Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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There is considerable evidence from studies on cats and monkeys that several cortical areas such as area 2v at the tip of the intraparietal sulcus, area 3av in the sulcus centralis, the parietoinsular vestibular cortex adjacent to the posterior insula (PIVC) and area 7 in the inferior parietal lobule are involved in the processing of vestibular information. Microelectrode recordings from these areas have shown that: (1) most of these cortical neurons are connected trisynaptically to the labyrinthine endorgans and (2) they receive converging vestibular, visual and somatosensory inputs. These data suggest that a multimodal cortical system is involved in postural and gaze control. ⋯ The latency period for the activation of five distinct cortical zones, including the prefrontal and/or the frontal lobe, the ipsilateral temporoparietal cortex, the anterior portion of the supplementary motor area (SMA) and the contralateral parietal cortex, was 6 ms. The short latency period recorded for each of these areas indicates that several trisynaptic pathways, passing through the vestibular nuclei and the thalamic neurons, link the primary vestibular afferents to the cortex. We suggest that all these areas, including the prefrontal area, process egomotion information and may be involved in planning motor synergies to counteract loss of equilibrium.
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Comparative Study
Differential response of synaptic zinc levels to sensory deprivation in the barrel cortex of young and adult mice.
The distribution of synaptic zinc after short-term (up to 48 h) tactile deprivation of vibrissae was investigated in the barrel cortex of mice using histochemical staining. In adult mice, 12 h after trimming selected rows of vibrissae, an increase in zinc staining in the deprived barrels was observed. This increase was still present 48 h after trimming. ⋯ In young (8-day-old) mice, the short-term deprivation did not alter zinc staining and only chronic sensory deprivation produced an increase in zinc staining. However, after long-term deprivation no changes were found in adult mice. These results suggest that different mechanisms might be involved in functional reorganization of zinc containing terminals in young and fully mature cerebral cortex.
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Mechanical changes underlying spastic hypertonia were explored using a parallel cascade system identification technique to evaluate the relative contributions of intrinsic and reflex mechanisms to dynamic ankle stiffness in healthy subjects (controls) and spastic, spinal cord injured (SCI) patients. We examined the modulation of the gain and dynamics of these components with ankle angle for both passive and active conditions. Four main findings emerged. ⋯ At full plantarflexion, there was no difference between SCI and control subjects; in the mid-range, reflex stiffness was abnormally high in SCI patients; at full dorsiflexion, both reflex and intrinsic stiffness were larger than normal. Fourth, differences between SCI and control subjects were smaller during the active than the passive condition, because intrinsic stiffness increased more in controls than SCI subjects; nevertheless, reflex gain remained abnormally high in SCI patients. These results elucidate the nature and origins of the mechanical abnormalities associated with hypertonia and provide a better understanding of its functional and clinical implications.