Cerebellar motor function in spina bifida meningomyelocele

Abstract

Spina bifida meningomyelocele (SBM), a congenital neurodevelopmental disorder, involves dysmorphology of the cerebellum, and its most obvious manifestations are motor deficits. This paper reviews cerebellar neuropathology and motor function across several motor systems well studied in SBM in relation to current models of cerebellar motor and timing function. Children and adults with SBM have widespread motor deficits in trunk, upper limbs, eyes, and speech articulators that are broadly congruent with those observed in adults with cerebellar lesions. The structure and function of the cerebellum are correlated with a range of motor functions. While motor learning is generally preserved in SBM, those motor functions requiring predictive signals and precise calibration of the temporal features of movement are impaired, resulting in deficits in smooth movement coordination as well as in the classical cerebellar triad of dysmetria, ataxia, and dysarthria. That motor function in individuals with SBM is disordered in a manner phenotypically similar to that in adult cerebellar lesions, and appears to involve similar deficits in predictive cerebellar motor control, suggests that age-based cerebellar motor plasticity is limited in individuals with this neurodevelopmental disorder.

Fig. 1

Cerebellar dysmorphologies described by John Cleland [1835–1925] in 1883. a, Corpora quadrigemina; b, hemispheres of cerebellum; c, the extremity of the elongated nodule [most inferior portion of cerebellar vermis]

Fig. 2

Motor model: movement programming. The move signal (A) includes movement parameters such as reach and force, and because timing is controlled separately from other movement parameters [141], we assume that there is a separate timing signal (B)

Fig. 3

Motor model: cerebellar calibration of movement. Efference copies represent move signal (C) and timing signal (D). A predictive timing signal may also be the actual output of the inferior olive (E). A forward output model involves a corollary discharge (F), which compensates for feedback delays in sensory–motor systems, and feeds into the sensory pathway to cancel out re-afferent signals (G) generated by the actual movement

Fig. 4

Motor model: adaptation and learning. Movement errors can arise from a mismatch between predicted and actual movement (H). Correction of the movement error (I) facilitates both performance (K) and learning (J). Before a motor act is executed, an internalization of the movement is calibrated by visual information (L) for example, about target and hand