Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Cortico-cortical neurons and pyramidal tract (PT) neurons of the cat cerebral cortex were tested for convergent inputs from electrically stimulated vestibular, neck, head and forelimb nerves. Neurons were recorded within forelimb and vestibular projection regions of cortical area 3a. Consideration was given to both suprathreshold and subthreshold inputs. ⋯ Further, one half of the PT neurons with vestibular input (12/24) received input from three somatic sources: forelimb group I deep, forelimb low threshold cutaneous and greater auricular (head) nerves. The input connectivities suggest a role for these projection neurons of somatosensory cortex in the coordination of head and forelimb movements. The convergence of vestibular information with somatic input from the forelimb implies that vestibular-influenced neurons of area 3a projecting to the motor cortex or through the pyramidal tract would signal head position or movement with respect to proprioceptive feedback from the limbs.
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Extracellular Na+ - and Cl- -concentrations ([Na+]o, [Cl-]o) were recorded with ion-selective microelectrodes during repetitive stimulation and stimulus-induced self-sustained neuronal afterdischarges (SAD) in the sensorimotor cortex of cats. In all cortical layers [Na+]o initially decreased by 4-7 mM. In depths of more than 600 micrometer below the cortical surface such decreases usually turned into increases of 2-6 mM during the course of the SADs, whereas in superficial layers [Na+]o never rose above its resting level. [Cl-]o always showed an increase in the course of the SADs often preceded by an initial small decrease. ⋯ However, the resulting reduction of the size of the ES is calculated to be less than 10% for an increase in intracellular osmolarity by 30 mOsm. This value is too small as compared to previously measured ES-reductions under similar conditions (i.e., 30% reduction at 1,000 micrometers; Dietzel et al. 1980). Reductions of the size of the ES that accompany the observed changes in the ionic environment, are quantitatively explained on the basis of the extended glial buffering mechanism described in the preceding paper.
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Cortico-cortical neurons and pyramidal tract neurons of the cat were tested for convergent inputs from forelimb afferents. Neurons were recorded in cortical areas 1, 2, and 3a. Consideration was given to both suprathreshold and subthreshold inputs evoked by electrical stimulation of forelimb nerves. ⋯ The convergent nature of the sensory inputs is discussed in relation to the proposed specificities of cortical columns. The patterns of afferent inputs reaching cortico-cortical neurons seem to be appropriate for them to have a role in the formation of sensory fields of motor cortex neurons. PT neurons of somatosensory cortex have possible roles as modifiers of ascending sensory systems, however, the convergent input which these PT neurons receive argues against a simple relationship between the modality of peripheral stimuli influencing them and the modality of the ascending tract neurons under their descending control.
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Activity of vestibular nerve fibers and eye movements were recorded in the alert monkey during natural stimulation. The animal was rotated about a vertical axis in the dark with velocity trapezoids (vestibular), or a striped cylinder was rotated around the stationary monkey ()optokinetic), or these stimuli were combined. ⋯ Vestibular nerve activity was not influenced by optokinetic patterns or additional visual stimuli during combined visual-vestibular stimulation. Thus, in contrast to vestibular nuclei neurons, vestibular nerve activity in the alert monkey is only determined by head acceleration and cannot be related to the nystagmus response or visual stimuli.
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1. In the alert monkey neuronal activity was recorded in the ventro-posterior nucleus (VP) of the thalamus in the dark during sinusoidal rotation over a frequency range from 0.01-1 Hz. 2. From 57 neurons 38 (67%) were activated with rotation to the ipsilateral side (type I) and 19 (33%) to the contralateral side (type II). ⋯ For both neuronal activity in the thalamus and nystagmus a time constant between 25-35 sec was calculated. 5. The data are compared with vestibular nerve and nuclei recordings. It is argued that the time constants of vestibular neurons in the thalamus are very similar to the time constants of neurons in the vestibular nuclei in alert animals.