Priming for Improved Hand Strength in Persons with Chronic Tetraplegia: A Comparison of Priming-Augmented Functional Task Practice, Priming Alone, and Conventional Exercise Training.

Joyce Gomes-Osman,Jacqueline A Tibbett,Edelle C Field-Fote,Brandon P Poe

doi:10.3389/fneur.2016.00242

Joyce Gomes-Osman, Jacqueline A Tibbett + Show 2 more

Open Access

https://doi.org/10.3389/fneur.2016.00242

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Abstract

Many everyday tasks cannot be accomplished without adequate grip strength, and corticomotor drive to the spinal motoneurons is a key determinant of grip strength. In persons with tetraplegia, damage to spinal pathways limits transmission of signals from motor cortex to spinal motoneurons. Corticomotor priming, which increases descending drive, should increase corticospinal transmission through the remaining spinal pathways resulting in increased grip strength. Since the motor and somatosensory cortices share reciprocal connections, corticomotor priming may also have potential to influence somatosensory function. The purpose of this study was to assess changes in grip (precision, power) force and tactile sensation associated with two different corticomotor priming approaches and a conventional training approach and to determine whether baseline values can predict responsiveness to training. Participants with chronic (≥1 year) tetraplegia (n = 49) were randomized to one of two corticomotor priming approaches: functional task practice plus peripheral nerve somatosensory stimulation (FTP + PNSS) or PNSS alone, or to conventional exercise training (CET). To assess whether baseline corticospinal excitability (CSE) is predictive of responsiveness to training, in a subset of participants, we assessed pre-intervention CSE of the thenar muscles. Participants were trained 2 h daily, 5 days/week for 4 weeks. Thirty-seven participants completed the study. Following intervention, significant improvements in precision grip force were observed in both the stronger and weaker hand in the FTP + PNSS group (effect size: 0.51, p = 0.04 and 0.54, p = 0.03, respectively), and significant improvements in weak hand precision grip force were associated with both PNSS and CET (effect size: 0.54, p = 0.03 and 0.75, p = 0.02, respectively). No significant changes were observed in power grip force or somatosensory scores in any group. Across all groups, responsiveness to training as measured by change in weak hand power grip force was correlated with baseline force. Change in precision grip strength was correlated with measures of baseline CSE. These findings indicate that corticomotor priming with FTP + PNSS had the greatest influence on precision grip strength in both the stronger and weaker hand; however, both PNSS and CET were associated with improved precision grip strength in the weaker hand. Responsiveness to training may be associated with baseline CSE.

Highlights

Injury to the cervical spinal cord results in tetraplegia and associated impairment or loss of upper extremity (UE) control and sensory function
Eleven participants withdrew over the course of the 4-week intervention: five after deciding they could not adhere to the time commitment due to other obligations, four were dissatisfied with their group allocation, one had a family emergency, and one declined to offer a reason
The findings indicate that the functional task practice (FTP) + peripheral nerve somatosensory stimulation (PNSS) intervention was associated with significant improvements in precision grip strength of both the stronger and weaker hand

Summary

Introduction

Injury to the cervical spinal cord results in tetraplegia and associated impairment or loss of upper extremity (UE) control and sensory function. Following tetraplegia damage to the descending tracts limits the amount and rate of transmission of information from the cortex to the spinal cord [8], this impaired transmission of signals through the corticospinal pathways limits the ability to generate hand muscle forces resulting in weak precision grip and power grip strength. For these reasons, corticospinal excitability (CSE) is of great relevance for individuals with tetraplegia, since increasing the ability of the cortex to drive signals through the spared spinal pathways should result in improved ability to activate the spinal motoneurons and be associated with increased strength

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