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Anastasopoulos D, Anastasopoulos L, Mergner T. Voluntary suppression of neck reflexes during passive head-on-trunk rotations - reflex gain control vs. proprioceptive feedback. J Neurophysiol 2021; 127:161-172. [PMID: 34907798 PMCID: PMC8858664 DOI: 10.1152/jn.00297.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Normal subjects can completely eliminate resistance upon imposed head-on-trunk rotations when they are asked to relax. It is not, however, clear how neck reflexes to stretch can be voluntarily suppressed. Reflexive responses might be modified by adjusting the gain of the reflex loop through descending control. Theoretically, necessary corrections upon interfering disturbances during coordinated motor performance requiring the interplay of relaxation/activation may be missing if muscle relaxation is taking place exclusively by this mechanism. It has been alternatively proposed that sensory information from the periphery may be allowed to “neutralize” neck reflexes if it is fed back with opposite sign to the structures driving the reflexes. Six healthy subjects were asked to relax while subjected to head-on-trunk rotations generated by a head motor. After any initial resistance had completely subsided, the head was unexpectedly exposed to “ramp-and-hold” perturbations of up to 2° amplitude and 0.7 s duration. Resistance to stretch consistently reappeared thereupon, suggesting that stretch reflex gain had not been set to zero during the previously achieved complete relaxation. Resistance to perturbations under these circumstances was compared with the forces generated when the same ramp-and-hold displacements were delivered unpredictably to the head held stationary. A quantitative model of neck proprioceptive reflexes suppression has been thus constructed. Gain scheduling or “motor set” cannot sufficiently account for the voluntary reflex suppression during slow passive head rotations. Instead, we propose as underlying mechanism, the “neutralization” of the controlling servo by means of continuous feedback tracking displacement and force signals from the periphery. NEW & NOTEWORTHY Head stabilizing neck reflexes can be voluntarily suppressed or activated depending on the task at hand. By applying brief perturbations unexpectedly, both during passive head-on-trunk movements and at rest, we investigated the mechanism of voluntary suppression of resistance to stretch. A physiologically plausible, neuromechanical model of voluntary/reflexive interactions was constructed favoring feedback over reflex gain adjustments. Accordingly, muscle relaxation during imposed head movements is based on sensory feedback similarly to muscle contractions during purposeful movements.
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Affiliation(s)
- Dimitri Anastasopoulos
- Department of Neurorehabilitation, Zurzachcare, Bad Zurzach, Switzerland.,Department of Physiology, University of Athens, Athens, Greece
| | | | - Thomas Mergner
- Department of Neurology, University of Freiburg, Germany
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BULBOACA AE, STANESCU I, NICULA C, BULBOACA A. Neuroplasticity pathophysiological mechanisms underlying neuro-optometric rehabilitation in ischemic stroke – a brief review. BALNEO AND PRM RESEARCH JOURNAL 2021. [DOI: 10.12680/balneo.2021.412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Neuroplasticity is an essential phenomenon underlying on neurorehabilitation process, by which the brain can remodel the dysfunction consequent to a lesion. Ischemic brain lesions are the most frequent brain lesions often associated with visual function disability. Experimental and clinical studies established that visual function disability can impede the neurorehabilitation therapy efficiency. Neuro-optometric therapy has been proved to significantly improve the patient outcome after brain lesions. The pathophysiological mechanisms underlying this process are yet to be deciphered. Current knowledge regarding the pathophysiological mechanisms involved in ischemic lesions and neuroplasticity as a reparation process offers real support to a more efficient neurorehabilitation therapy that can contribute to the improvement of life quality in stroke patients.
Keywords: neuroplasticity, neuro-optometric rehabilitation, ischemic stroke,
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Affiliation(s)
- Adriana Elena BULBOACA
- Functional Biosciences Department, University of Medicine and Pharmacy “Iuliu Hatieganu”, Cluj-Napoca, Romania, Clinical Rehabilitation Hospital, Cluj-Napoca, Romania
| | - Ioana STANESCU
- Neurosciences Department, University of Medicine and Pharmacy “Iuliu Hatieganu”, Cluj-Napoca, Romania, Clinical Rehabilitation Hospital, Cluj-Napoca, Romania
| | - Cristina NICULA
- Neurosciences Department, University of Medicine and Pharmacy “Iuliu Hatieganu”, Cluj-Napoca, Romania, Clinical Rehabilitation Hospital, Cluj-Napoca, Romania
| | - Angelo BULBOACA
- Neurosciences Department, University of Medicine and Pharmacy “Iuliu Hatieganu”, Cluj-Napoca, Romania, Clinical Rehabilitation Hospital, Cluj-Napoca, Romania
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Chen PY, Jheng YC, Huang SE, Po-Hung Li L, Wei SH, Schubert MC, Kao CL. Gaze shift dynamic visual acuity: A functional test of gaze stability that distinguishes unilateral vestibular hypofunction. J Vestib Res 2021; 31:23-32. [PMID: 33325420 PMCID: PMC9249280 DOI: 10.3233/ves-201506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND: Embedded within most rapid head rotations are gaze shifts, which is an initial eye rotation to a target of interest, followed by a head rotation towards the same target. Gaze shifts are used to acquire an image that initially is outside of the participant’s current field of vision. Currently, there are no tools available that evaluate the functional relevance of a gaze shift. OBJECTIVE: The purpose of our study was to measure dynamic visual acuity (DVA) while performing a gaze shift. METHODS: Seventy-one healthy participants (42.79±16.89 years) and 34 participants with unilateral vestibular hypofunction (UVH) (54.59±20.14 years) were tested while wearing an inertial measurement unit (IMU) sensor on the head and walking on a treadmill surrounded by three monitors. We measured visual acuity during three subcomponent tests: standing (static visual acuity), while performing an active head rotation gaze shift, and an active head rotation gaze shift while walking (gsDVAw). RESULTS: While doing gsDVAw, patients with Left UVH (n = 21) had scores worse (p = 0.023) for leftward (0.0446±0.0943 LogMAR) head rotation compared with the healthy controls (–0.0075±0.0410 LogMAR). Similarly, patients with right UVH (N = 13) had worse (p = 0.025) gsDVAw for rightward head motion (0.0307±0.0481 LogMAR) compared with healthy controls (–0.0047±0.0433 LogMAR). As a whole, gsDVAw scores were worse in UVH compared to the healthy controls when we included the ipsilesional head rotation on both sides gsDVAw (0.0061±0.0421 LogMAR healthy vs. 0.03926±0.0822 LogMAR UVH, p = 0.003). Controlling for age had no effect, the gsDVAw scores of the patients were always worse (p < 0.01). CONCLUSION: The gaze shift DVA test can distinguish gaze stability in patients with UVH from healthy controls. This test may be a useful measure of compensation for patients undergoing various therapies for their vestibular hypofunction.
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Affiliation(s)
- Po-Yin Chen
- Department of Physical Medicine and Rehabilitation, Taipei Veterans General Hospital, Taipei, Taiwan, ROC.,School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Center for Intelligent Drug Systems and Smart Bio-devices-IDS2B, National Chiao Tung University, Hsinchu, Taiwan, ROC.,Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Ying-Chun Jheng
- Department of Physical Medicine and Rehabilitation, Taipei Veterans General Hospital, Taipei, Taiwan, ROC.,School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Center for Intelligent Drug Systems and Smart Bio-devices-IDS2B, National Chiao Tung University, Hsinchu, Taiwan, ROC.,Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Shih-En Huang
- Department of Physical Medicine and Rehabilitation, Taipei Veterans General Hospital, Taipei, Taiwan, ROC.,School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Center for Intelligent Drug Systems and Smart Bio-devices-IDS2B, National Chiao Tung University, Hsinchu, Taiwan, ROC.,Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Lieber Po-Hung Li
- School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Department of Otolaryngology, Cheng Hsin General Hospital, Taipei, Taiwan, ROC.,Faculty of Medicine and Institute of Brain Science, School of Medicine, National Yang Ming University, Taipei, Taiwan, ROC
| | - Shun-Hwa Wei
- Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Michael C Schubert
- Laboratory of Vestibular NeuroAdaptation, Johns Hopkins University School of Medicine, Department of Otolaryngology Head and Neck Surgery, Department of Physical Medicine and Rehabilitation, Baltimore MD USA
| | - Chung-Lan Kao
- Department of Physical Medicine and Rehabilitation, Taipei Veterans General Hospital, Taipei, Taiwan, ROC.,School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Center for Intelligent Drug Systems and Smart Bio-devices-IDS2B, National Chiao Tung University, Hsinchu, Taiwan, ROC
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