Comparison of input-output patterns in the corticospinal system of normal subjects and incomplete spinal cord injured patients |
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Authors: | N J Davey Hazel C Smith Gordana Savic David W Maskill Peter H Ellaway Hans L Frankel |
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Institution: | (1) Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, Fulham Palace Road, London W6 8RF, UK e-mail: n.davey@ic.ac.uk Tel.: +44-181-8467284, Fax: +44-181-846 7338, GB;(2) National Spinal Injuries Centre, Stoke Mandeville Hospital, Aylesbury, Bucks, FW21 8AL, UK, GB |
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Abstract: | We have examined input-output patterns in the corticospinal system after incomplete spinal cord injury. The amplitude of the
motor evoked potential (MEP) to transcranial magnetic stimulation (TMS) was used to study the patterns of recruitment, with
increasing stimulus intensity, and facilitation, with increasing voluntary contraction, in thenar muscles of 12 patients with
incomplete spinal cord injuries and 13 control subjects. The patients had all suffered spinal cord injury at a segmental level
rostral to C8 and T1, the segments supplying innervation of thenar muscles. The patients showed a less pronounced increase
in MEP amplitude with increasing strength of TMS compared with the controls. Specifically, at a stimulus strength of 120%
threshold and above, the patients showed significantly smaller MEPs relative to the maximum ulnar nerve M-wave response than
the controls. The patients also showed a less steep pattern of facilitation with voluntary drive. The MEP continued to increase
up to 50% maximum voluntary contraction (MVC) whereas the controls reached a plateau around 10% MVC. The results indicate
that the patients show modified corticospinal recruitment and facilitation of the motoneurone pool. We speculate that the
function of the adapted corticospinal system after spinal cord injury might be to regulate and modulate drive to motoneurones
originating from segmental and other descending inputs. We discuss how such a modified corticospinal system might be of functional
benefit to the patients.
Received: 25 August 1998 / Accepted: 24 March 1999 |
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Keywords: | Spinal cord injury Corticospinal pathway Facilitation Recruitment Magnetic stimulation |
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