Julius Dewald – Abstract

Increased dependence on contralesional corticoreticulospinal pathways a form of maladaptive plasticity post hemiparetic stroke?

Dewald JPA[1, 2, 3]
1. Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, USA
2. Department of Physical Therapy and Human Movement Science, Northwestern University, Chicago, Illinois, USA
3. Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois, USA

Paretic arm and hand function is a major cause of chronic disability among stroke survivors. In addition to weakness or paralysis, the arm/hand is also affected by the flexion synergy -involuntary elbow, wrist, and finger flexion when an individual with stroke attempts to lift the paretic arm (1). The flexion synergy compromises the ability to reach and open the hand and reduces the control of grasp strength during functional tasks, thus compounding the stroke survivor’s functional deficits. The fine motor control required for normal arm/hand function is largely driven by the contralateral corticospinal tract. Evidence will be provided, using high-density electroencephalographic recordings, that suggests that following a loss of corticospinal and corticobulbar (i.e., corticofugal) pathways post stroke, there is increased activation of contralesional motor cortices with increasing levels of paretic limb weight support by stroke participants (2), indicating the use of indirect corticobulbospinal pathways based on primate research. Evidence will also be provided that in the most impaired stroke participants a greater reliance on contralesional motor cortices over time is resulting in an increase in structural tract integrity in contralesional reticulospinal tract integrity (3). Finally, evidence will be provided showing the reemergence of a developmental brainstem reflex, the asymmetrical tonic neck reflex, to show that anatomically diffuse reticulospinal motor pathways are active during flexion synergy expression (2). We interpret this progressive recruitment of contralesional cortico-reticulospinal pathways as an adaptive strategy that increases shoulder abduction strength at the cost of functional movement control in the paretic upper limb.

  1. Lan Y, Yao J, Dewald JPA. The Impact of Shoulder Abduction Loading on Volitional Hand Opening and Grasping in Chronic Hemiparetic Stroke. Neurorehabil Neural Repair. 2017;31(6):521-9. doi: 10.1177/1545968317697033. PMCID: PMC5505320.
  2. McPherson JG, Chen A, Ellis MD, Yao J, Heckman CJ, Dewald JPA. Progressive recruitment of contralesional cortico-reticulospinal pathways drives motor impairment post stroke. J Physiol. 2018. Epub 2018/02/20. doi: 10.1113/JP274968. PubMed PMID: 29457651