Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Temporomandibular disorders (TMD) are common pain problems in the population with uncertain pathophysiology and mechanisms. The aim of this experimental study was to: (1) Establish an experimental pain model using electrical stimuli to describe characteristics of nociception from the human temporomandibular joint (TMJ) and overlying skin. (2) Test the hypothesis that there would be sex-related differences in TMJ sensitivity. Forty-three healthy subjects (24 men and 19 women) participated. ⋯ The mechanisms underlying these findings are not clear but differences in the induction of long-term potentiation and depression is a possibility. From a clinical point of view, the lack of sex differences in most of the used measures indicates that the higher prevalence of women than men amongst patients with persistent TMJ pain problems not entirely can be ascribed to a higher sensitivity of the TMJ. Further studies will examine the somatosensory sensitivity of patients with TMJ pain problems.
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Lengthening and shortening contractions are the fundamental patterns of muscle activation underlying various movements. It is still unknown whether or not there is a muscle-specific difference in such a fundamental pattern of muscle activation. The purpose of this study was, therefore, to investigate whether or not the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability in the first dorsal interosseus (FDI) muscle is the same as that of previously tested muscles because the hand muscles are anatomically and functionally different from the other muscles. ⋯ These findings were different from the results of other muscles tested in previous studies (i.e., the soleus muscle and the elbow flexors). That is to say, the plateau value and the maximum slope during lengthening contractions were significantly lower than those during shortening contractions in previous studies. This study provides tentative evidence that the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability differs between muscles, indicating that the underlying neural control is not necessarily the same even though the fundamental patterns of muscle activation are carried out.
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We have previously proposed a model of motor lateralization, in which the two arms are differentially specialized for complementary control processes. During aimed movements, the dominant arm shows advantages for coordinating intersegmental dynamics as required for specifying trajectory speed and direction, while the nondominant arm shows advantages in controlling limb impedance, as required for accurate final position control. We now directly test this model of lateralization by comparing performance of the two arms under two different tasks: one in which reaching movement is made from one fixed starting position to three different target positions; and the other in which reaching is made from three different starting positions to one fixed target position. ⋯ In contrast, nondominant arm performance was most accurate when reaching toward a single target from multiple start locations. These findings contradict the idea that motor lateralization reflects a global advantage of one "dominant" hemisphere/limb system. Instead, each hemisphere/limb system appears specialized for stabilizing different aspects of task performance.
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The aim of the study was to examine the effect of experimental unilateral upper trapezius muscle pain on the relative activation of trapezius muscle subdivisions bilaterally during repetitive movement of the upper limb. Surface EMG signals were detected from nine healthy subjects from the upper, middle and lower divisions of trapezius during a repetitive bilateral shoulder flexion task. Measurements were performed before and after injection of 0.5 ml hypertonic (pain condition) and isotonic (control) saline into the upper division of the right trapezius muscle in two experimental sessions. ⋯ On the side contralateral to pain, greater estimates of ARV were identified for the upper division of trapezius as the task progressed (37.4 +/- 20.2 vs. 52.7 +/- 28.4 microV, at the end of the contraction). Muscle fiber conduction velocity did not change with pain in all three divisions of the right trapezius muscle. The results suggest that local elicitation of nociceptive afferents in the upper division of the trapezius induces reorganization in the coordinated activity of the three subdivisions of the trapezius in repetitive dynamic tasks.
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The adult human central nervous system (CNS) retains its ability to reorganize itself in response to altered afferent input. Intracortical inhibition is thought to play an important role in central motor reorganization. However, the mechanisms responsible for altered cortical sensory maps remain more elusive. ⋯ The N20 (S1) changes may reflect the mechanism responsible for altering the boundaries of cortical sensory maps, changing the way the CNS perceives and processes information from adjacent body parts. The N30 changes may be related to the intracortical inhibitory changes shown previously with both single and paired pulse TMS. These findings may have implications for understanding the role of the cortex in the initiation of overuse injuries.