Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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The present experiment examined the influence of final target position on grasp posture planning during a three-segment object manipulation task in which the required object orientation at the first target position was unconstrained. Participants grasped a cylindrical object from a home position, placed it at an intermediate position in a freely chosen orientation, and subsequently placed it at one of four final target positions. Considerable inter-individual differences in initial grasp selection were observed which also led to differences in final grasp postures. ⋯ These results provide further evidence for the interaction of multiple action selection constraints in grasp posture planning during multi-segment object manipulation tasks. Whereas some constraints may take strict precedence in a given task, other constraints may be more flexible and weighted differently among participants. This differentiated weighting leads to task- and subject-specific constraint hierarchies and is reflected in inter-individual differences in grasp selection.
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The underlying mechanism of spatial summation (SS) of pain, an essential component in pain perception and detection, is unknown. Because of the possible differential innervations by A-delta nociceptors and pain sensitivity of hairy and glabrous skin, a comparison of the SS characteristics between the two skin types could contribute to the elucidation of its subserving system and processing. The effect of sex on SS of pain was also evaluated due to the scarcity of information on the subject. ⋯ It would appear that AMH-II nociceptive fibers in particular subserve SS of pain. Furthermore, SS is increased under stronger stimulation intensities, probably as defense mechanism against tissue damage. Sex differences in dynamic sensory processes such as SS are revealed only under conditions where the phenomenon is subtle (as in glabrous skin).
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Standing upright requires the coordination of neural drives to a large set of muscles involved in controlling human bipedal stance (i.e., postural muscles). The coordination may deteriorate in situations where standing is performed under more challenging circumstances, such as standing on a smaller base of support or not having adequate visual information. The present study investigates the role of common neural inputs in the organization of multi-muscle synergies and the effects of visual input disruption to this mechanism of control. ⋯ Absence of visual information caused a significant decrease in intermuscular coherence. These findings are consistent with the hypothesis that correlated neural inputs are a mechanism used by the CNS to assemble synergistic muscle groups. Further, this mechanism is affected by interruption of visual input.