Influence of movement speed on accuracy and coordination of reaching movements to memorized targets in three-dimensional space in a deafferented subject.

Multiarticular reaching movements at different speeds produce differential demands for the on-line control of ongoing movements and for the predictive control of intersegmental dynamics. The aim of this study was to assess the ability of a proprioceptively deafferented patient and aged-matched control subjects to make precise and coordinated three-dimensional reaching movements at different speeds without vision during the movement. A patient with a complete loss of proprioception below the neck (C.

The interaction of visual and proprioceptive inputs in pointing to actual and remembered targets in Parkinson's disease.

We previously reported that Parkinson's disease patients could point with their eyes closed as accurately as normal subjects to targets in three-dimensional space that were initially presented with full vision. We have now further restricted visual information in order to more closely examine the individual and combined influences of visual information, proprioceptive feedback, and spatial working memory on the accuracy of Parkinson's disease patients. All trials were performed in the dark.

The timing of arm-trunk coordination is deficient and vision-dependent in Parkinson's patients during reaching movements.

The role of the basal ganglia in the coordination of different body segments and utilization of motor synergies was investigated by analyzing reaching movements to remembered three-dimensional (3D) targets in patients with Parkinson's disease (PD). Arm movements were produced alone or in combination with a forward bending of the trunk, with or without visual feedback. Movements in PD patients were more temporally segmented, as evidenced by irregular changes in tangential velocity profiles.

Pointing in 3D space to remembered targets. II. Effects of movement speed toward kinesthetically defined targets.

The accuracy of visually guided pointing movements decreases with speed. We have shown that for movements to a visually defined remembered target, the variability of the final arm endpoint position does not depend on movement speed. We put forward a hypothesis that this observation can be explained by suggesting that movements directed at remembered targets are produced without ongoing corrections.

Pointing to remembered targets in 3-D space in Parkinson's disease.

A three-dimensional tracking system was used to examine whether subjects with Parkinson's disease (PD) would show characteristic performance deficits in an unconstrained pointing task. Five targets were presented in a pyramidal array in space to 11 individuals with mild to moderate PD and 8 age-matched controls. After the target was indicated, subjects closed their eyes and pointed to the remembered target locations without vision.

Pointing in 3D space to remembered targets. I. Kinesthetic versus visual target presentation.

This study investigated the influence of different modalities of target information (visual, kinesthetic) on the accuracy, kinematics, and interjoint coordination of pointing movements to remembered targets. The targets were presented by a robot arm in five locations in three-dimensional (3D) space, either as a point of light in a dark room ("visual" condition), or kinesthetically. Relative pointing accuracy in the visual compared with kinesthetic conditions was influenced by the target location: pointing errors were the largest for the visual targets most eccentric relative to the subject's head.

The interaction of visual and proprioceptive inputs in pointing to actual and remembered targets.

Errors in pointing to actual and remembered targets presented in three-dimensional (3D) space in a dark room were studied under various conditions of visual feedback. During their movements, subjects either had no vision of their arms or of the target, vision of the target but not of their arms, vision of a light-emitting diode (LED) on their moving index fingertip but not of the target, or vision of an LED on their moving index fingertip and of the target. Errors depended critically upon feedback condition.

Influence of movement speed on accuracy of pointing to memorized targets in 3D space.

Subjects performed three-dimensional (3D) pointing movements as accurately as possible with their eyes closed under four different speed conditions: 'slow', 'normal', 'fast' and 'maximal' (peak velocities of 0.62, 1.61, 2.

Azimuth errors in pointing to remembered targets under extreme head rotations.

Errors in pointing to remembered target locations in 3-D space were studied when subjects were free to move their heads, and when they rotated their heads to the extreme right or left. Relative to pointing when the head was free to move, head rotations to the right shifted the final position of the responding arm to the left, whereas head rotations to the left shifted the final position of arm to the right. Horizontal rotation of the head had no systematic influence on elevation and radial distance errors.

[Steady state-kinetic model of the regulation by autoadrenoreceptors of noradrenaline secretion].

The process of noradrenaline secretion regulation by autoreceptors is described in the terms of the stationary-kinetic reaction. Constants of this reaction are determined using the authors' own data. Analysis of the model has permitted explaining some data from literature which were used to refute the principle of noradrenaline secretion self-regulation by autoreceptors.

[A model of control of the movement of the multiarticular extremity].

A model for coordinated execution of multijoint goal-directed limb movements is suggested from the following principles. (1) Central control signals for a single limb joint are individually formed, proceeding from its ability to bring the limb nearer to the target and leaving control signals directed simultaneously to other joint out of account. The joints thereby behave as a set of Tsetlin's abstract automata [11], each functioning independently and guided by a common, collective effect.

[Analysis of the regulation of noradrenaline secretion by autoadrenoreceptors and stimulation frequency].

A mathematical model is presented which quantitatively describes the value of secreted mediator to each subsequent impulse in the series of presynaptic impulses. The model is constructed with the account taken of the role of presynaptic adrenoreceptors regulating noradrenaline secretion. An analysis of the model shows that the observed decrease and further stabilization of presynaptic responses in the series of presynaptic impulses observed in neurophysiological experiments can be connected with the work of alpha- and beta-autoadrenoreceptors.

[Biomechanical characteristics of the wiping reflex cycle].

Multijoint goal-directed hindlimb movements in response to chemical stimulation delivered to different skin sites on the medial back surface (wiping reflex-WR) were filmed and analysed in spinal or intact frogs Rana temporaria. Each WR cycle was divisible into five phases (flexion, lifting, aiming, wiping and extension) usually separated from each other by postural interruptions. One or several of the phases might spontaneously be reduced or deleted at all (e.

[Analysis of late components of evoked potentials arising in the paramedian lobule of the cerebellum in response to stimulation of nerves and the cerebral cortex].

The field potentials in response to stimulation of the cerebral sensorimotor cortex and of the limb nerves were recorded in the granular layer of the cerebellar paramedian lobule in nonanesthetized cats. The field potentials contained long-latency components, i.e.

The spinal frog takes into account the scheme of its body during the wiping reflex.

The hindlimb of the spinal frog produces a wiping reflex evoked by electrically or chemically stimulating distal skin of the forelimb. The reflex was released in frogs supported on a flat surface or suspended. It was found to have two stages.

Activity of motoneurons during fictitious scratch reflex in the cat.

(1) Intracellular recording of motoneurons of different hindlimb muscles: tibialis anterior (TA), gastrocnemius and soleus (GS), vastus crureus (Vast), posterior biceps and semitendinosus (PBSt), was carried out during the fictitious scratch reflex in decerebrate cats. (2) During the postural stage of the reflex, a depolarizaiton (3.8 mV on average) was observed in TA motoneurons accompanied by tonic discharge.

[Possibility of using an analgesic (fentanyl) for electrophysiologic studies of the cerebellar cortex].

The effect of the central analgetic, fentanyl, on evoked potentials and Purkinje cells discharges in the cerbellar cortex to stimulation either the cerebral cortex or somatic nerves were studied in nonanaesthetized cats. It was found that the analgetic dose fentanyl (10-30 microgram/kg) did not affect the evoked potentials. The fentanyl dose of 30 microgram/kg suppressed the resting discharges and responses of Purkinje cells while the dose of 10 microgram/kg facilitated them.

Generation of scratching. II. Nonregular regimes of generation.

1. The activity of muscle nerves and that of spinal interneurons from the L4 and L5 segments was recorded during fictitious scratching (5), which was evoked in decerebrate curarized cats by stimulation of the cervical spinal cord. In some experiments, rhythmical generation was disturbed by stimulation of the fifth lumbar dorsal root (DL5).

Generation of scratching. I. Activity of spinal interneurons during scratching.

1. In decerebrate, curarized cats, stimulation of the cervical spinal cord evoked fictitious scratching (9), i.e.

[Variations in the membrane potentials of motor neurons during the generation of scratching].

The activity of motoneurons of the ankle flexor and extensor muscles was recorded intracellularly during fictitious scratching in decerebrate curarized cats. Before the beginning of rhythmical oscillation a large depolarization and tonic discharge were observed in flexor motoneurons, while the membrane potential of extensor ones did not change. When the rhythmical generation began, a short periodic hyperpolarization and corresponding pause in the discharge lasting for the extensor phase of the cycle appeared in flexor motoneurons.

[Formals for histogram analysis of Purkinje cell interspike intervals].

A hypothesis has been advanced proposing that the resting discharge of Purkinje cells depends on two factors: 1) tonic excitatory inflow and 2) Puasson's inhibitory inflow. This is why variety of interspike intervals is supposed to be the result of non-regular arrival of inhibitory impulses. From these assumptions an analytical expression was derived allowing to calculate probabilities of interspike intervals of various durations.

[Activity of propriospinal neurons in cats during the scratch reflex].

In the thalamic cats immobilized with flaxedil, the tactile stimulation of the pinna evoked fictitious scratching, i.e. rhythmical activity of the hindlimb motoneurons with a pattern of discharge typical of the actual scratching.