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PubMed2001

Altered cortical activation with finger movement after peripheral denervation: comparison of active and passive tasks.

We wished to contrast cortical activation during hand movements in profoundly weak patients with motor neuropathy and in normal controls using a paradigm that is behaviourally matched between the two groups. Previous work has suggested that a passive movement task could be appropriate. Using functional magnetic resonance imaging (fMRI), we first characterised patterns of brain activation during active and passive index finger movements in healthy controls (n=10). Although the relative activation differences were highly variable, there was a trend for the mean number of significantly activated voxels in the primary motor cortex contralateral to the hand moved (CMC) to be lower for the passive than for the active task (40% relative decrease, P=0.09). There was a small posterior shift in the centre of mass of the CMC (mean, 8 mm, P<0.02) and of the ipsilateral sensorimotor cortex (IMC) (mean, 11 mm, P<0.05). No activation with passive movement was found in the patients with severe distal sensory neuropathy (n=2), suggesting that activation with passive movements is dependent on sensory feedback and unlikely to be due to mental imagery alone. In contrast, patients with severe pure motor neuropathies (MN, n=2) showed substantial increases in the volumes of activation compared to controls. The relative increases in numbers of voxels activated above threshold in different regions of interest for both the active (MN/controls: CMC, 2. 1; IMC, 8.1; supplementary motor area [SMA], 5.2) and passive (CMC, 2.6; IMC, 8.0; SMA, 5.1) tasks were similar. These results confirm expansion of cortical representation for finger movement in patients with motor neuropathy and demonstrate central reorganisation as a consequence of the motor nerve loss. An expanded representation for finger movement in the primary motor cortex with peripheral weakness suggests the possibility that the primary motor cortex may encode motor unit activation rather directly.

Adult↗

PubMed2001

Fictive motor activity in rat after 14 days of hindlimb unloading.

The goal of the present study was to examine the effects of chronic hindlimb unloading on fictive motor patterns which can be developed in hindlimb nerves of adult rats. The animals were divided into two groups. The first group was submitted to hindlimb unloading for 2 weeks by tail suspension. The second group served as controls. After this initial phase, the animals of both groups were acutely decorticated, paralysed and electroneurographic efferent activity was recorded from hindlimb muscle nerves under conditions of "fictive locomotion" in order to evaluate variations in central locomotor command. Fictive rhythmic motor episodes were either spontaneous or evoked by electrical stimulation of the mesencephalic locomotor region. Only the second ones were recognised as locomotor-like activities. The motor pattern was not fundamentally affected by unloading except that, after the unloading period, extensor muscle nerves were significantly more frequently activated and their burst durations were increased compared to activity in control animals, despite the fact that the phasic sensory afferent inputs were suppressed. This suggests that unloading induces plastic modifications of the central networks of neurons implicated in the locomotor command. The origin of this extensor hyperactivity is discussed. It is proposed that it could be the consequence of either changes in motoneuronal properties or of an increase in afferent input to motoneurones.

Action Potentials↗

PubMed2001

On the role of static and dynamic visual afferent information in goal-directed aiming movements.

Movement planning has been shown to be optimized when the participant is permitted to see his or her hand resting on the starting base prior to movement initiation. However, this proposition is opposed by contradictory results. In the present study, we wanted to determine whether these conflicting results were caused by procedural differences. The results showed that seeing one's hand on the starting base did not result in more accurate aiming movement than when this information was not available. However, lower aiming errors were found when one was asked to foveate the starting base and then the target prior to movement initiation, but only when no dynamic visual information was available during movement. When an aiming movement was performed while one's hand was visible in visual periphery, foveating the starting base or not prior to movement initiation did not modify aiming accuracy. These results suggest that gazing at the starting base and then at the target provides an eye-based representation of the movement to be performed that can be used by the CNS to plan a manual aiming movement. Information for better planning of the direction--but not the extent--dimension of an upcoming movement can also be derived from dynamic visual information available in peripheral vision.

Adult↗

PubMed2001

Two kinds of body representation are used to control hand movements following tactile stimulation.

The task of reaching with a hand toward a target given in space is generally described as an ill-posed problem. It is often assumed that some kind of internal body model is required to solve this problem. This article provides information concerning the nature of this representation. Experiments were carried out in which blindfolded subjects were stimulated mechanically at one of eight possible stimulation sites on the legs and then asked to move one hand as quickly as possible to the stimulated site. In nine different postures of legs and hands, the frequency was recorded of the use of either hand. In addition, reaction times (RT) were measured and in two choice reaction tasks RTs were measured for different conditions (morphologically compatible vs morphologically incompatible, hands parallel vs hands crossed): The results support the hypothesis that the representation of the body is based on at least two systems, one which provides spatial information concerning the body position and a second one which is based on a morphological representation. According to this hypothesis, our results could be described by the following schema. Following the application of the stimulus, two processes were started in parallel. One concerned the activation of the spatial representation of body position, including the position of stimulus site and the possible response sites. This was more difficult, i.e., took more time, when the hands were crossed. Within this spatial representation, the distances between stimulus site and response sites were determined, and it was found that the smaller the distance, the more strongly the hands were activated. Simultaneously, in a second process the response site which was morphologically ipsilateral to the stimulus was excited. This schema could explain our results: In the behavioral experiments that hand which was most strongly excited, and which therefore exceeded a threshold sooner, won the decision and showed smaller RT values. In the choice reaction experiments, the winning hand was compared with the externally given task. The more strongly, according to the given task, the wrong hand was excited, the longer was the RT of the response.

Adult↗

PubMed2001

Neural compensation for mechanical loading of the hand during coupled oscillations of the hand and foot.

The role of kinaesthetic afferences in controlling coupling of voluntary oscillation of the hand and foot, both in-phase and anti-phase, was investigated by modifying the mechanical properties of one of the two segments (the hand) with applied inertial or elastic loads. Loads consisted of a lead disk, rotating coaxially with the wrist (total inertial momentum 15 g m2), or in two symmetrical rubber bands (elasticity, 4 g deg(-1)) connected 5 cm away from the wrist pivot. Experiments were performed on five male and five female subjects. Both the frequency responses of the hand and foot (i.e. the phase relations between the onset of muscular activation in limb extensors and the onset of the related movement) and the inter-limb phase relations (the phase differences between the hand and foot movement cycles and between the onsets of the electromyographic (EMG) activity in hand and foot extensors) were analysed. The hand frequency-response was fitted with a 2nd-order model, allowing us to describe the loaded and unloaded conditions through the changes in the model response. Inertial loading induced an immediate and steep decay in the frequency response, with a clear-cut reduction of the model resonance frequency, while elastic loading shifted the response to the right and upwards. Inter-limb phase relations were only partially affected by inertial loading of the hand. Despite the fact that the load strongly increased the difference between the frequency-responses of the hand and foot, when hand and foot were oscillated in-phase only about half of this difference remained as an increased phase-lag between hand and foot oscillations. The other half was offset by an advance of the contraction of the hand movers with respect to the foot movers. This compensation mechanism was more effective during anti-phase than during in-phase movements. Elastic loading improved inter-limb synchronisation, since it superimposed the hand frequency-response on that of the foot. In this condition, the requested synchronisation (in-phase or anti-phase) could be achieved by an almost simultaneous (or in strict phase opposition) contraction of the hand and foot movers. In conclusion, the main feedback reaction to the de-coupling effect of hand loading consisted in modifying the timing of activation of the muscles moving the extremities. An advance of hand movers on foot movers is already present in unloaded conditions to compensate for the difference in the natural mechanical properties of the two segments. This advance is enhanced when increasing the inertia of the hand system and attenuated when increasing its elasticity.

Adaptation, Physiological↗

PubMed2001

Proprioceptive control of cyclical bimanual forearm movements across different movement frequencies as revealed by means of tendon vibration.

The effect of unilateral tendon vibration on the performance of cyclical bimanual forearm movements was investigated across different cycling frequencies (from 0.67 to 2.53 Hz). The spatiotemporal features of the individual limb motions as well as their coordination were studied. Tendon vibration was found to result in a substantial reduction in the amplitude of the vibrated arm, leaving the nonvibrated arm unaffected. The vibration-induced amplitude reduction decreased from 26% to 11% as cycling frequency increased even though significant reductions were still observed at the highest cycling frequencies. Tendon vibration was also found to result in an increase of the phase lead of the dominant arm with respect to the nondominant arm, but this effect was not modulated by cycling frequency. The data argue in favor of a closed-loop mode of movement control during cyclical high-speed movements. It is suggested that kinesthetic afferent information is processed and used to guide action up to near-maximal movement speeds, reinforcing recent claims with respect to visual information processing.

Adolescent↗

PubMed2000

Influence of motion parallax in the control of spontaneous body sway.

Visual control of postural sway during quiet standing was investigated in normal subjects to see if motion parallax cues were able to improve postural stability. In experiment 1, six normal subjects fixated a fluorescent foreground target, either alone or in the presence of full room illumination. The results showed that subjects reduced body sway when the background was visible. This effect, however, could be mediated not only by parallax cues but also by an increase in the total area of visual field involved. In experiment 2, other parameters such as image angular size and target distance were controlled for. Twelve subjects fixated a two light-emitting diode (LED) target placed at 45 cm from their eyes in a dark room. A second similar two-LED target was placed either at 170 cm (maximum parallax) or at 85 cm (medium parallax) from the fixated target, or in the same plane of the fixated target (0 cm, no parallax). It was found that the amplitude of sway was reduced significantly, by approximately 20%, when the two targets were presented in depth (parallax present) as compared to when they were in the same plane (no parallax). The effect was only present in the lateral direction and for low frequency components of sway (up to 0.5 Hz). We confirmed in experiment 3 on eight subjects with a design similar to that used in experiment 2 that the effect of motion parallax on body sway was of monocular origin since observed with monocular and binocular vision. Geometrical considerations based on these results support the existence of two modes of visual detection of body sway, afferent (retinal slippage) and efferent (extra-retinal or eye-movement based).

Adult↗

PubMed2000

Effect of ethanol on dynamic visual acuity during vertical body oscillation in healthy volunteers.

Visual orientation is the most important sensory input during locomotion (e.g. walking, driving a car, riding a bicycle). We investigated dynamic visual acuity (DVA) during vertical body-oscillations (amplitude 5 cm; frequency 1.5 Hz) in 12 healthy subjects before and twice after ethanol consumption. During oscillation, vertical eye movements were recorded under two test conditions: with eyes closed (EC) and during DVA testing. A significant increase in vertical eye-amplitude after ethanol ingestion occurred only during EC tests, as a possible sign of vestibular hyperreaction. During vestibular stimulation alone (EC), ethanol did not affect the phase shift between stimulus and eye movements. However, when the subjects were given an additional visual stimulus (DVA), the post-alcohol phase shift rose significantly. Surprisingly, the post-alcohol phase shift values for the two test conditions showed no significant differences. After ethanol ingestion we found no changes in static visual acuity but a significant loss of DVA. Volunteers with a change of DVA threshold (DVAT) showed significantly (P = 0.004) higher post-alcoholic changes in the phase shift. In summary, low doses of ethanol disturbed the visually guided oculomotor response during fixation of an earth-fixed target while the observer was subject to linear vertical acceleration. This effect led to an increasing delay between the beginning of body and eye movements. The consequence was an increasing phase shift and thus a decrease in DVA during whole-body oscillation which was comparable to movements during human locomotion.

Acceleration↗

PubMed2000

The effects of intense click sounds on velocity storage in optokinetic after-nystagmus.

Vestibular evoked myogenic potentials (VEMP) occurring after click stimulation in cervical muscles are thought to be a polysynaptic response of otolith-vestibular nerve origin. In optokinetic after-nystagmus (OKAN) the direction of after-nystagmus changes and slow-phase velocity decreases with head tilt. This phenomenon may be an otolith response to the direction of gravity. We assumed that intense clicks might have some influence on OKAN via the otolith-vestibular nerve. Twelve normal subjects who showed VEMP at 75 dB normal hearing level (nHL) clicks were examined. The OKAN was recorded under four conditions: right monaural, left monaural and binaural stimulation by 75 dB nHL clicks, and absence of click stimulation. Horizontal optokinetic stimulation was applied using stepwise increasing speeds from 30 deg/s to 90 deg/s. Two seconds before the stimulus ended, clicks were sounded. The slow-phase velocity of the recorded electro-nystagmography was manually measured. There was no effect on OKAN with unilateral stimulation but binaural stimulation suppressed it. These results suggest that a velocity storage integrator is influenced by intense clicks via the otolithic area.

Acoustic Stimulation↗

PubMed2003

Idiopathic spasmodic torticollis is not associated with abnormal kinesthetic perception from neck proprioceptive and vestibular afferences.

Proceeding from recent evidence for a sensory involvement in the pathophysiology of idiopathic spasmodic torticollis (ST), we asked whether the abnormal head posture of these patients is associated with distortions of their internal spatial reference frames due to abnormal processing of neck proprioceptive and/or vestibular input. Twelve ST patients were instructed to estimate, by adjusting a light pointer in the dark, their head and trunk mid-sagittal directions (as representatives of ego-centric references) and to reproduce a remembered target location in space (space centric reference). They did so before and after horizontal head and trunk rotations, which evoked isolated or combined vestibular and/or neck stimulation. In ST patients, unlike in normal controls, pre-stimulus estimates of the head and trunk mid-sagittal directions (baselines) showed a pronounced across-subjects variability, with essentially normal mean values. Their post-stimulus estimates in all tasks, after correction for the individual baseline errors, were normal with respect to both amplitude and variability, independent of stimulus direction, modality and rotation dynamics. Our findings suggest that ST patients have a rather inaccurate knowledge of their head posture, but can effectively use neck proprioceptive input and vestibular cues when estimating head and trunk displacements in ego-centric and space centric spatial orientation tasks. We propose that an offset of a non-sensory set point signal in the neck proprioceptive loop for head-on-trunk control may be responsible for the pathological head deviation in ST.

Adult↗

PubMed2004

Coordination modes in the multisegmental dynamics of hula hooping.

In hula hooping, organized motions of the body keep the hoop in stable oscillatory motion parallel to the ground. We examined the hypothesis that the multiple degrees of freedom (DF) of the lower limbs in producing the oscillations are resolved into a few control DF. The Karhunen-Loève decomposition was applied to the kinematics of the lower limbs in three experiments in which oscillation amplitude and frequency were manipulated. Kinematic variance was accommodated by two modes whose relative contributions varied with task parameters. Complementary analyses of interjoint Hilbert relative phase suggested a lower-limb organization into a vertical suspension mode and an oscillatory fore-aft mode. These modes might stabilize the hoop's angular momentum by controlling, respectively, its vertical and horizontal components.

Adolescent↗

PubMed1996

A numerical simulation of muscle spindle ensemble encoding during planar movement of the human arm.

We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located within muscles of this limb. To accomplish this we developed a numerical simulation which could provide estimates of the length regimes experienced by a set of model receptors located within some of the principal muscles of the human arm during planar movement of this limb. These receptors were assumed to have characteristics analogous to those associated with a simple model of muscle spindle signalling of movement. To this end each spindle had proprioceptive 'channels' associated with it. These corresponded to primary and secondary spindle afferent fibers which could provide independent afferent output regarding the parent muscle the spindle monitored. The angles of the shoulder and elbow joints attained by subjects performing a task requiring movement of the right arm in a horizontal plane to a static visual target were recorded. For this angular data the lengths and rates of change of lengths experienced by muscle fascicles, and hence the model spindles, during movement were calculated by means of the numerical simulation. The discharge rates of the simulated spindles during the movement were calculated to derive a measure of the depth of modulation, induced by the movement, for each spindle. These values were then summed for all spindles to provide a first-order approximation of spindle ensemble coding of the movement. Significant correlations (P < 0.0001, Spearman's rank order) were found between the resulting ensemble encodings and, in order of significance, the angular velocity of the shoulder joint (rS = 0.945), the tangential velocity of the hand (rS = 0.942), and the angular velocity of the elbow joint (rS = 0.917). Correlations between the angular positions of the shoulder (rS = -0.623) and elbow (rS = 0.628) were lower. These findings indicate that the ensemble profiles of the simulated muscle spindles, encode information regarding kinematic parameters of movements related to both intrinsic and extrinsic coordinate systems. This suggests that motor structures capable of deriving such an ensemble encoding would be in a position to perform the sensory-motor transformations between intrinsic and extrinsic frames of reference necessary for controlling movements planned in extrinsic coordinates.

Arm↗

PubMed2002

Self-induced versus reactive triggering of synchronous movements in a deafferented patient and control subjects.

The present study investigates the contribution of tactile-kinesthetic information to the timing of movements. The relative timing of simultaneous tapping movements of finger and foot (hand-foot asynchrony) was examined in a simple reaction time task and in discrete self-initiated taps (Experiment 1), and in externally triggered synchronization tapping (Experiment 2). We compared the performance of a deafferented participant (IW) to the performance of two control groups of different ages. The pattern of results in control groups replicates previous findings: Whereas positive hand-foot asynchronies (hand precedes foot) are observed in a simultaneous reaction to an auditory stimulus, hand-foot asynchronies are negative with discrete self-initiated as well as auditorily paced sequences of synchronized finger and foot taps. In the first case, results are explained by a simultaneous triggering of motor commands. In contrast, self-initiated and auditorily paced movements are assumed to be controlled in terms of their afferent consequences, as provided by tactile-kinesthetic information. The performance of the deafferented participant differed from that of healthy participants in some aspects. As expected on the basis of unaffected motor functions, the participant was able to generate finger and foot movements in reaction to an external signal. In spite of the lack of movement-contingent sensory feedback, the deafferented participant showed comparable timing errors in self-initiated and regularly paced tapping as observed in control participants. However, in discrete self-initiated taps IW's hand-foot asynchronies were considerably larger than in control participants, while performance did not differ from that of controls in continuous movement generation. These findings are discussed in terms of an internal generation of the movement's sensory consequences (forward-modeling).

Adult↗

PubMed2002

The contribution of tactile reafference to temporal regularity during bimanual finger tapping.

In a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with both hands, as opposed to single-handed tapping. This bimanual advantage can be attributed to timer variance (according to the Wing-Kristofferson model). Separate timers have been proposed for each hand whose outputs are then averaged (Helmuth & Ivry, 1996, Journal of Experimental Psychology: Human Perception and Performance, 22, 278-293). Alternatively, timing might be based on sensory reafference and the bimanual advantage due to the enhancement of sensory reafferences. This alternative hypothesis was tested in three experiments. In the first experiment, we replicated the bimanual advantage in tapping with two fingers of the same hand compared with single finger tapping. In the second experiment, we demonstrated that the bimanual advantage decreased when tactile reafferences from left-hand taps were omitted (by contact-free tapping). In the third experiment, participants tapped bimanually with the index fingers of both hands firmly mechanically coupled. The bimanual advantage was replicated for this condition. Results are consistent with the assumption that the bimanual advantage is due to the sensory reafferences of the second hand. We suggest that our results are best explained by a reformulation of the Wing-Kristofferson model, in which the timer provides action goals in terms of sensory reafferences.

Adult↗

PubMed2002

Forces and displacements in colon surgery.

BACKGROUND: This study aims to find criteria for designing safer laparoscopic graspers for manipulation of delicate tissues. Since the experiment was performed in an open-surgery setup without any movement restrictions, the results are relevant to general surgery as well as laparoscopic. METHOD: Four surgeons were asked to apply via two clamps enough force to a pig's colon to stretch the mesocolon for dissection. Directions, magnitudes, and application points of the forces were recorded. RESULTS: The surgeons applied per clamp on average 2.5 N and maximally 5 N to the colon. These forces were at an angle of about 40 degrees to 70 degrees relative to the horizontal plane and approximately 60 degrees relative to each other. CONCLUSIONS: Safe laparoscopic graspers should be able to transmit at least a 5 N pull force to the tissue without damaging it. To minimize the forces used, the angles mentioned should be taken into account when placing the trocars.

Animals↗

PubMed2005

Evaluation of the kinesthetic sense and function of the hand in early period in operated cervical disc hernia.

A prospective study made into cervical disc hernias. To determine the kinesthetic sense and hand functions, which are important for the patients with cervical disc hernia to return to work life and daily activities that need skill. Neurosurgical department. Data Symptoms in cervical disc hernias and hand functions are affected depending on long-term pain. The evaluation of the hand is essential in assessing the patients' overall recovery and ability to return to daily activities and work life. Thirty-four patients with cervical disc hernia, who were operated on, were included in the study. Eight different test positions in the assessment of the hand's kinesthetic sense and hand function sort (HFS) in the evaluation of the hand function were applied. The disability levels of the patients were determined with The Neck Pain and Disability Scale, on the preoperative and postoperative discharge day and in the postoperative second month. Patients were divided into groups according to the side involved. In the evaluation of the kinesthetic test of the hand, only in the postoperative second month was a significant difference observed between the 1, 2, 3, and 4 test positions of the right side of the groups. On the other hand, no significant difference was found between the groups in the assessment of the hand function. In the measurement of hand functions and disability levels, strong and important correlations were determined. An early assessment of the hand's kinesthetic sense and function is instrumental in the patients' evaluation of recovery and resumption of work.

Activities of Daily Living↗

PubMed2005

Topo-kinesthetic memory in chronic headaches. A new test for chronic patients: preliminary report.

The objective of this study was to establish if chronic headaches with medication overuse can modify a topo-kinesthetic memory test. Nineteen patients with medication overuse headache (MOH), 13 patients with chronic tension-type headache (CTTH) without medication use and a group of "normal" subjects underwent a topo-kinesthetic memory test at T0 and after one month (T1); a control group of healthy volunteers was also tested to establish the baseline in our experimental setting. After one month, in the MOH patients there was a reduction of medication overuse from 3.3+/-2.65 to 1.1+/-2.23 (p<0.01), but no significant reduction in headache frequency and severity index, quality of life, anxiety and depression scores. The navigation time at T0 was 14.3+/-4.97, 27.9+/-10.12, 34.3+/-15.38 and 7.5+/-2.33, 10.1+/-2.95, 11.4+/-3.21 for control, MOH and CTTH with closed and open eyes, respectively (p<0.02). At T1, the MOH patients reached performances with open eyes similar to the healthy controls, while with closed eyes the navigation test reached times similar to those of CTTH patients. The topo-kinesthetic memory test seems both able to discriminate MOH and CTTH from healthy volunteers and to be related to pain scores but is not influenced by the use of drugs.

Chronic Disease↗

PubMed2005

The demystification of autoscopic phenomena: experimental propositions.

Autoscopic phenomena (AP) are rare, illusory visual experiences during which the subject has the impression of seeing a second own body in extrapersonal space. AP consist of out-of-body experience, autoscopic hallucination, and heautoscopy. Recent neurologic reports support the role of multisensory integration deficits of body-related information and vestibular dysfunctions in AP at the temporo-parietal junction. A caveat to test the underlying neurologic and cognitive mechanisms of AP has been their rare and spontaneous occurrence. Recent evidence linked AP to mental own-body imagery engaging brain mechanisms at the temporo-parietal junction. These recent observations open a new avenue for testing AP-related cognitive mechanisms in selected clinical and normal populations. We review evidence on several clinical syndromes (psychosis, depression, anxiety, depersonalization, body dysmorphic disorder), suggesting that some of these syndromes may relate to AP-proneness, thereby leading to testable propositions for future research on body and self processing in addition to AP.

Awareness↗