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PubMed1995

Evidence of positive force feedback among hindlimb extensors in the intact standing cat.

1. The functional organization of heterogenic reflexes produced by activation of extensor force receptors (Golgi tendon organs) was studied in intact cats during stationary stance. Intramuscular stimulation (200 Hz, 20 ms) of hindlimb extensor muscles via chronically implanted electrodes was used to evoke weak muscle contractions and naturally activate Golgi tendon organ Ib afferents while cats stood unrestrained with each paw on a moveable triaxial force plate. 2. Intramuscular stimulation of every hindlimb extensor muscle tested in this study evoked excitatory responses that were widely distributed among hindlimb extensor muscles. Source and target specializations in the functional organization of this positive force feedback system were also observed. For example, stimulation of ankle extensors typically excited extensors and flexors at the ankle and hip (but not knee), whereas stimulation of hip extensors typically excited only extensors at all three joints. In addition, intramuscular stimulation of either lateral (LG) or medial (MG) gastrocnemius consistently inhibited soleus while exciting other extensors at the ankle and more proximal joints. 3. The electromyographic (EMG) reflex responses described above are attributed to the natural (via muscle contraction) activation of extensor group Ib afferents. Direct activation of intramuscular afferents by the stimulus was unlikely because there was no evidence that Ia afferents, which have the lowest electrical thresholds, were activated. Both the observed inhibition of the synergist, soleus, and the excitation of the antagonist, tibialis anterior, produced by gastrocnemius stimulation are opposite to the reflex effects that would be produced at the ankle by activation of gastrocnemius Ia afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Long-term potentiation of the human blink reflex.

The trigeminal reflex blink is an ideal system to investigate whether stimulus paradigms that produce long-term potentiation (LTP) in vitro modify motor learning in humans. Presentation of 12 trains of low-intensity, high-frequency stimuli (HFS) to the supraorbital branch of the trigeminal nerve (SO) modified subsequent reflex blinks of human subjects. When HFS occurred concurrently with reflex blinks, the procedure potentiated subsequent blinks for >1 hr. Combining HFS with feedback from the lid movement was critical for this facilitation because presenting HFS immediately after the blink did not alter subsequent blinks. When HFS preceded the blink, however, this treatment suppressed subsequent blinks for 30 min. These effects appear to occur within the trigeminal reflex blink circuits rather than at motoneurons, because stimulation of the previously HFS-treated SO evoked altered blinks in both eyelids, whereas stimulation of the untreated SO elicited unaltered blinks in both eyelids. The modified blink amplitude resulted from altering the response to A-fiber inputs to the trigeminal nerve because all stimuli were too weak to activate C-fibers. The data suggest that HFS produce LTP- and long-term depression (LTD)-like effects on wide dynamic range neurons in the trigeminal reflex blink circuit. The data also support the hypothesis that LTP and LTD mechanisms play a role in adaptive modification of human reflex blinks.

Blinking↗

PubMed1988

Control of isometric finger force in patients with cerebellar disease.

Control of isometric forces during grasping or handling of objects is an essential feature of all skilled manual performances. Previous studies of hand function in cerebellar patients were restricted to movements; force control was only investigated under isotonic conditions in combination with movements. Control of isometric forces during voluntary contraction of finger muscles was investigated in 31 patients with chronic cerebellar disease and in 20 normal controls. Eight patients with Friedreich's ataxia were considered to be typical for a disease affecting the afferents to the cerebellum; 4 patients with anterior lobe atrophy, which affects leg movements to a greater extent than finger movements, were compared with 3 patients with hemisphere lesions; 16 patients suffered from diffuse cerebellar atrophy. Using a recently developed microcomputer system for the continuous measurement of finger force, control of isometric force was studied in several tasks within the same subjects. The tasks included the maintenance of constant force output at different force levels with and without visual feedback, fast repetitive force changes, tracking of a sinusoidal target presented visually, and measurement of maximum grip force. The amount of voluntary contraction in terms of muscular power was normal in all patients; in all other tasks clear deficits were observed. The extent of the disturbances was highly variable between patients even within the same clinical subgroup. The detailed analysis of force traces revealed a great variety in types of disturbance. The frequently observed slowing of the speed in repetitive force changes can be attributed to different components in different patients and not only to difficulties at turning points as might be predicted from comparable movement studies. In addition, performance deficits across different tasks were not uniform, indicating dissociation of impairment. Deficits in maintaining force, which may be interpreted as dysmetria or due to tremor, do not necessarily imply an abnormality in diadochokinesis, as measured in fast repetitive force changes, nor does the converse apply.

Adolescent↗

PubMed2005

Parallel neuronal mechanisms underlying physiological force tremor in steady muscle contractions of humans.

We present results from a study of the 6-to 12-Hz force tremor in relation to motor unit (MU) firing synchrony. Our experimental observations from 32 subjects, 321 contractions, and 427 recorded MUs reveal that tremor is accompanied by corresponding, in-phase MU rhythms that are additional to the ones at the MU intrinsic firing rates. This rhythmical synchrony is widespread and has a uniform strength that ranges from near zero to very large (MU/MU coherence > 0.50) in different contractions. Both the synchrony and the tremor are suppressed during ischemia, and this strongly suggests an involvement of spindle feedback in their generation. Furthermore, in the presence of substantial synchrony, the tremor enhancement, relative to the minimal tremor of ischemia, reflects the strength of the synchrony. Theoretical considerations based on these observations indicate that the muscle force signal is expected to show 1) frequency components in the band of the firing rates of the last-recruited, large MUs, and 2) because of the synchronized MU rhythms, an additional, distinct component with a size reflecting the strength of synchrony. Furthermore, synchronized MU rhythms, with frequencies in the 6- to 12-Hz range, are expected to arise from self-oscillations in the monosynaptic stretch reflex loop, due primarily to the associated muscle delay (several tens of milliseconds). Our results therefore reveal the parallel action of two tremor mechanisms, one of which involves MU synchrony probably caused by loop action. Clearly, the results on the synchrony and its impact also apply to other possible generators of tremor synchrony, including supraspinal ones.

Action Potentials↗

PubMed2004

Response monitoring without sensory feedback.

OBJECTIVE: The elicitation of an evoked potential, the 'error negativity' (Ne) when subjects commit errors in speeded tasks, is often taken as an index of response monitoring processes. The presence of a Ne-like wave on purely correct trials challenges the current conceptions about the nature of such a monitoring system. Here, we evaluate the possibility that the Ne-like wave on correct trials is merely due to reafferences, and at the same time, we test directly the general opinion according to which the Ne is generated by an internal signal. METHODS: We studied the presence of a Ne-like wave in a completely deafferented patient. The patient performed two reaction time (RT) tasks: a two-responses RT task and a go/no-go task. RESULTS: In this patient, a Ne occurs on errors, on incorrect EMG activations, and on purely correct responses. On errors, the Ne was clearly followed by an error positivity (Pe). CONCLUSIONS: The Ne and the Ne-like wave are not generated by reafferences. This similarity is a further argument to consider that these two waves are of same nature. SIGNIFICANCE: The present data demonstrate that sensory information is not mandatory for the brain to monitor and correct ongoing responses.

Afferent Pathways↗

PubMed1990

Electromyographic versus rhythmic positional biofeedback in computerized gait retraining with stroke patients.

This research provides a preliminary investigation of the relative efficacy of electromyographic (EMG) versus a novel biofeedback (BFB) approach to improve ankle control and functional gait in stroke patients. A computerized system was designed to provide audiovisual feedback of either muscle activity or ankle position during dorsiflexion and plantar flexion. The novel approach also included rhythmic pacing to emphasize the rapid timing of ankle motion necessary to switch from stance to swing during walking. Thirty-seven subjects were randomly assigned to one of the following groups: (1) no-treatment control, (2) EMG BFB, and (3) rhythmic positional BFB. Blind evaluations of ankle performance, gait, and perceived exertion were performed at regular intervals. Analyses of covariance revealed that subjects receiving rhythmic positional BFB significantly increased their walking speeds relative to other groups at posttest (p = .02) and at three-month follow-up (p = .035), without any increase in subjectively reported energy cost. The ability of positional BFB to emphasize the timing events during walking provided optimistic results for carry-over into gait functioning. The degree of sensorimotor recovery and time since onset of stroke were considered important factors in determining outcomes.

Adult↗

PubMed2004

[Feedback control of muscle relaxation with a varying on-off controller using cisatracurium].

BACKGROUND: Under clinical conditions constant neuromuscular blockade can also be maintained by a simple closed-loop system. However, delayed onset time, non-linearity of the dose-response curve and different sensitivity to muscle relaxants for each patient are limiting factors. METHODS: In 20 patients who underwent elective surgical procedures under continuous propofol/alfentanil anaesthesia and relaxation with cisatracurium, the maintenance of an electromyographically controlled cisatracurium block of 90% was achieved by a varying on-off control system. Using an own computer-aided measuring device, the course of the neuromuscular blockade and deviations from the desired neuromuscular block were registered. RESULTS: Over a period of 64.2+/-14.0 min, neuromuscular block could be controlled on average at a T(1)-level of 10% (90% block). The mean error of the deviation of the obtained neuromuscular blockade from the set-point was -1.6+/-0.9% on average. To maintain this neuromuscular blockade, a dose rate of 1.4+/-0.9 micro g x kg(-1) x min(-1) cisatracurium was necessary. CONCLUSIONS: It can be concluded that a simple closed-loop system allows the safe use of the intermediate term muscle relaxant cisatracurium for the performance of surgical procedures.

Adult↗

PubMed1998

Swallowing-related perihypoglossal neurons projecting to hypoglossal motoneurons in the cat.

Although previous studies have examined the functional role of the neurons in the area ventrolateral to the hypoglossal nucleus (perihypoglossal neurons) in the trigemino-hypoglossal reflex, no convincing evidence for the direct connection from the perihypoglossal neurons to the hypoglossal motoneurons has yet been provided. In addition, the role of the perihypoglossal neurons in swallowing has not been studied. The purpose of this study was to investigate (1) the input-output relationship of the perihypoglossal neurons and (2) whether the afferent feedback was essential for their swallowing-related activity in chloralose-anesthetized cats. Before and after the cats were paralyzed, single-unit activities were recorded extracellularly from 30 perihypoglossal neurons during swallowing elicited by electrical stimulation of the superior laryngeal nerve. These perihypoglossal neurons responded with spike potentials after short latencies to stimulation of the inferior alveolar and hypoglossal nerves. The neurons also responded with spike potentials to single shocks applied to the superior laryngeal nerve, but were activated transiently at the initial phase of repetitive stimulation of the nerve and kept silent until the occurrence of swallowing before and after the animal was paralyzed. They showed burst activities in coincidence with swallowing. Averaging of intracellular potentials of a hypoglossal motoneuron by simultaneously recorded extracellular spikes of a perihypoglossal neuron revealed monosynaptic inhibitory post-synaptic potentials. We conclude that, in the region ventrolateral to the hypoglossal nucleus, there are neurons which relay trigeminal, hypoglossal, and vagal afferents. Furthermore, some of these perihypoglossal neurons are inhibitory hypoglossal premotor neurons that are involved in the central programming of swallowing.

Afferent Pathways↗

PubMed2006

Neuromuscular fatigue differs with biofeedback type when performing a submaximal contraction.

The aim of the study was to examine alterations in contractile and neural processes in response to an isometric fatiguing contraction performed with EMG feedback (constant-EMG task) when exerting 40% of maximal voluntary contraction (MVC) torque with the knee extensor muscles. A task with a torque feedback (constant-torque task) set at a similar intensity served as a reference task. Thirteen men (26+/-5 yr) attended two experimental sessions that were randomized across days. Endurance time was greater for the constant-EMG task compared with the constant-torque task (230+/-156 s vs. 101+/-32s, P<0.01). Average EMG activity for the knee extensor muscles increased from 33.5+/-4.5% to 54.7+/-21.7% MVC EMG during the constant-torque task (P<0.001), whereas the torque exerted during the constant-EMG task decreased from 42.8+/-3.0% to 17.9+/-5.6% MVC torque (P<0.001). Comparable reductions in knee extensors MVC (-15.7+/-8.7% for the constant-torque task vs. -17.5+/-9.8% for the constant-EMG task, P>0.05) and voluntary activation level were observed at exhaustion. In contrast, excitation-contraction coupling process, assessed with an electrically evoked twitch and doublet, was altered significantly more at the end of the constant-EMG task despite the absence of M-wave changes for both tasks. Present results suggest that prolonged contractions using EMG biofeedback should be used cautiously in rehabilitation programs.

Adult↗

PubMed2000

Variability of the masticatory process during chewing of elastic model foods.

Many studies show a consistent individual chewing pattern; chewing being governed by a pattern generator and regulated by sensory feedback. The aim of this study was to determine the variation in chewing between sessions, replicates and subjects using elastic model foods. Fifteen young male subjects were selected to chew four food products differing in hardness. Four sessions were performed at 1-wk intervals for each subject and, within each session, the four model foods were presented 3 times each. Jaw movement was recorded simultaneously with masseter and anterior temporalis electromyographic activities. Several chewing characteristics increased progressively from one session to the next; the largest increase occurred from the 1st to the 2nd session, with little difference between the last two sessions. No differences were observed between the samples of the same food product within a session. As mastication progressed, the amplitude and speed of the cycles and the muscular work decreased progressively. The first cycle appeared to be very different from the subsequent for all parameters except for occlusal duration. Thus, under our experimental conditions, the origin and amount of variation in chewing patterns were identified and provide information to improve the accuracy and comparability of results in studies of mastication.

Adult↗

PubMed1978

Modifications of ongoing tremors and locomotion by sensory feedback.

In principle tremors can be produced by (1) mechanical oscillators (combination of masses and springs), (2) reflex oscillators arising from sensory feedback pathways, or (3) central oscillators generated by single "pacemaker" neurones or interconnected networks. Recent studies supporting each of these mechanisms under certain conditions are discussed. Differences between these mechanisms are clarified by recent studies in Edmonton on the premammillary cat. This preparation shows a prominent reflexly-induced tremor which can be modified by mechanical loading and electrical stimulation. It also shows spontaneous stepping on a treadmill which is known to be produced by a spinal "stepping generator", but can be modified in interesting ways by sensory perturbations. The applicability of these animal studies to human tremors is considered in relation to preliminary studies in Calgary on patients with Parkinson's disease or essential tremor. We have attempted to modify these tremors by application of torque pulses applied to the wrist. The results are described in terms of a normalized "resetting" index which has a high value (greater than 0.6) for all essential tremor patients studied, and a wide range of values for different parkinsonian patients. The resetting index may be useful in determining the relative importance of peripheral and central factors in producing tremor in a variety of patients.

Animals↗

PubMed1994

Control of breathing patterns and abdominal muscles during graded loads and tilt.

Tilting from supine to upright purportedly enhances both segmental and pulmonary proprioceptive feedback, whereas an expiratory threshold load (ETL) preferentially enhances pulmonary feedback. To test this we studied 13 adults when supine and 60 degrees and 90 degrees head up. We measured tidal volume, inspiratory duration (TI), and expiratory duration (TE) from flow; estimated end-expiratory lung volume from inspiratory capacity; and determined burst amplitudes and durations from abdominal electromyograms (EMGs). ETLs were incremented from 0 (control) to 25 cmH2O in 5-cmH2O steps. Tidal volume was significantly increased by ETL but was unaffected by body position. Every load prolonged TE, whereas TI remained unchanged. When subjects were supine, abdominal EMGs were silent but became tonically active when subjects were upright. During ETL, abdominal activity became rhythmical and phase locked to expiration. Bursts amplitudes were enhanced with each increment in ETL, but burst durations did not change even though TE was prolonged. The altered breathing pattern and active expiration augmented inspiratory flow and decreased end-tidal PCO2. Responses were greatest when subjects were 90 degrees head up. The load-related increments in abdominal recruitment, with no change in burst durations, fit the concept of two central pattern generators: one controlling pattern and the other controlling rhythm of the central respiratory drive.

Abdominal Muscles↗

PubMed2003

The musician's brain: functional imaging of amateurs and professionals during performance and imagery.

We compared activation maps of professional and amateur violinists during actual and imagined performance of Mozart's violin concerto in G major (KV216). Execution and imagination of (left hand) fingering movements of the first 16 bars of the concerto were performed. Electromyography (EMG) feedback was used during imagery training to avoid actual movement execution and EMG recording was employed during the scanning of both executed and imagined musical performances. We observed that professional musicians generated higher EMG amplitudes during movement execution and showed focused cerebral activations in the contralateral primary sensorimotor cortex, the bilateral superior parietal lobes, and the ipsilateral anterior cerebellar hemisphere. The finding that professionals exhibited higher activity of the right primary auditory cortex during execution may reflect an increased strength of audio-motor associative connectivity. It appears that during execution of musical sequences in professionals, a higher economy of motor areas frees resources for increased connectivity between the finger sequences and auditory as well as somatosensory loops, which may account for the superior musical performance. Professionals also demonstrated more focused activation patterns during imagined musical performance. However, the auditory-motor loop was not involved during imagined performances in either musician group. It seems that the motor and auditory systems are coactivated as a consequence of musical training but only if one system (motor or auditory) becomes activated by actual movement execution or live musical auditory stimuli.

Acoustic Stimulation↗

PubMed2006

Forearm electromyographic changes with the use of a haptic force-feedback computer mouse.

OBJECTIVE: To examine changes in biomechanical and motor control associated with a force-feedback computer mouse. BACKGROUND: Haptic computer mice can improve the movement times for point-and-click tasks; however, changes in upper extremity biomechanics and motor control are unknown. METHOD: Eighteen people (ages 22-37 years) performed a point-and-click task 80 times using a force-feedback computer mouse across three different conditions: (a) no force feedback, emulating a conventional mouse; (b) a single attractive force field at the desired target that pulls the mouse to the center of the target; and (c) an attractive force field at the desired target as well as others between the two possible targets, distracting the user from the intended target. Cursor kinematics, wrist posture, and electromyographic (EMG) forearm muscle activity were recorded. RESULTS: The point-and-click movements were 30% faster with the addition of a single force field and 3% faster with the addition of multiple force fields. The Fitts' law index of performance metrics improved from 2.9 bits/response to 4.1 bits/response for multiple attractive fields and to 6.0 bits/response for a single force field. For the distracting force fields, the cursor maximum velocities were over 50% faster. EMG amplitude values were largest for the distracting force fields. These data suggest that the operator uses increased muscle activity to accelerate the mouse through the distracting force fields. CONCLUSION: When implementing attractive haptic force fields, one needs to consider how to reduce these observed effects of potential distracting force fields. APPLICATION: Applications include human-computer interface design for pointing devices extensively used for the graphical user interface.

Adult↗

PubMed2004

Online mutability of step direction during rapid stepping reactions evoked by postural perturbation.

Stepping reactions are often triggered rapidly in response to loss of balance. It has been unclear whether spatial step parameters are defined at time of step-initiation or whether they can be modulated online, during step execution, in response to sensory feedback about the evolving state of instability. This study explored the capacity to actively alter step direction subsequent to step initiation in six healthy young-adult subjects. To elicit forward-step reactions, subjects were released suddenly from a tethered forward lean. A second perturbation (medio-lateral support-surface translation) was applied at lags of 0-200 ms. Active reaction to the second perturbation was determined primarily through analysis of swing-leg hip-abductor activation. In addition, to gauge the biomechanical consequence of the changes in muscle activation, we compared the measured medio-lateral swing-foot displacement to that predicted by a simple passive mechanical model. Perturbations at 0-100 ms lag evoked active medio-lateral swing-foot deviation, allowing balance to be recovered with a single step. However, when the second perturbation occurred near foot-off (200-ms lag), there was no evidence of active alteration of step direction and subjects typically required additional steps to recover balance. The results suggest that step direction can be reparameterized during early stages of stepping reactions, but that step direction was not actively modulated in response to perturbation arising near start of swing phase.

Acceleration↗

PubMed1997

Regional variability of stretch reflex amplitude in the cat medial gastrocnemius muscle during a postural task.

The relationship between local fibre stretch velocity (mechanical input) and the corresponding local reflex electromyographic (EMG) amplitude (a measure of the neural output) was assessed to determine the contribution of muscle spindle feedback in postural control. We hypothesized that traditionally measured input variables (e.g., the velocity of an external movement or whole muscle velocity) may not accurately represent the mechanical input to the muscle spindles, especially when the background forces are small. Three cats were trained to stand on pedestals while ankle rotations were applied to the left hindlimb. EMG and fiber movement in both proximal and distal regions of the muscle were recorded in addition to muscle length and tendon force. We found that local muscle velocity was correlated poorly with whole muscle velocity, demonstrating that internal and external muscle movements are often dissimilar, particularly during tasks that involve modest levels of muscle activation. Local EMG reflex amplitudes were correlated well with the corresponding local fiber stretch velocities (R values ranging from 0.5 to 0.8) but not with muscle stretch velocity. The lack of crossed correlations between fiber stretch velocities and reflex EMG amplitudes measured in proximal versus distal regions of the muscle suggests the presence of a local reflex component. It is concluded that changes in local muscle fiber length represent the mechanical input to spindles better than changes in the total muscle length. Additionally, spindles have a specific role in the reflex activation of nearby muscle fibers.

Animals↗

PubMed2007

Movement-dependent positioning errors in human elbow joint movements.

Healthy adult humans performed elbow movements in a horizontal plane under a small external extending torque (2.1-3.3 Nm). Test movements (TMs) consisted of slow ramp-and-hold flexions in the absence of visual feedback, with the target joint angle to be remembered from a preceding conditioning movement (CM). The CM was produced by matching two beams on the monitor screen: (1) command representing the target position (a straight line); and (2) a signal from the sensor of the elbow joint angle. Two kinds of CM were applied, which had the same target position (50 degrees in most experiments) but differed in initial positions: (1) fully extended joint (0 degrees, P1 CMs); (2) flexed joint (100 degrees, P2 CMs). In a group of 25 subjects, the target in TMs was usually overshot, with the position errors depending on the CMs: 2.7 +/- 0.6 degree (mean +/- SEM) for P1 CMs, and 10.9 +/- 0.7 degree (P < 0.001) for P2 CMs. Vibration of the elbow flexors substantially diminished the difference between the position errors, amounting to--0.31 +/- 0.5 degree and 2.33 +/- 0.6 degrees, respectively. It is suggested that the observed position errors resulted from after-effects in the activity of muscle spindles in agonist and antagonist muscles, but influence of differences in dynamic components of the afferent signals during oppositely directed approaches to the target cannot be excluded.

Adult↗

PubMed2001

Continuous, bilateral Achilles' tendon vibration is not detrimental to human walk.

Sensory feedback from the moving limbs contributes to the regulation of animal and human locomotion. However, the question of the specific role of the various modalities is still open. Further, functional loss of leg afferent fibres due to peripheral neuropathy does not always lead to major alteration in the gait pattern. In order to gain further insight on proprioceptive control of human gait, we applied vibratory tendon stimulation, known to recruit spindle primary afferent fibres, to both triceps surae muscles during normal floor walk. This procedure would disturb organisation and execution of walking, especially if spindles fire continuously and subjects are blindfolded. Vibration induced significant, though minor, changes in duration and length of stance and swing phase, and on speed of walking and kinematics of lower limb segments. No effect was induced on angular displacement of the ankle joint or trunk and head kinematics. This paucity of effects was at variance with the perception of the subjects, who reported illusion of leg stiffness and gait imbalance. These findings would speak for a selective gating of Ia input during locomotion and emphasise the notion that the central nervous system can cope with an unusual continuous input along the Ia fibres from a key muscle like the soleus.

Achilles Tendon↗