Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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A total of 260 neurons were recorded in the rostral pontine tegmentum of freely moving cats during the sleep-waking cycle. Of these, 207 neurons (80%) were located in the dorsal pontine tegmentum containing monoaminergic and choline acetyltransferase (ChAT)-immunoreactive, or cholinergic neurons. In addition to presumably monoaminergic PS-off cells (n = 51) showing a cessation of discharge during paradoxical sleep (PS) and presumably cholinergic PGO-on cells (n = 40) exhibiting a burst of discharge just prior to and during ponto-geniculo-occipital (PGO) waves, we observed tonic (n = 108) and phasic (n = 61) neurons exhibiting, respectively, tonic and phasic patterns of discharge during wakefulness and/or paradoxical sleep. ⋯ Tonic type I neurons were further divided into two subclasses on the basis of discharge rates during waking: a) rapid (Type I-R; n = 17); and b) slow (Type I-S; n = 11) units with a discharge frequency of more than 12 spikes/s or less than 5 spikes/s, respectively. Like monoaminergic PS-off and cholinergic PGO-on cells, both tonic type II and type I-S cells were characterized by a long spike duration (median: 3.3 and 3.5 ms), as well as by a slow conduction velocity (median = 1.8 and 1.7 m/s). In the light of these data, we discuss the possible cholinergic nature and functional significance of these ascending tonic neurons in the generation of neocortical electroencephalographic desynchronization occurring during waking and paradoxical sleep.
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This study was undertaken in order to determine the time course of the process by which information derived from a visual target is used to accurately set the amplitude of a simple motor response. We refer to this process as response specification. Separate auditory and visual cues were given to the subjects in order to independently control the moment of response initiation and the time available for processing amplitude information from the target. ⋯ At S-R intervals comparable to a reaction time, the range of peak forces was constricted to a similar extent as previously observed in a reaction time task (Hening et al. 1988). We found that the gradual improvement of accuracy was not achieved through changes in trajectory control: at all S-R intervals, subjects utilized a pulse-height control policy (Gordon and Ghez 1987a). Different peak forces were achieved by varying the rate of rise of force, while force rise time was held relatively invariant.(ABSTRACT TRUNCATED AT 400 WORDS)
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The present study examines the influences of target predictability, level of practice and response urgency upon the latency and trajectory of a simple motor response. This response is an impulse of isometric force produced by the index finger and aimed to match a step change in a visual target. As expected (Welford 1980), the responses of naive subjects responding as soon as possible after target presentation were initiated at longer latencies when the target steps were of unpredictable amplitudes (choice condition) than when their amplitudes were all the same (simple condition). ⋯ The changes in trajectory of urgent responses suggests that their inaccuracy occurs because the subjects initiate their responses before the specification of amplitude is complete. The central tendency bias of such incompletely specified responses suggests further that, prior to target presentation, subjects prepare a default response reflecting their expectations. This default may then be modified by information obtained from the target in a process that lasts longer than a minimal reaction time.
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An assessment has been made of the effect of partial and complete section of the spinal cord on the discharges of gamma motoneurones to hind limb muscles in the decerebrated cat. The degree to which the discharges of pairs of individual gamma motoneurones exhibit short-term synchrony and the variability in interspike intervals of the discharge in individual neurones was measured. Variability of discharge was assessed as coefficient of variation of interspike intervals and degree of synchronization assessed from cross correlation analysis. ⋯ Both were markedly reduced following administration of the precursors of monoamines (either L-Dopa or 5-HTP). We conclude that a bilateral, monoaminergic pathway descending in the dorsolateral funiculus from the brainstem controls synchrony of gamma motoneurone discharge in the decerebrated cat. The possibility is discussed that synchrony of discharge between alpha motoneurones may be controlled by a similar pathway.
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The postural adjustments associated with a voluntary contraction of the postural muscles themselves have been studied in the legs of normal standing men. We focussed on the following questions. Do postural adjustments precede the focal movement as in the case of movements of the upper limb? Which muscle(s) are involved in the task of stabilizing posture? Can the same postural muscle be activated in postural stabilization and in voluntary movement at the same time, in spite of the opposite changes in activity possibly required by these conditions? Six subjects standing on a dynamometric platform were asked to rise onto the tips their toes by contracting their soleus muscles, or to rock on their heels by contracting their tibialis anterior muscles. ⋯ If the subjects held onto the frame, the early features in the soleus or tibialis anterior EMG were absent, and the corresponding changes in the foot-floor reaction forces were lacking. The anticipatory phenomena observed are considered postural adjustments because they appear only in the free-standing situation, and induce a body sway in the appropriate direction to counteract the destabilizing thrust due to the voluntary contraction of soleus or tibialis anterior. The central organization and descending control of posture and movements are briefly discussed in the light of the short latency of the anticipatory phenomena and of their close association with the focal movement.