The physiological neocerebellar extinction syndrome likely exists for human handedness but not footedness – a study on healthy young adults

The cerebellum, a lateralised organ, plays a crucial role in motor control. Still, its involvement in hand and foot dominance remains inadequately understood, primarily in the right and left-side dominant population. A potential manifestation of this lateralisation is the neocerebellar extinction syndrome, previously linked to mild muscle hypotonia and moderate passivity in the non-preferred hand. A more precise understanding of the cerebellum's role in limb dominance patterns could provide valuable insights into motor learning, rehabilitation therapies, and neuroplasticity. This study explored the relationship between physiological neocerebellar extinction syndrome and hand/ft dominance in left and right-side dominant individuals. Data were collected from 80 university participants (40 left-side dominant, 40 right-side dominant, mean age = 24.7 ± 0.92 years) during controlled limb falls using 3D kinematic analysis. In these falls, theoretically suggested hypotonia in non-dominant limbs was analysed through attenuation coefficients and frequency differences. Using a linear mixed model, we found significantly lower hand attenuation in the non-dominant hand-(β = 0.10, p < 0.001), showing hypotonia compared to the dominant hand regardless of upper limb side dominance. Foot preference and dominance had minimal influence on leg attenuation or frequency, although right-footed, right-dominant individuals demonstrated significantly higher leg oscillation frequency, likely due to increased proximal muscle mass. Our findings suggest that distinct differences in cortical representation, lateralised control, and pathway specialisation exist due to the unique demands of each limb's motor functions, which are pronounced more neocerebellar extinction syndrome in the upper extremities. Therefore, the results showed potentially new perspectives on the cerebellum's nuanced role in motor control and laterality. The differential effects observed between the upper and lower limbs point to distinct cerebellar pathways and hypotonia. This work could significantly enhance the precision of therapeutic approaches and broaden our knowledge of laterality in motor function.