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Short-Interval Cortical Inhibition and Intracortical Facilitation during Submaximal Voluntary Contractions Changes with Fatigue

This study determined whether short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) change during a sustained submaximal isometric contraction. On 2 days, 12 participants (6 men, 6 women) performed brief (7-s) elbow flexor contractions before and after a 10-min fatiguing contraction; all contractions were performed at the level of integrated electromyographic activity (EMG) which produced 25 % maximal unfatigued torque. During the brief 7-s and 10-min submaximal contractions, single (test) and paired (conditioning–test) transcranial magnetic stimuli were applied over the motor cortex (5 s apart) to elicit motor-evoked potentials (MEPs) in biceps brachii. SICI and ICF were elicited on separate days, with a conditioning–test interstimulus interval of 2.5 and 15 ms, respectively. On both days, integrated EMG remained constant while torque fell during the sustained contraction by ~51.5 % from control contractions, perceived effort increased threefold, and MVC declined by 21–22 %. For SICI, the conditioned MEP during control contractions (74.1 ± 2.5 % of unconditioned MEP) increased (less inhibition) during the sustained contraction (last 2.5 min: 86.0 ± 5.1 %; P \u3c 0.05). It remained elevated in recovery contractions at 2 min (82.0 ± 3.8 %; P \u3c 0.05) and returned toward control at 7-min recovery (76.3 ± 3.2 %). ICF during control contractions (conditioned MEP 129.7 ± 4.8 % of unconditioned MEP) decreased (less facilitation) during the sustained contraction (last 2.5 min: 107.6 ± 6.8 %; P \u3c 0.05) and recovered to 122.8 ± 4.3 % during contractions after 2 min of recovery. Both intracortical inhibitory and facilitatory circuits become less excitable with fatigue when assessed during voluntary activity, but their different time courses of recovery suggest different mechanisms for the fatigue-related changes of SICI and ICF

Functional Role of Neural Injury in Obstructive Sleep Apnea

The causes of obstructive sleep apnea (OSA) are multifactorial. Neural injury affecting the upper airway muscles due to repetitive exposure to intermittent hypoxia and/or mechanical strain resulting from snoring and recurrent upper airway closure have been proposed to contribute to OSA disease progression. Multiple studies have demonstrated altered sensory and motor function in patients with OSA using a variety of neurophysiological and histological approaches. However, the extent to which the alterations contribute to impairments in upper airway muscle function, and thus OSA disease progression, remains uncertain. This brief review, primarily focused on data in humans, summarizes: (1) the evidence for upper airway sensorimotor injury in OSA and (2) current understanding of how these changes affect upper airway function and their potential to change OSA progression. Some unresolved questions including possible treatment targets are noted

Visual Experiences during Paralysis

Rationale: Paralyzed human volunteers (n = 6) participated in several studies the primary one of which required full neuromuscular paralysis while awake. After the primary experiment, while still paralyzed and awake, subjects undertook studies of humor and of attempted eye-movement. The attempted eye-movements tested a central, intentional component to one’s internal visual model and are the subject of this report. Methods: Subjects reclined in a supportive chair and were ventilated after paralysis (cisatracurium, 20 mg intravenously). In illumination, subjects were requested to focus alternately on the faces of investigators standing on the left and the right within peripheral vision. In darkness, subjects were instructed to look away from a point source of light. Subjects were to report their experiences after reversal of paralysis. Results: During attempted eye-movement in illumination, one subject had an illusion of environmental movement but four subjects perceived faces as clearly as if they were in central vision. In darkness, four subjects reported movement of the target light in the direction of attempted eye-movements and three could control the movement of the light at will. Conclusion: The hypothesis that internal visual models receive intended ocular-movement-information directly from oculomotor centers is strengthened by this evidence

Visual Experiences during Paralysis

Rationale: Paralyzed human volunteers (n = 6) participated in several studies the primary one of which required full neuromuscular paralysis while awake. After the primary experiment, while still paralyzed and awake, subjects undertook studies of humor and of attempted eye-movement. The attempted eye-movements tested a central, intentional component to one’s internal visual model and are the subject of this report. Methods: Subjects reclined in a supportive chair and were ventilated after paralysis (cisatracurium, 20 mg intravenously). In illumination, subjects were requested to focus alternately on the faces of investigators standing on the left and the right within peripheral vision. In darkness, subjects were instructed to look away from a point source of light. Subjects were to report their experiences after reversal of paralysis. Results: During attempted eye-movement in illumination, one subject had an illusion of environmental movement but four subjects perceived faces as clearly as if they were in central vision. In darkness, four subjects reported movement of the target light in the direction of attempted eye-movements and three could control the movement of the light at will. Conclusion: The hypothesis that internal visual models receive intended ocular-movement-information directly from oculomotor centers is strengthened by this evidence

Proprioceptive Movement Illusions Due to Prolonged Stimulation: Reversals and Aftereffects

Background. Adaptation to constant stimulation has often been used to investigate the mechanisms of perceptual coding, but the adaptive processes within the proprioceptive channels that encode body movement have not been well described. We investigated them using vibration as a stimulus because vibration of muscle tendons results in a powerful illusion of movement. Methodology/Principal Findings. We applied sustained 90 Hz vibratory stimulation to biceps brachii, an elbow flexor and induced the expected illusion of elbow extension (in 12 participants). There was clear evidence of adaptation to the movement signal both during the 6-min long vibration and on its cessation. During vibration, the strong initial illusion of extension waxed and waned, with diminishing duration of periods of illusory movement and occasional reversals in the direction of the illusion. After vibration there was an aftereffect in which the stationary elbow seemed to move into flexion. Muscle activity shows no consistent relationship with the variations in perceived movement. Conclusion. We interpret the observed effects as adaptive changes in the central mechanisms that code movement in direction-selective opponent channels

Motor cortical excitability and pre-supplementary motor area neurochemistry in healthy adults with substantia nigra hyperechogenicity

Substantia nigra (SN) hyperechogenicity, viewed with transcranial ultrasound, is a risk marker for Parkinson\u27s disease. We hypothesized that SN hyperechogenicity in healthy adults aged 50 – 70 years is associated with reduced short-interval intracortical inhibition in primary motor cortex, and that the reduced intracortical inhibition is associated with neurochemical markers of activity in the pre-supplementary motor area (pre-SMA). Short-interval intracortical inhibition and intracortical facilitation in primary motor cortex was assessed with paired-pulse transcranial magnetic stimulation in 23 healthy adults with normal (n = 14; 61 ± 7 yrs) or abnormally enlarged (hyperechogenic; n = 9; 60 ± 6 yrs) area of SN echogenicity. Thirteen of these participants (7 SN − and 6 SN+) also underwent brain magnetic resonance spectroscopy to investigate pre-SMA neurochemistry. There was no relationship between area of SN echogenicity and short-interval intracortical inhibition in the ipsilateral primary motor cortex. There was a significant positive relationship, however, between area of echogenicity in the right SN and the magnitude of intracortical facilitation in the right (ipsilateral) primary motor cortex (p = .005; multivariate regression), evidenced by the amplitude of the conditioned motor evoked potential (MEP) at the 10 – 12 ms interstimulus interval. This relationship was not present on the left side. Pre-SMA glutamate did not predict primary motor cortex inhibition or facilitation. The results suggest that SN hyperechogenicity in healthy older adults may be associated with changes in excitability of motor cortical circuitry. The results advance understanding of brain changes in healthy older adults at risk of Parkinson\u27s disease

Consensus for experimental design in electromyography (CEDE) project:Checklist for reporting and critically appraising studies using EMG (CEDE-Check)

The diversity in electromyography (EMG) techniques and their reporting present significant challenges across multiple disciplines in research and clinical practice, where EMG is commonly used. To address these challenges and augment the reproducibility and interpretation of studies using EMG, the Consensus for Experimental Design in Electromyography (CEDE) project has developed a checklist (CEDE-Check) to assist researchers to thoroughly report their EMG methodologies. Development involved a multi-stage Delphi process with seventeen EMG experts from various disciplines. After two rounds, consensus was achieved. The final CEDE-Check consists of forty items that address four critical areas that demand precise reporting when EMG is employed: the task investigated, electrode placement, recording electrode characteristics, and acquisition and pre-processing of EMG signals. This checklist aims to guide researchers to accurately report and critically appraise EMG studies, thereby promoting a standardised critical evaluation, and greater scientific rigor in research that uses EMG signals. This approach not only aims to facilitate interpretation of study results and comparisons between studies, but it is also expected to contribute to advancing research quality and facilitate clinical and other practical applications of knowledge generated through the use of EMG.</p

Commentaries on Viewpoint: The ongoing need for good physiological investigation: Obstructive sleep apnea in HIV patients as a paradigm

The final publication is available via http://dx.doi.org/10.1152/japplphysiol.00989.2014[Abstract] The intriguing paradigm put forth by Darquenne et al. (3) highlighted that improved therapy against human immunodeficiency virus (HIV) has come at the cost of elevated rates of chronic diseases, such as obstructive sleep apnea (OSA) and obesity, during the highly active antiretroviral therapy (HAART) era.Ministerio de Economía y Competitividad; TIN2013-40686-P