Journal of neurophysiology
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Comparative Study
Hemispheric differences in the relationship between corticomotor excitability changes following a fine-motor task and motor learning.
Motor performance induces a postexercise increase in corticomotor excitability that may be associated with motor learning. We investigated whether there are hemispheric differences in the extent and/or time course of changes in corticomotor excitability following a manipulation task (Purdue pegboard) and their relationship with motor performance. Single- and paired-pulse (3 ms) transcranial magnetic stimulation (TMS) was used to assess task-induced facilitation of the muscle evoked potential (MEP) and intracortical inhibition (ICI) for three intrinsic hand muscles acting on digits 1, 2, and 5. ⋯ We conclude that the pegboard task induces a selective, short-lasting change in excitability of corticospinal neurons controlling intrinsic hand muscles engaged in the task. Only left hemisphere changes were related to motor learning. This asymmetry may reflect different behavioral strategies for performance improvement with left and right upper limb in this task or hemispheric differences in the control of skilled hand movements.
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Comparative Study
Effect of rhythmic arm movement on reflexes in the legs: modulation of soleus H-reflexes and somatosensory conditioning.
During locomotor tasks such as walking, running, and swimming, the arms move rhythmically with the legs. It has been suggested that connections between the cervical and lumbosacral spinal cord may mediate some of this interlimb coordination. However, it is unclear how these interlimb pathways modulate reflex excitability during movement. ⋯ Therefore modulation occurred at a pre-motoneuronal level, probably by presynaptic inhibition of the IA afferent volley. Results indicate that neural networks coupling the cervical and lumbosacral spinal cord in humans are activated during rhythmic arm movement. It is proposed that activation of these networks may assist in reflex linkages between the arms and legs during locomotor tasks.
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Comparative Study
Spontaneous REM sleep is modulated by the activation of the pedunculopontine tegmental GABAB receptors in the freely moving rat.
Considerable evidence suggests that the neurotransmitter gamma-aminobutyric acid (GABA)-ergic system and pedunculopontine tegmentum (PPT) in the brain stem are critically involved in the regulation of rapid-eye-movement (REM) sleep. GABA and its various receptors are normally present in the PPT cholinergic cell compartment. The aim of this study was to identify the role of GABA and its receptors in the regulation of REM sleep. ⋯ In another eight freely moving rats, effects of baclofen application was tested on firing rates of REM-on cells (n = 12). Of those 12 neurons, 11 stopped firing immediately after application of baclofen [latency: 50 +/- 14 s (SD)] and remained almost silent for 130 +/- 12 min. Findings of the present study provide direct evidence that the PPT GABAB receptors and REM-on cells are involved in the regulation of REM sleep.
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Clinical Trial
Effect of experimental muscle pain on motor unit firing rate and conduction velocity.
The aim of this human study was to investigate the relationship between experimentally induced muscle pain intensity (i.e., amount of nociceptive activity) and motor unit (MU) firing decrease and MU conduction velocity (CV). In 12 healthy subjects, nociceptive afferents were stimulated in the right tibialis anterior muscle by three intramuscular injections of hypertonic saline (0.2, 0.5, and 0.9 ml) separated by 140 s. The subjects performed six isometric contractions (20 s long) at 10% of the maximal voluntary contraction during the experimental muscle pain. ⋯ Progressively increased muscle pain intensity causes a gradual decrease of MU firing rates. This decrease is not associated with a change in MU membrane properties, indirectly assessed by CV. This study demonstrates a central inhibitory motor control mechanism with an efficacy correlated to the nociceptive activity.
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The origin of variability in goal-directed movements is not well understood. Variability can originate from several neural processes such as target localization, movement planning, and movement execution. Here we examine variability resulting from noise in movement execution. ⋯ We show that the variability observed in these experiments cannot be explained by planning noise but is well explained by noise in movement execution. A combination of both signal-dependent and signal-independent noise in the amplitude of the motor commands and temporal noise in their duration can explain the observed variability. Our results suggest that, in general, execution noise accounts for at least a large proportion of movement variability.