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M.A. Urbin

Goal-directed movement is possible because the cortical regions regulating movement have continuous access to visual information. Extensive research from the various domains of motor control (i.e., neurophysiology, neuropsychology, and psychophysics) has documented the extent to which the unremitting availability of visual information enables the sensorimotor system to facilitate online control of goal-directed limb movement. However, the control mechanism guiding appreciably more complex movements characterized by ballistic, whole-body coordination is not well understood. In the overarm throw, for example, joint rotations must be optimally timed between body segments to exploit the passive flow of kinetic energy and, in turn, maximize projectile speed while maintaining accuracy. The purpose of this review is to draw from the various research domains in motor control and speculate on the nature of the sensorimotor control mechanism facilitating overarm throwing performance.

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Ina M. Tarkka, Pekka Hautasaari, Heidi Pesonen, Eini Niskanen, Mirva Rottensteiner, Jaakko Kaprio, Andrej M. Savić and Urho M. Kujala

adult owl monkeys after behaviorally controlled tactile stimulation . Journal of Neurophysiology . 1990 ; 63 ( 1 ): 82 . http://jn.physiology.org/cgi/content/abstract/63/1/82 2299388 10.1152/jn.1990.63.1.82 27. Erickson KI , Leckie RL , Weinstein AM . Physical activity, fitness, and gray

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Scott C. Livingston

Edited by Monique Mokha

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Andrew Hooyman, Alexander Garbin and Beth Fisher

research . Clinical Neurophysiology, 120 ( 12 ), 2008 – 2039 . PubMed ID: 19833552 doi:10.1016/j.clinph.2009.08.016 10.1016/j.clinph.2009.08.016 Rossini , P.M. , Burke , D. , Chen , R. , Cohen , L.G. , Daskalakis , Z. , Di Iorio , R. , . . . Ziemann , U. ( 2015 ). Non-invasive electrical

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Joanne E. Folker, Bruce E. Murdoch, Louise M. Cahill, Kristin M. Rosen, Martin B. Delatycki, Louise A. Corben and Adam P. Vogel

Electromagnetic articulography (EMA) was used to investigate the tongue kinematics in the dysarthria associated with Friedreich’s ataxia (FRDA). The subject group consisted of four individuals diagnosed with FRDA. Five nonneurologically impaired individuals, matched for age and gender, served as controls. Each participant was assessed using the AG-200 EMA system during six repetitions of the tongue tip sentence Tess told Dan to stay fit and the tongue back sentence Karl got a croaking frog. Results revealed reduced speed measures (i.e., maximum acceleration / deceleration / velocity), greater movement durations and increased articulatory distances for the approach phases of consonant productions. The approach phase, involving movement up to the palate, was more affected than the release phase. It is suggested that deviant lingual kinematics could be the outcome of disturbances to cerebellar function, or possibly in combination with disturbances to upper motor neuron systems.

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Jeff A. Nessler, Tomas Gonzales, Eric Rhoden, Matthew Steinbrick and Charles J. De Leone

The purpose of this study was to examine the effects of interpersonal synchronization of stepping on stride interval dynamics during over-ground walking. Twenty-seven footswitch instrumented subjects walked under three conditions: independent (SOLO), alongside a partner (PAIRED), and side by side with intentional synchronization (FORCED). A subset of subjects also synchronized stepping to a metronome (MET). Stride time power spectral density and detrended fluctuation analysis revealed that the rate of autocorrelation decay in stride time was similar for both the SOLO and PAIRED conditions, but was significantly reduced during the FORCED and MET conditions (p=0.03 & 0.002). Stride time variability was also significantly increased for the FORCED and MET conditions (p<0.001). These data suggest that forced synchronization of stepping results in altered stride interval dynamics, likely through increased active control by the CNS. Passive side by side stepping, where synchronization is subconscious, does not appreciably alter stepping in this manner.

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Jacinto Javier Martínez-Payá, José Ríos-Díaz, María Elena del Baño-Aledo, David García-Martínez, Ana de Groot-Ferrando and Javier Meroño-Gallut

The objective of this observational cross-sectional study was to investigate the normal motion of the median nerve when stretched during a neurodynamic exercise. In recent years, ultrasonography has been increasingly accepted as an imaging technique for examining peripheral nerves in vivo, offering a reliable and noninvasive method for a precise evaluation of nerve movement. Transverse motion of the median nerve in the arm during a neurodynamic test was measured. A volunteer sample of 22 healthy subjects (11 women) participated in the study. Nerve displacement and deformation were assessed by dynamic ultrasonography. Excellent interobserver agreement was obtained, with kappa coefficient of .7–.8. Ultrasonography showed no lateral motion during wrist extension in 68% of nerves, while 73% moved dorsally, with statistically significant differences between sexes (ORlat = 6.3; 95% CI = 1.4–27.7 and ORdor = 8.3; 95% CI = 1.6–44.6). The cross-sectional area was significantly greater in men (3.6 mm2). Quantitative analysis revealed no other statistically significant differences. Our results provide evidence of substantial individual differences in median nerve transverse displacement in response to a neurodynamic exercise.

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Matt S. Stock and Brennan J. Thompson

We examined the means, medians, and variability for motor-unit interpulse intervals (IPIs) during voluntary, high force contractions. Eight men (mean age = 22 years) attempted to perform isometric contractions at 90% of their maximal voluntary contraction force while bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and vastus medialis muscles. Surface EMG signal decomposition was used to determine the recruitment thresholds and IPIs of motor units that demonstrated accuracy levels ≥ 96.0%. Motor units with high recruitment thresholds demonstrated longer mean IPIs, but the coefficients of variation were similar across all recruitment thresholds. Polynomial regression analyses indicated that for both muscles, the relationship between the means and standard deviations of the IPIs was linear. The majority of IPI histograms were positively skewed. Although low-threshold motor units were associated with shorter IPIs, the variability among motor units with differing recruitment thresholds was comparable.