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  • 1.
    Albert, Frederic
    et al.
    Laboratoire de Neurobiologie Humaine, Université de Provence, Marseille, France.
    Bergenheim, Mikael
    Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Surgery, Central Hospital Karlstad, Karlstad, Sweden.
    Ribot-Ciscar, Edith
    Laboratoire de Neurobiologie Humaine, Université de Provence, Marseille, France.
    Roll, Jean-Pierre
    Laboratoire de Neurobiologie Humaine, Université de Provence, Marseille, France.
    The Ia afferent feedback of a given movement evokes the illusion of the same movement when returned to the subject via muscle tendon vibration2006Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 172, nr 2, s. 163-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present study was to further investigate the contribution of primary muscle spindle feedback to proprioception and higher brain functions, such as movement trajectory recognition. For this purpose, complex illusory movements were evoked in subjects by applying patterns of muscle tendon vibration mimicking the natural Ia afferent pattern. Ia afferent messages were previously recorded using microneurographic method from the six main muscle groups acting on the ankle joint during imposed "writing like" movements. The mean Ia afferent pattern was calculated for each muscle group and used as a template to pilot each vibrator. Eleven different vibratory patterns were applied to ten volunteers. Subjects were asked both to copy the perceived illusory movements by hand on a digitizing tablet and to recognize and name the corresponding graphic symbol. The results show that the Ia afferent feedback of a given movement evokes the illusion of the same movement when it is applied to the subject via the appropriate pattern of muscle tendon vibration. The geometry and the kinematic parameters of the imposed and illusory movements are very similar and the so-called "two-thirds power law" is present in the reproduction of the vibration-induced illusory movements. Vibrations within the "natural" frequency range of Ia fibres firing (around 30 Hz) produce clear illusions of movements in all the tested subjects. In addition, increasing the mean frequency of the vibration patterns resulted in a linear increase in the size of the illusory movements. Lastly, the subjects were able to recognize and name the symbols evoked by the vibration-induced primary muscle spindle afferent patterns in 83% of the trials. These findings suggest that the "proprioceptive signature" of a given movement is associated with the corresponding "perceptual signature". The neural mechanisms possibly underlying the sensory to perceptual transformation are discussed in the general framework of "the neuronal population vector model".

  • 2. Albert, Frederic
    et al.
    Ribot-Ciscar, Edith
    Fiocchi, Michel
    Bergenheim, Mikael
    Högskolan i Gävle, Belastningsskadecentrum.
    Roll, Jean-Pierre
    Proprioceptive feedback in humans expresses motor invariants during writing.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 164, nr 2, s. 242-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Proprioceptive feedback from populations of muscle spindle afferents feeds the brain with information relating to the instantaneous velocity and direction of ongoing movements. In this paper, we investigate whether the invariant relationship between the velocity and curvature of a trajectory, i.e. the two-thirds power law, is reflected in this muscle spindle feedback. Sixty unitary muscle spindle afferents from six ankle muscle groups were recorded using intraneural microelectrodes during imposed "writing-like" movements. The movements had kinematic parameters obeying the two-thirds power law and were imposed so that the tip of the foot followed trajectories forming four different letters and six numbers. The responses of the muscle spindle afferent populations were analysed using the population vector model. The results demonstrate that the neuronal trajectories attained from populations of muscle spindles clearly depict the path and kinematic parameters and express the movement invariants, i.e. the trajectory segmentation into units of action and the two-thirds power law. The central vs peripheral origin of such constraints involved in the motor system is discussed.

  • 3.
    Domkin, Dmitry
    et al.
    Högskolan i Gävle, Belastningsskadecentrum.
    Laczko, Jozsef
    Djupsjöbacka, Mats
    Högskolan i Gävle, Belastningsskadecentrum.
    Jaric, Slobodan
    Latash, Mark L
    Joint angle variability in 3D bimanual pointing: uncontrolled manifold analysis.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, nr 1, s. 44-57Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V(COMP)) and affecting (V(UN)) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R(V)=V(COMP)/V(UN) served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R(V) values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R(V). Both V(COMP) and V(UN) variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.

  • 4.
    Hellström, Fredrik
    et al.
    Högskolan i Gävle, Belastningsskadecentrum.
    Roatta, S
    Thunberg, Johan
    Högskolan i Gävle, Belastningsskadecentrum.
    Passatore, Magda
    Djupsjöbacka, Mats
    Högskolan i Gävle, Belastningsskadecentrum.
    Responses of muscle spindles in feline dorsal neck muscles to electrical stimulation of the cervical sympathetic nerve.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 165, nr 3, s. 328-42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous studies performed in jaw muscles of rabbits and rats have demonstrated that sympathetic outflow may affect the activity of muscle spindle afferents (MSAs). The resulting impairment of MSA information has been suggested to be involved in the genesis and spread of chronic muscle pain. The present study was designed to investigate sympathetic influences on muscle spindles in feline trapezius and splenius muscles (TrSp), as these muscles are commonly affected by chronic pain in humans. Experiments were carried out in cats anesthetized with alpha-chloralose. The effect of electrical stimulation (10 Hz for 90 s or 3 Hz for 5 min) of the peripheral stump of the cervical sympathetic nerve (CSN) was investigated on the discharge of TrSp MSAs (units classified as Ia-like and II-like) and on their responses to sinusoidal stretching of these muscles. In some of the experiments, the local microcirculation of the muscles was monitored by laser Doppler flowmetry. In total, 46 MSAs were recorded. Stimulation of the CSN at 10 Hz powerfully depressed the mean discharge rate of the majority of the tested MSAs (73%) and also affected the sensitivity of MSAs to sinusoidal changes of muscle length, which were evaluated in terms of amplitude and phase of the sinusoidal fitting of unitary activity. The amplitude was significantly reduced in Ia-like units and variably affected in II-like units, while in general the phase was affected little and not changed significantly in either group. The discharge of a smaller percentage of tested units was also modulated by 3-Hz CSN stimulation. Blockade of the neuromuscular junctions by pancuronium did not induce any changes in MSA responses to CSN stimulation, showing that these responses were not secondary to changes in extrafusal or fusimotor activity. Further data showed that the sympathetically induced modulation of MSA discharge was not secondary to the concomitant reduction of muscle blood flow induced by the stimulation. Hence, changes in sympathetic outflow can modulate the afferent signals from muscle spindles through an action exerted directly on the spindles, independent of changes in blood flow. It is suggested that such an action may be one of the mechanisms mediating the onset of chronic muscle pain in these muscles in humans.

  • 5.
    Korotkov, Alexander
    et al.
    Högskolan i Gävle, Belastningsskadecentrum.
    Radovanovic, Sasa
    Högskolan i Gävle, Belastningsskadecentrum.
    Ljubisavljevic, Milos
    Högskolan i Gävle, Belastningsskadecentrum.
    Lyskov, Eugene
    Högskolan i Gävle, Belastningsskadecentrum.
    Kataeva, Galina
    Roudas, Marina
    Pakhomov, Sergey
    Thunberg, Johan
    Högskolan i Gävle, Belastningsskadecentrum.
    Medvedev, Sviatoslav
    Johansson, Håkan
    Högskolan i Gävle, Belastningsskadecentrum.
    Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, nr 1, s. 65-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.

  • 6. Kostyukov, Alexander I
    et al.
    Bugaychenko, Larisa A
    Kalezic, Ivana
    Högskolan i Gävle, Belastningsskadecentrum.
    Pilyavskii, Alexander I
    Windhorst, Uwe
    Högskolan i Gävle, Belastningsskadecentrum.
    Djupsjöbacka, Mats
    Högskolan i Gävle, Belastningsskadecentrum.
    Effects in feline gastrocnemius-soleus motoneurones induced by muscle fatigue.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, nr 3, s. 284-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Responses of gastrocnemius-soleus (G-S) motoneurones to stretches of the homonymous muscles were recorded intracellularly in decerebrate cats before, during and after fatiguing stimulation (FST) of G-S muscles. Ventral roots (VR) L7 and S1 were cut, and FST was applied to VR S1, a single FST session including 4 to 5 repetitions of 12-s periods of regular 40 s(-1) stimulation. Muscle stretches consisted of several phases of slow sinusoidal shortening-lengthening cycles and intermediate constant lengths. The maximal stretch of the muscles was 8.8 mm above the rest length. Effects of FST on excitatory postsynaptic potentials (EPSPs) and spikes evoked by the muscle stretches were studied in 12 motoneurones from ten experiments. Stretch-evoked EPSPs and firing were predominantly suppressed after FST, with the exception of a post-contraction increase of the first EPSP after FST, which was most likely due to after-effects in the activity of muscle spindle afferents. The post-fatigue suppression of EPSPs and spike activity was followed by restoration within 60-100 s. Additional bouts of FST augmented the intensity of post-fatigue suppression of EPSPs, with the spike activity sometimes disappearing completely. FST itself elicited EPSPs at latencies suggesting activation of muscle spindle group Ia afferents via stimulation of beta-fibres. The suppression of the stretch-evoked responses most likely resulted from fatigue-evoked activity of group III and IV muscle afferents. Presynaptic inhibition could be one of the mechanisms involved, but homosynaptic depression in the FST-activated group Ia afferents may also have contributed.

  • 7.
    Madeleine, Pascal
    et al.
    Laboratory for Work-Related Pain and Biomechanics, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Arendt-Nielsen, Lars
    Laboratory for Work-Related Pain and Biomechanics, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
    Changes in the degree of motor variability associated with experimental and chronic neck-shoulder pain during a standardised repetitive arm movement2008Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 185, nr 4, s. 689-698Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present study was to investigate the effect of experimental and chronic neck-shoulder pain on the magnitude of cycle-to-cycle variability of task timing, kinematics and muscle activation during repetitive arm movement performed for 3 or 5 min. In an experimental part, acute muscle pain was induced in healthy subjects by intramuscular injection of hypertonic saline in trapezius (n = 10) and infraspinatus (n = 10) muscles. In a clinical part, workers with (n = 12) and without (n = 6) chronic neck-shoulder pain were compared. Cycle-to-cycle standard deviations of task duration, arm and trunk movement in 3D and surface electromyographic (EMG) root mean square activity were computed to assess the degree of variability. The variability in task timing increased in presence of both experimental and chronic pain (P < 0.05) compared with non-painful conditions. Experimental pain increased the variability of the starting position of the arm (P < 0.05), the arm range of motion (P < 0.01), the arm and trunk movement area (P < 0.01) and the acceleration of the arm (P < 0.01). In the chronic pain condition, the variability of arm and trunk acceleration (P < 0.01) and EMG activity (P < 0.05) was decreased compared with healthy controls. These results indicate that pain alters the magnitude of motor variability, and that the transition from acute to chronic pain is accompanied by changes in motor patterns. Experimental pain likely resulted in a quest for a motor solution reducing nociceptive influx, while chronic pain was characterised by a diminished motor flexibility.

  • 8. Mel'nichouk, Alexander P
    et al.
    Bulgakova, Natalia V
    Tal'nov, Arkadij N
    Hellström, Fredrik
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Windhorst, Uwe
    Kostyukov, Alexander I
    Movement-dependent positioning errors in human elbow joint movements2007Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 176, nr 2, s. 237-247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Healthy adult humans performed elbow movements in a horizontal plane under a small external extending torque (2.1-3.3 Nm). Test movements (TMs) consisted of slow ramp-and-hold flexions in the absence of visual feedback, with the target joint angle to be remembered from a preceding conditioning movement (CM). The CM was produced by matching two beams on the monitor screen: (1) command representing the target position (a straight line); and (2) a signal from the sensor of the elbow joint angle. Two kinds of CM were applied, which had the same target position (50 degrees in most experiments) but differed in initial positions: (1) fully extended joint (0 degrees, P1 CMs); (2) flexed joint (100 degrees, P2 CMs). In a group of 25 subjects, the target in TMs was usually overshot, with the position errors depending on the CMs: 2.7 +/- 0.6 degree (mean +/- SEM) for P1 CMs, and 10.9 +/- 0.7 degree (P < 0.001) for P2 CMs. Vibration of the elbow flexors substantially diminished the difference between the position errors, amounting to--0.31 +/- 0.5 degree and 2.33 +/- 0.6 degrees, respectively. It is suggested that the observed position errors resulted from after-effects in the activity of muscle spindles in agonist and antagonist muscles, but influence of differences in dynamic components of the afferent signals during oppositely directed approaches to the target cannot be excluded.

  • 9.
    Richter, Hans
    et al.
    Högskolan i Gävle, Institutionen för pedagogik, didaktik och psykologi, Ämnesavdelningen för psykologi.
    Magnusson, S.
    Imamura, K.
    Fredrikson, M.
    Okura, M.
    Watanabe, Y.
    Långström, B.
    Long-term adaptation to prism-induced inversion of the retinal images2002Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 144, nr 4, s. 445-457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For 1 week, healthy human participants (n=7) were devoid of normal vision by exposure to prism lenses that optically rotated their perceived world around the line of sight by 180degrees. Adaptation to such prisms involved sustained and vigorous practice of the ability to redirect the unadapted efferent motor command; because prior to all visually guided movements, the to-be executed efferent command was based on incorrect (prismatically reversed) spatial information. The time course of this sort of adaptation was systematically explored in Cooper-Shepard mental rotation (MR) tests and in naturalistic motor-tasks for the purpose of investigating whether mental rotations of the direction of the intended movement share common aspects with the process of MR. A control group (n=7) intermittently exposed to the distorted spatial organization of the central visual field was studied in parallel. The main results were as follows: (a) the MR reaction times (RTs) day 1 with prisms appeared to be very similar to the normal RTs (day 1, noprisms) with the one exception that subjects now responded within a prism (rotated) frame of spatial reference rather than within the environmentally upright. The visuomotor performance became grossly irregular and dysmetric. (b) The majority of the visuomotor adaptation functions began to level off on the 3rd day. (c) The increases in natural motor proficiency were accompanied by a systematic and noticeable decrease in magnitude of the MR Y-intercept obtained from the linear regression line calculated between each subject's RT and the various stimulus angles. MR slopes were stable through days 1-7 for both the experimental and control group. An increased correlation between rotational stimulus angle and RT suggested that the MR function also became progressively more tightly coupled to the stimulus angles. (d) Postadaptation measures of performance indicated the occurrence of selective and minimal adaptation in the natural motor tasks only. It is suggested that these results reflect an improved attentional (strategic) ability to replace incorrect (error producing) control signals with correct (error reducing) control signals. As a result, perceptual-motor start-up processes directly related to spatial coding and to the planning, initiation and correction of the intended direction of motor-or-mental movement improved while the subprocess ("stage") concerned with transformations of such movements remained unchanged. Visuomotor adaptation to inverting prisms engages, and thereby stimulates, a cortical system also invoked in the preparatory process of MR.

  • 10.
    Richter, Hans O.
    et al.
    Högskolan i Gävle, Centrum för belastningsskadeforskning. Högskolan i Gävle, Institutionen för pedagogik, didaktik och psykologi, Ämnesavdelningen för folkhälsovetenskap. Department of Optometry and Optical Science, Faculty of Physics and Mathematics, University of Latvia, Riga, Latvia.
    Wennberg, Patrik
    Department of Optometry and Optical Science, Faculty of Physics and Mathematics, University of Latvia, Riga, Latvia.
    Raudsepp, Jaanus
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    The effects of inverting prisms on the horizontal-vertical illusion: a systematic effect of downward gaze2007Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 183, nr 1, s. 9-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this work is to compare the relative contributions from the extraocular and sensory systems on the magnitude of the horizontal-vertical illusion (HVI). The visual HVI refers to the general tendency to overestimate vertical extensions of small-scale lines on a picture plane relative to the horizontal by 4-16% depending on the method of measurement. The HVI line stimuli consisted of luminous vertical and horizontal lines forming "L-profiles" located in the frontoparallel plane at a 45 cm viewing distance, collinearly with a binocular gaze. The home position of gaze was aligned to the center of the screen with the ear-eye angle concordant with the environmental horizontal. Illusion strength was quantified when subjects fixated the HVI line stimuli in four quadrants of the visual field. The HVI was also viewed through prism lenses that inverted the retinal images by 180 degrees , thereby dissociating the sensory "up-down" direction from the oculomotor up-down frame of reference. The results revealed a systematically lower magnitude of the HVI in the bottom visual field regardless of whether subjects fixated the HVI with the distorting prisms or without. Taken together, these results suggest that the HVI is sensitive to small-angle gaze shifts. In agreement with several recent findings, these results are interpreted as implying that the brain imposes an enhanced analytic structure on the ascending sensory information during downward gaze.

  • 11. Roatta, Silvestro
    et al.
    Windhorst, Uwe
    Högskolan i Gävle, Belastningsskadecentrum.
    Djupsjöbacka, Mats
    Högskolan i Gävle, Belastningsskadecentrum.
    Lytvynenko, S
    Passatore, Magda
    Effects of sympathetic stimulation on the rhythmical jaw movements produced by electrical stimulation of the cortical masticatory areas of rabbits.2005Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 162, nr 1, s. 14-22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The somatomotor and sympathetic nervous systems are intimately linked. One example is the influence of peripheral sympathetic fibers on the discharge characteristics of muscle spindles. Since muscle spindles play important roles in various motor behaviors, including rhythmic movements, the working hypothesis of this research was that changes in sympathetic outflow to muscle spindles can change rhythmic movement patterns. We tested this hypothesis in the masticatory system of rabbits. Rhythmic jaw movements and EMG activity induced by long-lasting electrical cortical stimulation were powerfully modulated by electrical stimulation of the peripheral stump of the cervical sympathetic nerve (CSN). This modulation manifested itself as a consistent and marked reduction in the excursion of the mandibular movements (often preceded by a transient modest enhancement), which could be attributed mainly to corresponding changes in masseter muscle activity. These changes outlasted the duration of CSN stimulation. In some of the cortically evoked rhythmic jaw movements (CRJMs) changes in masticatory frequency were also observed. When the jaw-closing muscles were subjected to repetitive ramp-and-hold force pulses, the CRMJs changed characteristics. Masseter EMG activity was strongly enhanced and digastric EMG slightly decreased. This change was considerably depressed during CSN stimulation. These effects of CSN stimulation are similar in sign and time course to the depression exerted by sympathetic activity on the jaw-closing muscle spindle discharge. It is suggested that the change in proprioceptive information induced by an increase in sympathetic outflow (a) has important implications even under normal conditions for the control of motor function in states of high sympathetic activity, and (b) is one of the mechanisms responsible for motor impairment under certain pathological conditions such as chronic musculoskeletal head-neck disorders, associated with stress conditions.

  • 12. Roll, Jean-Pierre
    et al.
    Albert, Frédéric
    Ribot-Ciscar, Edith
    Bergenheim, Mikael
    Högskolan i Gävle, Belastningsskadecentrum.
    Proprioceptive signature of cursive writing in humans: a multi-population coding.2004Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 157, nr 3, s. 359-368Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The goal of the present study was to investigate the firing behavior of populations of muscle spindle afferents in all the muscles acting on the ankle while this joint was being subjected to "writing-like" movements. First it was proposed to determine whether the ensemble of muscle spindles give rise to a unique, specific, and reproducible feedback information characterizing each letter, number or short word. Secondly, we analyzed how the proprioceptive feedback on the whole encodes the spatial and temporal characteristics of writing movements using the "vector population model". The unitary activity of 51 primary and secondary muscle spindle afferents was recorded in the tibial and common peroneal nerves at the level of the popliteal fossea, using the microneurographic method. The units recorded from belonged to the tibialis anterior, the extensor digitorum longus, the extensor hallucis longus, the peroneus lateralis, the gastrocnemius-soleus and the tibialis posterior muscles. The "writing-like" movements were randomly imposed at a "natural" velocity via a computer-controlled machine in a two-dimensional space. In general, muscle spindle afferents from any of the six muscles responded according to the tuning properties of the parent muscle, i.e. increasing their discharge rate during the phases where the direction of movement was within the preferred sensory sector of the parent muscle. The whole trajectory of the writing movements was coded in turn by the activity of Ia afferents arising from all the muscles acting on the joint. Both single afferent responses and population responses were found to be highly specific and reproducible with each graphic sign. The complex multi-muscle afferent pattern involved, with its timing and distribution in the muscle space, seems to constitute a true "proprioceptive signature" for each graphic symbol. The ensemble of muscle spindle afferents were therefore found to encode the instantaneous direction and velocity of writing movements remarkably accurately. It was concluded that the proprioceptive feedback from all the muscles with which the moving joint is equipped provides the CNS with highly specific information that might contribute to a graphic sign identification process.

  • 13.
    Samani, Afshin
    et al.
    Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
    Srinivasan, Divya
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Madeleine, Pascal
    Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
    Variability in spatio-temporal pattern of trapezius activity and coordination of hand-arm muscles during a sustained repetitive dynamic task2017Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 235, nr 2, s. 389-400Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The spatio-temporal distribution of muscle activity has been suggested to be a determinant of fatigue development. Pursuing this hypothesis, we investigated the pattern of muscular activity in the shoulder and arm during a repetitive dynamic task performed until participants' rating of perceived exertion reached 8 on Borg's CR-10 scale. We collected high density surface electromyogram (HD-EMG) over the upper trapezius, as well as bipolar EMG from biceps brachii, triceps brachii, deltoideus anterior, serratus anterior, upper and lower trapezius from 21 healthy women. Root mean square (RMS) and mean power frequency (MNF) were calculated for all EMG signals. The barycenter of RMS values over the HD-EMG grid was also determined, as well as normalized mutual information (NMI) for each pair of muscles. Cycle-to-cycle variability of these metrics was also assessed. With time, EMG RMS increased for most of the muscles, and MNF decreased. Trapezius activity became higher on the lateral side than on the medial side of the HD-EMG grid and the barycenter moved in a lateral direction. NMI between muscle pairs increased with time while its variability decreased. The variability of the metrics during the initial 10% of task performance was not associated with the time to task termination. Our results suggest that the considerable variability in force and posture contained in the dynamic task per se masks any possible effects of differences between subjects in initial motor variability on the rate of fatigue development.

  • 14.
    Wiesinger, Birgitta
    et al.
    Umeå University and Västernorrland County Council.
    Häggman-Henriksson, Birgitta
    Umeå University and Malmö University.
    Wänman, Anders
    Umeå University.
    Lindqvist, Mikael
    Umeå University.
    Hellström, Fredrik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Jaw-opening accuracy is not affected by masseter muscle vibration in healthy men2014Ingår i: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 232, nr 11, s. 3501-3508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is a functional integration between the jaw and neck regions with head extension–flexion movements during jaw-opening/closing tasks. We recently reported that trigeminal nociceptive input by injection of hypertonic saline into the masseter muscle altered this integrated jaw–neck function during jaw-opening/closing tasks. Thus, in jaw-opening to a predefined position, the head–neck component increased during pain. Previous studies have indicated that muscle spindle stimulation by vibration of the masseter muscle may influence jaw movement amplitudes, but the possible effect on the integrated jaw–neck function is unknown. The aim of this study was to investigate the effect of masseter muscle vibration on jaw–head movements during a continuous jaw-opening/closing task to a target position. Sixteen healthy men performed two trials without vibration (Control) and two trials with bilateral masseter muscle vibration (Vibration). Movements of the mandible and the head were registered with a wireless three-dimensional optoelectronic recording system. Differences in jaw-opening and head movement amplitudes between Control and Vibration, as well as achievement of the predefined jaw-opening target position, were analysed with Wilcoxon’s matched pairs test. No significant group effects from vibration were found for jaw or head movement amplitudes, or in the achievement of the target jaw-opening position. A covariation between the jaw and head movement amplitudes was observed. The results imply a high stability for the jaw motor system in a target jaw-opening task and that this task was achieved with the head–neck and jaw working as an integrated system.

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