Transcutaneous spinal cord stimulation as a tool to investigate function of vestibulospinal, reticulospinal, and corticospinal descending pathways

Quantification of the function of the descending vestibulospinal, reticulospinal, and corticospinal pathways is critical to understanding the connectivity and neuroplasticity in the central nervous system. Previous works have examined the effects of galvanic vestibular stimulation (GVS), auditory startle response (ASR), and transcranial magnetic stimulation (TMS) at the spinal level using the soleus H-reflex to assess motor neuron excitability. The Hreflex is limited in that it only provides information from unilateral spinal segments projecting to a single muscle. The present study was designed to systematically investigate the bilateral effects of the multi-segmental convergence of the vestibulospinal, reticulospinal, and corticospinal pathways on lumbosacral motor pools, using transcutaneous electrical spinal cord stimulation (TESS). We hypothesized that modulation of spinal motor output due to the convergence of descending and afferent volleys will depend on the specific pathway tested, as well as on the delay between the conditioning and test stimuli. Spinally evoked motor potentials were recorded in non-injured individuals using TESS, delivered over the intra-spinous space between the spinous processes of the T10 and T12 vertebrae, with subjects lying in a supine position. Reponses were recorded via surface electrodes in vastus lateralis, medial hamstrings, tibialis anterior, and soleus muscles bilaterally. Vestibulospinal, reticulospinal, and corticospinal pathways were evaluated using conditioning binaural GVS (200 ms, up to 4 mA), ASR (30 ms, 90 dB, 700 Hz), and TMS (sub- and supra-motor threshold intensity), respectively, at different conditioning-test intervals (CTI). The conditioning stimulation resulted in the most robust facilitation at CTI between 90 and 160 ms following GVS and ASR, and at CTI between 10 and 25 ms and 90 and 140 ms following TMS. These results demonstrate that the lumbosacral motor pools can interact with the supraspinal descending volleys to facilitate the motor response. This method of investigating the descending supraspinal pathways allows objective quantification of the multi-segmental convergence of the vestibulospinal, reticulospinal, and corticospinal descending pathways with lumbosacral motor pools. Ultimately, this approach may provide a way to monitor and predict neuronal network plasticity associated with motor learning and functional recovery.

Society for Neuroscience Chicago Motoneuron Excitability Location: Hall A SCI and Plasticity
Disclosures: D. Sayenko: None. D. Atkinson: None. A. Mink: None. K. Gurley: None. Y. Gerasimenko: None. S. Harkema: None.
Support: Frazier Rehab Institute and Kentucky One Health Kentucky Spinal Cord & Head Injury Research Trust Grant no. 11-7 National Institute of General Medical Sciences Grant 8 P30 GM-103507 Helmsley Foundation Grant #2011PG-MED011 Commonwealth of Kentucky Challenge of Excellence Trust Fund Owsley Brown Frazier Chair in Neurological Rehabilitation Endowment Russian Foundation for Basic Research Grant 13-04-12030 ofi-m
Authors: *D. SAYENKO1, D. ATKINSON2,3, A. MINK2,4, K. GURLEY6, Y. GERASIMENKO1,7, S. HARKEMA2,5; 1Dept. of Integrative Biol. and Physiol., Univ. of California Los Angeles, Los Angeles, CA; 2Neurosci. Collaborative Ctr., Frazier Rehab Inst., Louisville, KY; 3Dept. of Anatom. Sci. and Neurobio., 4Dept. Physiol. and Biophysics, 5Dept. of Neurolog. Surgery, Univ. of Louisville, Louisville, KY; 6Sch. of Med., Louisiana State Univ. Hlth. Sci. Ctr. New Orleans, New Orleans, LA; 7Pavlov Inst. of Physiol., St. Petersburg, Russian Federation

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