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Gordineer EA, Stokic DS, Krenn MJ. Distinguishing reflex from non-reflex responses elicited by transcutaneous spinal stimulation targeting the lumbosacral cord in healthy individuals. Exp Brain Res 2024:10.1007/s00221-024-06790-2. [PMID: 38416179 DOI: 10.1007/s00221-024-06790-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2023] [Accepted: 01/21/2024] [Indexed: 02/29/2024]
Abstract
Transcutaneous spinal stimulation (TSS) studies rely on the depolarization of afferent fibers to provide input to the spinal cord; however, this has not been routinely ascertained. Thus, we aimed to characterize the types of responses evoked by TSS and establish paired-pulse ratio cutoffs that distinguish posterior root reflexes, evoked by stimulation of afferent nerve fibers, from motor responses, evoked by stimulation of efferent nerve fibers. Twelve neurologically intact participants (six women) underwent unipolar TSS (cathode over T11-12 spinal processes, anode paraumbilically) while resting supine. In six participants, unipolar TSS was repeated 2-3 months later and also compared to a bipolar TSS configuration (cathode 2.5 cm below T11-12, anode 5 cm above cathode). EMG signals were recorded from 16 leg muscles. A paired-pulse paradigm was applied at interstimulus intervals (ISIs) of 25, 50, 100, 200, and 400 ms. Responses were categorized by three assessors into reflexes, motor responses, or their combination (mixed responses) based on the visual presence/absence of paired-pulse suppression across ISIs. The paired-pulse ratio that best discriminated between response types was derived for each ISI. These cutoffs were validated by repeating unipolar TSS 2-3 months later and with bipolar TSS. Unipolar TSS evoked only reflexes (90%) and mixed responses (10%), which were mainly recorded in the quadriceps muscles (25-42%). Paired-pulse ratios of 0.51 (25-ms ISI) and 0.47 (50-ms ISI) best distinguished reflexes from mixed responses (100% sensitivity, > 99.2% specificity). These cutoffs performed well in the repeated unipolar TSS session (100% sensitivity, > 89% specificity). Bipolar TSS exclusively elicited reflexes which were all correctly classified. These results can be utilized in future studies to ensure that the input to the spinal cord originates from the depolarization of large afferents. This knowledge can be applied to improve the design of future neurophysiological studies and increase the fidelity of neuromodulation interventions.
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Affiliation(s)
- Elizabeth A Gordineer
- School of Graduate Studies in the Health Sciences, Program in Neuroscience, University of Mississippi Medical Center, Jackson, MS, USA
- Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, MS, USA
| | - Dobrivoje S Stokic
- Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, MS, USA
| | - Matthias J Krenn
- Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, MS, USA.
- Department of Neurosurgery, University of Mississippi Medical Center, 2500 N State St, Jackson, MS, 39216, USA.
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LaMarca AL, Krenn MJ, Kelso-Trass MA, MacDonald KC, Demeo CC, Bazarek SF, Brown JM. Selective Tibial Neurotomy Outcomes for Spastic Equinovarus Foot: Patient Expectations and Functional Assessment. Neurosurgery 2023; 93:1026-1035. [PMID: 37199494 DOI: 10.1227/neu.0000000000002530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 03/27/2023] [Indexed: 05/19/2023] Open
Abstract
BACKGROUND Spastic equinovarus foot (SEF) is a common dysfunctional foot posture after stroke that impairs balance and mobility. Selective tibial neurotomy (STN) is a simple but underutilized surgical option that can effectively address critical aspects of SEF and thereby provide enduring quality of life gains. There are few studies that examine both functional outcomes and patient satisfaction with this treatment option. OBJECTIVE To elucidate the patient goals that motivated their decision to undergo the procedure and compare subjective and objective changes in balance and functional mobility as a consequence of surgery. METHODS Thirteen patients with problematic SEF who had previously failed conservative measures were treated with STN. Preoperative and postoperative (on average 6 months) assessments evaluated gait quality and functional mobility. In addition, a custom survey was conducted to investigate patient perspectives on STN intervention. RESULTS The survey showed that participants who opted for STN were dissatisfied with their previous spasticity management. The most common preoperative expectation for STN treatment was to improve walking, followed by improving balance, brace comfort, pain, and tone. Postoperatively, participants rated the improvement in their expectations and were, on average, 71 on a 100-point scale, indicating high satisfaction. The gait quality, assessed with the Gait Intervention and Assessment Tool, improved significantly between preoperative and postoperative assessment (M = -4.1, P = .01) with a higher average difference in stance of -3.3 than in swing -0.5. Improvement in both gait endurance (M = 36 m, P = .01) and self-selected gait speed (M = .12 m/s, P = .03) was statistically significant. Finally, static balance (M = 5.0, P = .03) and dynamic balance (M = 3.5, P = .02) were also significantly improved. CONCLUSION STN improved gait quality and functional mobility and was associated with high satisfaction in patients with SEF.
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Affiliation(s)
- Amber L LaMarca
- Department of Neurosurgery, The Paralysis Center, Massachusetts General Hospital, Boston , Massachusetts , USA
- Rehabilitation Sciences, MGH Institute of Health Professions, Boston , Massachusetts , USA
- Physical Therapy Department, Spaulding Rehabilitation Hospital, Boston , Massachusetts , USA
| | - Matthias J Krenn
- Department of Neurosurgery, The Paralysis Center, Massachusetts General Hospital, Boston , Massachusetts , USA
- Department of Neurosurgery, University of Mississippi Medical Center, Jackson , Mississippi , USA
- Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson , Mississippi , USA
| | - Molly A Kelso-Trass
- Physical Therapy Department, Wentworth-Douglass Hospital, Dover , New Hampshire , USA
| | - Kathryn C MacDonald
- Rehabilitation Sciences, MGH Institute of Health Professions, Boston , Massachusetts , USA
- Physical Therapy Department, Spaulding Rehabilitation Hospital, Boston , Massachusetts , USA
- Physical Therapy Department, Wentworth-Douglass Hospital, Dover , New Hampshire , USA
| | - Cristina C Demeo
- Department of Neurosurgery, The Paralysis Center, Massachusetts General Hospital, Boston , Massachusetts , USA
| | - Stanley F Bazarek
- Department of Neurosurgery, The Paralysis Center, Massachusetts General Hospital, Boston , Massachusetts , USA
- Harvard Medical School, Cambridge , Massachusetts , USA
- Brigham and Women's Hospital, Boston , Massachusetts , USA
| | - Justin M Brown
- Department of Neurosurgery, The Paralysis Center, Massachusetts General Hospital, Boston , Massachusetts , USA
- Rehabilitation Sciences, MGH Institute of Health Professions, Boston , Massachusetts , USA
- Harvard Medical School, Cambridge , Massachusetts , USA
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Vargas Luna JL, Brown J, Krenn MJ, McKay B, Mayr W, Rothwell JC, Dimitrijevic MR. Neurophysiology of epidurally evoked spinal cord reflexes in clinically motor-complete posttraumatic spinal cord injury. Exp Brain Res 2021; 239:2605-2620. [PMID: 34213632 PMCID: PMC8354937 DOI: 10.1007/s00221-021-06153-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Accepted: 06/13/2021] [Indexed: 11/24/2022]
Abstract
Increased use of epidural Spinal Cord Stimulation (eSCS) for the rehabilitation of spinal cord injury (SCI) has highlighted the need for a greater understanding of the properties of reflex circuits in the isolated spinal cord, particularly in response to repetitive stimulation. Here, we investigate the frequency-dependence of modulation of short- and long-latency EMG responses of lower limb muscles in patients with SCI at rest. Single stimuli could evoke short-latency responses as well as long-latency (likely polysynaptic) responses. The short-latency component was enhanced at low frequencies and declined at higher rates. In all muscles, the effects of eSCS were more complex if polysynaptic activity was elicited, making the motor output become an active process expressed either as suppression, tonic or rhythmical activity. The polysynaptic activity threshold is not constant and might vary with different stimulation frequencies, which speaks for its temporal dependency. Polysynaptic components can be observed as direct responses, neuromodulation of monosynaptic responses or driving the muscle activity by themselves, depending on the frequency level. We suggest that the presence of polysynaptic activity could be a potential predictor for appropriate stimulation conditions. This work studies the complex behaviour of spinal circuits deprived of voluntary motor control from the brain and in the absence of any other inputs. This is done by describing the monosynaptic responses, polysynaptic activity, and its interaction through its input–output interaction with sustain stimulation that, unlike single stimuli used to study the reflex pathway, can strongly influence the interneuron circuitry and reveal a broader spectrum of connectivity.
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Affiliation(s)
- Jose Luis Vargas Luna
- Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20/4L, 1090, Vienna, Austria.
| | - Justin Brown
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St, Boston, MA, 02114, USA
| | - Matthias J Krenn
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS, 39216, USA.,Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, 1350 East Woodrow Wilson, Jackson, MS, 39216, USA
| | - Barry McKay
- Hulse S.C.I. Research Lab, Shepherd Center, 2020 Peachtree Rd NW, Atlanta, GA, 30309, USA
| | - Winfried Mayr
- Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20/4L, 1090, Vienna, Austria
| | - John C Rothwell
- Institute of Neurology, University College London, Queen Square, London, WC1N 3BG, UK
| | - Milan R Dimitrijevic
- Department of Rehabilitation and Physical Medicine, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX, 77030, USA.,Foundation for Movement Recovery, Bolette Brygge 1, 0252, Oslo, Norway
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Krenn MJ, Vargas Luna JL, Mayr W, Stokic DS. Bipolar transcutaneous spinal stimulation evokes short-latency reflex responses in human lower limbs alike standard unipolar electrode configuration. J Neurophysiol 2020; 124:1072-1082. [PMID: 32845202 DOI: 10.1152/jn.00433.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Noninvasive electrical stimulation targeting the posterior lumbosacral roots has been applied recently in reflexes studies and as a neuromodulation intervention for modifying spinal cord circuitry after an injury. Here, we characterized short-latency responses evoked by four bipolar electrode configurations placed longitudinally over the spinal column at different vertebral levels from L1 to T9. They were compared with the responses evoked by the standard unipolar (aka monopolar) electrode configuration (cathode at T11/12, anode over the abdominal wall). Short-latency responses were recorded in the rectus femoris, medial hamstrings, tibialis anterior, and soleus muscles, bilaterally, in 11 neurologically intact participants. The response recruitment characteristics (maximal amplitude, motor threshold) and amplitude-matched onset latencies and paired-pulse suppression (35-ms interstimulus interval) were assessed with 1-ms current-controlled pulses at intensities up to 100 mA. The results showed that short-latency responses can be elicited with all bipolar electrode configurations. However, only with the cathode at T11/12 and the anode 10 cm cranially (∼T9), the maximum response amplitudes were statistical equivalent (P < 0.05) in the medial hamstrings, tibialis anterior, and soleus but not the rectus femoris, whereas motor thresholds were not significantly different across all muscles. The onset latency and paired-pulse suppression were also not significantly different across the tested electrode configurations, thereby confirming the reflex nature of the bipolar short-latency responses. We conclude that the bipolar configuration (cathode T11/12, anode ∼T9) produces reflex responses that are ostensibly similar to those evoked by the standard unipolar configuration. This provides an alternative approach for neuromodulation intervention.NEW & NOTEWORTHY Transcutaneous spinal stimulation with the identified bipolar electrode configuration may offer several advantages for neuromodulation interventions over commonly used unipolar configurations: there are no associated abdominal contractions, which improves the participant's comfort; additional dermatomes are not stimulated as when the anode is over the abdominal wall or iliac crest, which may have unwanted effects; and, due to a more localized electrical field, the bipolar configuration offers the possibility of targeting cord segments more selectively.
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Affiliation(s)
- Matthias J Krenn
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi.,Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, Mississippi
| | - Jose L Vargas Luna
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Winfried Mayr
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Dobrivoje S Stokic
- Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, Mississippi
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Hofstoetter US, Freundl B, Danner SM, Krenn MJ, Mayr W, Binder H, Minassian K. Transcutaneous Spinal Cord Stimulation Induces Temporary Attenuation of Spasticity in Individuals with Spinal Cord Injury. J Neurotrauma 2019; 37:481-493. [PMID: 31333064 DOI: 10.1089/neu.2019.6588] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Epidural spinal cord stimulation (SCS) is currently regarded as a breakthrough procedure for enabling movement after spinal cord injury (SCI), yet one of its original applications was for spinal spasticity. An emergent method that activates similar target neural structures non-invasively is transcutaneous SCS. Its clinical value for spasticity control would depend on inducing carry-over effects, because the surface-electrode-based approach cannot be applied chronically. We evaluated single-session effects of transcutaneous lumbar SCS in 12 individuals with SCI by a test-battery approach, before, immediately after and 2 h after intervention. Stimulation was applied for 30 min at 50 Hz with an intensity sub-threshold for eliciting reflexes in lower extremity muscles. The tests included evaluations of stretch-induced spasticity (Modified Ashworth Scale [MAS] sum score, pendulum test, electromyography-based evaluation of tonic stretch reflexes), clonus, cutaneous-input-evoked spasms, and the timed 10 m walk test. Across participants, the MAS sum score, clonus, and spasms were significantly reduced immediately after SCS, and all spasticity measures were improved 2 h post-intervention, with large effect sizes and including clinically meaningful improvements. The effect on walking speed varied across individuals. We further conducted a single-case multi-session study over 6 weeks to explore the applicability of transcutaneous SCS as a home-based therapy. Self-application of the intervention was successful; weekly evaluations suggested progressively improving therapeutic effects during the active period and carry-over effects for 7 days. Our results suggest that transcutaneous SCS can be a viable non-pharmacological option for managing spasticity, likely working through enhancing pre- and post-synaptic spinal inhibitory mechanisms, and may additionally serve to identify responders to treatments with epidural SCS.
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Affiliation(s)
- Ursula S Hofstoetter
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Brigitta Freundl
- Neurological Center, SMZ Baumgartner Hoehe, Otto-Wagner-Hospital, Vienna, Austria
| | - Simon M Danner
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Matthias J Krenn
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi.,Center for Neuroscience and Neurological Recovery, Methodist Rehabilitation Center, Jackson, Mississippi
| | - Winfried Mayr
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Heinrich Binder
- Neurological Center, SMZ Baumgartner Hoehe, Otto-Wagner-Hospital, Vienna, Austria
| | - Karen Minassian
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
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Krenn MJ, Whiteley JH. Perception of figure orientation by nonambulatory children with profound mental retardation. Percept Mot Skills 1990; 70:867-70. [PMID: 2143012 DOI: 10.2466/pms.1990.70.3.867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
An habituation-dishabituation procedure was used to study perception of changes in figure orientation by nonambulatory children with profound mental retardation. On each of 3 days, 16 participants were given familiarization trials with either a vertical or an horizontal pattern, followed by test trials with the familiarized stimulus and one of three novel stimuli--a 90 degree or 45 degree rotation of the pattern, or a rearrangement of the pattern elements into a square. Visual fixation times decreased over familiarization trials. Fixation times on test trials were longer for novel than for familiar stimuli, indicating that these children discriminated changes in form and orientation.
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Affiliation(s)
- M J Krenn
- Department of Psychology, University of Manitoba, Winnipeg, Canada
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Whiteley JH, Krenn MJ. Uses of the Bayley mental scale with nonambulatory profoundly mentally retarded children. Am J Ment Defic 1986; 90:425-31. [PMID: 3946478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A set of 45 mental scale items from the Bayley Scales of Infant Development was administered by two testers to 33 nonambulatory, profoundly mentally retarded subjects. Interobserver agreement was high for overall scores and for 42 of 45 individual items. Total number of items passed was significantly correlated with activity level. Division of these items into a stimulus set and a response set provided a qualitative description of performance that supported previous research indicating that these individuals have deficits in exploratory motivation and perceptual curiosity. Bayley raw scores predicted success in conditioning programs, suggesting that this test is useful for educational programming.
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