Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Human stance control beyond steady state response and inverted pendulum simplification.
Systems theory analyses have suggested that human upright stance can be modelled in terms of continuous multi-sensory feedback control. So far, these analyses have considered mainly steady-state responses to periodic stimuli and relied on a simplifying model of the body's mechanics in the form of an inverted pendulum. Therefore, they may have ignored relevant aspects of the postural behaviour. ⋯ We also conclude that the 'inverted pendulum' simplification is a legitimate simplification. We demonstrate the utility of the model by implementing it into a humanoid robot that then mimics closely the human experimental data. Finally, we present a hypothetical concept on sensory reweighting mechanisms in human stance control, which is meant to serve as a framework for future research.
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The multidimensional experience of pain is thought to be partially influenced by the pain modulation system as well as by individual psychological components. Recent studies demonstrated possible common neural network mediating both domains. The present study examined the relationships between pain perception, pain modulation, and catastrophizing in healthy subjects. ⋯ In addition, significant negative correlations were found between PCS and DNIC effect (r = -0.34, p = 0.02). Moreover, once catastrophizing was entered into the regression analysis, the previously significant effect of gender was no longer found. In conclusion, individuals with high catastrophizing levels demonstrated higher pain intensities and lower effects of DNIC indicating that catastrophizing might have a significant impact on pain perception via an association with pain modulation.
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Comparative Study
Survival and regeneration of cutaneous and muscular afferent neurons after peripheral nerve injury in adult rats.
Peripheral nerve injury induces the retrograde degeneration of dorsal root ganglion (DRG) cells, which affects predominantly the small-diameter cutaneous afferent neurons. This study compares the time-course of retrograde cell death in cutaneous and muscular DRG cells after peripheral nerve transection as well as neuronal survival and axonal regeneration after primary repair or nerve grafting. For comparison, spinal motoneurons were also included in the study. ⋯ In the cutaneous DRG neurons, primary repair or peripheral nerve grafting increased survival by 19-30% and promoted regeneration of 46-66% of the cells. The present results suggest that cutaneous DRG neurons are more sensitive to peripheral nerve injury than muscular DRG cells, but that their regenerative capacity does not differ from that of the latter cells. However, the retrograde loss of cutaneous DRG cells taking place despite immediate nerve repair would still limit the recovery of cutaneous sensory functions.
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In healthy subjects, sensorimotor after-effects of prism adaptation are known to be symmetric (they appear after using leftward and rightward optical deviations), whereas cognitive after-effects are asymmetric (they appear after using a leftward optical deviation) and rightward oriented. Sensorimotor and cognitive after-effects have been classically studied using different specific tasks. The purpose of the current study was to investigate whether both after-effects may be involved in a same visuo-spatial task. ⋯ This means that cognitive after-effects may add to sensorimotor after-effects following adaptation to a leftward optical deviation. This asymmetry challenges the classical distinction between sensorimotor and cognitive after-effects of prism adaptation. Implications for the functional mechanisms and the neuroanatomical substrate of prism adaptation are discussed.
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The aim of this study was to quantify the dynamic response of locomotion to the first oral levodopa administration of the day in patients with fluctuating Parkinson's disease (PD). Stride length, walking speed, cadence and gait variability were measured with an ambulatory gait monitor in 13 PD patients (8 males) with a clinical history of motor fluctuations. The Unified Parkinson's Disease Rating Scale (UPDRS) gait score (part 29) was also determined by a movement disorders specialist from video recordings. ⋯ UPDRS gait score also reflected improving gait in the majority of subjects (8), providing clinical confirmation of the objective measures of the locomotor response to levodopa. Increasing abruptness (H) of the 'off-on' transition with disease duration is consistent with results from finger-tapping studies, and may reflect reduced buffering capacity of pre-synaptic nigrostriatal dopaminergic neurons. Ambulatory monitoring of gait objectively measures the dynamic locomotor response to levodopa, and this information could be used to improve daily management of motor fluctuations.