[Zurück]

S. M. Danner, M. Dimitrijevic, U Hofstötter, M. Krenn, W. Mayr, K. Minassian, F. Rattay, J. Rothwell:
"Motor behavior of the human lumbar spinal cord network responding to externally controlled activity: A neurophysiological study";
Poster: 2nd Annual Minnesota Neuromodulation Symposium, Minneapolis, MN, USA; 10.04.2014 - 11.04.2014; in: "Abstract Book of The 2nd Annual Minnesota Neuromodulation Symposium", (2014), S. 8.

Background:
Epidural spinal cord stimulation has been used since the 1970ies for neuromodulation in motor disorders. Electrophysiological studies have utilized single stimuli delivered close to the posterior lumbar spinal cord to produce reflexes in several lower limb muscles simultaneously, so-called posterior root-muscle reflexes. When elicited in series they can be intrinsically modulated to form patterned output in motor complete spinal cord injured (SCI) individuals. We systematically analyzed stimulation parameters in order to predict the configuration of the interneuronal network shaping these outputs.

Material and Methods
In 10 motor complete SCI people lying supine, epidural stimulation was delivered with the cathode located between T11-T12 vertebral levels, stimulating lumbar and upper sacral posterior roots. Frequencies between 5 Hz and 100 Hz were applied for 10 s with different intensities. Electromyographic activities were recorded from extensor and flexor muscle groups of thigh and leg bilaterally. Dynamics of the peak-to-peak amplitudes and shapes of the stimulus time-related responses were analyzed.

Results
Four distinct muscle response patterns could be observed: (i) tonic activity, (ii) partially mixed tonic and rhythmic, phasic activity, (iii) rhythmic activity, and (iv) suppression of activity. The patterns were preferentially expressed at different stimulation frequency ranges. Rhythmic activity occurred at frequencies higher than 20 Hz and most often at 50 Hz. Irrespective of stimulation frequency most outputs were tonic. Increasing stimulation frequency significantly attenuated the output and increased its complexity. Yet, stimulation intensity had no significant influence on whether rhythmic or tonic activity was expressed.

Conclusions
Non-patterned inputs through the lumbar posterior roots can be processed into a wealth of patterned, coordinated motor unit outputs by the lumbar neural circuitry. Stimulation frequency is the strongest predictor for the outcome. To utilize the spinal motor repertoire in neuromodulation applications the next step will be to unravel how to select an appropriately coordinated combination of patterns needed for a specific motor task.

Funding
Vienna Science and Technology Fund (WWTF) LS11-057, Wings for Life Spinal Cord Research Foundation WFL-AT-007/11 and Foundation for Movement Recovery, Oslo, Norway.