Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Randomized Controlled Trial Controlled Clinical Trial
Effects of NGF-induced muscle sensitization on proprioception and nociception.
Temporomandibular disorders (TMDs) are associated with perturbation of proprioceptive and nociceptive function. Recent studies have shown that injection of the neurotrophic protein nerve growth factor (NGF) into the masseter muscle causes sensitization to mechanical pressure stimuli; however, it is not clear if vibration sense and jaw stretch reflexes as measures of proprioceptive function as well as glutamate-evoked pain are also altered. We tested the hypothesis that NGF-induced mechanical sensitization would be associated with changes in vibration sense and stretch reflex sensitivity as well as facilitation of glutamate-evoked pain responses. ⋯ In conclusion, this study confirms that masseter muscle injection of NGF is associated with a distinct and prolonged sensitization to mechanical stimuli, but without an effect on large-diameter mechanoreceptive and the muscle spindle afferents. Additional challenge of the NGF pretreated muscle with glutamate did not indicate a conspicuous sensitization to noxious chemical stimuli. These findings are discussed in terms of the concept of "proprioceptive allodynia".
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Randomized Controlled Trial Controlled Clinical Trial
Induction of muscle cramps by nociceptive stimulation of latent myofascial trigger points.
The aim of this present study is to test the hypothesis that nociceptive stimulation of latent myofascial trigger points (MTrPs) increases the occurrence of local muscle cramps. Nociceptive muscle stimulation was obtained by a bolus injection of glutamate (0.1 ml, 0.5 M) into a latent MTrP and a control point (a non-MTrP) located in the right or left gastrocnemius medialis muscles in 14 healthy subjects. A bolus of isotonic saline (0.9%, 0.1 ml) injection served as a control. ⋯ No muscle cramps were recorded following isotonic saline injection into either the latent MTrPs or the non-MTrPs. These results suggest that latent MTrPs could be involved in the genesis of muscle cramps. Focal increase in nociceptive sensitivity at MTrPs constitutes one of the mechanisms underlying muscle cramps.
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This paper contrasts responses in the soleus muscle of normal human subjects to two major inputs: the tibial nerve (TN) and the corticospinal tract. Paired transcranial magnetic stimulation (TMS) of the motor cortex at intervals of 10-25 ms strongly facilitated the motor evoked potential (MEP) produced by the second stimulus. In contrast, paired TN stimulation produced a depression of the reflex response to the second stimulus. ⋯ When TN and TMS pulses were paired, the largest facilitation occurred when TMS preceded TN by about 5 ms, which is optimal for summation of the two pathways at the level of the spinal motor neurons. A later, smaller facilitation occurred when a single TN stimulus preceded TMS by 50-60 ms, an interval that allows enough time for the sensory afferent input to reach the sensory cortex and be relayed to the motor cortex. Other work indicates that repetitively pairing nerve stimuli and TMS at these intervals, known as paired associative stimulation, produces long-term increases in the MEP and may be useful in strengthening residual pathways after damage to the central nervous system.
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Recent functional neuroimaging and lesion studies demonstrate the involvement of the orbitofrontal/ventromedial prefrontal cortex as a key structure in decision making processes. This region seems to be particularly crucial when contingencies between options and consequences are unknown but have to be learned by the use of feedback following previous decisions (decision making under ambiguity). However, little is known about the neural correlates of decision making under risk conditions in which information about probabilities and potential outcomes is given. ⋯ In contrast to previous decision making studies, we completely removed the outcome phase following a decision to exclude the potential influence of feedback previously received on current decisions. The results indicate that the integration of information about probabilities and incentives leads to activations within the dorsolateral prefrontal cortex, the posterior parietal lobe, the anterior cingulate and the right lingual gyrus. We assume that this pattern of activation is due to the involvement of executive functions, conflict detection mechanisms and arithmetic operations during the deliberation phase of decisional processes that are based on explicit information.
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The purpose of the present study was to investigate the coordination of the two effectors when one or both targets were displaced in a bimanual prehension task. Sixteen right-handed volunteers were asked to reach 20 cm to grasp and lift two cubic objects with the right and left hands. Upon initiation of the reach: (1) both objects could remain at the initial position (NN); (2) the right object could be displaced toward the subject (NJ); (3) the left object could be displaced (JN); or (4) both objects could be displaced (JJ). ⋯ Furthermore, subjects' expectations about the performance and goal of the task could have a further influence on the level of interference seen during bimanual movements. Finally, despite interference effects which caused multiple accelerations and decelerations, the hand moving to the non-perturbed target still achieved the target location in the same movement time as during control conditions. This final result indicates the efficiency with which subjects can reorganize both limbs in the face of altered task requirements.