Search results for "Motor"
showing 10 items of 3137 documents
Does the Recruitment of Excitation and Inhibition in the Motor Cortex Differ?
2007
The level of excitability within the motor cortex can be described as a balance between excitation and inhibition, but it is unknown how well both processes correlate. To address this question, the authors measured motor cortical excitability and inhibition in healthy human subjects, comparing the recruitment of motor evoked potentials (MEPs) and the duration of the cortical silent period (CSP) after transcranial magnetic stimulation (TMS). Single-pulse "focal" TMS was applied at intensities varying between 90% and 200% of motor thresholds to the right motor cortex of 15 healthy volunteers. The peak-to peak size of MEP responses and the duration of the CSP were measured in small hand muscle…
The effects of a startle on awareness of action
2003
The execution of a ballistic movement within a reaction time task paradigm is significantly speeded up when an unexpected startling auditory stimulus (SAS) is delivered together with the imperative signal. Using Libet's clock, we investigated whether acceleration involves also the subjective appraisal of the time of task execution. In trials containing the SAS, reaction time shortened to 68.7% of control values. However, subjective judgment of task execution remained a similar time with respect to the imperative signal as in control trials. The dissociation between task execution and its subjective perception indicates the existence of separate circuits for action execution and action aware…
Reduced reflex sensitivity persists several days after long-lasting stretch-shortening cycle exercise
1999
The mechanisms related to the acute and delayed secondary impairment of the stretch reflex function were investigated after long-lasting stretch-shortening cycle exercise. The results demonstrated a clear deterioration in muscle function immediately after fatigue, which was accompanied by a clear reduction in active and passive reflex sensitivity. For active and passive stretch reflexes, this reduction was biphasic ( P < 0.05 to P < 0.001). However, for the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential, only one significant reduction was seen immediately after fatigue (71.2%, P < 0.01). A similar significant ( P < 0.01) d…
Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches
2004
Experiments were carried out to examine interaction between mechanical changes of the muscletendon unit and reduced reflex sensitivity after repeated and prolonged passive muscle stretching (RPS). There is some evidence that this interaction might be relevant also during active stretch-shortening cycle type of fatigue tasks. The results demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions after RPS. Maximal voluntary contraction (MVC), average electromyographic activities of the gastrocnemius and soleus muscles, and maximal twitch contraction decreased on average by 13.8, 10.4, 7.6, and 16.8%, respectively. In addition, there was a 14% lengthening …
Disturbed motor control of rhythmic movement at 2 h and delayed after maximal eccentric actions.
2008
The aim of this study was to examine the influence of exercise-induced muscle damage on elbow rhythmic movement (RM) performance and neural activity pattern and to investigate whether this influence is joint angle specific. Ten males performed an exercise of 50 maximal eccentric elbow flexions in isokinetic machine with duty cycle of 1:15. Maximal dynamic and isometric force tests (90 degrees , 110 degrees and 130 degrees elbow angle) and both active and passive stretch reflex tests of elbow flexors were applied to the elbow joint. The intentional RM was performed in the horizontal plane at elbow angles; 60-120 degrees (SA-RM), 80-140 degrees (MA-RM) and 100-160 degrees (LA-RM). All measure…
Neuromuscular changes after long-lasting mechanically and electrically elicited fatigue
2001
Central fatigue was investigated under an isolated active condition whereby the possible effects of supraspinal fatigue were minimized. Therefore, ten subjects were fatigued by simultaneously and repeatedly mechanically stretching and electrically stimulating their calf muscles for 1 h. This was performed using an ankle ergometer. The active fatigue task included a total of 2400 muscle stretches with an intensity of 10% of the maximal voluntary contraction (MVC). This protocol clearly impaired neuromuscular function, as revealed by a significant reduction in MVC (P < 0.01) and the neural input to the muscle (average EMG) (P < 0.01-0.001). The interpolated nerve stimulation compensated for t…
Analysis of F response in upper motoneurone lesions
2009
The F response can provide a measure of motoneurone excitability (MNE) and so it may be used to investigate upper motoneurone disorders. This report studies the F-wave configuration in patients with stroke to evaluate the changes of the central excitability of the motoneurones at different times after an acute cerebral insult. Various parameters of the F response, including amplitude (absolute and F%/M), duration, and persistence have been determined in 26 patients with unilateral hemiplegia and in 32 healthy subjects of both sexes in the same age range. The investigation was carried out applying a series of 20 supramaximal stimuli at 0.5 Hz on tibial and ulnar nerves bilaterally. In all pa…
Heart rate variability related to effort at work
2011
Changes in autonomic nervous system function have been related to work stress induced increases in cardiovascular morbidity and mortality. Our purpose was to examine whether various heart rate variability (HRV) measures and new HRV-based relaxation measures are related to self-reported chronic work stress and daily emotions. The relaxation measures are based on neural network modelling of individual baseline heart rate and HRV information. Nineteen healthy hospital workers were studied during two work days during the same work period. Daytime, work time and night time heart rate, as well as physical activity were recorded. An effort-reward imbalance (ERI) questionnaire was used to assess ch…
Subthreshold low frequency repetitive transcranial magnetic stimulation selectively decreases facilitation in the motor cortex
2002
Objective: To investigate the modulatory effect of a subthreshold low frequency repetitive transcranial magnetic stimulation (rTMS) train on motor cortex excitability. Methods: The study consisted of two separate experiments. Subjects received a 10 min long subthreshold 1Hz rTMS train. In the first experiment, (single pulse paradigm), cortical excitability was assessed by measuring the amplitude of motor evoked potentials (MEPs) before and after the rTMS train. In the second experiment, a paired pulse paradigm was employed. Results: Corticospinal excitability, as measured by the MEP amplitude, was reduced by the rTMS train (experiment 1), with a significant effect lasting for about 10 min a…
Modulation of input–output curves by low and high frequency repetitive transcranial magnetic stimulation of the motor cortex
2002
Objectives: Exploring the modulatory effects of different frequencies of repetitive transcranial magnetic stimulation (rTMS) on the excitability of the motor cortex as measured by the input-output curve technique (I-O curve). Methods: Sixteen healthy subjects participated in this experiment. On two different sessions, conducted 1 week apart, rTMS was applied either at a frequency of 20 or 1Hz at 90% of individual motor threshold (MT) for a total of 1600 pulses each. Before and after rTMS, the cortical excitability was assessed by measuring MT and the size of motor evoked potentials (MEPs) collected at different intensities of stimulation. Results: The analysis on the whole population showed…