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

John Cirillo, Finnegan J. Calabro, Monica A Perez*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)2167-2177
Number of pages11
JournalCerebral Cortex
Issue number5
StatePublished - May 1 2016


  • corticospinal volleys
  • primary motor cortex
  • spinal cord injury
  • transcranial magnetic stimulation
  • voluntary movement

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Cognitive Neuroscience


Dive into the research topics of 'Impaired Organization of Paired-Pulse TMS-Induced I-Waves After Human Spinal Cord Injury'. Together they form a unique fingerprint.

Cite this