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Biomedical subjects

W J Daunicht

Publications and source records attributed to W J Daunicht.

11 recordsLinked to original sources
PubMed1991

Autoassociation and novelty detection by neuromechanics.

Many biomechanical systems contain ball joints with several elastic actuators (muscles) obliquely attached to the links. The problem of calculating the optimum actuator commands to achieve a desired link orientation is a difficult one for any control system; however, the elasticity of the actuators may be part of the solution. Mechanoreceptors such as those found in muscles and tendons are capable of performing operations that can be regarded as autoassociation and novelty detection, respectively, by minimization of potential energy. The information provided by such sensors may then be exploited for optimization of muscle coordination.

Animals↗
PubMed1988

A biophysical approach to the spatial function of eye movements, extraocular proprioception and the vestibulo-ocular reflex.

The eyeball and the extraocular muscles are used as a paradigm to design a linear spatial model of a single joint with a redundant set of muscles. On the basis of this model relations are derived between orientation, torque, motor commands, and proprioceptive signals. These relations show that the tenet underlying the tensorial interpretation of neural signals in sensorimotor systems does not have general validity. A mechanism is proposed to show how proprioception may play a role in optimizing the coordination of muscles during spatial tasks. Further, a new concept is suggested that allows one to predict the neural connectivities mediating the redundant spatial vestibulo-ocular reflex. This concept has the advantage of minimizing both sensorial error and motor effort.

Biophysical Phenomena↗
PubMed1987

Spatial arrangement of the vestibular and the oculomotor system in the rat.

The treatment of the spatial aspects of vestibular sensation, ocular movement near primary position, and their neural processing requires numerical information about the directions of maximal sensitivity of the semicircular canals (SCC), the direction of gaze at primary position, and the directions of eye rotation generated by each individual extraocular muscle (EOM). A good approximation of this information can be gained from stereotaxic measurements of the geometrical arrangement of the canals' bony structure, from measurements of the pupil's orientation, and from measurements of the directions of muscle pull as well as of the center of eye rotation. The results of measurements in pigmented rats are given as unit sensitivity vectors and unit action vectors in head-fixed coordinate systems and compared with data from rabbit, cat, monkey, and human. The misalignment of 'coplanar' SCC with 2.5-15.6 degrees is second only to humans, while the misalignment of the vectors of 'antagonistic' EOM with 27.2-39 degrees is even more oblique than in humans and thereby even more so than in the other mammals. Misalignment of SCC and 'corresponding' EOM with 15.5-34.2 degrees again is largest, followed by that in humans and then the other mammals. The rat may therefore be useful in studying those mechanisms by which the central nervous system deals with the obliqueness of systems that play such an important role in humans, too.

Animals↗
PubMed1987

Information processing in goal-directed movements.

Sensory-motor interaction in pointing at visual targets without sight of the pointing arm was evaluated in human subjects, using information theory. Equations were derived to determine transformation in channels with amplitude-continuous output signals, which overcome the problems involved in dividing the output into discrete bins. The equations were applied to calculate transinformation in our pointing experiment, and to predict transinformation under a variety of different experimental conditions. The results apply also to other systems that can be regarded as channels with similar properties.

Feedback↗
PubMed1986

Extraocular proprioceptive signals affect ocular motor activity neither directly nor parametrically in the presence of optokinetic or vestibular stimulation in the frog.

Direct and parametric effects of stretch receptors in the extraocular muscles on abducens nerve activity were investigated in the unanesthetized immobilized frog. Horizontal passive rotations of one eye in the physiological range (+/- 5 degrees) did not elicit responses in the activity of abducens nerve on either side; however, larger rotations or pull of one eye evoked long latency direction-unspecific responses simultaneously in both nerves. When the animal was stimulated vestibulary in the horizontal plane with sinusoidal or constant acceleration, abducens activity was not altered in correlation to passive eye movements in the physiological range. Similarly, the activity of either nerve evoked by simultaneous or preceding optokinetic stimulation of one eye with constant pattern velocity was not modified by passive rotation of the contralateral eye.

Abducens Nerve↗
PubMed1986

An on-line spike form discriminator for extracellular recordings based on an analog correlation technique.

The discrimination of single unit activity in extracellular recordings presents a serious problem when the signal-to-noise ratio is low or when the amplitudes of interspersed spikes are similar. By exploiting spike form, the system described here performs discrimination using on-line hardware template matching. Using analog delay lines, the combined deviation of 8 input signal values from 8 stored template values is calculated simultaneously. The 8 template values are selected by adjusting 8 cursors to the desired spike trace on a CRT; the spike form discriminator (SPIFODIS) then generates a deviation function which steeply drops to zero whenever form similarity occurs, allowing for easy triggering. The performance of SPIFODIS was compared quantitatively with that of a conventional amplitude trigger in two cases: when detecting a single unit with varied signal-to-noise ratios and when separating double units of equal amplitude. At signal-to-noise ratios between 2 and 1 the error rate for SPIFODIS was only 15-50% of that of an amplitude trigger. In double-unit recordings showing only form differences, spikes are discriminated with very low error rate, while an amplitude trigger fails completely.

Action Potentials↗
PubMed1985

Afferent innervation of extraocular muscles in the rat studied by retrograde and anterograde horseradish peroxidase transport.

After injection of horseradish peroxidase (HRP) into extraocular muscles of rat perikarya were labeled mainly along the medial edge of the ophthalmic subdivision of the trigeminal ganglion but not in the mesencephalic nucleus of the trigeminal nerve. Injections of HRP into the trigeminal ganglion labeled simple as well as branching and meandering free fiber endings in extraocular muscles. No evidence for muscle spindles was found, but the meandering endings may be considered as candidates for stretch receptors.

Animals↗
PubMed1985

Painless head holder for unitary recordings from alert rats.

The construction and implantation of a device is described that holds the head of an alert rat in a well-defined position. The main parts of the head holder consist of a plate with a wide opening to allow for vertical access to virtually all parts of the brain, a rectangular recording well, and two specially shaped elastic steel skull clamps. It is easy to fabricate, painless, long-lasting, and suitable for stable stereotaxic recordings of single units in small alert mammals.

Animals↗
PubMed1983

Proprioception in extraocular muscles of the rat.

Stretch receptor afferents from extraocular muscles were found in the rat. Their first-order somata, responding specifically to eye muscle displacements, were restricted to the ipsilateral semilunar ganglion. Over a broad range of stimulus frequencies the sensitivity of receptors increased by a factor of 2.2 per decade with a mean sensitivity of 125 imp. s-1 mm-1 at 1 Hz.

Animals↗
PubMed1983

Re-examination of a linear systems approach to the behavior of mammalian muscle spindles.

A model consisting of the parallel arrangement of one position-dependent and three first order velocity-dependent components is proposed in order to describe the behavior of muscle spindles. The responses of spindle receptors to ramp stretches have previously been characterized by fractional power functions; the aim of this study is to generate these functions on the basis of a simple additive linear model. A procedure is described which yields model parameters from responses to ramp and triangular displacements. Tests of the model are performed by comparing its predictions with experimental data from muscle spindles in cat and rat.

Animals↗