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PubMed2006

Two-dimensional spatial distribution of surface mechanomyographical response to single motor unit activity.

In order to better understand the mechanisms of generation of mechanomyography (MMG) signals, the two-dimensional distribution of surface MMG produced by the activity of single motor units was analyzed by a novel two-dimensional recording method. Motor unit action potentials were identified from intramuscular electromyographic (EMG) signals and used to trigger the averaging of MMG signals detected over the tibialis anterior muscle of 11 volunteers with a grid of 5x3 accelerometers (20-mm inter-accelerometer distance). The intramuscular wires were inserted between the first and second accelerometer in the middle column of the grid, proximal to the innervation zone. The subjects performed three contractions with visual feedback of the intramuscular EMG signals. In each contraction, a new motor unit was recruited at the minimum stable discharge rate (mean+/-S.D., N = 11 subjects, 7.3+/-2.3 pulse/s), resulting in torque of 2.4+/-2.8% of the maximal voluntary contraction (MVC), 4.6+/-2.7% MVC, and 6.3+/-3.1% MVC (all different, P < 0.01). For 23 out of 33 detected motor units, it was possible to extract the motor unit surface acceleration map (MUAM). A negative MUAM peak (-2.7+/-2.2 mm/s2) was detected laterally and a positive MUAM peak (4.1+/-2.4 mm/s2) medially (P < 0.001). The time-to-peak was shorter in the medial part of the muscle (2.9+/-0.4 ms) than in the other locations (3.4+/-0.5 ms, P < 0.001). The double integrated signals (muscle displacement) indicated negative deflection in the lateral part and inflation close to the tibia bone. The maps of acceleration showed spatial dependency in single motor unit MMG activities. The technique provides a new insight into motor unit contractile properties.

Acceleration↗

PubMed2004

G. Paul Moore Lecture: Unifying the disciplines of our voice smorgasbord.

A look at the many disciplines working with voice over the past 50 years is provided from the perspective of a speech-language pathologist (SLP). Some of the earliest collaborations between medicine and speech-language pathology were seen in the management of cleft palate and velopharyngeal inadequacy problems and observed, also, in laryngectomee rehabilitation. The earlier concern of the SLP for the emotional and psychological aspects of patients with voice disorders appeared replaced with the rise of symptomatic therapy. Dramatic improvement in instrumentation assisted by computer analyses increased our awareness and understanding of both normal and disordered phonation. Although instrumentation today allows for many forms of visual feedback in voice training and therapy, this may be often at the expense of providing needed kinesthetic-proprioceptive and auditory feedback. Particular voice therapy approaches (cognitive, gestalt-holistic, imagery, resonant therapy, muscle training, and symptomatic therapy) used today are described. Suggestions are given for improving educational requirements and clinical experience in voice for SLPs.

Cleft Palate↗

PubMed2003

The neural substrates of driving at a safe distance: a functional MRI study.

An important driving skill is the ability to maintain a safe distance from a preceding car. To determine the neural substrates of this skill we performed functional magnetic resonance imaging of simulated driving in 21 subjects. Subjects used a joystick to adjust their own driving speed in order to maintain a constant distance from a preceding car traveling at varying speeds. The task activated multiple brain regions. Activation of the cerebellum may reflect visual feedback during smooth tracking of the preceding car. Co-activation of the basal ganglia, thalamus and premotor cortex is related to movement selection. Activation of a premotor-parietal network is related to visuo-motor co-ordination. Task performance was negatively correlated with anterior cingulate activity, consistent with the role of this region in error detection and response selection.

Adult↗

PubMed2005

Reinnervation of motor units in intrinsic muscles of a transplanted hand.

Functional recovery of transplanted hand can be evaluated clinically but until now there has been no direct assessment of muscle control. In October 2000 we transplanted the right hand of a brain-dead man aged 43 onto a man aged 35 who had lost his right dominant hand 22 years before. Starting from day 205 after the transplant, multi-channel surface electromyographic (EMG) signals were recorded from intrinsic muscles of the transplanted hand in order to assess their degree of reinnervation. Eleven months post-operatively, the first motor unit action potential train was detected from the abductor digiti minimi. One month later, also the abductor pollicis brevis and the opponens pollicis muscles showed motor unit activity, while, after 15 and 24 months, the first dorsal interosseous and the first lumbricalis muscles, respectively, showed activation of their first motor units. An increase in the number of active motor units was observed after the first signs of reinnervation, although the process was rather slow. In sustained maximal contractions, the motor unit discharge rate decreased from (mean +/- S.D.) 34.0+/-6.7 pps to 23.4+/-5.1 pps in 60 s for the abductor digiti minimi, although the subject was verbally encouraged to maintain a maximal activation. Moreover, the subject was able to perform basic control tasks involving voluntary modulation of motor unit discharge rate. With a visual feedback, he could increase discharge rate of the abductor digiti minimi approximately linearly over time, from 13.4+/-6.7 pps to 32.5+/-11.2 pps in 60 s. In conclusion, we showed reinnervation of single motor units in a transplanted hand after 22 years of denervation. Moreover, voluntary modulation of discharge rates of these motor units could be performed since the first sign of reinnervation.

Adult↗

PubMed2003

Illusory movements of the paralyzed limb restore motor cortex activity.

In humans, limb amputation or brachial plexus avulsion (BPA) often results in phantom pain sensation. Actively observing movements made by a substitute of the injured limb can reduce phantom pain, Proc. R. Soc. London B Biol. Sci. 263, 377-386). The neural basis of phantom limb sensation and its amelioration remains unclear. Here, we studied the effects of visuomotor training on motor cortex (M1) activity in three patients with BPA. Functional magnetic resonance imaging scans were obtained before and after an 8-week training program during which patients learned to match voluntary "movements" of the phantom limb with prerecorded movements of a virtual hand. Before training, phantom limb movements activated the contralateral premotor cortex. After training, two subjects showed increased activity in the contralateral primary motor area. This change was paralleled by a significant reduction in phantom pain. The third subject showed no increase in motor cortex activity and no improvement in phantom pain. We suggest that successful visuomotor training restores a coherent body image in the M1 region and, as a result, directly affects the experience of phantom pain sensation. Artificial visual feedback on the movements of the phantom limb may thus "fool" the brain and reestablish the original hand/arm cortical representation.

Adult↗

PubMed2006

Digit displacement, not object compliance, underlies task dependent modulations in human corticomuscular coherence.

Human sensorimotor EEG shows oscillatory activity at approximately 10 and approximately 20 Hz; the latter frequency is coherent with contralateral EMG. The functional significance of this activity is obscure. A recent study found that corticomuscular coherence varied systematically with increasing lever compliance during a precision grip task. However, since subjects exerted the same force in all conditions, changes in lever compliance also produced changes in how far the digits moved. In this study, we disambiguated whether corticomuscular coherence modulates with object compliance or digit displacement. Subjects performed a precision grip task. Under computer control, the manipulandum could simulate a load of arbitrary compliance (spring constant). Subjects were required to produce a hold-ramp-hold profile of lever displacement, under visual feedback. Subjects first performed tasks with different sized lever movements, against an isotonic load (zero spring constant). Corticomuscular coherence was calculated between left sensorimotor EEG and EMG from five right hand and forearm muscles during the hold phase of the task. Coherence magnitude showed a clear dependence on the extent of digit displacement. In the next task, lever compliance instantaneously changed at the onset of the second hold phase of the task. Corticomuscular coherence modulated not with lever compliance during the analysed hold phase, but with digit displacement during the preceding ramp movement. These data suggest that human corticomuscular coherence is directly related to digit displacement during the preceding movement and not to object compliance. We speculate that corticomuscular coherence may reflect a sensorimotor recalibration, providing updated information about system state following movement.

Brain Mapping↗

PubMed2004

The role of cutaneous sensation in the motor function of the hand.

We studied the effect of abolishing cutaneous sensation (by infiltrating local anaesthetic around the median nerve at the wrist) on the ability of 10 healthy volunteers (a) to maintain a submaximal isometric pinch-grip force for 30 s without visual feedback, and (b) to perform a fine finger-manipulation 'handwriting' task. Blocking cutaneous sensation had no effect on ability to maintain pinch force, suggesting that muscle afferents have the major role in force-control feedback. However, a near-linear fall in force, present with or without block (mean slope=-1.3+/-0.2% s(-1)), which cannot be attributed to motor fatigue, reveals a shortcoming of the afferent feedback system. Blocking cutaneous sensation did impair ability to perform the more demanding writing task, as judged by an 18+/-6% increase in the length of the path between target points, a 22+/-9% increase in the duration of the movement and a 63+/-24% in 'normalised averaged rectified jerk', an averaged time-derivative of acceleration (all significantly nonzero, P < 0.04). These experiments demonstrate the relative importance of muscular and cutaneous afferent feedback on two aspects of hand performance, and provide a way to quantify the deficit resulting from the lack of cutaneous sensation.

Electromyography↗

PubMedDate not supplied

Use of sequential electrical nerve stimuli (SENS) for location of the sciatic nerve and lumbar plexus.

BACKGROUND AND OBJECTIVES: Conventional electrical stimulation has been done by continuous adjustment of current amplitude at a single, set pulse duration (conventionally, 0.1 ms). This study evaluated a novel technique for nerve location by utilization of a peripheral-nerve stimulator (PNS) programmed to deliver sequential electrical nerve stimuli (SENS). A repeating series of alternating sequential pulses of 0.1, 0.3, and 1.0 ms at 1/3-second period intervals between pulses were generated so that at a greater distance from the nerve, only higher-duration pulses would stimulate the targeted nerve and result in 1 or 2 motor responses (MR) per second. Three MR per second at 0.5 mA or less signified the conventional endpoint for nerve location (</=0.5 mA, 0.1 ms) because that value indicated that the 0.1-ms pulse was effective. The conventional 0.1-ms pulse served as a built-in control to which the SENS was compared. METHODS: Sixteen sciatic/psoas blocks were performed on 8 patients. Nerve location was by SENS, with an 80-mm block needle. Needle advance began at 1.0 mA until MR. If 1 or 2 MR/s occurred, the needle was advanced until 3 MR/s were obtained. When 3 MR/s occurred at 0.5 mA or less, needle position was fixed (final position), and mA further decreased until MR disappeared. Two digital video cameras separately recorded needle depth and MR for analysis. Final needle position was designated as zero, and distance was calculated relative to it. RESULTS: In 12 of 16 of the performed blocks, SENS resulted in advanced notification (1 or 2 MR/s), which yielded additional visual feedback compared with control before final nerve location and, thus, increased range. In 15 of 16 blocks, MR did not disappear, once elicited, through final needle location. CONCLUSIONS: SENS resulted in increased sensitivity without compromising specificity of nerve location.

Adult↗

PubMed2005

Ocular compensation for alternating myopic and hyperopic defocus.

During development, the eye grows under visual feedback control, as shown by its compensating for defocus imposed by spectacle lenses. Under normal conditions the sign and magnitude of defocus vary with viewing distance, accommodative status and other factors. To explore how periods of myopic and hyperopic defocus are integrated over time we presented rapidly alternating episodes of myopic and hyperopic defocus by sequentially illuminating a nearby scrim and the wall beyond it to chick eyes wearing lenses that put the far point between the two surfaces. We found that equal periods of myopic and hyperopic defocus generally led to compensatory hyperopia, showing that myopic defocus had a disproportionate effect. Furthermore, the degree of hyperopia depended on the frequency of alternation: low frequencies (1 cycle/30 min) resulted in more hyperopia, whereas at high frequencies (1 cycle/s) the myopic and hyperopic defocus nearly cancelled each other. If similar temporal integration effects apply to humans, they may help explain why brief accommodation events may not influence lens-compensation and why a child's total reading time may be a poor predictor of myopic progression.

Accommodation, Ocular↗

PubMed2006

Characterisation of ocular fixation in humans by analysis of saccadic intrusions and fixation periods: a pragmatic approach.

Eye movements during fixation were recorded in 55 normal subjects with ages ranging from 21 to 81 years. We analysed ocular fixation recordings using measurements of saccadic intrusion amplitudes and frequencies along with fixation periods and mean fixation displacement. Viewing conditions included monocular, binocular and presence or absence of a visual fixation target. Visual feedback reduced the saccadic intrusion amplitudes but had no effect on fixation periods or mean fixation displacements. Binocular viewing had no effect on saccadic intrusion amplitudes, fixation periods or mean fixation displacements. A decrease in fixation periods and an increase in the number of saccadic intrusions with age was observed. This approach could be a clinically useful tool to quantify ocular fixation in neurological disease.

Adult↗

PubMed2002

Co-ordination of bimanual movements in a centrally deafferented patient executing open loop reach-to-grasp movements.

Many everyday tasks require that we use our hands co-operatively. For tasks where both hands are required to perform the same action, a common motor program can be used. But, where each hand must perform a different action, some degree of independent control of each hand is required. In this paper we examine the co-ordination of bimanual movement kinematics in a female patient recovering from brain injury involving anterior regions of the parietal lobe of the right hemisphere, which has resulted in a dense hemianaesthesia of her left arm. A particular focus of this paper is the co-ordination of bimanual movements for reaches executed without visual feedback. Specifically we present new data, which quantify the synchronisation of patient D.B.'s hands by comparing their relative time lag at the start and the end of her bimanual reaches. The results are discussed with particular reference to the role played by limb proprioception in the planning and control of prehension movements.

Aged↗

PubMed1998

Axial pen force increases with processing demands in handwriting.

In two experiments, during handwriting movements, the on-line visual feedback of either slant (Experiment 1) or size (Experiment 2) was transformed to study the time course and biomechanics of the participants' compensations for these distortions. Fluency, movement time, and axial pen force were measured. According to our theory, changing the scaling factor of slant or size is equivalent to a processing demand that is reflected in deteriorated signal-to-noise ratios (SNRs) in the neuromotor system. At the behavioral level, deteriorated SNRs will result in less fluent writing, which can be compensated by applying a biomechanical noise-filtering strategy of increased limb stiffness. This strategy will lead to increased axial pen force, and, with higher degrees of difficulty, to a loss of movement speed. Results revealed decrements in writing fluency together with increments in axial pen force and increments in movement time when compensations to the feedback transformations coincided with the more difficult task conditions. These findings contrast with the traditional resource theory (Kahneman, 1973) in which chronometric measures alone indicate increased processing demands.

Biomechanical Phenomena↗

PubMed1998

Differences in fine control of forces generated by the tongue, lips and fingers in humans.

This study compared the fine control of forces generated by the tongue, lips and fingers in middle-aged adults. The aims were to determine whether (1) the articulatory organs (tongue, lips) and fingers differed in the manner of motor control, (2) force control of the various articulatory organs was similar, and (3) control of forces generated by males was different from that of forces generated by females. The relation among several variables of the ramp-and-hold force contraction and target force level was quantified for the articulatory organs and the fingers in 14 normal individuals (7 males and 7 females). Using visual feedback, participants produced ramp-and-hold compression forces as rapidly and accurately as possible to targets ranging from 0.25 to 2 N. The results showed differences in the profiles of forces generated by the articulatory organs and fingers. In particular, the forefingers were characterized by a greater accuracy of force control and precision of movement, a greater stability of the hold phase, but by slower velocities than the articulatory organs. Motor control of the lower lip differed from that of the upper lip and tongue. Mostly, the lower lip was characterized by a greater precision of contraction, faster development of the force, and greater stability of the hold phase than the upper lip and tongue. Gender was a distinguishing factor in the force task; males were able to produce forces with higher velocities and greater precision than females.

Analog-Digital Conversion↗

PubMed1996

Suboptimal muscular performance: measuring isokinetic strength of knee extensors with new testing protocol.

OBJECTIVE: To analyze the relevance of several isokinetics-based variables for the differentiation of suboptimal from optimal knee extension efforts. DESIGN: Three experimental conditions using 4 intermittent-reciprocal concentric (Con) and eccentric (Ecc) efforts at 30/sec and 180/sec. The first condition (MAX) served as the baseline; subjects were instructed to exert maximal Con and Ecc effort. In the second condition (50%MAX), subjects were asked to exert 50% of the strength measured in the first condition based on the initial use of visual feedback. In the third condition (BREP), subjects repeated the second condition but were asked to exert what they thought was a reproducible level of strength. SETTING: A motor performance laboratory in rehabilitation department of a major hospital. PARTICIPANTS: 16 healthy men, ages 21 to 30. RESULTS: Among several parameters that included variability of results and Ecc/Con strength ratios, the one with the highest differentiating power among MAX, 50%MAX, and BREP was the difference between the Ecc/Con ratios at high and low velocities (P < .0006). CONCLUSIONS: Suboptimal knee extension effort can effectively be differentiated from optimal effort in healthy subjects using this protocol.

Adult↗

PubMed1995

Reliability of a portable electromyographic unit to measure bruxism.

This study evaluated the effect of different rates of increase of occlusal force and of removal and replacement of the electromyographic electrodes on the amount of occlusal force needed to trigger a modified electromyographic measuring unit. Seven subjects placed the electrodes on the masseter area on one side, and bit ipsilaterally on a bite force transducer. The electromyographic recorder was adjusted to be triggered only when the subject clenched. Occlusal force was recorded simultaneously with triggering of the electromyographic recorder. The subjects performed two series of five repetitions of clenching at each of four different rates of increase of force, by visual feedback from a second oscilloscope until the electromyographic recorder was triggered, and an occlusal force measurement was made from the first oscilloscope. Repeated measures of ANOVA analysis revealed no statistically significant differences among the different rates of increase in occlusal force or between the two recording series. Interaction between the two factors also was not significant. The intraclass correlation coefficient was large and statistically significant, indicating that this device was reliable for this method.

Adult↗

PubMed1998

Cutaneous reflexes in patients with acute lacunar infarctions.

Cutaneous reflex (CR) was measured in 15 patients with acute lacunar stroke and in 15 age- and sex-matched normal subjects. EMG activities were recorded from the first dorsal interosseous muscle with surface electrodes, rectified and averaged. Intensity of the stimulation on the index finger was four times the sensory threshold. Aided by audio- and visual-feedback monitoring, the subjects abducted the index finger. Side-to-side comparison was made on all the subjects. CR abnormalities were found in all of our patients. The early inhibitory (I1) and second excitatory (E2) components were attenuated in 11 of 15 patients. The I1-E2 interpeak amplitude (A2) was significantly reduced in all the patients. Prolonged latency of I1-E2 components was found to be pronounced in six of eight patients with sensory symptoms. Eight patients were followed up 1 month later. By that time, the abnormal CR had reversed to some degree in all of them. CR alternation was still present in two fully recovered patients. Our results implied a thalamic relay in the afferent limb of the CR. CR could be a valuable adjunct for assessing long tract dysfunction and monitoring functional recovery.

Aged↗

PubMed2000

Binocular cues are important in controlling the grasp but not the reach in natural prehension movements.

Binocular cues are typically considered to be pre-eminent in the control of reaching and grasping behaviour. However, in the absence of such information prehension movements can still be accurate and reliable. The present study therefore was designed to assess further the contribution of binocular information in the control of human reaching and grasping movements. Participants reached for and picked up objects under binocular and monocular viewing, both in the absence of a visible scene around the target objects (complete darkness with 'self-illuminated' objects and hand), and under normal (fully illuminated) viewing. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect the major indices of the transport component, although it did affect the grasp component. In contrast, the kinematic parameters in the unlit conditions revealed that both the transport component and the grasp component of the reach were severely disrupted whether binocular cues were available or not. Our results suggest that binocular information may be more important for the control of grasp formation than for the control of the transport component. Elimination of the surrounding scene and normal visual feedback affects both the transport and the grasp. It is concluded that in normal viewing conditions, reaching and grasping movements are less dependent on binocular information than has previously been thought.

Adult↗

PubMed2001

Contralesional directional hypermetria associated with line bisection-specific ipsilesional neglect.

Patients with contralesional neglect from right hemisphere injuries often fail to be aware of or respond to visual stimuli in the left hemispace. In contrast, other patients with right hemisphere damage rarely demonstrate behavior consistent with task-specific ipsilesional neglect (IN). We performed a series of experiments in a patient with IN on a line bisection task after a right frontal infarct. When asked to perform horizontal limb movements without visual feedback, the patient showed a leftward directional hypermetria. Similar performance was also observed during a representational production of a given distance without sensory input. These results suggest that IN is induced by a directional hypermetria resulting from disruption of the motor-intentional system.

Aged↗