991). However, some doubt has been cast as to whether that is truly the case (e.g., Guttman, Maclay, & Stokes, 1939). The present study aimed to identify somatosensory system irregularities among individuals who have CMM. Via a survey, participants ranked themselves as having a greater likelihood of failing to perceive sensations in their intentionally moving and mirroring hands while distracted, but also less likely to experience synchiria (i.e., feeling as if sensations originating in one hand are instead happening bilaterally) under that condition. As a follow-up, an experiment featuring tactile perceptual learning was conducted with a subset of the Experiment 1 participants (see Table 1) and control subjects. The goal was to ascertain if an extensive history of synchronized bimanual activity would be reflected in the transfer patterns of roughness discrimination learning between the fingers. Contrary to the expectation that learning would spread more readily bilaterally for the CMM participants, the between-group differences were non-significant, but did not definitively negate the possibility that CMM is associated with increased bilateral connectivity of the hand regions within the somatosensory cortex. Future research on the somatosensory system and CMM would benefit from using more sensitive measures and attracting larger numbers of participants to strengthen between-group comparisons.