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U Windhorst

Publications and source records attributed to U Windhorst.

71 records · Page 4Linked to original sources
PubMed1982

Measures of transinformation for multiple input/single output neuronal systems.

This paper presents a method for the calculation of the information transfer, or transinformation, in multiple input/single output neuronal systems. Our approach is an extension of an approach introduced by Eckhorn and Poepel in 1974. These authors computed the transinformation in single input/single output neuronal channels by regarding the spike (or stimulus) trains involved as finite Markov chains. The expressions for multiple input systems presented here are derived in close analogy to formulae in linear systems theory which show explicitly the correlations between the different input channels. A number of equivalent forms for the transinformation are discussed.

Animals↗
PubMed1982

Analysis of bimodal interspike interval histograms of primary muscle spindle endings in active triceps surae muscles of cats.

A feature frequently observed in interspike interval histograms (IH) derived from stationary Ia fibre discharge patterns was a bimodality suggesting a mixed population composed of two sub-populations of possibly different origins. To verify this hypothesis a separation of these subpopulations was attempted by assuming a Gaussian distribution for the longer intervals. The success of such a separation depended on the distinctness of the histogram peaks and the relative sizes of each mode. Both factors in turn depended on the overall muscle length and, hence, on the mean spindle discharge rate. The smaller intervals were then isolated from the spike trains and submitted to further statistical analysis. By averaging overall muscle tension with respect to the smaller intervals, the latter could often be linked to tension trajectories which were of higher amplitude and faster time course than the trajectories obtained by averaging with respect to the rest of the spikes. In some cases, auto-correlation histograms of isolated small intervals as well as serial correlograms computed for all intervals indicated that some muscle spindle afferents responded sensitively to activity of single motor units. This would confirm recent results of Cameron et al. (1980).

Afferent Pathways↗
PubMed1982

Interactions between motor units in modulating discharge patterns of primary muscle spindle endings.

Discharge patterns of group Ia afferents of muscle spindles in the (isometric) cat semitendinosus muscle were recorded when subjected to the influence of contractions of three motor units elicited by stimulation of three alpha-efferents with different regular or stochastic stimulus patterns. In order to study conditioning interactions between motor unit contractions, defined time constellations of stimuli to different motor units were isolated from the stimulus trains by electronic means. This technique was also applied to discharge patterns of two Ia fibres to isolate "correlated discharges." The effects of defined time constellations of stimuli upon discharge patterns of single Ia afferents or "correlated discharges" of pairs of Ia afferents were assessed by poststimulus time histograms (PSTHs). It turned out that the influence exerted by one motor unit on spindle discharges was more or less strongly modulated by actions of the other motor units, dependent on the relative timing of their contractions. These effects could in part be explained by the relative locations of motor units and spindles within the muscle. These results are discussed with respect to possible mechanisms of low-amplitude physiological tremor.

Afferent Pathways↗
PubMed1981

Patterns of parallel signal transmission between multiple alpha efferents and multiple Ia afferents in the cat semitendinosus muscle.

1. Certain features of signal transmission from multiple alpha-axons to multiple Ia fibres via extrafusal muscle tissue were studied by stimulating three ventral root filaments separately and simultaneously and by recording spike trains from three dorsal root filaments. 2. Post-stimulus time histograms (PSTH) revealed widely graded influences of single motor unit contractions on different muscle spindles, thus confirming results of Binder et al. (1976, 1980a). 3. In most instances, the signal transmission from a single motor unit to a single Ia fibre was disturbed to varying degrees by concomitant activity from other motor units. 4. This deterioration of signal transmission can probably be compensated for, at least in part, by correlations between discharge patterns of two or more Ia fibres induced by the "common input" of motor unit activity. 5. These correlations showed a topographical pattern such that a peak in the cross-correlogram (CCH) occurred at zero time for pairs of spindles located virtually in parallel to each other, and was shifted away from zero time as a function of the serial distance between spindles in the longitudinal muscle fibre direction. 6. Fusimotor innervation had complex effects on correlations between Ia fibre discharge patterns. It might de-correlate the latter as well as favour new correlations. 7. The possible role of topographical correlation patterns in the afferent reflex limb for tremor suppression is discussed.

Afferent Pathways↗
PubMed1981

Frequency response characteristics of a multi-loop representation of the segmental muscle stretch reflex.

This paper continues the investigation of a three-loop representation of the segmental muscle stretch reflex system introduced in a preceding communication. Frequency response characteristics were computed for open-loop conditions, control and disturbance signal inputs under a variety of conditions: (i) "in parallel" and "in series" peripheral arrangements of muscle compartments, (ii) various patterns of central connectivity, (iii) various recruitment levels of motor units, (iv) various overall reflex gains, (v) absence or presence of muscle spindle acceleration sensitivity. These computations disclose a number of mechanisms by which the nervous system might improve system stability and behaviour. These mechanisms are discussed with regard to physiological data.

Feedback↗
PubMed1981

Some methods to study information transmission through multi-channel neuronal systems.

Methods are proposed to isolate nearly simultaneous events or events with specific time relations to each other from two (or more) stimulus or spike trains. The methods can be implemented by means of a digital computer, but were implemented here with simple electronic hardware to present an alternative. The usefulness of these methods is demonstrated on data from cat experiments in which the influences of several motor units activated in parallel upon muscle spindle discharge patterns were studied by use of poststimulus time histograms (PSTHs). The contractions of one motor unit can interfere with the effects of others on muscle spindle discharges. In order to show this conditioning influence quantitatively, the integral of the PSTH is shown graphically as a function of the time interval between contractions of two motor units. These methods may help to elucidate some features of interactions between parallel neuronal channels bearing on the problem of the kind of information and how the latter is transmitted through complex multichannel systems.

Animals↗
PubMed1980

Multi-loop representation of the segmental muscle stretch reflex. Its risk of instability.

The multi-channel system of the segmental muscle stretch reflex arc is modelled as an arrangement of two or three parallel "component" loops coupled to each other at spinal and at muscle level. Such a model is thought to be more realistic than the usually adopted representation of the stretch reflex as a single negative feedback loop. Anatomical and physiological data were taken from the literature for an extensive simulation of the compound system with special reference to the problem of its stability. Particular emphasis was put on the question of which kind of central (spinal) connectivity is appropriate to best reduce the risk for instability which arises easily in certain system configurations. This paper describes the system and presents simple introductory computations apt to demonstrate the problems the physiological system has to cope with.

Animals↗
PubMed1979

A possible partitioning of segmental muscle stretch reflex into incompletely de-coupled parallel loops.

Based on previous investigations on focused signal transmission through the muscle stretch reflex system, a model is presented suggesting that different muscle areas (especially in large complex muscles such as the triceps surae muscle) may be regulated rather independently with respect to certain internal state variables, particularly internal length. Since the parallel localized reflex loops necessary for such local control tasks are inevitably coupled peripherally through the muscle and connective tissues, compensatory de-coupling elements would be required to reestablish at least partial independence. Whether and how this can be achieved at the level of spinal neuronal circuitry is investigated in connection with a discussion of the advantages of partially de-coupled reflex loops.

Animals↗
PubMed1979

Auxiliary spinal networks for signal focussing in the segmental stretch reflex system.

In continuation of a previous paper, the auxiliary signal focussing properties of more complicated spinal neuronal networks are considered here. Special emphasis is put on the distributive function of the recurrent feedback system of alpha-motoneurones, but also the inhomogeneous distribution of excitatory and inhibitor input to motoneurones is taken into account as an essential prerequisite for signal focussing. Simple hypothetical calculations for steady-state conditions yield a more vivid insight into the interaction of the two types of neuronal circuitry contributing to signal focussing.

Feedback↗
PubMed1978

Origin and nature of correlations in the Ia feedback pathway of the muscle control system.

Mammalian primary muscle spindle endings receive two inputs from fusimotor fibres and length changes of their extrafusal environment. Both inputs are also powerful noise sources disturbing the discharge patterns of the receptors. In this paper emphasis is laid on the extrafusal component. It is shown that extrafusal muscle activity can be viewed as a stochastic process which, acting as a common source, can correlate discharge patterns of adjacent muscle spindles. Some quantitative characteristics of these correlations and their relation to the underlying mechanical events are investigated in some detail in order to provide data for more theoretical considerations on their possible physiological importance.

Action Potentials↗
PubMed1978

Considerations on mechanisms of focussed signal transmission in the multi-channel muscle stretch reflex system.

This paper presents theoretical considerations on the possibility of topographically ordered signal transmission in the control system of the muscle stretch reflex. It is investigated how correlations between Ia fibres from primary muscle spindle endings in conjunction with an appropriate connectivity of Ia fibres and motoneurones enable the stretch reflex system to trace local routes through the spinal cord. The complex data processing capabilities of the motoneuronal soma-dendritic membrane system are fully taken into account, and it is argued that correlations between inputs to this system may play an important role for signal transmission through the spinal cord.

Action Potentials↗
PubMed1977

The influence of extrafusal muscle activity on discharge patterns of primary muscle spindle endings.

The influence of extrafusal muscle activity in anaemically decerebrate cats upon discharge patterns of primary spindle endings was ascertained by simultaneously recording spike trains from several Ia afferents and muscle tension fluctuations of the triceps-surae muscle. 1. Tension fluctuations were averaged with respect to spikes from primary endings yielding tension "trajectories" of specific shape for each spindle and probably reflecting frequently recurring mechanical events in the spindles' surroundings. 2. Spindles situated in close vicinity and influenced by similar mechanical events as evidenced by similar average tension trajectories are correlated in their discharge patterns to a degree depending on the strength of their mechanical coupling. 3. The modulation of spindle discharge frequency in response to average tension changes at the muscle tendon is very different in amplitude for different spindles; this response may show a high sensitivity. It is usually phase advanced by 90-180 degrees with respect to the "internal length" changes; between spindles ther may be phase differences of up to 180 degrees. 4. It is concluded that primary endings react very sensitively to local extrafusal events. The CNS receives much more accurate information about these events in the correlation of several Ia afferents than in the discharge of a single fibre.

Anemia↗
PubMed1976

Analysis of the dynamic responses of deefferented primary muscle spindle endings to ramp stretch.

A detailed analysis of the complex dynamic response of 8 deefferented primary muscle spindle endings to ramp stretches of the extensor digitorum longus muscle (EDL) was made in anaesthetized cats. The analysis was based on Lennerstand's linear muscle spindle model, in which the dynamic peak, i.e. the peak frequency at the end of the dynamic phase of a ramp stretch, is assumed to consist of three components: a position response, a slow velocity response, and a quick velocity response. The components of the dynamic peaks analysed were fairly well correlated with the static behaviour of the primary muscle spindle endings, the latter, in turn, being regarded as an indicator of the spindles' location in the non-homogeneous extrafusal muscle. The results thus provide a satisfactory explanation of the high correlations between the static and gross dynamic behaviour of deefferented primary muscle spindle endings of the EDL previously reported from our laboratory.

Animals↗
PubMed1975

Correlation of the dynamic behaviour of deefferented primary muscle spindle endings with their static behaviour.

20 deefferented primary muscle spindle endings, 8 afferents from the extensor digitorum longus muscle (EDL) and 12 from the tibialis anterior muscle (TA), were investigated in 12 anesthetized cats. Dynamic responses of muscle spindles to ramp stretches were correlated with their static responses. The variation in the state and dynamic behaviour was found to be interdependent. The correlation coefficients were higher for EDL spindles than for TA spindles. The correlation coefficients depended upon the definition of the dynamic responses.

Animals↗