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M Hulliger

Publications and source records attributed to M Hulliger.

At least 19 recordsLinked to original sources
PubMed2003

Chemical ablation of sensory afferents in the walking system of the cat abolishes the capacity for functional recovery after peripheral nerve lesions.

Weakening the ankle extensor muscles of cats by denervation of the synergists of the medial gastrocnemius (MG) muscle results in transient increase in yield at the ankle during early stance. Recovery of ankle function occurs over a period of 1-2 weeks, is use-dependent, and is associated with increases in the strength of reflexes from MG group I muscle afferents and an increase in the magnitude of bursts in the MG muscles during stance. These observations have led to the hypothesis that feedback from large muscle afferents is necessary for functional recovery. In this investigation we have tested this hypothesis by examining functional recovery in animals treated with pyridoxine, a drug known to destroy large muscle afferents. In four adult animals we confirmed that pyridoxine abolished the group I-mediated tendon-tap reflex in the ankle extensor muscle, and subsequently found that group I afferents from MG were either destroyed or non-conducting. Immediately after pyridoxine treatment the animals showed severe locomotor dysfunction but all recovered significantly over a period of 1 or 2 months and showed only minor kinematics deficits at the time of the muscle denervations. In all four pyridoxine-treated animals, weakening of the ankle extensors by denervation of the synergists of the MG muscle resulted in a large increase in yield at the ankle that persisted almost unchanged for a month after the operation. The magnitude of burst activity in the MG muscle during early stance of the pyridoxine-treated animals either did not increase or increased only slightly after the denervation of synergists. These observations are consistent with the hypothesis that feedback from group I afferents is necessary for functional recovery in untreated animals.

Afferent Pathways↗
PubMed2001

A new method for experimental simulation of EMG using multi-channel independent stimulation of small groups of motor units.

The experimental simulation method was based upon the separate activation of up to 10 small groups of motor units (MU) in an acute nerve-muscle preparation. The investigator was able to precisely control and systematically alter the features of MU pool activation strategies. No implicit assumptions were made regarding MU properties. The purpose of this study was to evaluate the validity of this method. Three criteria were formulated and found to be satisfied: First, in the time domain, visual and audio displays of simulated EMG were indistinguishable from physiological EMG. Secondly, in the frequency domain, power spectra of simulated EMG revealed the typical features of EMG recorded during voluntary activation in the cat. Thirdly, the well-known monotonic relationship between EMG magnitude and force was readily reproduced, although strictly linear relations were not found. In addition, the relationship between the pool's ensemble activation rate and EMG magnitude showed distinct gain compression, mostly attributable to signal cancellation.

Animals↗
PubMed2001

Experimental simulation of cat electromyogram: evidence for algebraic summation of motor-unit action-potential trains.

Prompted by the observation that the slope of the relationship between average rectified electromyography (EMG) and the ensemble activation rate of a pool of motor units progressively decreased (showing a downward nonlinearity), an experimental study was carried out to test the widely held notion that the EMG is the simple algebraic sum of motor-unit action-potential trains. The experiments were performed on the cat soleus muscle under isometric conditions, using electrical stimulation of alpha-motor axons isolated in ventral root filaments. The EMG signals were simulated experimentally under conditions where the activation of nearly the entire pool of motor units or of subsets of motor units was completely controlled by the experimenter. Sets of individual motor units or of small groups of motor units were stimulated independently, using stimulation profiles that were strictly repeatable between trials. This permitted a rigorous quantitative comparison of EMGs that were recorded during combined activation of multiple motor filaments with EMGs that were synthesized from the algebraic summation of motor unit action potential trains generated by individual nerve filaments. These were recorded separately by individually stimulating the same filaments with the same activation profiles that were employed during combined stimulation. During combined activation of up to 10 motor filaments, experimentally recorded and computationally synthesized EMGs were virtually identical. This indicates that EMG signals indeed are the outcome of the simple algebraic summation of motor-unit action-potential trains generated by concurrently active motor units. For both recorded and synthesized EMGs, it was confirmed that EMG magnitude increased nonlinearly with the ensemble activation rate of a pool of motor units. The nonlinearity was largely abolished when EMG magnitude was estimated as the sum of rectified, instead of raw, motor-unit action-potential trains. This suggests that the downward nonlinearity in the EMG-ensemble activation rate relation is due to signal cancellation arising from the perfectly linear summation of positive and negative components of action-potential waveforms. The findings provide a much needed post hoc validation of the concept of EMG generation by strict algebraic summation of motor unit action potentials that is generally relied on in theoretical modeling studies of EMG and in EMG decomposition algorithms.

Action Potentials↗
PubMed1998

Proprioceptive control of posture: a review of new concepts.

The assumption that proprioceptive inputs from the lower legs are used to trigger balance and gait movements is questioned in this review (an outgrowth of discussions initiated during the Neural Control of Movement Satellite meeting held in Cozumel, Mexico, April 1997). Recent findings presented here suggest that trunk or hip inputs may be more important in triggering human balance corrections and that proprioceptive input from the lower legs mainly helps with the final shaping and intermuscular coordination of postural and gait movements. Three major questions were considered. First, what role, if any, do lower-leg proprioceptive inputs play in the triggering of normal balance corrections? If this role is negligible, which alternative proprioceptive inputs then trigger balance corrections? Second, what is the effect of proprioceptive loss on the triggering of postural and gait movements? Third, how does proprioceptive loss affect the output of central pattern generators in providing the final shaping of postural movements? The authors conclude that postural and gait movements are centrally organized at two levels. The first level involves the generation of the basic directional-specific response pattern based primarily on hip or trunk proprioceptive input secondarily on vestibular inputs. This pattern specifies the spatial characteristics of muscle activation, that is which muscles are primarily activated, as well as intermuscular timing, that is, the sequence in which muscles are activated. The second level is involved in the shaping of centrally set activation patterns on the basis of multisensorial afferent input (including proprioceptive input from all body segments and vestibular sensors) in order that movements can adapt to different task conditions. Copyright 1998 Elsevier Science B.V.

Journal Article↗
PubMed1998

Correlated histological and physiological observations on a case of common sensory output and motor input of the bag1 fibre and a chain fibre in a cat tenuissimus spindle.

In muscle spindles of the cat, independent control of dynamic and static components of the response of the primary sensory ending to stretch is provided by separate motor inputs to the various kinds of intrafusal muscle fibre: dynamic axons (gamma or beta) to the bag1 fibres and static axons to the bag2 (typically gamma only) and chain (gamma or beta) fibres. Nonlinear summation of separately evoked effects during combined stimulation of dynamic and static motor axons appears to be due to mutual resetting by antidromic invasion of separate encoding sites, leading to partial occlusion of the momentarily lesser response by the greater. The encoding sites are thought to be located within the primary ending's preterminal branches which from first-order level are normally segregated to the bag1 fibre and to the bag2 and chain fibres. Here we describe the analysis of a special case that arose in a histophysiological study which had shown that the degree of occlusion was related to the minimum number of nodes between the putative encoding sites. Three-dimensional reconstruction of the primary ending revealed that the terminals of one chain fibre were derived entirely from the first-order branch that supplied the bag1 fibre, including one terminal that was shared directly with the bag1 (sensory cross-terminal). The other first-order branch supplied the bag2 and remaining chain fibres as normal. The degree of occlusion seen during simultaneous stimulation of a dynamic beta axon and a static gamma axon indicated that the encoding sites were separated by both first-order branches. Schematic reconstruction of the motor innervation revealed that the static gamma axon was most unlikely to have supplied the chain fibre which shared sensory terminals with the bag1, but that these fibres also shared a motor input with histological characteristics of beta type. Ramp-frequency stimulation of the dynamic beta axon at constant length evoked a driving effect which persisted after fatiguing the extrafusal component and was therefore explicable on the basis of the observed pattern of motor innervation, though the identity of the axon could not be conclusively proved. Individually, instances of shared sensory terminals and motor input of bag1 and chain fibres are rare in the cat; their combination in a single spindle with correlated physiology is described here for the first time. The observation is considered in relation to the importance of dynamic and static segregation in motor control, since it may imply that there is a lower limit to the degree of segregation that the developmental programme can provide.

Animals↗
PubMed1998

Intrinsic muscle properties facilitate locomotor control - a computer simulation study.

The purpose of this study was to investigate, theoretically, to what extent muscle properties could contribute to recovery from perturbations during locomotion. Four models with different actuator properties were created: the FLVT model, which encompassed force-length (FL) and force-velocity (FV) characteristics of human muscles as well as muscle stimulation inputs as functions of time (T); the FLT model, which had muscles without force-velocity characteristics; the FVT model, which had muscles without specific force-length characteristics; and the MT model, which had no muscles but was driven by joint moments (M) as a function of time. Each model was exposed to static and dynamic perturbations and its response was examined. FLVT showed good resistance to both static can dynamic perturbations. FLT was resistant to static perturbation but could not counteract dynamic perturbation, whereas the opposite was found for FVT. MT could not counteract either of the perturbations. Based on the results of the simulations, skeletal muscle force-length-velocity properties, although interactively complex, contribute substantially to the dynamic stability of the musculoskeletal system.

Computer Simulation↗
PubMed1998

A modified Bessel filter for amplitude demodulation of respiratory electromyograms.

We studied a device that is commonly used for amplitude demodulation of respiratory muscle electromyograms (EMG). This device contains a rectifier and a low-pass filter called a modified third-order Paynter filter. We characterized this filter and found that it has good transient characteristics that suit its task as an EMG demodulator, but it has poor high-frequency attenuation that passes interfering, higher frequency components to the output waveform. Therefore, we designed and constructed a new filter with transient characteristics that are comparable to those of the modified Paynter filter but with superior high-frequency attenuation. This new filter is a modified seventh-order Bessel filter. We also identified a simple technique to convert an existing modified Paynter filter back to an original Paynter filter. The original Paynter filter has a wider pass band than the modified Paynter filter but superior stop-band attenuation.

Electrocardiography↗
PubMed1997

Pacemaker activity in a sensory ending with multiple encoding sites: the cat muscle spindle primary ending.

1. A combined physiological, histological and computer modelling study was carried out on muscle spindles of the cat tenuissimus muscle to examine whether there was any correlation between the functional interaction of putative encoding sites, operated separately by static and dynamic fusimotor neurones, and the topological structure of the preterminal branches of the primary sensory ending. 2. Spindles, whose I a responses to stretch and separate and combined static and dynamic fusimotor stimulation were recorded in physiological experiments, were located in situ. Subsequently the ramifications of the sensory ending were reconstructed histologically, and the topology of the branch tree was used in computer simulations of I a responses to examine the effect of the electronic separation of encoding sites on the static-dynamic interaction pattern. 3. Interactions between separate static and dynamic inputs, manifest in responses to combineed stimulation, were quantified by a coefficient of interaction (Ci) which, by definition, was 1 for strictly linear summation of separate inputs and zero for maximum occlusion between inputs. 4. For the majority of spindles static-dynamic interactions were characterized by pronounced occlusion (C1 < 0.35). In these spindles putative encoding sites (the peripheral heminodes of the branches supplying the intrafusal fibres activated by individual fusimotor efferents) were separated by a minimum conduction path of between three and ten myelinated segments (2-9 nodes of Ranvier). In contrast, significant summation (C1, approximately 0.7) was found in only one spindle. In this case putative encoding sites were separated by a single node. 5. Occlusion was not due to encoder saturation and it could not be accounted for by any other known physiological mechanisms (intrafusal fatigue or unloading). It is therefore attributed to competitive pacemaker interaction between encoding sites which are largely selectively operated by static and dynamic fusimotor efferents. 6. Model simulations of real preterminal-branch tree structures confirmed that short conduction paths between encoding sites were associated with manifest summation, whereas longer minimum conduction paths favoured pronounced occlusion. 7. In the extreme, occlusion could be so pronounced as to give rise to negative values of C1 during critical segments of response cycles. This was associated with lower discharge rates during combined static and dynamic stimulation than the higher of the individual stimulation effects. This phenomenon is referred to as hyperocclusion. Computer simulations demonstrated that hyperocclusion could be accounted for by a slow ionic adaptation process. e.g. by a very slowly activating K+ conductance.

Animals↗
PubMed1995

A model study on the influence of a slowly activating potassium conductance on repetitive firing patterns of muscle spindle primary endings.

The general mathematical model of Frankenhaeuser and Huxley, which describes the generation of action potentials in myelinated nerve fibres, has been used as a kernel for a model of a sensory nerve ending. Two types of modifications were implemented. First, the four original permeability constants (those of potassium, sodium, non-specific and leak) were changed simultaneously (using an automated tuning algorithm), in order to introduce low-frequency repetitive firing capability (down to 15 Hz), keeping the deviations from the original values as small as possible. Second, a slow potassium conductance was added, in order to model slow processes (like accommodation) with time constants longer than those required to simulate short-lasting action potentials. Sensory stimuli were simulated as changes in passive conductance. The model displayed the following properties, which are typical of many sensory endings in general and of muscle spindle primary endings in particular: (i) The range of sustained repetitive firing was extended into the domain of low discharge rates, so as to span the entire physiological range (from 2 to 700 sec-1). (ii) The relation between firing rate and receptor potential was roughly linear over the full range of firing. (iii) Following a step increase of stimulus, the firing rate showed adaptation with a time constant of about 70 msec. (iv) Sudden reduction of the stimulus was followed by post-release silence. (v) Following a step increase of stimulus, the receptor potential showed a short dynamic peak. (vi) Following a step decrease of stimulus, the receptor potential displayed a post-release undershoot and recovery with a time constant of approximately 100 msec. (vii) With sinusoidal stimuli the receptor potential showed band-pass filter properties with phase advance below and phase lag above 12 Hz and a peak in gain at about 20 Hz. Thus the present equations adequately describe a range of known properties of muscle spindle primary endings. Based on minimal modification and extension of the Frankenhaeuser-Huxley model of action potential generation in myelinated fibres, they constitute a theory of sensory encoding. This theory is further corroborated by the experimental evidence of the presence of calcium-activated potassium channels in numerous sensory--including primary spindle--endings.

Action Potentials↗
PubMed1995

Influence of sensory input on plantar pressure distribution.

The sensory feedback control system plays a central role in human locomotion. However, few studies have been published discussing the influence of sensory input at the plantar surface of the foot on the kinematics and kinetics of locomotion. The purpose of this study was to examine the effect of changes in sensory input at the plantar surface of the foot on the pressure distribution measured at the plantar surface of the foot. Three pairs of specially made socks with sand at the plantar surface of the foot and one pair of normal socks were used to simulate different sensory inputs. Pressure distribution at the plantar surface of the foot was measured using an emed system for 10 subjects for each of the four sensory input conditions during walking and running on a treadmill. The results showed significant and substantial changes in pressure in selected areas for changes in sensory input. The pressure increased in the midfoot area and decreased in the toe area with increasing sensory inputs. These results are similar to results of a previous study where similar changes were found in a comparison between comfortable and uncomfortable shoes. RELEVANCE: Pressure distribution is increasingly used in clinical assessments. However, the factors influencing the pressure distribution pattern are only partially understood. One factor may be the sensory input into the foot. It is important to understand this influence in order to provide appropriate interpretation of the pressure distribution data.

Journal Article↗
PubMed1994

Component analysis of the responses of sensory neurons to combined sinusoidal and triangular stimulation.

A method for quantitative estimation of sensory neuron sensitivity to small sinusoidal stimuli in the presence of sizable background drift (in the stimulus or response) was developed. The performance of the method was tested by analyzing the responses of 17 muscle spindle primary (Ia) afferent neurons to concomitant sinusoidal and triangular stretching of the soleus muscle. The efficacy and accuracy of several variations of the method were examined. The variations included the use of probability density (PD) and average frequency (AF) histograms as the basis for calculations and two different algorithms for the decomposition of responses to combined sinusoidal and triangular stimulation. One algorithm called the 'inherent-drift' method exploited the inherent half-cycle repeat property of a sine wave to extract the drift component. Another algorithm called the 'forced-drift' method first estimated the drift by linear regression to a response to triangular stimulation alone. The drift estimate (a slope value) was then subtracted from the response to combined sinusoidal and triangular stimulation of the same triangular (background) velocity. A comparison of the performance of the drift correction method applied either to PD or AF histograms revealed no significant differences in the estimates of sinusoidal modulation. The limitations of the AF method were manifest primarily by phase lags at low mean levels of action potential discharge. Calculation of the response parameters using the 'inherent-drift' correction procedure proved straightforward as long as there were at least two pairs of non-empty bins in the sine-cycle histograms on which to base the estimate of drift. The method remained effective in determining sinusoidal sensitivity in the face of distinct non-linearities (harmonic distortions) in the sine-cycle histograms. However, estimates of slope and the extraction of sinusoidal phase by the 'inherent' slope correction method became subject to large errors. Under such circumstances, more reliable estimates could be obtained by using the forced drift-correction method instead. The importance of extracting the drift component prior to estimating the sinusoidal response parameters was evaluated experimentally and theoretically. In general, omission of a drift correction introduced a large bias in the estimates of the phase of sinusoidal response, whereas the estimate of sinusoidal modulation was rather insensitive. Experimental findings were fully accounted for by theoretical considerations. Analytically derived relationships identified low- and high-risk regions more clearly for the estimate of sinusoidal modulation than of phase. The relationship between biased modulation estimate and underlying drift showed minima characteristics with a low-risk region, where absolute errors and dependence on slope variations were small.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1994

Quantitative analysis of human movement synergies: constructive pattern analysis for gait.

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

Journal Article↗
PubMed1994

EMG-force relationship of the cat soleus muscle studied with distributed and non-periodic stimulation of ventral root filaments.

Distributed stimulation of ventral root (VR) filaments and pseudo-random interpulse intervals (based on a Gaussian distribution with a coefficient of variation of 12.5%) were used to modulate electromyographic activity (EMG) and force of the cat soleus muscle to assess the EMG-force relationship. A protocol consisting of addition and rate modulation of ten VR filaments that contain alpha motoneurones to the soleus muscle was adopted. EMG was measured using indwelling electrodes and forces were measured at the distal tendon using a strain transducer. EMG records obtained using this approach were similar in the time and frequency domains to those obtained during voluntary contractions. Force records obtained from stimulation of single VR filaments showed summation effects typical of irregular interpulse intervals. The overall relationship between integrated rectified EMG (IEMG) and mean force was found to be non-linear. At low and high stimulation levels, IEMG tended to increase proportionally more than mean force. In the intermediate stimulation region (i.e. producing forces between approximately 5% and 88% of the maximal tetanic force), the IEMG-mean force relationship was virtually linear. Muscles with a homogeneous fibre type composition, such as the cat soleus muscle, have been reported to have a linear EMG-force relationship.

Animals↗
PubMed1994

Effects of muscle length on the EMG-force relationship of the cat soleus muscle studied using non-periodic stimulation of ventral root filaments.

The effects of changing the length of the cat soleus muscle on electromyographic (EMG) signals, muscle force and the corresponding EMG-force relationship were assessed using distributed stimulation of ten ventral root filaments and irregular interpulse intervals. EMG-force relationships were first determined for four muscle lengths using a protocol of simultaneous addition and rate modulation of ventral root filaments. In the second test, three submaximal levels of stimulation were applied at eight muscle lengths. EMG signals were obtained using surface and wire electrodes, and force was measured using a strain transducer. For most muscle lengths, the relationships between integrated EMG and mean force obtained using wire and surface electrodes were sigmoid with a linear intermediate region. The effects of muscle length on EMG signals were likely to be associated with movement of the recording electrodes relative to each other and to the active motor units. Mean forces increased with increasing muscle length and with increasing levels of stimulation. Mean force-length relationships obtained using submaximal stimulation were not simply scaled down versions of the force-length relationship obtained using supramaximal stimulation of the soleus nerve, but appeared to be shifted towards longer muscle lengths.

Action Potentials↗
PubMed1993

Fusimotor control of proprioceptive feedback during locomotion and balancing: can simple lessons be learned for artificial control of gait?

The possibilities for central control of primary spindle afferents through fusimotor efferents for gain control in motor control mechanisms are briefly reviewed. While the existence of separate pathways for independent control of static and dynamic gamma-motoneurones is well established, it proved more difficult to demonstrate that gain control of spindle feedback, attributable to alterations in static and dynamic fusimotor drive, indeed took place in voluntary movements. However, earlier qualitative indications, that Ia sensitivity (and hence the balance of static over dynamic drive) was adjusted differently in different motor tasks, have recently been confirmed in experimental simulation studies, in which the fusimotor activation profiles, that were required to reproduce chronically recorded spindle Ia discharge patterns, were reconstructed. These studies indicated that Ia sensitivity and dynamic gamma-drive were low in routine movements (walking), but that they could be dramatically increased in motor tasks which were either difficult or unfamiliar (landing from falls, balancing on narrow walk beams, adjustment to imposed disturbances). This suggested that sensitization of spindle feedback could play a significant role in motor adaptation. In line with this, studies in patients with large fibre sensory (including proprioceptive) neuropathies indicated that long-term motor deficits (affecting motor adaptation and learning) could be at least as serious as short-term motor dysfunction (due to loss of reflex control). It is suggested that spindle Ia feedback may play a dual role: in addition to its contribution to short-term reflex control of posture and movement, it may also be used for optimization or maintenance of motor programs, especially if its gain is increased by significant dynamic fusimotor drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1991

Reciprocal Ia inhibition in patients with spinal spasticity.

Reciprocal Ia inhibition from ankle flexors to extensors was studied in five patients with spasticity due to incomplete traumatic spinal cord lesions. Nine healthy subjects were tested as controls. Excitability of the soleus motoneuron pool was estimated by H-reflex testing in the resting state. Ia inhibition was activated by conditioning stimuli to the peroneal nerve. Ia inhibition was detected in all patients tested, the amount of inhibition ranging from 8% to more than 50% of the test H-reflex size. In the control subjects only weak Ia inhibitory effects were present. These findings indicate increased excitability of the Ia inhibitory pathway to ankle extensor motoneurons in patients with spasticity due to spinal cord injury.

Adult↗