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M. Krenn, K. Minassian, U Hofstötter, S. M. Danner, M. Dimitrijevic, W. Mayr:
"Electrophysiology Of Posterior Root-Muscle Reflexes";
Talk: International Symposium on Spasticity and Neural Control of Movement with the 30th Dr. Janez Faganel Memorial Lecture, Ljubljana, Slovenia (invited); 2014-09-04 - 2014-09-06; in: "International Symposium on Spasticity and Neural Control of Movement with the 30th Dr. Janez Faganel Memorial Lecture: Program and Proceedings", J. Zidar (ed.); Section for Clinical Neurophysiology of the Slovenian Medical Association, Ljubljana, Slovenia (2014), ISBN: 978-961-6956-04-8; 52 - 53.

Posterior root-muscle (PRM) reflexes can be elicited by epidural as well as recently also
transcutaneous electrical stimulation of the lumbar spinal cord (1). Epidural spinal cord
stimulation can be used for neuromodulation of spinal spasticity and generation of rhythmicity
(2, 3). For these purposes it was evident that the stimulation site was causative for the
effect (2, 3). Thus, here we tested the selectivity of transcutaneous stimulation of the lumbar
spinal cord by eliciting PRM reflexes and recording the compound muscle action potentials.
Ten subjects (5 f.) with intact nervous system were studied in supine, standing and prone
position. The stimulation set-up consisted of an electrode array centered at the spinal level
of T12 and large electrodes over the abdomen. The array had 7 levels, spanning 12 cm in
rostrocaudal direction and each consisting of 3 x 1 cm electrodes. Every level was separately
used for stimulation. Stimulation was delivered up to 125 mA. Electromyographic activities
were recorded in thigh and shank muscle groups bilaterally.
With the variation of the stimulation level a definite change in the recruitment of PRM
reflexes and M waves was observed. PRM reflexes of the quadriceps muscle group had the
lowest thresholds and highest peak-to-peak (PTP) amplitudes at the rostral and triceps
surae muscle at the caudal electrode levels. PRM reflexes in quadriceps were markedly
reduced and the probability of eliciting M waves increased at the caudal stimulation sites.
Whereas, in triceps surae M waves were rarely recorded. Changes of the body position
clearly influenced the stimulation effect. In the supine position fewest M waves and lowest
reflex thresholds were recorded. The PTP amplitudes of the responses in standing position
were in mean 80% of the corresponding responses in supine position. Whereas, in prone
position M waves were the predominate finding.
Even though the distribution of the generated electrical field with transcutaneous electrodes
is unfocused in relation to the target structures (4), a selective stimulation is possible. The
anatomical structure and electrical properties of the spine, i.e. relatively high conductivities
of the intervertebral discs, might cause a segmental shift of the field, by changing the
stimulation level. Changes of the PRM reflex elicitation with body position changes were
most probably related to changes of the volume conductor as well as due to additional
physiological influences.

References
1. Minassian K, Persy I, Rattay F, Dimitrijevic MR, Hofer C, Kern H. Posterior root-muscle reflexes elicited by transcutaneous stimulation of the human lumbosacral cord. Muscle Nerve 2007; 35 (3): 327-36.
2. Dimitrijevic MR, Gerasimenko Y, Pinter MM. Evidence for a spinal central pattern generator in humans. Ann N Y Acad Sci 1998; 860: 360-76.
3. Pinter MM, Gerstenbrand F, Dimitrijevic MR. Epidural electrical stimulation of posterior structures of the human lumbosacral cord: 3. Control of spasticity. Spinal Cord 2000; 38 (9): 524-31.
4. Danner SM, Hofstoetter US, Ladenbauer J, Rattay F, Minassian K. Can the human lumbar posterior columns be stimulated by transcutaneous spinal cord stimulation? A modeling study. Artif Organs 2011; 35(3): 257-62.

Project Head Frank Rattay:
Life Sciences - Linking Research and Patients' Needs Augmentation of residual neural control by non-invasive spinal cord stimulation to modify spasticity in spinal cord injured people