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PubMed1986

Visually displayed EMG feedback: single case studies of hemiplegic upper extremity rehabilitation.

The efficacy of visually displayed EMG feedback in treating hemiplegic upper limb motor disorders was investigated in 5 patients (0.5-4 years poststroke). A single case experimental method "multiple-baseline across target behaviors" was used to compare performance during the feedback phase to that occurring in the monitored baseline phase. The nonfeedback baseline phase was followed by the staggered introduction of audiovisual feedback for each of the targeted pairs of muscles. EMG feedback obtained from muscle pairs (shoulder: anterior deltoid and upper trapezius; elbow: brachial triceps and biceps; digits: extensor digitorum communis and digit flexors) was displayed as two distinct waveforms on a videomonitor during therapy. Nonfeedback assessment of each of the three pairs was performed during each session. The effects of feedback were not uniformly distributed. Elbow control responded best, and statistical tests confirmed the effects of intervention observed clinically in all 5 patients. Clinical improvements in shoulder flexion were observed in 4 patients but could be statistically attributed to EMG gains in just 1. Improvement in finger extension observed clinically in 3 patients was statistically attributable to EMG gains in 2. All patients regained control of at least one target activity. EMG gains were accompanied by increases in active range of motion and by varying functional improvement. Marked functional gains in 3 patients were obtained with recovery of finger control.

Adult↗

PubMed1993

Role of the cerebellum in visuomotor coordination. I. Delayed eye and arm initiation in patients with mild cerebellar ataxia.

The initiation of coupled eye and arm movements was studied in six patients with mild cerebellar dysfunction and in six age-matched control subjects. The experimental paradigm consisted of 40 deg step-tracking elbow movements made under different feedback conditions. During tracking with the eyes only, saccadic latencies in patients were within normal limits. When patients were required to make coordinated eye and arm movements, however, eye movement onset was significantly delayed. In addition, removal of visual information about arm versus target position had a pronounced differential effect on movement latencies. When the target was extinguished for 3 s immediately following a step change in target position, both eye and arm onset times were further prolonged compared to movements made to continuously visible targets. When visual information concerning arm position was removed, onset times were reduced. Eye and arm latencies in control subjects were unaffected by changes in visual feedback. The results of this study clearly demonstrate that, in contrast to earlier reports of normal saccadic latencies associated with cerebellar dysfunction, initiation of both eye and arm movements is prolonged during coordinated visuomotor tracking thus supporting a coordinative role for the cerebellum during oculo-manual tracking tasks.

Adult↗

PubMed2000

Effect of tonic muscle pain on short-latency jaw-stretch reflexes in humans.

The modulation of human jaw-stretch reflexes by experimental muscle pain was studied in three experiments. Short-latency reflex responses were evoked in the masseter and temporalis muscles by fast stretches (1 mm displacement, 10 ms ramp time) before, during and 15 min after a period with tonic pain. In Expt. I, a dose of 5.8% hypertonic or 0.9% isotonic (control) saline was infused in random order into the left masseter for up to 15 min (n=12). The level of excitation of the left masseter was kept constant at 15% of maximal effort by visual feedback and on-line calculation of the root-mean-square value of the surface electromyogram (sEMG). In Expt. II, a dose of 5.8% saline was infused into the left masseter but with feedback from the right masseter sEMG (n=12). In Expt. III, both sEMG and intramuscular (im) EMG was recorded from the left and right masseter muscles. The feedback was from either the sEMG or imEMG of the left masseter in which 5.8% saline was infused (n=12). In all experiments, subjects continuously rated their perceived pain intensity on a 10-cm visual analogue scale (VAS). Infusion of 5.8% saline caused moderate levels of pain (mean VAS 4.9-5.0 cm) whereas infusion of 0.9% saline was almost pain-free (mean VAS 0.3 cm). The pre-stimulus EMG activity in the masseter, which served as the feedback muscle during the recording, was constant across the different conditions. During painful infusion of 5.8% saline in Expts. I and III, the pre-stimulus sEMG activity in the non-painful masseter was significantly higher than baseline when the sEMG on the painful side was used as feedback signal, and in Expt. II significantly lower on the painful side when the non-painful side served as feedback signal (Student-Newman-Keuls: P<0.05). Isotonic saline did not affect the pre-stimulus sEMG activity or the jaw-stretch reflex parameters. The peak-to-peak amplitude of the stretch reflex in the painful masseter normalized to the pre-stimulus EMG activity was significantly higher during the pain conditions compared with the pre- and post-infusion conditions in all experiments. These results indicate that experimental jaw-muscle pain facilitates the short-latency (8-9 ms), probably monosynaptic, jaw-stretch reflex as revealed by both sEMG and imEMG. This effect could not be accounted for by variability in pre-stimulus EMG activity. An increased sensitivity of the fusimotor system at this level of static muscle excitation is suggested as a possible mechanism, which could contribute to an increased stiffness of the jaw-muscles during pain.

Adult↗

PubMed2005

Parametric modulation of cortical activation during smooth pursuit with and without target blanking. an fMRI study.

Smooth pursuit eye movements (SPEM) are performed to track slowly moving visual targets and are accompanied by saccades whenever foveal representation is lost. In the present study, we correlated the cerebral activation as assessed by functional magnetic resonance imaging with parameters of eye movement performance in order to determine the cortical areas involved in the retinal and extraretinal processing of maintaining smooth pursuit velocity (SPV) and generating saccades in 16 healthy males. The stimulus consisted of a target moving at a constant velocity of 10 degrees/s with and without target blanking. During constant target presentation, SPV was positively correlated with the BOLD signal in the right V5 complex and negatively correlated with the BOLD response in the left dorsolateral prefrontal cortex (DLPFC). In the condition with target blanking, additional negative correlations with SPV were found in the left frontal eye field (FEF), the left parietoinsular vestibular cortex (PIVC) and the left angular gyrus. Saccadic frequency was negatively correlated with activations of the right mesial intraparietal sulcus (IPS) during both conditions and the right premotor area during continuous target presentation. We conclude that V5 is directly related to the maintenance of an optimal smooth pursuit velocity during visual feedback, whereas the FEF, PFC, angular gyrus and PIVC are involved in reconstitution and prediction whenever SPV decreases, especially during maintenance of smooth pursuit in the absence of a visual target. Furthermore, we suggest that parietal areas are related to the suppression of saccades during smooth pursuit.

Adult↗

PubMed2001

Interference with performance of a response selection task that has no working memory component: an rTMS comparison of the dorsolateral prefrontal and medial frontal cortex.

It has been suggested that the dorsolateral prefrontal cortex (DLPFC) is involved in free selection (FS), the process by which subjects themselves decide what action to perform. Evidence for this proposal has been provided by imaging studies showing activation of the DLPFC when subjects randomly generate responses. However, these response selection tasks have a hidden working memory element and it has been widely reported that the DLPFC is activated when subjects perform tasks which involve working memory. The primary aim of this experiment was to establish if the DLPFC is genuinely involved in response selection. We used repetitive transcranial magnetic stimulation (rTMS) to investigate whether temporary interference of the DLPFC could disrupt performance of a response selection task that had no working memory component. Subjects performed tasks in which they made bimanual sequences of eight nonrepeating finger movements. In the FS task, subjects chose their movements at random while a computer monitor displayed these moves. This visual feedback obviated the need for subjects to maintain their previous moves "on-line." No selection was required for the two control tasks as responses were cued by the visual display. The attentional demands of the control tasks varied. In the high load (HL) version, subjects had to maintain their attention throughout the sequence, but this requirement was absent in the low load (LL) task. rTMS over the DLPFC slowed response times on the FS task and at the end of the sequence on the HL task, but had no effect on the LL task. rTMS over the medial frontal cortex (MFC) slowed response times on the FS task but had no effect on the HL task. This suggests that a response selection task without a working memory load will depend on the DLPFC and the MFC. The difference appears to be that the DLPFC is important when selecting between competing responses or when concentrating if there is a high attentional demand, but that the MFC is only important during the response selection task.

Attention↗

PubMed1990

Prey capture in the praying mantis Tenodera aridifolia sinensis: coordination of the capture sequence and strike movements.

Coordination of the complete capture sequence of the praying mantis has been studied in detail using several specially developed photographic techniques. The mantis was able to attack prey throughout a large three-dimensional capture zone by changing body orientation relative to its perch. This orientation centred prey on the median plane and brought it within an attack zone relative to the prothorax. Alignment with the median plane simplifies the attack since the prey can then be localized using only two dimensions. The attack comprised several stereotyped components which together formed a single movement sequence of all six legs. Although too rapid for visual feedback, a simple mechanism permits steering of these movements to capture prey at particular locations within the attack zone. These findings are contrasted with those from studies of mantis visual behaviour and a simple mechanism is suggested for how prey location is encoded to produce steering of the attack.

Animals↗

PubMed1998

Human oculomotor system accounts for 3-D eye orientation in the visual-motor transformation for saccades.

A recent theoretical investigation has demonstrated that three-dimensional (3-D) eye position dependencies in the geometry of retinal stimulation must be accounted for neurally (i.e., in a visuomotor reference frame transformation) if saccades are to be both accurate and obey Listing's law from all initial eye positions. Our goal was to determine whether the human saccade generator correctly implements this eye-to-head reference frame transformation (RFT), or if it approximates this function with a visuomotor look-up table (LT). Six head-fixed subjects participated in three experiments in complete darkness. We recorded 60 degrees horizontal saccades between five parallel pairs of lights, over a vertical range of +/-40 degrees (experiment 1), and 30 degrees radial saccades from a central target, with the head upright or tilted 45 degrees clockwise/counterclockwise to induce torsional ocular counterroll, under both binocular and monocular viewing conditions (experiments 2 and 3). 3-D eye orientation and oculocentric target direction (i.e., retinal error) were computed from search coil signals in the right eye. Experiment 1: as predicted, retinal error was a nontrivial function of both target displacement in space and 3-D eye orientation (e.g., horizontally displaced targets could induce horizontal or oblique retinal errors, depending on eye position). These data were input to a 3-D visuomotor LT model, which implemented Listing's law, but predicted position-dependent errors in final gaze direction of up to 19.8 degrees. Actual saccades obeyed Listing's law but did not show the predicted pattern of inaccuracies in final gaze direction, i.e., the slope of actual error, as a function of predicted error, was only -0. 01 +/- 0.14 (compared with 0 for RFT model and 1.0 for LT model), suggesting near-perfect compensation for eye position. Experiments 2 and 3: actual directional errors from initial torsional eye positions were only a fraction of those predicted by the LT model (e. g., 32% for clockwise and 33% for counterclockwise counterroll during binocular viewing). Furthermore, any residual errors were immediately reduced when visual feedback was provided during saccades. Thus, other than sporadic miscalibrations for torsion, saccades were accurate from all 3-D eye positions. We conclude that 1) the hypothesis of a visuomotor look-up table for saccades fails to account even for saccades made directly toward visual targets, but rather, 2) the oculomotor system takes 3-D eye orientation into account in a visuomotor reference frame transformation. This transformation is probably implemented physiologically between retinotopically organized saccade centers (in cortex and superior colliculus) and the brain stem burst generator.

Adult↗

PubMed1981

A method to increase compliance to exercise regimens in rheumatoid arthritis patients.

A hand exerciser with an electronic counter and a visual display was used to measure compliance objectively, to investigate the effects of visual feedback on compliance, and to assess the impact of exercise on seven mild and five moderate rheumatoid arthritis patients. A multiple time-series design varying the onset of the visual display was utilized. Compliance was assessed weekly over the 7 weeks of the study. Pretest and posttest measures of various indicators of hand functioning were taken by an occupational therapist. Visual display of the number of exercises completed decreased the number of noncompliant patients from six to two, with the maximum degree of noncompliance reduced from 44 to 5%. Thus the use of visual display is effective in producing compliance to exercise regimens. In light of the small sample size, however, no definitive conclusions can be drawn regarding the effects of exercise on hand functioning.

Adult↗

PubMed1993

An electromyographic study of whether the digastric muscles are controlled by jaw-closing proprioceptors in man.

Whether in the oral system the digastric muscles (which lack muscle spindles) are under the control of proprioceptive information from the masseter muscles (which contain muscle spindles) was investigated by analysing whether and how the masseters and digastrics showed coordinated behaviour during a static, forceful bite. Subjects were asked to maintain a 100-N force for 15 s with and without visual guidance; bite force exerted, and masseter and digastric electromyograms (EMGs) were recorded. Under visual guidance all subjects co-contracted their digastric muscles during the isometric bite. They held the force for a short time, followed by periods with fluctuations (peak-to-peak force amplitude about 15-20 N). Fluctuations in bite force correlated with the masseter EMGs, the maximum in the correlogram occurring at about -50 ms with the force lagging the masseter. In 75% of the subjects a significant periodic component in the masseter and in the force spectra was found at about 4 Hz. This was also seen in the amplitude spectra of the forces, which showed in 80% of the subjects a significant elevation between 7-10 Hz as well. No correlation between the digastric EMGs and the bite forces, and between the EMGs of masseter and digastric could be detected. Spectra of digastric EMGs showed no prominent maxima. When subjects were deprived of visual feedback, maxima at -50 ms in the cross-correlation functions of the masseters and the forces were reduced considerably; periodicities of +/- 250 ms disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Bite Force↗

PubMed1996

Effects of changes in ventilation on respiratory discomfort during isocapnic exercise.

We studied the effects of changes in the level of ventilation on respiratory discomfort during isocapnic exercise. Six subjects exercised at 60 W on a cycle ergometer. They initially breathed 2.5% CO2 in oxygen for 75 breaths. Ventilatory parameters of the last 10 breaths were used as controls. In 7 subsequent test sessions each lasting 2 min alternating with 2 min free breathing periods, subjects tried to achieve a target ventilation ranging from 0.7 to 1.3 times the control with a visual feedback system. End-tidal CO2 was regulated automatically at the control level by changing the inspired CO2. Breathing discomfort was measured at the end of each session using a visual analog scale. Isocapnic constraining of ventilation (0.7 times the control) during exercise significantly increased respiratory discomfort (p < 0.05). Increases in ventilation had no significant effect. These results indicate that respiratory discomfort during exercise is exaggerated when the level of ventilation falls below that spontaneously adopted even when chemical drives are held constant.

Adult↗

PubMed2006

Gaze-centered updating of remembered visual space during active whole-body translations.

Various cortical and sub-cortical brain structures update the gaze-centered coordinates of remembered stimuli to maintain an accurate representation of visual space across eyes rotations and to produce suitable motor plans. A major challenge for the computations by these structures is updating across eye translations. When the eyes translate, objects in front of and behind the eyes' fixation point shift in opposite directions on the retina due to motion parallax. It is not known if the brain uses gaze coordinates to compute parallax in the translational updating of remembered space or if it uses gaze-independent coordinates to maintain spatial constancy across translational motion. We tested this by having subjects view targets, flashed in darkness in front of or behind fixation, then translate their body sideways, and subsequently reach to the memorized target. Reach responses showed parallax-sensitive updating errors: errors increased with depth from fixation and reversed in lateral direction for targets presented at opposite depths from fixation. In a series of control experiments, we ruled out possible biasing factors such as the presence of a fixation light during the translation, the eyes accompanying the hand to the target, and the presence of visual feedback about hand position. Quantitative geometrical analysis confirmed that updating errors were better described by using gaze-centered than gaze-independent coordinates. We conclude that spatial updating for translational motion operates in gaze-centered coordinates. Neural network simulations are presented suggesting that the brain relies on ego-velocity signals and stereoscopic depth and direction information in spatial updating during self-motion.

Adult↗

PubMed2001

Acquisition of a sensorimotor skill in younger and older adults.

The present study compared the learning of sensorimotor transformation rules in young and elderly subjects. In a first experimental session, participants executed manual tracking movements first under normal, and then under left-right reversed visual feedback. Overall, seniors' tracking performance was lower. However, both age groups responded in a quantitatively similar way to the feedback change: Tracking errors increased by a similar amount at the onset of left-right reversal, and then gradually returned to the respective baseline levels. In a second session, visual up-down reversal was added to the left-right reversal. The initial increase of tracking error was substantially smaller than in the first session, and this benefit was even more pronounced in seniors. We interpret the benefit of the second session as learning-to-learn, i.e., as enhancement of a general ability to learn new skills, and conclude that in our study, learning-to-learn was more pronounced in elderly subjects.

Adult↗

PubMed1981

Emergent textural contours: a new technique for visual monitoring in nystagmus, oculomotor dysfunction, and accommodative disorders.

Emergent textural contours, the perceptual effect seen during continuous rotation of symmetrical arrays of uniform pattern elements, provide a unique source of visual feedback for eye movements and resolutional states and have potential for use as a new clinical tool. The phenomenon is produced by a combination of factors including the effects of visual persistence and differential resolution. A total of 28 subjects including 17 normals, 4 nystagmus, 4 oculomotor dysfunction, and 3 accommodative facility cases were shown an emergent textural contour with an instrument (the Goldrich Contour Rotator) for its display. Subjects were enabled to monitor their own eye movements and accommodative training. Nystagmus subjects were provided with a continuous source of visual input reflecting their ocular oscillations and a determination of the null point of nystagmus was made with the instrument.

Accommodation, Ocular↗

PubMed1993

Feedback and delays in neurological diseases: a modeling study using dynamical systems.

Numerous regulatory mechanisms in motor control involve the presence of time delays in the controlled behavior of the system. Experimentally, we have shown that an increase of the time delay in visual feedback induces different oscillations in control subjects and in patients with neurological diseases during the performance of a simple compensatory tracking task. A preliminary model is proposed to describe the oscillations observed in control subjects and in patients with neurological diseases. The influence of delays in two feedback loops are the main components of the motor control circuitry involved in this task and are studied from an analytical and physiological perspective. We analytically determine the influence in the model of each of these delays on the stability of the finger position. In addition, the influence of stochastic elements ("noise") in the modeling equation is seen to contribute qualitatively to a more accurate reproduction of experimental traces in patients with Parkinson's disease but not in patients with cerebellar disease.

Cerebellar Diseases↗

PubMed1972

Locomotion: control by positive-feedback optokinetic responses.

Several species of arthropods perform forward locomotory movements when restrained in place and exposed to a pattern of stripes moving backward at normal locomotory velocities. Locomotory effort varies directly with stripe velocity. In nature such locomotory reactions would increase the visual stimulus that elicits them; hence, the reactions represent a new class of optokinetic responses employing positive visual feedback. Stabilizing mechanisms include response decrement during constant stripe velocities.

Animals↗

PubMed2006

Response delay and spatial representation in pointing movements.

Pointing movements decrease in accuracy when target information is removed before movement onset. This time effect was analyzed in relation with the spatial representation of the target location, which can be egocentric (i.e. in relation to the body) or exocentric (i.e. in relation to the external world) depending on the visual environment of the target. The accuracy of pointing movements performed without visual feedback was measured in two delay conditions: 0 and 5-s delay between target removal and movement onset. In each delay condition, targets were presented either in the darkness (egocentric localization) or within a structured visual background (exocentric localization). The results show that pointing was more accurate when targets were presented within a visual background than in the darkness. The time-related decrease in accuracy was observed in the darkness condition, whereas no delay effect was found in the presence of a visual background. Therefore, contextual factors applied to a simple pointing action might induce different spatial representations: a short-lived sensorimotor egocentric representation used in immediate action control, or a long-lived perceptual exocentric representation which drives perception and delayed action.

Adult↗

PubMed2007

The effect of target modality on visual and proprioceptive contributions to the control of movement distance.

Abstract The goal of this study was to determine whether the sensory nature of a target influences the roles of vision and proprioception in the planning of movement distance. Two groups of subjects made rapid, elbow extension movements, either toward a visual target or toward the index fingertip of the unseen opposite hand. Visual feedback of the reaching index fingertip was only available before movement onset. Using a virtual reality display, we randomly introduced a discrepancy between actual and virtual (cursor) fingertip location. When subjects reached toward the visual target, movement distance varied with changes in visual information about initial hand position. For the proprioceptive target, movement distance varied mostly with changes in proprioceptive information about initial position. The effect of target modality was already present at the time of peak acceleration, indicating that this effect include feedforward processes. Our results suggest that the relative contributions of vision and proprioception to motor planning can change, depending on the modality in which task relevant information is represented.

Adult↗

PubMed1987

Neuropsychological analysis of a typewriting disturbance following cerebral damage.

Following a left CVA, a skilled professional typist sustained a disturbance of typing disproportionate to her handwriting disturbance. Typing errors were predominantly of the sequencing type, with spatial errors much less frequent, suggesting that the impairment was based on a relatively early (premotor) stage of processing. Depriving the subject of visual feedback during handwriting greatly increased her error rate. Similarly, interfering with auditory feedback during speech substantially reduced her self-correction of speech errors. These findings suggested that impaired ability to utilize somesthetic information--probably caused by the subject's parietal lobe lesion--may have been the basis of the typing disorder.

Aphasia↗