Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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The preceding study of this series (Hening, Favilla and Ghez 1988) examined the time course of the processes by which human subjects use information from a target to set the amplitude of an impulse of isometric elbow force. In that study, subjects were provided with separate cues to time response initiation and to inform them of the required amplitude of the response. When the time between target presentation and response initiation was too brief for them to incorporate information from the target, subjects produced default responses whose amplitudes reflected their prior experience. ⋯ Over the same range of S-R intervals, the amplitudes of both right and wrong direction responses to the different targets separated and converged on their respective target amplitudes. Specification of both direction and amplitude was complete at S-R intervals greater than 300 ms. The time course of amplitude specification in this bidirectional paradigm was prolonged over that in a paradigm where response direction was predictable.(ABSTRACT TRUNCATED AT 400 WORDS)
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This experiment examined the preparation and the production of isometric force in Parkinson's disease (PD). PD patients, elderly, and young subjects generated force levels that were a percentage of their maximum (15, 30, 45, and 60%). Subjects were cued on the upcoming target force level and they were asked to produce the required response as fast as possible. ⋯ PD patients had more irregular force-time curves that were characterized by changes in the rate of force production. The results suggest a more "noisy" output from the motor system and an inability to produce smooth forces. PD patients were also substantially slower in initiating a force production and the delay was localized in the pre-motor reaction time.
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The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the experimenter (control) or by the subject voluntarily moving the other arm. ⋯ An interlimb coordination was built up and stabilized after 40-60 trials. Pressing a button with the wrist (weak force and displacement) was a less effective means of inducing an anticipatory control of the flexors of the postural forearm, which indicates that the intensity of the central control plays a role in the building up of the coordination. 3. A distal grip action exerting either weak (100 g) or a high (1 kg) force was able to reduce the maximal amplitude of the forearm rotation, but not the maximal velocity, which indicates that an improved reflex action takes place, but not a feedforward anticipatory postural control.(ABSTRACT TRUNCATED AT 400 WORDS)
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In order to relate single cell performance to behavioral discrimination one needs measurements of the response variance of the units. We recorded from 183 single units of area V1 of monkeys performing an orientation discrimination task. ⋯ The response variance was on average 1.9 times the response strength. Despite important differences in preparation, the behaving monkey data are in good agreement with those previously obtained in paralysed and anesthetised animals.
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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.