Segmental specificity in belly dance mimics primal trunk locomotor patterns

Voluntary control of pelvic frontal rotations in belly dance experts

The present study investigated how belly dance experts perform the "hip shimmy", a complex rhythmic dance movement consisting in a voluntary oscillation of the pelvis exclusively in the frontal plane with maximised amplitude, with no movement of the upper trunk. The aims of this study were to 1) assess whether the amplitude and stability of the pelvic movement can be maximised in certain postural and frequency conditions; and 2) investigate in a 1 to 3 Hz range whether it is indeed possible to oscillate the pelvis only in the frontal plane and to dissociate this one-axis pelvic rotation from potential spontaneous upper-trunk oscillations. Nineteen belly dance experts performed this task in three frequencies and three knee bending postures. Eight joint angles were calculated using the kinematic data of 20 markers over the entire body collected with a motion capture system. Mean amplitude, frequency, and spatial and temporal variability of frontal pelvic oscillations were analysed to characterise motor performance and movement stability. Five Continuous Relative Phases (CRP) were computed to identify the modes and stability of coordination patterns. The results showed that a low posture enhances amplitude performance and that the pelvic oscillation amplitude tended to decrease at 3 Hz, although between-condition differences remained small. Temporal stability was highest at 2 Hz and significant inter-individual differences emerged at 3 Hz. CRP analysis revealed an unpreventable coupling between pelvis and upper-trunk oscillations in the frontal and transversal planes. A consistent antiphase coordination between transversal pelvis and upper-trunk may have been caused by anatomical and counter-balancing constraints. In the frontal plane, multiple stable pelvis-upper trunk patterns including inphase, out-of-phase and antiphase evolved to antiphase predominance and inphase disappearance upon reaching 3 Hz. In sum, increasing frequency highlighted the concomitance of two control phenomena: the inter-individual differentiation in performance and standardisation of the possible pelvis-upper-trunk patterns.

Locomotion and dynamic posture: neuro-evolutionary basis of bipedal gait

Body displacement during locomotion is a major challenge for motor control, requiring complex synergistic postural regulation and the integrated functioning of all body musculature, including that of the four limbs, trunk and neck. Despite the obvious pivotal role played by the trunk during locomotion, most studies devoted to understanding the neural basis of locomotor control have only addressed the operation of the neural circuits driving leg movements, and relatively little is known of the networks that control trunk muscles in limbed vertebrates. This review addresses this issue, both in animals and humans. We first review studies addressing the central role played by central pattern generator (CPG) circuit interactions within the spinal cord in coordinating trunk and hind limb muscle activities in a variety of vertebrates, and present evidence that vestibulo-spinal reflexes are differentially involved in trunk and hind limb control. We finally highlight the role of the various components that participate in maintaining dynamic equilibrium during stepping, including connective tissues. We propose that many aspects of the organization of the motor systems involved in trunk-hind limb movement control in vertebrates have been highly conserved throughout evolution.

Dancing Dorsal Quadrilaterals: A Novel Peripherally Induced Movement Disorder

Importance

Recognized peripherally induced movement disorders include the painful legs moving toes syndrome, postamputation dyskinesias, and belly dancer dyskinesias.

Objective

To introduce and characterize the dancing dorsal quadrilaterals, a novel peripherally induced movement disorder that predominantly affects dorsal quadrilateral muscles (trapezius and rhomboids) after upper spine instrumentation.

Design, Setting, and Participants

Between 1990 and 2015, a total of 4 patients who developed abnormal movements of the dorsal quadrilateral muscles after upper spine instrumentation were referred to movement disorders clinics at 3 academic medical centers in the United States, Canada, and Argentina. A prospective and retrospective analysis of the clinical and electrophysiologic characteristics of their abnormal movements is presented in this brief report. Data were analyzed between July 2015 and January 2018.

Exposures

Extensive upper spine instrumentation complicated with misalignment and prolonged postsurgical neuropathic pain.

Main Outcomes and Measures

Video documentation of clinical and electrophysiologic characteristics of dancing dorsal quadrilaterals.

Results

Four patients with upper spine disease (2 women and 2 men, ranging in age from early 30s to early 70s) required extensive surgical manipulation and instrumentation that was complicated by misalignment, prolonged dorsal neuropathic pain, and unusual abnormal movements. These movements consisted of semirhythmic, repetitive writhing, and jerky movements of the scapular region with distinctive rotatory motions. They are referred to as the dancing dorsal quadrilaterals because they predominantly affected the bilateral trapezius and rhomboids (dorsal quadrilateral muscles) but could spread to adjacent muscles, and they are similar in appearance and possibly pathogenesis to "belly dancer" dyskinetic movements. The movements of the dancing dorsal quadrilaterals occur when upright but not when lying down or during voluntary muscle activation. Sensory stimulation also diminishes the movements. Long-duration bursts of normal motor unit potentials with normal recruitment pattern were evidenced.

Conclusions and Relevance

The dancing dorsal quadrilaterals syndrome represents a further example of a peripherally induced movement disorder characterized by neuropathic pain preceding a regional movement disorder following soft-tissue or nerve injury.

Crossed activation of thoracic trunk motoneurons by medullary reticulospinal neurons

Activation of contralateral muscles by supraspinal neurons, or crossed activation, is critical for bilateral coordination. Studies in mammals have focused on the neural circuits that mediate cross activation of limb muscles, but the neural circuits involved in crossed activation of trunk muscles are still poorly understood. In this study, we characterized functional connections between reticulospinal (RS) neurons in the medial and lateral regions of the medullary reticular formation (medMRF and latMRF) and contralateral trunk motoneurons (MNs) in the thoracic cord (T7 and T10 segments). To do this, we combined electrical microstimulation of the medMRF and latMRF and calcium imaging from single cells in an ex vivo brain stem-spinal cord preparation of neonatal mice. Our findings substantiate two spatially distinct RS pathways to contralateral trunk MNs. Both pathways originate in the latMRF and are midline crossing, one at the level of the spinal cord via excitatory descending commissural interneurons (reticulo-commissural pathway) and the other at the level of the brain stem (crossed RS pathway). Activation of these RS pathways may enable different patterns of bilateral trunk coordination. Possible implications for recovery of trunk function after stroke or spinal cord injury are discussed.NEW & NOTEWORTHY We identify two spatially distinct reticulospinal pathways for crossed activation of trunk motoneurons. Both pathways cross the midline, one at the level of the brain stem and the other at the level of the spinal cord via excitatory commissural interneurons. Jointly, these pathways provide new opportunities for repair interventions aimed at recovering trunk functions after stroke or spinal cord injury.