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H T Weiler

Publications and source records attributed to H T Weiler.

18 recordsLinked to original sources
PubMed2004

Brain potentials and behavioral responses associated with attention to hard- and easy-to-discriminate passive knee joint movements.

We investigated event-related brain potentials (ERPs) to passive ramp movements of the knee joint. The knee movements were either attended or unattended and were either very easy or very hard to detect. We used special methods to ensure that movement only activated muscle spindle and joint receptors. The first movement-related ERP started 20 ms after movement onset, and had a contralateral maximum. This initial ERP did not differ as a function of attention and movement discriminability. Signal detection analysis of the behavioral data suggested that hard-to-detect movements could be discriminated above chance level, but were not reported because of a decision bias. At 60-100 ms, an ERP was observed that discriminated detected from undetected hard-to-detect movements. Starting at 80 ms, we found an ERP that was unique to movements that were attended and easy to detect. We discuss that (1) the initial ERP reflects activation of preconscious sensory processors, (2) the second ERP may reflect detection that fails to attract attention, and (3) the third ERP reflects active focusing of attention on the movement.

Adult↗
PubMed2001

Characterisation of human knee-joint proprioception by means of a signal-detection theory.

Human proprioceptive performance of movement detection in joints is currently believed to be based on information from muscle spindles. In previous studies investigating proprioception, we found remarkable differences in threshold values using a conventional movement-detection paradigm and a threshold-hunting paradigm. One reason could be that central processing, the evaluation of the peripheral sensation, was responsible. Therefore, the study was designed to determine, besides the proprioceptive performance, the central processing of movement detection in the knee joint by means of a signal-detection technique (SDT). Only this technique provides parameters such as detectability (d') and the decision criterion (beta), which distinguish between these performances. From the resulting psychometric functions, the threshold (a parameter of classical psychophysics) also was evaluated. This threshold parameter (PCmax), derived from the SDT parameter d', indicates that detection is above threshold when subjects detect only 20-30% of the applied stimuli, as sham stimuli were detected also. The detectability increased with increasing velocity and up to a certain value with increasing amplitude. The threshold for movement detection was lower than 0.25 degree for the three faster angular velocities (0.1 degree s-1, 0.5 degree s-1, 0.6 degree s-1) and lower than 0.75 degree for the slowest velocity (0.05 degree s-1). The decision criterion beta, a measure for central processing which determines acuity, might reflect the central processing output on fusimotor neurones and thus be an indirect measure of the gamma-drive evoked by fusimotor neurones.

Adult↗
PubMed2000

Differences between motion-direction perception and unspecific motion perception in the human knee joint.

Perception has commonly been seen as a conscious performance. Thus, regarding proprioception in some publications, it has been proposed that the term is properly used only when subjects are able to report on the direction as well as presence of imposed movements. Consequently, detections of movements without movement-direction perception have not been accepted as perceived, since these detections were regarded as unspecific. Unspecific sensation has been suggested to precede perception. From this "two-state model", it follows that threshold values should be lower for unconscious unspecific perception than for conscious specific perception. The aim of the present study was to test this suggested dichotomy. Proprioception was compared in unspecific detection trials (only the occurrence of a movement had to be detected, not its direction) and direction-specific detection trials (the occurrence of a movement of a specific direction had to be detected). Two types of specific detection trials and two types of unspecific detection trials were studied. Pairs of threshold values were determined, regarding amplitude detection using different angular velocities and regarding velocity detection using different angular displacements, for flexion and extension. Our results showed that, independent of each other, both threshold paradigms (amplitude detection and velocity detection) revealed the same perception characteristics. In specific detection paradigms, the proprioceptive thresholds were two times lower than in unspecific detection paradigms. Thus, movements of a particular type could be detected more easily than movement per se. The suggested "two-state model" might, therefore, not be appropriate in describing proprioceptive perception.

Adult↗
PubMed2000

Influence of hysteresis on joint position sense in the human knee joint.

During muscle lengthening in a movement cycle the firing rate of muscle spindles is higher than during shortening. This phenomenon, known as hysteresis, has implications for movement control. Therefore, it should have an impact on joint position sense (JPS), the subject's awareness of the static position of a joint. JPS has been tested on the human knee joint by means of an angle reproduction test. This task included the following sequences. The leg was moved passively, by means of a motor drive, from two different start positions (15 degrees and 75 degrees) to a certain target angle and, after a time of 8 s, it was returned to the start position; subjects had to reproduce the former target angle. Several target angles, mild flexion (30 degrees), intermediate flexion (45 degrees), and strong flexion (60 degrees), were used. Depending on the start position, the movements matching these targets were flexions or extensions. At least for the intermediate position different threshold values should be expected for flexions and extensions, if hysteresis has an impact. Moreover, the JPS measure should show a dependence on movement velocity and independence on distance. Of the variables tested, only movement direction but not movement velocity or distance had a statistically significant impact on the dependent constant angle error (difference between reproduction and target angle). The target angle of 30 degrees was exactly reproduced (-0.14 degrees), independently of the start position. The 45 degrees target angle was significantly underestimated (-4.39 degrees) when matching that position by flexions (starting at 15 degrees) compared to an overestimation (2.27 degrees) when matching that position by extensions (starting at 75 degrees). The target angle of 60 degrees has been constantly underestimated (-3.80 degrees), independently of the start position. Therefore, hysteresis, the dependency of the movement's direction, neglected in the past, should be considered in future tests of JPS or studies considering the role of movement parameters for motor control.

Adult↗
PubMed2000

Nonspecific velocity and amplitude hunting reveals different specific detection performance of flexion and extension movements in the human knee joint.

A debate exists in the literature as to what extent perception is conscious. In some publications regarding proprioception, the term proprioception has explicitly only been seen as properly used when subjects were able to report the imposed movement's direction. Detections of movements without movement-direction perception, have been seen as nonspecific. Since a lot of studies discussed this point but never tested it explicitly, we tested it by using nonspecific hunting paradigms (only the occurrence of a movement has to be detected, not its direction) with the following rationale. If the perception performance is really nonspecific, no difference regarding the movement's direction should be found. Thus, if we found a different detection performance regarding flexion and extension by means of a nonspecific paradigm, it would demonstrate that this "nonspecific" perception is already specific. Therefore, we measured the perception characteristics separately for flexion and extension. The perception characteristics have been determined from the amplitude-velocity-relation curve. Two different, nonspecific hunting paradigms, modifications of our previously published specific hunting paradigm, have been used. Thus, we determined pairs of threshold values, regarding amplitude hunting using three different angular velocities (0.1 degrees s(-1), 0.25 degrees s(-1), and 0.5 degrees s(-1)) and regarding velocity hunting using three different angular displacements (0.25 degrees, 0.5 degrees, and 1 degrees) as well, for flexion and extension, respectively. We found that both threshold paradigms (velocity hunting and amplitude hunting) revealed the same perception characteristics for a given movement direction. With an increasing angular velocity, angular displacement threshold values converged toward a common value for flexion and extension (about 0.2 degrees); with an increasing angular displacement, angular velocity threshold values converged toward separate values for flexion (about 0.06 degrees s(-1)) and extension (about 0.1 degrees s(-1)). Thus, our findings demonstrate that detection performance is specific and not bound to conscious perception, since specific thresholds for flexion and extension were revealed with nonspecific hunting paradigms.

Adult↗
PubMed2000

Proprioception after total knee arthroplasty: a comparison with clinical outcome.

We determined proprioception in replaced and unreplaced arthrotic knees by measuring threshold levels for the perception of passive knee motion. In addition, results of these proprioception measurements were compared with the clinical outcomes in patients with a total knee arthroplasty. Threshold detection levels were significantly higher in the replaced than in the unreplaced knees. Moreover, detection-failure rates were significantly higher in the replaced knees as well. In contrast to this diminished movement sense in the replaced knees, clinical examination of these knees showed good or excellent outcome in all cases. A correlation between the clinical outcome and the ability to perceive passive motion in either patient group could not be found. We hypothesize that our findings may be due to the operative removal of intraarticular receptor-rich tissue that is affected by arthrosis. This would not only contribute to marked clinical improvements but also to a significant decrease in proprioception.

Activities of Daily Living↗
PubMed2000

The role of joint afferents in sensory processing in osteoarthritic knees.

OBJECTIVE: To test the role of joint receptors for proprioception in patients with bilateral knee osteoarthritis (OA) and patients who had undergone unilateral total knee arthroplasty (TKA). METHODS: Nine patients were tested bilaterally with a conventional movement detection paradigm that evaluated conscious detection perception and a newly developed hunting paradigm that measured maximal sensory performance (hunting perception). RESULTS: For detection perception, patients exhibited a slightly lower threshold on the arthritic side than on their TKA side. For hunting perception, the patients showed threshold values that were an order of magnitude smaller than for the conventional paradigm in both knees. Performance was much better on prosthetic knees than on OA knees. CONCLUSION: The joint receptors of OA knees might have an adverse effect on the maximal proprioceptive performance, being important for the normal reflexive knee joint functions. These deficits may be overcome by joint receptor removal during knee replacement.

Knee Joint↗
PubMed1999

Bilateral deficit of voluntary quadriceps muscle activation after unilateral ACL tear.

PURPOSE: The inability to fully activate the quadriceps femoris muscle voluntarily is known to accompany several different knee-joint pathologies. The extent of a voluntary-activation deficit in patients after isolated rupture of the anterior cruciate ligament (ACL), however, has been reported to be small or nonexistent, making it questionable if a voluntary-activation deficit is a relevant factor for these patients at all. METHODS: In this study the ability to voluntarily activate the quadriceps femoris muscles was quantified in 22 male patients with arthroscopically-proven isolated ACL ruptures using an established highly sensitive twitch-interpolation technique. Furthermore, the maximal voluntary contraction force of the quadriceps muscle was obtained by isometric knee-joint torque measurements. The results were compared with an age-, gender-, and activity-matched control group. RESULTS: There was a moderate but significant mean reduction in maximal voluntary activation (VA) in both the injured (VA: 83.9 +/- 2.3%, mean +/- SEM) and uninjured side (VA: 84.7 +/- 2.2%) in comparison with controls (VA: 91.1 +/- 0.8%). However, of the patients the 23% who presented a considerably reduced voluntary-activation of less than 80% were mainly responsible for the significant mean deficit. CONCLUSIONS: The deficit of isometric muscle strength on the injured side compared with that of controls was explained by the voluntary-activation deficit and a true muscle weakness. On the other hand, the diminished muscle strength of the uninjured side was explained sufficiently by the voluntary-activation deficit alone. Considering the bilateral voluntary-activation deficit, functional muscle tests might not be valid when the uninjured extremity serves as reference.

Adolescent↗
PubMed1998

Characterization of human joint proprioception by means of a threshold hunting paradigm.

A method has been developed to measure the proprioceptive performance of movement detection in human joints, with the threshold hunting paradigm commonly used in other sensory modalities. Methods applied in former studies regarding movement detection were very time consuming (hours), making them not applicable to patients. Using the threshold hunting paradigm, the subject changes the parameter value continuously around the threshold producing a threshold hunting curve, which itself might be valuable for investigation of movement detection performance. The method presented here, is very quick compared to other studies in this field, especially when velocity is hunted and the threshold values are very low. The threshold parameter value is stable since there is a control at any time over the subject's stimulus perception. Furthermore, a Monte Carlo simulation showed that hunting curves can clearly be distinguished from guessing. Also reliability is given. All these points allow to use the method to evaluate the proprioceptive performance of a single individual. Considering the results, the method described may be useful for basic and clinical investigations regarding the proprioceptive performance limits of movement detection aspects.

Adult↗
PubMed1998

Differential modulation of hippocampal signal transfer by tuberomammillary nucleus stimulation in freely moving rats dependent on behavioral state.

Tuberomammillary histamine neurons (TM) in the posterior hypothalamus project to extensive parts of the brain, including the hippocampal formation. The purpose of the present experiments was to investigate whether activation of the TM modulates signal transfer from the perforant pathway (PP) or ventral hippocampal commissure (VHC) to the dentate gyrus (DG) in freely moving rats. Paired pulses of electrical stimulation were delivered to PP or VHC, and evoked field potentials (fEPSPs and pop spikes) were recorded in the DG. Before activating PP or VHC, the TM was triggered by electrical stimulation. Experimentation was performed during four behavioral conditions: exploration, grooming, awake immobility, and slow-wave sleep. Electrical activation of the TM was found to modify dentate fEPSPs evoked by PP or VHC stimulation without generating a field potential by itself. Train stimulation of the TM (100 Hz, 500 ms) preceding paired pulses on the hippocampus by 50 ms decreased dentate fEPSPs in dependence of the ongoing behavior and the pathway stimulated. During exploration but not consummatory behavior, the PP signal was reduced when preceded by TM stimulation; during consummatory behavior but not exploration, the VHC signal was reduced. In contrast to other hippocampal afferents which increase pop spikes but leave fEPSPs unchanged, TM stimulation decreased dentate fEPSPs without affecting pop-spike activity. Thus, the TM-histaminergic system seems to modulate signal processing in the dentate gyrus in a specific way, exerting an inhibitory action on the entorhinal input only during learning-related exploratory behavior.

Animals↗
PubMed1998

Facilitation of learning after lesions of the tuberomammillary nucleus region in adult and aged rats.

The tuberomammillary nucleus (TM) located in the posterior part of the hypothalamus is the main source of neuronal histamine in the central nervous system. Recent work from our laboratories has indicated an involvement of the TM region in neuronal plasticity and reinforcement processes. In the present study, we investigated the effects of TM lesions on the performance of adult and aged Wistar rats in a set of learning tasks, which differed in terms of complexity and reward contingencies (habituation learning, inhibitory avoidance, discrimination learning, Morris water maze). An improvement was found in every test applied, indicating that TM lesions seem to generally enhance learning and memory capacities independent of the special demands of a given task. Age-related learning deficits were strongly diminished. Immunohistochemistry revealed that the excitotoxic lesions used to destroy the TM region led to a marked decrease in the number of histamine-positive neurons in the vicinity of the injection site, indicating an involvement of the brain histaminergic system in the observed behavioral changes.

Aging↗
PubMed1993

Amplification of rewarding hypothalamic stimulation following a unilateral lesion in the region of the tuberomammillary nucleus.

The tuberomammillary nucleus, a cluster of cells in the posterior hypothalamus, is the only known source of brain histamine. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. In the present study, the effect of a lesion in the region of this nucleus on intracranial self-stimulation was examined. Rats were implanted bilaterally with stimulating electrodes in the lateral hypothalamus and unilaterally with one lesion electrode in the region of this nucleus. After three days of baseline testing, half of the animals were given an electrolytic lesion. The animals were retested for six consecutive days, and thereafter weekly for another seven weeks. From the second day postlesion on, we unexpectedly found a gradual increase in response rate, which peaked on day 13 in the ipsilateral hemisphere only. Although there was no further increase over subsequent days, response rates remained elevated during the following seven weekly tests. The observed increase in lateral hypothalamic self-stimulation after an electrolytic lesion of the tuberomammillary nucleus is discussed in terms of an inhibitory system, possibly located in the region of this nucleus which, when removed by the lesion, increased reinforcing effects of the electrical brain stimulation. The fact that the effects on self-stimulation were lateralized to one hemisphere rules out an interpretation in terms of unspecific "performance" variables that could influence rate of lever pressing.

Animals↗
PubMed1992

Unilateral lesion in the tuberomammillary nucleus region: behavioral asymmetries and effects of histamine precursor.

The subnuclei of tuberomammillary nucleus are located in the posterior part of the hypothalamus adjacent to the basolateral surface of the mammillary bodies. The neurons of this nucleus innervate extensive parts of the brain with several transmitters, particularly with histamine. In fact, they represent the only source of histaminergic projections in the brain. The present study deals with the effects of a lesion in this region on behavior. Unilateral electrolytic direct current (DC) lesions in the tuberomammillary nucleus led to an asymmetry in thigmotactic scanning; i.e., at 11 days, but not 1 day postlesion, the rats scanned the walls of an open field more with the vibrissae contralateral to the lesion than with those of the ipsilateral side. Furthermore, they emitted more ipsiversive than contraversive wide angle turns. The behavioral asymmetries are, in general, opposite in direction to those induced by lesion of the neighboring lateral hypothalamus and substantia nigra, indicating that they are specific to the tuberomammillary region destroyed. Application of the histamine precursor histidine led to a compensation of these asymmetries, suggesting that the tuberomammillary's histaminergic efferents are functionally related to the lesion-induced behavioral effects.

Animals↗
PubMed1992

Time-dependent neuroplasticity in mesostriatal projections after unilateral removal of vibrissae in the adult rat: compartment-specific effects on horseradish peroxidase transport and cell size.

In adult rats the mystacial vibrissae were clipped on one side of the snout, and the influence of this sensory deprivation on crossed and uncrossed striatal afferents from the substantia nigra, ventral tegmental area, and retrorubral area was examined with the horseradish peroxidase tract tracing technique. Unilateral removal of vibrissae was found to affect crossed and uncrossed nigrostriatal projections in a time-dependent manner. One to three days after hemivibrissotomy an apparent neuronal asymmetry was found in the crossed nigrostriatal projection arising in the rostral part of the substantia nigra, with more labeled neurons in the projection to the caudate-putamen on the side of vibrissae removal. This asymmetry resulted mainly from an asymmetry in the subset of nigrostriatal neurons reported to project to the striatal matrix ("dorsal cell type"). In contrast, 4-20 days after hemivibrissotomy reversed asymmetries were found in crossed and uncrossed nigrostriatal projections, with more labeled neurons in the projections to the caudate-putamen of the hemisphere opposite to vibrissae removal (the sensory deprived hemisphere). The asymmetry in the uncrossed projection was found throughout the substantia nigra, but was also most substantial in the projection from its rostral part. The asymmetry in the crossed projection was again restricted to the rostral substantia nigra; interestingly, however, it was limited to the subset of neurons reported to terminate in the striosomes ("ventral cell type"). Evidence was also found for time-dependent changes in size of neurons of the crossed nigrostriatal projections, as well as for changes in striatal afferents from the ventral tegmental area. The time course of these apparent changes in strength of mesostriatal projections is similar to the known time course of recovery from behavioral asymmetries induced by hemivibrissotomy, which is suggestive of a functional relationship between neuronal and behavioral changes. Moreover, the finding of a differential influence of hemivibrissotomy on nigrostriatal afferents to striosomes and matrix is indicative of a functional dissociation of these two systems.

Analysis of Variance↗
PubMed1990

Plasticity in crossed and uncrossed tuberomammillary-striatal projections in relation to recovery from behavioral asymmetries induced by hemivibrissotomy.

The influence of unilateral removal of the adult rat's vibrissae on crossed and uncrossed tuberomammillary-striatal projections was examined with the horseradish peroxidase tract tracing technique. Striatal afferents from the caudal magnocellular and the postmammillary caudal magnocellular subnuclei of the tuberomammillary nucleus were investigated. Between four and 20 days after clipping the vibrissae on one side, more retrogradely labeled cells were found in the crossed and uncrossed projections from both subnuclei to the caudate-putamen of the hemisphere opposite to vibrissae removal (i.e. the sensory deprived hemisphere) than in the projections to the caudate-putamen on the vibrissae-clipped side. In contrast, between one and three days after clipping the vibrissae no asymmetries in cell-labeling in these projections were found. This time-course of changes in the tuberomammillary-striatal projections is similar to the time-course of behavioral recovery reported after unilateral removal of vibrissae. Thus, the neural changes in these projections appeared at the point in time when rats recovered from behavioral asymmetries induced by vibrissae removal.

Animals↗
PubMed1990

The basal ganglia-orofacial system: studies on neurobehavioral plasticity and sensory-motor tuning.

We have employed the unilateral removal of the vibrissae as a tool to examine ensuing behavioral changes in relation to concomitant changes in the central nervous system. In this paper we review a series of studies showing that unilateral removal of the vibrissae leads to behavioral asymmetries (e.g., in thigmotactic scanning) from which rats recover over time. Time-related to these behavioral changes we found neuronal alterations in striatal afferents, that is, in uncrossed and crossed projections from the substantia nigra and the tuberomammillary nucleus. The involvement of dopaminergic mechanisms was indicated by results showing that dopaminergic agonists can induce asymmetries in thigmotactic scanning and turning; the direction of these asymmetries was also dependent on time after vibrissae removal. Furthermore, it was shown that endogenous preferential use of one vibrissae side in thigmotactic scanning interacts with the expression of spontaneous and drug-induced behavioral asymmetries exhibited after unilateral vibrissae removal. Neurochemical studies indicated that both unilateral vibrissae removal and unilateral perioral stimulation can have lateralized effects on biogenic amines in the brain. Finally, using electrical stimulation of the substantia nigra, evidence was found for a lateralized and bidirectional interaction between basal ganglia and the orofacial systems, indicating an involvement in mechanisms of motivation and particular stimulation. These results are important from several perspectives. One, they indicate functional links between the orofacial systems and the basal ganglia. Two, they raise the possibility that unilateral removal of the vibrissae can serve as a model (a) to investigate the dynamics of recovery of function after CNS insults, in general, and specifically, (b) to study neuronal plasticity in the nigrostriatal and tuberomammillary-striatal pathways, and (c) to investigate the neuropharmacology of catecholamine systems in the brain.

Animals↗
PubMed1989

Asymmetries in crossed and uncrossed nigrostriatal projections dependent on duration of unilateral removal of vibrissae in rats.

The influence of unilateral removal of vibrissae on the crossed and uncrossed nigrostriatal projections was examined with the horseradish peroxidase tract tracing technique. Hemivibrissotomy mainly affected the projections arising from the rostral part of the substantia nigra. One to three days after clipping the vibrissae, rats were found to have more labeled neurons in the crossed projection to the caudate-putamen (CPU) on the same side as vibrissae removal than in the crossed projection to the CPU opposite to vibrissae removal. A reversed asymmetry was seen in rats examined 4-20 days after vibrissae removal. These animals had more labeled cells in the crossed and uncrossed projections terminating in the CPU opposite to the shaved side, i.e. in the hemisphere deprived of vibrissal sensory input. This time-course of neural alterations is similar to that of the recovery from behavioral asymmetries seen after hemivibrissotomy. Similar time-dependent alterations in the nigrostriatal projection had been found after unilateral injection of 6-OHDA into the substantia nigra.

Animals↗