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PubMed2006

Is the movement-evoked potential mandatory for movement execution? A high-resolution EEG study in a deafferented patient.

During simple self-paced index finger flexion with and without visual feedback of the finger, we compared the movement-evoked potentials of the completely deafferented patient GL with those of 7 age-matched healthy subjects. EEG was recorded from 58 scalp positions, together with the electromyogram (EMG) from the first dorsal interosseous muscle and the movement trace. We analyzed the movement parameters and the contralateral movement-evoked potential and its source. The patient performed the voluntary movements almost as well as the controls in spite of her lack of sensory information from the periphery. In contrast, the movement-evoked potential was observed only in the controls and not in the patient. These findings clearly demonstrate that the movement-evoked potential reflects cutaneous and proprioceptive feedback from the moving part of the body. They also indicate that in absence of sensory peripheral input the motor control switches from an internal "sensory feedback-driven" to a "feedforward" mode. The role of the sensory feedback in updating the internal models and of the movement-evoked potential as a possible cortical correlate of motor awareness is discussed.

Biomechanical Phenomena↗

PubMed1997

Interlimb coordination in patients with Parkinson's disease: motor learning deficits and the importance of augmented information feedback.

The basal ganglia have traditionally been associated with motor control functions and this view has prevailed since the late nineteenth century. Recent experimental studies suggest that this neuroanatomical system is also critically involved in motor learning. In the present study, motor learning/transfer capabilities were compared between patients with Parkinson's disease and a group of normal elderly people. Subjects practiced a bimanual coordination task that required continuous flexion-extension movements in the transverse plane with a 90 degrees phase offset between the forearms. During acquisition, augmented visual feedback of the relative motions was provided in real time. The findings revealed improvements in the bimanual coordination pattern across practice in both groups when the augmented concurrent feedback was present. However, when transferred to performance conditions in which the augmented information was withheld, performance deteriorated (relative to the augmented condition) and this effect was more prevalent in the Parkinson patients. More specifically, no improvement in interlimb coordination was observed under nonaugmented feedback conditions across practice. Instead, a drift toward the preferred in-phase and antiphase coordination patterns was evident. The present findings suggest that Parkinson patients can improve their performance on a new motor task, but they remain strongly dependent on augmented visual information to guide these newly acquired movements. The apparent adoption of a closed-loop control mode is accompanied with decreases in movement speed in order to use the feedback to ensure accuracy. When the augmented feedback is withheld and the movement pattern is to be controlled by means of intrinsic information feedback sources, performance is severely hampered. The findings are hypothesized to indicate that learning/transfer is affected in Parkinson patients who apparently prefer some constancy in the environmental contingencies under which practice takes place. The present findings are consistent with the notion that the basal ganglia form a critical neuroanatomical substrate for motor learning.

Aged↗

PubMed2005

Seeing and hearing others and oneself talk.

We studied the modification of auditory perception in three different conditions in twenty subjects. Observing other person's discordant articulatory gestures deteriorated identification of acoustic speech stimuli and modified the auditory percept, causing a strong McGurk effect. A similar effect was found when the subjects watched their own silent articulation in a mirror and acoustic stimuli were simultaneously presented to their ears. Interestingly, a smaller but significant effect was even obtained when the subjects just silently articulated the syllables without visual feedback. On the other hand, observing other person's or one's own concordant articulation and silently articulating a concordant syllable improved identification of the acoustic stimuli. The modification of auditory percepts caused by visual observation of speech and silently articulating it are both suggested to be due to the alteration of activity in the auditory cortex. Our findings support the idea of a close relationship between speech perception and production.

Acoustic Stimulation↗

PubMed2000

Aspects of body self-calibration.

The representation of body orientation and configuration is dependent on multiple sources of afferent and efferent information about ongoing and intended patterns of movement and posture. Under normal terrestrial conditions, we feel virtually weightless and we do not perceive the actual forces associated with movement and support of our body. It is during exposure to unusual forces and patterns of sensory feedback during locomotion that computations and mechanisms underlying the ongoing calibration of our body dimensions and movements are revealed. This review discusses the normal mechanisms of our position sense and calibration of our kinaesthetic, visual and auditory sensory systems, and then explores the adaptations that take place to transient Coriolis forces generated during passive body rotation. The latter are very rapid adaptations that allow body movements to become accurate again, even in the absence of visual feedback. Muscle spindle activity interpreted in relation to motor commands and internally modeled reafference is an important component in permitting this adaptation. During voluntary rotary movements of the body, the central nervous system automatically compensates for the Coriolis forces generated by limb movements. This allows accurate control to be maintained without our perceiving the forces generated.

Adaptation, Physiological↗

PubMed2004

First-trial adaptation to prism exposure: artifact of visual capture.

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than is expected from the optical displacement magnitude. The authors confirmed 1st-trial adaptation in the task of pointing toward optically displaced targets while visual feedback was delayed until movement completion. Measurement of head-shoulder posture while participants (N = 24) viewed the optically displaced field revealed that their shoulders felt turned in the direction opposite to the displacement (visual capture), accounting for all but about 4% to 10% of 1st-trial adaptation. First-trial adaptation was unrelated to realignment aftereffects. First-trial adaptation is largely an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt body rotation, thereby reducing the effective optical displacement.

Adaptation, Physiological↗

PubMed2004

An endoscopic sinus surgery training system for assessment of surgical skill.

The apprenticeship of procedures in endoscopic sinus surgery has several limitations, including potential risk for the patients and lack of feedback to the trainees. In this paper, we present a new surgical training system that combines a head dummy, force and position sensors: this system can be used to assess surgical skills and provide visual feedback to the trainees.

Clinical Competence↗

PubMed2005

Dissociation between "where" and "how" judgements of one's own motor performance in a video-controlled reaching task.

The aim of the present study is to show that the sensorimotor system makes a differential use of visual and internal (proprioception and efferent copy) signals when evaluating either the spatial or the dynamical components of our own motor response carried out under a remote visual feedback. Subjects were required to monitor target-directed pointings from the images furnished by a video camera overhanging the workspace. By rotating the camera, the orientation of the movement perceived on the screen was either changed by 45 degrees (visual bias) or maintained in conformity with the actual trajectory (0 degrees ). In either condition, after completing twenty pointings, participants had to evaluate their visuomotor performance in two non visual testing: They were both asked to reach the target in a single movement (evaluation of "how to reach the target"), and to evaluate the mapping of the spatial layout where they acted (evaluations of "where the starting position was and, what movement direction was"). Results revealed that though motor performance in the 45 degrees conditions was adapted to the visuomotor conflict, participants' evaluation of the spatial aspect of the performance was affected by the biased visual information. A different pattern was revealed for the evaluation of "how" the target was reached which was not affected by the visual bias. Thus, it is suggested that segregated processing of visual and kinesthetic information occurs depending upon the dimension of the performance that is judged. Visual information prevails when identifying the spatial context of a motor act whereas proprioception and/or efferent copy related signals are privileged when evaluating the dynamical component of the response.

Adaptation, Physiological↗

PubMed1978

Training of voluntary torsion.

By means of a visual feedback technique, human subjects were trained to make large conjugate cyclorotary eye movements at will. The range of movement increased with training at a rate of approximately 0.8 degrees per hour of practice, reaching 30 degrees at the end of training. Photographs recorded the ability to make voluntary cyclofixations at any amplitude within the subject's range. Cyclotorsional pursuit was also trained, with ability increasing with greater amounts of fisual feedback. In addition, torsional saccadic tracking was trained, showing a magnitude vs. peak velocity relationship similar to that seen for normal saccades. Control experiments indicate that all of these movements were voluntary, with no significant visual induction. With extended practice, large torsional movements could be made without any visual stimulation. The emergence of voluntary torsion through training demonstrates that the oculomotor system has more plasticity than has generally been assumed, reopening the issue as to whether other movements could also be trained to alleviate the symptoms of strabismus.

Adult↗

PubMed1991

Properties of the feedback loops controlling eye growth and refractive state in the chicken.

Recent experiments in chickens provide evidence that axial eye growth and refractive state are guided by mechanisms sensitive to refractive error. To determine whether or not the sign of refractive error is derived from longitudinal chromatic aberration we raised chicks with spectacle lenses in monochromatic light. The eyes showed an appropriate growth response to correct for the defocus imposed by the lenses no different than in previous experiments in white light. Thus, in normally accommodating chicks chromatic cues are not necessary for emmetropization to occur. We examined the linearity of feedback loops controlling axial eye growth: positive spectacle lenses were found to inhibit axial growth very efficiently making the eyes shorter than normal whereas negative lenses had little effect on axial elongation: feedback loops for regulation of axial growth are highly nonlinear and act most efficiently on the myopic side. We found that, subsequent to a period of binocular deprivation of form vision, the refractive errors acquired are highly correlated in both eyes. Since both eyes grew without visual feedback we conclude that the gains in the feedback loops that control axial growth must be similar in both eyes. We suggest that the gains are genetically determined and are typical for each individual. Chicks made near-sighted in both eyes by "deprivation of form vision" were corrected by appropriate negative lenses. Three out of five chicks recovered from myopia despite the correction. Also two chicks that were made near-sighted in one eye recovered with no regard to the correcting lens. Three chicks remained more myopic than the correcting lens required and finally started to recover while the lens was still in place. Two out of three chicks that were made far-sighted showed recovery despite appropriate correction by positive lenses. We conclude that there must be a nonvisual mechanism highly sensitive to abnormal eye shape. During expt (4) we found unexpectedly that the development of form deprivation myopia is inhibited if no part of the retina in an animal is exposed to normal visual experience. The result indicates that some communication between both eyes exists, although form deprivation myopia itself has been shown to develop independently in both eyes.

Animals↗

PubMed2006

On the distribution of attention in a visuo-manual adaptation task.

We have observed in a previous study that adaptation to reversed visual feedback in a tracking task is better when subjects are instructed to look at the cursor providing feedback (group C) rather than at the target (group T). Since both groups actually looked at the target, irrespective of their instructions, we suggested that the advantage of group C is not related to their eye movements, but rather to their allocation of spatial attention. The present study scrutinized this view by combining the same adaptation task with a concurrent reaction-time task, designed to spread subjects' attention across the whole display area. Again, subjects were instructed to look at the cursor or at the target, and again, both groups actually looked at the target. Adaptation was similar to group T, and poorer than group C of the previous study. We therefore concluded that adaptation indeed depends on the subjects' allocation of attention: focussing attention mainly on the target, or spreading it across the whole display area, is not as good as distributing attention between target and cursor.

Adaptation, Physiological↗

PubMed1985

A surface electrode array for detecting action potential trains of single motor units.

Action potentials of single motor units were detected by a linear surface electrode array placed perpendicular to the longitudinal axis of the biceps brachii. Twelve myoelectric signals were derived simultaneously from a voluntarily contracting muscle. Using a visual feedback control, 3 subjects produced spike trains of single motor unit action potentials (MUAPs) at a weak contraction. When the myoelectric signals showed an interference pattern at a moderate contraction, several MUAPs were isolated by a visual analysis. MUAPs occurring at about fixed intervals with constant amplitudes and with identical wave forms were presumed to be the action potential trains of single motor units. Reliable estimates of single MUAP wave forms were obtained by averaging and superimposing the detected signals at a timing of characteristic potential peaks. Then not only the firing rate of the spikes but also the territory and the wave form of single MUAPs were investigated. Most MUAPs had a sharp and symmetrical distribution of potentials on a skin surface along the muscle circumference, while some MUAPs showed complex wave forms with some separate potential peaks. The possible arrangement of muscle fibers belonging to the motor units was estimated from the MUAP wave forms.

Action Potentials↗

PubMed1980

Preliminary observations on the response of perioral single motor units to mechanical stretch.

This research represents part of a series of investigations into the function of mechanoreceptor feedback in lip motor control for speech. In the present study, precise mechanical stretches were applied to subjects' lips while they held the firing frequency of a given single motor unit relatively constant using audio and visual feedback. Preliminary data indicate that mechanical stimulation produces a range of short and long latency excitatory and inhibitory effects in perioral motor units. Of particular interest are short latency inhibitory effects in the depressor labii inferior and platysma muscles. These short latency inhibitory effects suggest that the central organization of the perioral sensorimotor system may possess a form of reciprocal innervation. The operation of a circuit is described which permits improved experimental control over the timing of stretch application relative to moter unit discharge. Initial data collected with this circuit suggest that it may be effectively used to assess the time course of subthreshold excitability changes associated with individual motor units during their repeated discharge.

Adult↗

PubMedDate not supplied

Callosally projecting neurons in the macaque monkey V1/V2 border are enriched in nonphosphorylated neurofilament protein.

Previous immunohistochemical studies combined with retrograde tracing in macaque monkeys have demonstrated that corticocortical projections can be differentiated by their content of neurofilament protein. The present study analyzed the distribution of nonphosphorylated neurofilament protein in callosally projecting neurons located at the V1/V2 border. All of the retrogradely labeled neurons were located in layer III at the V1/V2 border and at an immediately adjacent zone of area V2. A quantitative analysis showed that the vast majority (almost 95%) of these interhemispheric projection neurons contain neurofilament protein immunoreactivity. This observation differs from data obtained in other sets of callosal connections, including homotypical interhemispheric projections in the prefrontal, temporal, and parietal association cortices, that were found to contain uniformly low proportions of neurofilament protein-immunoreactive neurons. Comparably, highly variable proportions of neurofilament protein-containing neurons have been reported in intrahemispheric corticocortical pathways, including feedforward and feedback visual connections. These results indicate that neurofilament protein is a prominent neurochemical feature that identifies a particular population of interhemispheric projection neurons at the V1/V2 border and suggest that this biochemical attribute may be critical for the function of this subset of callosal neurons.

Animals↗

PubMed2004

Extrastriate body area in human occipital cortex responds to the performance of motor actions.

A region in human lateral occipital cortex (the 'extrastriate body area' or EBA) has been implicated in the perception of body parts. Here we report functional magnetic resonance imaging (fMRI) evidence that the EBA is strongly modulated by limb (arm, foot) movements to a visual target stimulus, even in the absence of visual feedback from the movement. Therefore, the EBA responds not only during the perception of other people's body parts, but also during goal-directed movements of the observer's body parts. In addition, both limb movements and saccades to a detected stimulus produced stronger signals than stimulus detection without motor movements ('covert detection') in the calcarine sulcus and lingual gyrus. These motor-related modulations cannot be explained by simple visual or attentional factors related to the target stimulus, and suggest a potentially widespread influence of actions on visual cortex.

Adult↗

PubMed2004

Target-directed running in gymnastics: a preliminary exploration of vaulting.

Research to date has demonstrated the importance of running speed and an accurate take-off on gymnastics vaulting performance (Krug et al., 1998; Bohne et al., 2000). Current training practice for gymnastics vaulting is to stereotype the 15-25 m run-ups to the board, which assumes that a fast and reliable approach is best controlled predominantly without visual feedback. Incidences where gymnasts make errors during their run-ups, often landing onto the back of the board, occur frequently, even at the international level. The standard deviation method (e.g. Lee et al., 1982) for identifying visual regulation in long jump run-ups was employed in this first exploration of gymnastics vaulting to examine whether visual regulation processes are utilised. Secondly, the question of how a small number of gymnasts can run fast during the approach and perform more difficult vaults was addressed. Five elite female gymnasts aged 13-15 years performed five round-off entry vaults. One panning 50 Hz video camera recorded each trial from an elevated platform to evaluate the approach step, hurdle, and round-off characteristics, whilst two 250 Hz cameras recorded vaulting performance. Two qualified judges viewed each vaulting trial and provided a performance score. A precursor for a fast take-off from the board when vaulting is to utilise vision early to control the approach kinematics (p = 0.02). High take-off velocity was directly related to judge's score (p = 0.03). Coaches need to supplement gymnasts' vault training to include exercises that improve the gymnasts' ability to visually regulate their gait pattern whilst running.

Adolescent↗

PubMed1991

Event-related potentials to different feedback stimuli.

Event-related potentials (ERPs) were recorded in a time estimation task under different feedback conditions, in which the informative value of the feedback signals (true versus false) was manipulated. A control condition was added in which no signal was presented. Fifteen subjects pressed a button 3 seconds after presentation of a warning signal. Two seconds after the response, a visual feedback signal was presented, indicating whether the preceding interval was estimated correctly. Two different slow waves were observed: the response was preceded by a readiness potential and the feedback stimulus was preceded by a negative slow wave called the stimulus-preceding negativity. The readiness potential was not influenced by the different feedback conditions. The stimulus-preceding negativity was larger in the true feedback condition compared to the false feedback and no feedback conditions. The P300 to the feedback signal was also larger following a true as compared to a false feedback signal. The conclusion is that the stimulus-preceding negativity is an anticipatory component contingent upon the presentation of an informative feedback signal.

Adult↗

PubMed1980

Experimental manipulation of head posture.

Variations in natural head position have been noted by previous workers to be associated with both dentoalveolar and craniofacial skeletal morphologic features. The determinants of cranial posture are as yet not known. Three experiments are described, dealing with the influence of (1) total nasal obstruction, (2) visual feedback deprivation, and (3) a combination of (1) and (2) on the posture of the cranium measured relative to a gravity-defined true vertical reference plane. The results indicate that total nasal obstruction results in all cases in an extended head position. Visual deprivation produces adaptation of a smaller magnitude and unpredictable direction. Combination of both experimentally induced conditions indicates a dominance of the respiratory adaptation in terms of postural response to these stimuli.

Adaptation, Physiological↗

PubMed1979

Optimal response of eye and hand motor systems in pointing at a visual target. II. Static and dynamic visual cues in the control of hand movement.

The closed loop situation of hand pointing at a target has been experimentally divided into its static and dynamic components. When the subjects see their hand at first (closed loop) until the start of the hand movement cuts off the vision of the hand (open loop), the pointing is significantly more accurate than when it is performed without any vision of the hand before and throughout the movement (fully open loop). This suggests that initial cues as regards hand and target position, improve the motor program by a better identification of initial and final states. As poor as it is, the extra retinal signal (encoding of eye position) improves performance when the foveation is done under closed loop; it allows a better redefinition of target position, and thus modulates the hand motor program through a direct central pathway, which is quicker than the processing of the visual feedback of the hand movement error.

Eye Movements↗