TITLE
Title: Impaired Organization of Paired-Pulse TMS-Induced I-Waves After Human Spinal Cord Injury

AUTHORS
Cirillo J; Calabro FJ; Perez MA. Institution Cirillo, John. Department of Physical Medicine and Rehabilitation, Center for the Neural Basis of Cognition, Systems Neuroscience Institute, University of Pittsburgh, Pittsburgh, PA 15261, USA. Calabro, Finnegan J. Department of Physical Medicine and Rehabilitation, Center for the Neural Basis of Cognition, Systems Neuroscience Institute, University of Pittsburgh, Pittsburgh, PA 15261, USA. Perez, Monica A. Department of Physical Medicine and Rehabilitation Center for the Neural Basis of Cognition, Systems Neuroscience Institute, University of Pittsburgh, Pittsburgh, PA 15261, USA.

SOURCE
Cerebral Cortex. 26(5):2167-77, 2016 May.

ABSTRACT
Paired-pulse transcranial magnetic stimulation (TMS) of the human motor cortex results in consecutive facilitatory motor-evoked potential (MEP) peaks in surface electromyography in intact humans. Here, we tested the effect of an incomplete cervical spinal cord injury (SCI) on early (first) and late (second and third) MEP peaks in a resting intrinsic finger muscle. We found that all peaks had decreased amplitude in SCI subjects compared with controls. The second and third peaks were delayed with the third peak also showing an increased duration. The delay of the third peak was smaller than that seen in controls at lower stimulation intensity, suggesting lesser influence of decreased corticospinal inputs. A mathematical model showed that after SCI the third peak aberrantly contributed to spinal motoneurone recruitment, regardless on the motor unit threshold tested. Temporal and spatial aspects of the late peaks correlated with MEP size and hand motor output. Thus, early and late TMS-induced MEP peaks undergo distinct modulation after SCI, with the third peak likely reflecting a decreased ability to summate descending volleys at the spinal level. We argue that the later corticospinal inputs on the spinal cord might be crucial for recruitment of motoneurones after human SCI.

COPYRIGHT
The Author 2015. Published by Oxford University Press. All rights reserved.

PUBLICATION TYPE
Journal Article