Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Many studies show consistently that repetitive transcranial magnetic stimulation (rTMS) with a frequency of 1 Hz and an intensity above the resting motor threshold (RMT) performed for several minutes over the primary motor cortex (M1) leads to a depression of cortical excitability. Furthermore, most studies concur on a facilitation of the non-stimulated contralateral M1. Little is known, however, about the physiological mechanisms underlying these effects. ⋯ In conclusion, the MEP increase in the non-stimulated M1 lasted longer than the MEP decrease in the stimulated M1. Only the long-lasting MEP increase was associated with a specific change in intracortical excitability (increase in SICF). Modulation of motor cortical inhibition did not play a role in explaining the rTMS induced changes in MEP amplitude.
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Balance control is influenced by the availability and integrity of sensory inputs as well as the ability of the balance control mechanisms to tailor the corrective action to the gravitational torque. In this study, to challenge balance control, visual and ankle proprioceptive information were perturbed (eyes closed and/or tendon vibration). We masked sensory inputs in order: (1) to test the hypothesis that adolescent idiopathic scoliosis (AIS), compared to healthy adolescent, relies more on ankle proprioception and/or visual inputs to regulate balance and (2) to determine whether it is the variation or the amplitude of the balance control commands of AIS that leads to greater body sway oscillations during sensory deprivation. ⋯ This was observed regardless of whether vision was available or not. The analysis of the sway density curves revealed that the amplitude rather than the variation of the balance control commands was related to a larger CP range and greater RMS CP velocity for AIS. The present results suggest that AIS, compared to control participants, relies much more on ankle proprioception to control the amplitude of the balance control commands.
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The central processes occurring during fatiguing exercise are not well understood, however transcranial magnetic stimulation (TMS) studies have reported increases both in corticomotor excitability, as measured by the motor-evoked potential (MEP) amplitude, and in long-interval intracortical inhibition, as measured by the duration of the post-MEP silent period. To determine whether short-interval cortical inhibition (SICI) is modulated by fatiguing exercise, we used single and paired-pulse TMS to measure MEP amplitude and SICI for the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the hand during, and for 20 min after, a 10-min intermittent maximal voluntary abduction of the index finger designed to fatigue the FDI muscle. For the FDI, the index of SICI increased at the onset of exercise (from 0.25+/-0.05 to 0.55+/-0.11, P < 0.05) and then decreased progressively as force declined. ⋯ MEP amplitude for both the FDI and ADM increased above baseline during exercise and then decreased below baseline during the recovery period. These results demonstrate that there are significant changes in SICI during and after a fatiguing exercise protocol that are isolated to the representation of the fatigued muscle. The inter-relationship between the changes in excitation and inhibition suggests the presence of a measured and adaptive process of modulation in central excitation and inhibition acting to increase corticomotor drive to the exercising muscle as fatigue is developing.
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Effects of persistent temporomandibular joint (TMJ) inflammation on nociceptive responses of remote bodily areas of the rat were investigated. Monoarthritis of the TMJ region was evoked by the injection of complete Freund's adjuvant (CFA) into the left TMJ region. Rats without injection of CFA into the TMJ region served as controls (non-CFA group). ⋯ The number of Fos-positive neurons in the lumbar dorsal horn ipsilateral to the formalin injection at 1 and 7 days after CFA injection into the TMJ were similar to those in the non-CFA group; however, those were significantly increased in the laminae I-II and V-VI of the lumbar dorsal horn at 14 days after CFA injection. TMJ inflammation for 7 and 14 days alone produced a small number of Fos-expressing neurons in the lumbar dorsal horn. These results provide evidence that persistent unilateral inflammation of the TMJ region causes an increase in behavioral hyperalgesia of the hindpaw, which is attributed to the modulation of neural activities, in part, in the lumbar dorsal horn, likely mediated by supraspinal neural mechanisms.
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We examined the interaction between the control of posture and an aiming movement. Balance control was varied by having subjects aim at a target from a seated or a standing position. The aiming difficulty was varied using a Fitts'-like paradigm (movement amplitude=30 cm; target widths=0.5, 1.0, 2.5 and 5 cm). ⋯ When seated, the CP kinematics was scaled with the hand movement kinematics. Increasing the index of difficulty led to a strong correlation between the hand speed and CP displacement and speed. The complex organization between posture and movement was revealed only by examining the specific interactions between speed-accuracy and postural constraints.