Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Clinical Trial
Movement-related potentials associated with self-paced, cued and imagined arm movements.
Self-paced movements, movement to a cue and imagined movement have all been reported to be preceded by a prolonged negativity on averaged electroencephalograph (EEG) recordings. Considerable evidence supports an important contribution from the supplementary motor area (SMA) to this potential and all three types of movement have been shown to be associated with SMA activation. This study was designed to compare the premovement component of these movement-related potentials (MRPs) in a group of subjects who performed each of these three types of movement. ⋯ Our results indicate that the MRPs prior to the three types of movement have distinct characteristics, most notably for the NS' phase. The MRP associated with movement to a regular cue may be analogous to the S2-related negativity of the contingent negative variation (CNV). We discuss the findings in the light of current evidence from functional imaging as to the cortical areas activated in similar movements.
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In normal subjects, focal repetitive transcranial magnetic stimulation (rTMS) of the hand motor area evokes muscle potentials (MEPs) from muscles in the hand (target muscles) and the arm (non-target muscles). In this study we investigated the mechanisms underlying the spread of MEPs induced by focal rTMS in non-target muscles. rTMS was delivered with a Magstim stimulator and a figure-of-eight coil placed over the first dorsal interosseus (FDI) motor area of the left hemisphere. Trains of 10 stimuli were given at a suprathreshold intensity (120% of motor threshold) and at frequencies of 5, 10 and 20 Hz at rest. ⋯ Using a control MEP size matched with that observed after a conditioning contralateral rTMS, we found that paired-pulse inhibition remained unchanged. Yet a single TMS conditioning pulse sufficiently strong to evoke a MEP in the contralateral FDI and biceps muscles simultaneously (as rTMS did) left paired-pulse inhibition unchanged. We conclude that the spread of EMG activity to non-target muscles depends on cortical mechanisms, mainly including changes in the excitability of the interneurones mediating intracortical inhibition.
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Subjects' awareness of motor corrections was investigated in a double-step pointing task. An unpredictable lateral target displacement of 10 cm, either left or right, during an ongoing reaching movement led to corrections of the trajectory. Subjects were required either to follow the target (pointing) or move in the opposite direction (anti-pointing). ⋯ Anti-pointing corrections did not show this dissociation between performance and awareness. We suggest that anti-point corrections, but not standard pointing corrections, involve an additional supervisory system. This system is characterised by its slow operation and its access to conscious awareness.
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Musculoskeletal pains are often characterised by referred pain and hyperalgesia. The aim of the present study was to examine the sensitivity to pressure and pinprick at sites ipsi- and contralateral to capsaicin-induced pain in the tibialis anterior (TA) muscle. Visual analogue scale (VAS) scores of the sensation to sub- and supra-pain threshold stimuli by pressure and pinprick were recorded before, during and after experimental muscle pain. ⋯ Thus, the generalised decreased sensitivity may reflect activation of non-opioid endogenous pain inhibitory systems. The lack of change in sensitivity at some sites could indicate a competitive balance between excitatory and inhibitory mechanisms. The deep peroneal nerve specifically innervates both the TA muscle and the only site of hyperalgesia indicating spatial summation of afferent activity from these structures.
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Comparative Study
Modulation of visual cortical excitability in migraine with aura: effects of 1 Hz repetitive transcranial magnetic stimulation.
Recent studies showed hyperexcitability of the occipital cortex in subjects affected by migraine with aura. It has been shown that 1 Hz repetitive transcranial magnetic stimulation (rTMS) reduces excitability of visual cortex in normal subjects. The aim of the study was to investigate the effects of low frequency (1 Hz) rTMS on visual cortical excitability by measuring changes in phosphene threshold (PT) in subjects with migraine with aura. ⋯ The difference in the proportion of subjects reporting phosphenes in migrainer and control groups was significant (migrainers: 100% vs controls 47%; P<0.05), and 1 Hz rTMS over the occipital cortex led to a significantly increased visual cortex excitability expressed as a decrease in PT in subjects affected by migraine with aura. Conversely, after a 1-Hz TMS train normal subjects showed increased PT values, which suggests a decreased visual cortex excitability. Our findings confirm that the visual cortex is hyperexcitable in migrainers and suggest a failure of inhibitory circuits, which are unable to be upregulated by low frequency rTMS.