Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Greater amount of visual information exacerbates force control in older adults during constant isometric contractions.
The purpose of this study was to compare control of force and modulation of agonist muscle activity of young and older adults when the amount of visual feedback was varied at two different force levels. Ten young adults (25 years ± 4 years, 5 men and 5 women) and ten older adults (71 years ± 5 years, 4 men and 6 women) were instructed to accurately match a constant target force at 2 and 30% of their maximal isometric force with abduction of the index finger. Each trial lasted 35 s, and the amount of visual feedback was varied by changing the visual angle at 0.05, 0.5, and 1.5°. ⋯ In addition, there were age-associated differences in the modulation of the agonist muscle activity. Young adults increased normalized power in the EMG signal from 13 to 60 Hz with an increase in visual angle, whereas older adults did not. These findings suggest that greater amount of visual information may be detrimental to the control of a constant isometric contraction in older adults, and this impairment may be due to their inability to effectively modulate the motor neuron pool of the agonist muscle.
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Comparative Study
Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study.
Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. ⋯ The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.
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Comparative Study
Two stages and three components of the postural preparation to action.
Previous studies of postural preparation to action/perturbation have primarily focused on anticipatory postural adjustments (APAs), the changes in muscle activation levels resulting in the production of net forces and moments of force. We hypothesized that postural preparation to action consists of two stages: (1) Early postural adjustments (EPAs), seen a few hundred ms prior to an expected external perturbation and (2) APAs seen about 100 ms prior to the perturbation. We also hypothesized that each stage consists of three components, anticipatory synergy adjustments seen as changes in covariation of the magnitudes of commands to muscle groups (M-modes), changes in averaged across trials levels of muscle activation, and mechanical effects such as shifts of the center of pressure. ⋯ This is the first study to document anticipatory synergy adjustments in whole-body tasks. We interpret the results within the referent configuration hypothesis (an extension of the equilibrium-point hypothesis): The early postural adjustment is based primarily on changes in the coactivation command, while the APAs involve changes in the reciprocal command. The results fit an earlier hypothesis that whole-body movements are controlled by a neuromotor hierarchy where each level involves a few-to-many mappings organized to stabilize its overall output.
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Randomized Controlled Trial Comparative Study
Heterotopic low-frequency stimulation induces nociceptive LTD within the same central receptive field in man.
Electrical low-frequency stimulation (LFS) evokes long-term depression (LTD) of nociception. Human studies suggested a strictly homotopic organization. This study hypothesizes that even heterotopic LFS evokes LTD within the same receptive field (RF). ⋯ In ExpArm (n = 20), LFS to the center of the RF induced a stronger pain reduction than LFS applied outside the RF (P < 0.001). This study demonstrates a heterosynaptic organization of LTD within the same RF. Profound knowledge about RF involvement on LTD seems crucial in order to judge the quality of LFS as a possible neuromodulatory treatment of pain.
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The present experiment was designed to assess the effect of active (deliberate) maintenance of a small forward (FL) or backward body lean (BL) (about 2° ankle flexion) with respect to the spontaneous direction of balance (or neutral posture, N) on postural balance. We questioned whether BL and FL stances, which impose a volitional proprioceptive control of the body-on-support angle, could efficiently reduce mediolateral displacements of the centre of pressure (CoP) induced by the visual motion of a room and darkness. Subjects (n = 15) were asked to stand upright quietly feet together while confronted to a large visual scene rolling to 10° on either side in peripheral vision (and surrounding vertical visual references in central vision) at 0.05 Hz. ⋯ Interestingly, the visual quotient positively correlated with the proprioceptive quotient, indicating that the more the subjects relied heavily on the visual frame of reference (FOR) the more they were influenced by body leaning. This result suggested hence a lesser ability to use efficiently body-ground proprioceptive cues. On the whole, the present findings indicate that body leaning could provide a useful mean to assess the subject's ability to use body-ground proprioceptive cues not only to improve postural stability during eyes opening (especially during forward leaning), but also as a mean to disclose subjects' visual dependency and their associated difficulties to shift from visual to proprioceptive-based FOR.