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PubMed1982

Manual motor performance in a deafferented man.

We have studied manual motor function in a man deafferented by a severe peripheral sensory neuropathy. Motor power was almost unaffected. Our patients could produce a very wide range of preprogrammed finger movements with remarkable accuracy, involving complex muscle synergies of the hand and forearm muscles. He could perform individual finger movements and outline figures in the air with high eyes closed. He had normal pre- and postmovement EEG potentials, and showed the normal bi/triphasic pattern of muscle activation in agonist and antagonist muscles during fast limb movements. He could also move his thumb accurately through three different distances at three different speeds, and could produce three different levels of force at his thumb pad when required. Although he could not judge the weights of objects placed in his hands without vision, he was able to match forces applied by the experimenter to the pad of each thumb if he was given a minimal indication of thumb movement. Despite his success with these laboratory tasks, his hands were relatively useless to him in daily life. He was unable to grasp a pen and write, to fasten his shirt buttons or to hold a cup in one hand. Part of hist difficulty lay in the absence of any automatic reflex correction in his voluntary movements, and also to an inability to sustain constant levels of muscle contraction without visual feedback over periods of more than one or two seconds. He was also unable to maintain long sequences of simple motor programmes without vision.

Adult↗

PubMed1983

Ocular motor deficits in Parkinson's disease. II. Control of the saccadic and smooth pursuit systems.

We quantified the horizontal pursuit and saccadic function of 14 parkinsonian patients and 10 normal subjects matched for age. Eight patients had mild, and 6 advanced disease. Ocular motor deficits were more marked in patients with advanced disease. Saccadic reaction times and postsaccadic refractory periods were prolonged. Peak saccadic velocities were significantly reduced. Slow saccades may be caused by inappropriate coactivation of opposing ocular muscles. Multiple step, hypometric saccades were abnormally frequent. Correct final eye position towards a brief target flash was attained without visual feedback. Brief corrective intervals occurred after hypometric saccades. They are attributed to internal (nonvisual) efference copy feedback of eye position errors. Frequent square wave jerks were also a feature of Parkinson's disease. Smooth pursuit gain was lowered in all patients while tracking sinusoidal targets at frequencies from 0.25 to 1 Hz. Pursuit gain was uniformly reduced at all target velocities at each frequency. This decrease in gain indicates that dysfunction of the gain element, rather than abnormal drop acceleration saturation is responsible for impaired smooth pursuit. The results indicate that Parkinson's disease damages structures involved in the regulation of the saccadic and pursuit systems. We infer that nigrostriatal pathways, known to be damaged in Parkinson's disease, control the latency, velocity and amplitude of saccades, and the gain element of smooth pursuit.

Adult↗

PubMed1984

Initiation and execution of predictable and unpredictable movements in Parkinson's disease.

Nine patients with Parkinson's disease were compared with aged-matched normal controls on a tracking and a reaction time task. In the tracking task, subjects had to follow a target moving either predictably or unpredictably at various frequencies. There were no differences between the groups on this task. Both groups were able to use the predictable target movements to eliminate the lag between the target movements and their own movements, indicating that they could emit preprogrammed responses which did not depend on visual feedback. The reaction time task also contrasted predictable and unpredictable movements since the subjects were sometimes told in advance which finger they would have to lift in response to the imperative signal. The patients were significantly less able than controls to use this predictability to reduce their reaction times. It is concluded that parkinsonian patients can use prior information to control the form of a preprogrammed movement, but cannot use this information to help initiate such a movement.

Adult↗

PubMed1992

A quantitative study of eye and head movements during smooth pursuit in patients with cerebellar disease.

Eye and head movements were analysed during smooth pursuit in 16 patients with various forms of cerebellar disease. Smooth pursuit gain was reduced across all frequencies and velocities of target motion for the patient group as a whole, during both sinusoidal and pseudo-random target motion. The graded breakdown in the pursuit response, as pseudo-random target motion became less predictable, was of a similar magnitude in patients and controls, implying that the predictive pursuit mechanisms were intact in these patients. During head-free pursuit, when vestibulo-ocular reflex (VOR) suppression was necessary, performance was not significantly different from that observed during head-fixed pursuit in the patient group. This finding is similar to that noted in control subjects, and is consistent with the observation that the VOR gains associated with head movements in darkness were similar in the patient and control groups. The deficits in pursuit and VOR suppression in patients with cerebellar disease therefore represent a decrease in gain in the closed-loop visual feedback pathways with apparent sparing of the predictive pathways.

Adult↗

PubMed1995

Motion imagery in Parkinson's disease.

Patients with Parkinson's disease fail to fully profit from advance information about a target's movement in tracking tasks, possibly indicating deficient anticipation of the target's movement. Time estimation has been claimed to be deficient in Parkinson's disease. On the background of these studies, we tested the hypothesis that motion imagery is impaired in Parkinson's disease. Eleven non-demented patients with Parkinson's disease and nine age-matched controls participated in experiments testing their ability to anticipate trajectories of moving points (prediction whether two moving points would crash or not) and to estimate the time needed for completion of an invisible target's movement (a point moving around a circle). In addition, mirror drawing, a task involving motor learning and adjustment of movement to incongruent visual feedback, was tested. The Parkinson's disease patients, who failed to improve on mirror drawing, were not impaired on the imagery tasks: they estimated movement time and predicted trajectories with equal precision as the controls. Motion imagery thus appears to be intact in Parkinson's disease. However, Parkinson's disease patients did not accelerate their predictions of trajectories with practice as fast as the controls, a deficit which may be interpreted in terms of the fronto-striatal dysfunction repeatedly demonstrated in Parkinson's disease.

Aged↗

PubMed1996

Cerebral control of eye movements. II. Timing of anticipatory eye movements, predictive pursuit and phase errors in focal cerebral lesions.

Smooth pursuit eye movements are known to be driven by a mixture of visual feedback and predictive strategies. Prediction in pursuit allows humans to track predictable stimuli with minimal phase lag. But in certain disease states and focal neurological lesions, normal phase relationships are lost and humans track with increased phase errors. Using a sinusoidal pursuit paradigm, we sorted patients into those with large phase errors and those without. Then, working on the premise that large phase errors may have resulted from lack of prediction, we compared predictive and non-predictive ocular pursuit in patients with large phase errors, patients with normal phase errors and control subjects. Subjects sat in darkness and pursued an intermittently illuminated target moving with constant velocity to the right or left. When the movements were in alternate directions and predictable, all the groups possessed the ability to preprogramme appropriate anticipatory eye movements before target onset, and to use this for predictive pursuit. The difference between patients with large phase errors and normal subjects was not an absolute lack or possession of predictive ability but a difference in the timing at which a preprogrammed motor behaviour was initiated or terminated. The timing variability was wide and formed a graded continuum, the control subjects initiating anticipatory pursuit earlier, and the patients with large phase errors initiating much later. In a second experiment, subjects pursued a predictable ramp stimulus presented at various fixed frequencies. We found that in patients where anticipatory pursuit seemed abolished at one frequency of target presentation, changing the frequency of presentation elicited an anticipatory response. Patients adjusted their pursuit latencies to match the temporal demands of target presentation. At target frequencies above 0.8 Hz, there was a significant positive correlation between latencies in ramp pursuit and phase lags in sinusoidal pursuit. None of our patients showed complete loss of prediction irrespective of how large the phase errors were. Even when severe time delays in the system made it impossible for a subject to initiate anticipatory pursuit before target onset, prediction could still be demonstrated by the significant velocity and timing advantage the subject had in the pursuit of a predictable target stimulus or by the technique of unexpectedly blanking the target.

Adolescent↗

PubMed2000

Stride length regulation in Parkinson's disease: the use of extrinsic, visual cues.

It has been well documented that marked improvements in the hypokinetic gait pattern of Parkinson's disease patients are possible with the use of appropriate visual cues. This project served to evaluate Parkinson's disease gait performance as well as residual processing capacity while using fixed or gait-regulated visual cues. Three-dimensional kinematic, kinetic and electromyographic gait analysis was carried out on 14 patients and 14 matched controls in baseline conditions and with two types of visual cues: taped step length (SL) markers and an individualized subject-mounted light device (SMLD). A probe reaction time paradigm was invoked to assess residual processing capacity. Ratings of perceived task load were also made using the NASA-Task Load Index. Stride length and gait velocity were reduced in patients in baseline conditions. Both of these parameters increased to control levels with the use of visual cues. These alterations were generally accompanied by modifications of lower limb kinematics and kinetics towards control subjects. Perceived task load was higher in all conditions and was further elevated by the use of the SMLD for both groups. Patients produced larger overall reaction times, although reaction time was not different between baseline and SL marker conditions. Reaction time was increased in both groups when using the SMLD. The overarching finding is that stride length can be regulated in Parkinson's disease using stationary visual cues without increased central processing capacity or perceived effort. This may occur via utilization of visual feedback, reducing the patients' reliance on kinaesthetic feedback for the regulation of movement amplitude.

Aged↗

PubMed2003

Age-related changes in the neural correlates of motor performance.

Age-related neurodegenerative and neurochemical changes are thought to underlie decline in motor and cognitive functions, but compensatory processes in cortical and subcortical function may allow maintenance of performance level in some people. Our objective was to investigate age-related changes in the motor system of the human brain using functional MRI. Twenty six right handed volunteers were scanned whilst performing an isometric, dynamic, visually paced hand grip task, using dominant (right) and non-dominant (left) hands in separate sessions. Hand grip with visual feedback activated a network of cortical and subcortical regions known to be involved in the generation of simple motor acts. In addition, activation was seen in a putative human 'grasping circuit', involving rostral ventral premotor cortex (Brodmann area 44) and intraparietal sulcus. Within this network, a number of regions were more likely to be activated the older the subject. In particular, age-related changes in task- specific activations were demonstrated in left deep anterior central sulcus when using the dominant or non-dominant hand. Additional age-related increases were seen in caudal dorsal premotor cortex, caudal cingulate sulcus, intraparietal sulcus, insula, frontal operculum and cerebellar vermis. We have demonstrated a clear age-related effect in the neural correlates of motor performance, and furthermore suggest that these changes are non-linear. These results support the notion that an adaptable and plastic motor network is able to respond to age-related degenerative changes in order to maintain performance levels.

Adult↗

PubMed2003

Impairment of context-adapted movement selection in a primate model of presymptomatic Parkinson's disease.

The MPTP model allows the presymptomatic stage of parkinsonism to be studied in primates and hence specific behavioural manifestations of moderate nigrostriatal denervation to be identified. On the basis of the physiological literature, we hypothesized that depletion of striatal dopamine could impair the selection of context-relevant habits. To examine this hypothesis, we trained three African green monkeys to perform a simple reach-and-grasp task, including three contexts differing only in terms of the presence and position of transparent obstacles. At the end of training, the analysis of reaching trajectories showed that intact monkeys had built a repertoire of movements, from which they could select the appropriate one depending on the context. In the course of MPTP intoxication (0.3-0.4 mg/kg every 4-5 days) and before parkinsonian motor symptoms appeared, the reaction time (RT), movement time (MT) and variability of reaching trajectories increased in all monkeys. Frequently, the initial direction was not adapted to the context, and consequently the movement was either corrected online or restarted under visual assistance. These non-adapted trajectories appeared to be the main reason for the increase in both RT (because of difficulty in selecting) and MT (because of the need to make corrections). These observations indicate that moderate MPTP-induced dopamine depletion results in a deficit in the selection of context-adapted movement, which is compensated by corrections using either proprioceptive or visual feedback. Similar behavioural disorders might therefore occur in the presymptomatic stage of human Parkinson's disease.

Animals↗

PubMed1976

Myofeedback: a new method of teaching breathing exercises in emphysematous patients.

The diaphragm of the emphysematous patient is low and limited in its excursions, producing an increased functional residual capacity and decreased pulmonary ventilation. This report describes our experiences with a new technique for 1) the training of abdominal-diaphragmatic (A-D) breathing and 2) the relaxation of accessory respiratory muscles in emphysematous patients. Abdominal muscle contraction during expiration has been shown to increase diaphragmatic excursions and, hence, pulmonary ventilation. Use of this technique has been limited, however, because of the difficulty in learning this breathing pattern. Through continuous audio and visual feedback of myoelectric potentials (myofeedback) from abdominal muscles, 12 patients learned A-D breathing. The lower rectus abdominis muscle was found to be the most suitable muscle for obtaining the myoelectric potentials. Similarly, by providing the patients with myofeedback from their accessory muscles, they decreased the use of these muscles, thus increasing their respiratory efficiency. With myofeedback, patients appear to learn new breathing patterns effectively and in fewer sessions than with conventional procedures.

Abdominal Muscles↗

PubMed1989

Halstedian technique revisited. Innovations in teaching surgical skills.

This paper reviews the laboratory models used to teach fundamental surgical skills in our general surgery residency. The laboratory modules allow supervision and self-instruction, practice, and videotape monitoring of the following techniques: skin incision, suturing, knot tying, hemostasis, vascular anastomosis, and intestinal anastomosis. Pigs' feet simulate human skin for exercises in skin incision, lesion excision, suturing, and basic plastic surgical techniques. Latex tubing and penrose drains allow experience in suturing, knot tying, and hemostasis. Polytetrafluoroethylene vascular prostheses permit quantification of the precision of needle passage and suturing by measurement of leakage of water through a vascular anastomosis. Reconstituted, lyophilized, irradiated bovine arteries and ileum provide models of biologic tissue for creating handsewn vascular anastomoses and sutured or stapled gastrointestinal anastomoses. A headlamp videocamera allows unobstructive recording of the resident's technical performance and provides subsequent visual feedback for self-improvement when compared to reference instructional videotapes. We feel that these innovations may enhance surgical dexterity of residents without the need for animal sacrifice. Our goal is to foreshorten the learning curve for basic surgical skills and improve performance in the clinical operating room.

General Surgery↗

PubMed2001

Self-monitoring in schizophrenia revisited.

According to a widespread theory, the first-rank symptoms such as delusions of control or thought insertion met in schizophrenia result from a failure in predicting the consequences of an action on the basis of a forward model based of the intended motor commands (efference copy). This assumption of an impairment in the central monitoring of their own actions is inferred from experiments showing that it is more difficult for schizophrenic patients than for controls to correct erroneous movements in the absence of visual feedback. In our study, 19 schizophrenic patients (10 with Schneiderian symptoms and nine without) and 19 paired control subjects were subjected to a sensorimotor adjustment task to reassess this hypothesis. We show that the patients who succeeded the task not differently from the control subjects were those who were aware of the manual correction (n = 9). Surprisingly, most of them presented Schneiderian symptoms. This suggests that the experience of alien control observed in certain schizophrenic patients cannot be directly related to an underlying cognitive deficit in the conscious monitoring of their own actions.

Adult↗

PubMed2002

Functional MRI for neurofeedback: feasibility study on a hand motor task.

We present an fMRI-based method that enables subjects to monitor and actively modulate their own brain activity as a form of biofeedback. On a 1.5 T clinical MR scanner, functional areas during a simple hand motor task were delineated by detecting signal variations associated with the brain activity. Then, the subject adopted a different strategy to expand the activation in motor and somatosensory areas that were not activated previously. Statistical maps of brain activity were visually presented back to the subject, being updated at the end of each segmented rest-task block in near real-time manner. Our results suggest that the visual feedback of the functional brain activation maps guided subjects to adjust their task performance to achieve the desired modulation of cortical activity. This method may offer a potential utility for fMRI-based neurofeedback.

Acoustic Stimulation↗

PubMedDate not supplied

Interactive 3D segmentation of MRI and CT volumes using morphological operations.

Analysis of tomographic volume imagery would be greatly facilitated if the objects within the volume could be presented in three-dimensionally (3D) rendered views. Such a capability has not been developed in large part because the problem of image segmentation remains unsolved. We describe a new approach that circumvents this problem by allowing the human user to segment images interactively using morphology functions. This segmentation is performed concurrently with 3D visualization providing direct visual feedback to guide the user in the segmentation process. Thus, rather than attempting to duplicate the complex and poorly understood human pattern recognition capability, our approach uses the human's own judgment and knowledge. We present a research study to demonstrate the general feasibility of this approach using MR and CT images. The massive data and computational requirements for interactive 3D image processing exceed current processor limits, but the increased capacities of the next generation of computers are expected to make this approach practical.

Humans↗

PubMed2000

Web-based surgical simulation for ventricular catheterization.

We have used new developments in computer technology and the Internet to create a small program that simulates catheterization of the lateral ventricle. The program can run on most personal computers connected to the Internet. The program allows trainee surgeons to practice the technique with varying degrees of visual feedback--and no risk to the patient. It allows them to learn both the technique and the associated anatomy. The trainees can be assessed while performing the procedure. This is a small, early-stage application of virtual reality in surgical education. There is a demand for surgical training techniques that expose the patient to no risk; the use of computers is appropriate to meet this demand. The technique presented here requires further development; in particular, it needs a standardized assessment element that will allow it to be tested by established surgeons and trainees. The real test of a good training technique is how well it discriminates between trainee and trainer.

Cerebral Ventricles↗

PubMed1985

Adaptation to lens-induced heterophorias.

In previous studies we have shown that subjects with normal binocular vision adapt to prism-induced heterophorias. In this study we have continued the work by investigating whether the oculomotor system can also adapt to lens-induced heterophorias. It was found that subjects gradually adapted to the esophoria induced when viewing a distance chart through negative lenses. Adaptation also occurred to lens-induced esophoria and exophoria at near, while at distance, where the visual feedback was unaltered, the phoria remained virtually constant. These findings demonstrate the flexibility of the oculomotor system.

Adaptation, Ocular↗

PubMed1998

Spectacle lenses and emmetropization: the role of optical defocus in regulating ocular development.

The purpose of our investigation was to determine whether early ocular growth and refractive development was regulated by visual feedback in infant monkeys. Specifically, we examined the ability of infant monkeys to compensate for optically induced changes in the eye's refractive state and to recover from experimentally induced refractive errors. For moderate-powered anisometropic lenses, infants exhibited differential interocular axial growth rates that reduced the lens-induced refractive imbalance between the two eyes. Infants treated with equal-powered lenses over both eyes also showed compensating growth. For lens powers between approximately -3 and +6 D, the resulting refractive-error changes, which were primarily due to alterations in vitreous chamber growth rates, were well correlated with the effective refractive state produced by the treatment lenses. When the stimulus for altered eye growth was removed and the infants were provided unrestricted vision, monkey eyes consistently grew toward emmetropia. The remarkable degree of adaptability exhibited by the eyes of infant monkeys demonstrates that emmetropization in this higher primate is an active process that is regulated on a continuous basis by optical defocus. Consequently, early in life spectacle lenses by changing the eye's effective focus can predictably alter ocular growth and the refractive status of one or both eyes.

Animals↗

PubMedDate not supplied

Voluntary control of penile tumescence.

This study investigated the voluntary control of penile tumescence in the absence of external erotic stimulation. Twelve experimental subjects were given analogue visual feedback and monetary rewards for increase in penile diameter as measured by a strain gauge. Twelve control subjects were given no analogue feedback and noncontingent rewards but the same instructions to maximize erections. While both groups were capable of voluntary penile tumescence, significantly improved performance was observed in the experimental group. Two distinct psychophysiological patterns of voluntary penile tumescence were observed. A "tension" pattern was associated with marked heart rate acceleration, irregular respiration, and variable penile response. A "relaxation" pattern was associated with stable heart rate, regular respiration, and smooth tumescence curves. In using these procedures for the treatment of sexual dysfunctions, it is suggested that feedback and reward be given for a combined pattern of sexual and autonomic responses.

Autonomic Nervous System↗