A Neuroanatomical Framework for Upper Limb Synergies after Stroke

Lots of big words and complicated explanations but ultimately useless for helping us to 100% recovery.  Nothing here that can be taken to our therapists for our recovery needs.

A Neuroanatomical Framework for Upper Limb Synergies after Stroke

   HUMAN NEUROSCIENCE PERSPECTIVEARTICLE published: 16 February 2015doi: 10.3389/fnhum.2015.00082 A neuroanatomical framework for upper limb synergiesafter strokeAngus J. C. McMorland , Keith D. Runnalls  and Winston D. Byblow Movement Neuroscience Laboratory, Department of Sport and Exercise Science, Centre for Brain Research,The University of Auckland, Auckland, New Zealand Edited by:  Ana Bengoetxea, Universidad del País Vasco-Euskal Herriko Unibertsitatea,SpainReviewed by:  Jean-Louis Thonnard, Université Catholique de Louvain, BelgiumAaron Batista, University of Pittsburgh, USA*Correspondence: Winston D. Byblow, Movement Neuroscience Laboratory,Department of Sport and Exercise Science, Centre for The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand e-mail:  w.byblow@auckland.ac.nz 
Muscle synergies describe common patterns of co- or reciprocal activation that occur during movement. After stroke, these synergies change, often in stereotypical ways.The mechanism underlying this change reflects damage to key motor pathways as a result of the stroke lesion, and the subsequent reorganization along the neuroaxis, which may be further detrimental or restorative to motor function.The time course of abnormal synergy formation seems to lag spontaneous recovery that occurs in the initial weeks after stroke.In healthy individuals, motor cortical activity, descending via the corticospinal tract (CST) is the predominant driver of voluntary behavior. When the CST is damaged after stroke,other descending pathways maybe upregulated to compensate.The contribution of these pathways may emerge as new synergies take shape at the chronic stage after stroke, as a result of plasticity along the neuroaxis.The location of the stroke lesion and properties of the secondary descending pathways and their regulation are then critical for shaping the synergies in the remaining motor behavior. A consideration of the integrity of remaining descending motor pathways may aid in the design of new rehabilitation therapies.Keywords: muscle synergy, stroke, corticospinal tract, proximal–distal patterning, upper limb
DEFINITIONS “Muscle synergy” can mean subtly different things, creating the opportunity for confusion. As a biological phenomenon, a commonly accepted general definition of muscle synergy is simply a stable spatiotemporal pattern of activity across muscles simultaneously involved in the performance of a movement. Descending neural activity may result in a net excitation or inhibition of the alpha motor neurons innervating each muscle. If motor neurons of two muscles are excited simultaneously, the muscles are coactivated. Conversely, activity in one muscle may coincide with quiescence in another due to reciprocal inhibition. Natural motor behaviors may result from the additive effect of several synergies. In recent experiments, the term “muscle synergy” has been used to label estimates of synergies derived from quantitative matrix factorization methods applied to simultaneous electromyographic (EMG) measurements (Tresch et al., 2006). The details of the mathematical operation determine specific properties of the synergy estimates extracted. For example,non-negative matrix factorization (NNMF) does not capture inhibitory relationships, which maybe alimitationof themethod.Anotherusage of synergy arises in clinical settings, where the term “abnormal muscle synergies” may refer only to the pathological patterns of muscle co-activation that emerge after disruption of the motor
Abbreviations:  BB,biceps brachii; cM1,contralesional M1; CRPP,cortico-reticulo-propriospinal pathway; CST, corticospinal tract; c-tDCS, cathodal tDCS; EMG,electromyography; FM, Fugl-Meyer assessment; M1, primary motor cortex; MEP,motor evoked potential; MRI, magnetic resonance imaging; NNMF, non-negative matrix factorization; PLIC, posterior limb of the internal capsule; SR, synergy ratio; tDCS, transcranial direct current stimulation; TMS, transcranial magneticstimulation. system, such as stroke Brunnström, 1970). This phrasing stems from the fact that pathological synergies are “lower dimensional”than in healthy individuals,hence there are more co-dependencies(synergies) present. In the present article, we adopt the general definitionof the term synergy given above, although reference will also be made to clinically abnormal synergies as well as synergies identified by matrix factorization, and the caveats with regard to the definitions of each should be borne in mind.