Ipsilateral Motor Pathways after Stroke: Implications for Non-Invasive Brain Stimulation

Abstract

In humans the two cerebral hemispheres have essential roles in controlling the upper limb. The purpose of this article is to draw attention to the potential importance of ipsilateral descending pathways for functional recovery after stroke, and the use of non-invasive brain stimulation (NBS) protocols of the contralesional primary motor cortex (M1). Conventionally NBS is used to suppress contralesional M1, and to attenuate transcallosal inhibition onto the ipsilesional M1. There has been little consideration of the fact that contralesional M1 suppression may also reduce excitability of ipsilateral descending pathways that may be important for paretic upper limb control for some patients. One such ipsilateral pathway is the cortico-reticulo-propriospinal pathway (CRPP). In this review we outline a neurophysiological model to explain how contralesional M1 may gain control of the paretic arm via the CRPP. We conclude that the relative importance of the CRPP for motor control in individual patients must be considered before using NBS to suppress contralesional M1. Neurophysiological, neuroimaging, and clinical assessments can assist this decision making and facilitate the translation of NBS into the clinical setting.

The spasticity in the motor and functional disability in adults with post-stroke hemiparetic

“…After stroke, some of these pathways may be damaged, leading to loss of dexterity, strength and voluntary movement. Several plastic processes of the central nervous system act after injury in order to restore motor and functional control, such as reorganization of intracortical connections, appearance of collateral cortico-spinal projections from other regions of the primary motor cortex or other areas of the brain,increased cortical activation of descending pathways from the midbrain and increased activity of ipsilateral cortico-spinal projections from the unaffected cortex (27,28). However, the loss of distal selective motricity due to injury to the cortico-spinal tract is not repaired and/or replaced (29).…”

Stance limb ground reaction forces in high functioning stroke and healthy subjects during gait initiation

“…Regardless of the functional implications of the present data, the mechanism that is driving this novel finding can only be speculated upon. One possibility is that after stroke, increased contralesional ipsilateral drive (Bradnam et al, 2013;Schwerin et al, 2008) strongly activates axial and lower limb muscles. It is unlikely that only the left hemisphere has ipsilateral connections, although there is some support for the notion that these connections are more prevalent on the left side in the lower (Chin, 2013) limbs of healthy adults.…”

Personalized Neuroprosthetics

“…The BMI toolbox enables monitoring motor attention during training to ensure active participation of the brain, which is essential to trigger activity-dependent neuroplasticity (17,82,88). Although preliminary, these studies are mapping the future of multisystem neurorehabilitation-bidirectional BMI technology to relay decoded intent to networked prosthetic systems (Fig.…”

“…These achievements have demonstrated that current neurotechnologies are safe and may improve quality of life. The time has come to broaden the spectrum of targeted neurological impairments, specifically to evaluate the therapeutic effect of neuroprosthetic treatments in individuals with less-severe deficits than severely paralyzed persons, the latter being the typical subjects for early clinical investigations (11,12,16,88). For example, implementation of neuroprosthetic systems may uncover distinct treatment mechanisms for individuals with moderate versus severe SCI, including growth of new connections through variable volume of spared tissue (17).…”