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Biomedical subjects

B Maton

Publications and source records attributed to B Maton.

At least 37 records · Page 2Linked to original sources
PubMed1999

Anticipatory postural adjustments are associated with single vertical jump and their timing is predictive of jump amplitude.

This study was carried out to determine the existence and the specificity of anticipatory postural adjustments (APA) associated with vertical jump. Single vertical jump is an upward-oriented movement with identical initial and final postures. A consistent backward shift of the center of pressure (CP) clearly demonstrated the existence of APA. This shift mainly resulted from a soleus (SO) deactivation and tibialis anterior (TA) activation. As in gait initiation, the main role of APA associated with vertical jump is to create the necessary disequilibrium to initiate the movement. A comparison of CP and CG (center of gravity) forward shifts between single jump and tip-toe rising allowed us to propose that forward disequilibrium ends when a critical CP position is reached. As in gait initiation, the duration of jump's APA was several hundreds of milliseconds. This showed that when the role of the APA is to create the initial disequilibrium, their duration is greater than when their role is to compensate for the forthcoming postural disturbance due to the movement. Since the goal of the voluntary movement was to jump at a given height, one expected that this parameter could be programmed. APA's timing depended on the amplitude of the vertical jump: the time of onset of SO deactivation and TA activation and that of backward CP shift were dependent on the peak amplitude of the jump. Nevertheless, there was no relationship between the backward CP shift amplitude and the vertical impulse. Thus, it appears that the amplitude of the jump is not fully programmed but must be adjusted after the onset of the movement, i.e., there is a sequential programming of forward and upward movement. It is also of interest to stress that the SO-TA synergy, which is shown here to be at the basis of the APA associated with single vertical jump, has been also found in many forward-oriented movements. Thus, the present data reinforce the idea that SO-TA synergy is part of a functional synergy used by the central nervous system to simplify the postural motor command.

Adult↗
PubMed1998

Role of proprioceptive information in the temporal coordination between joints.

Ten subjects made rapid, simultaneous movements of jaw (elevation or lowering) and right foot (ankle flexion or extension) in two experimental situations: (1) in response to an external signal (reaction-time situation), and (2) in a self-paced situation. We calculated the mean time intervals between the onsets of electromyographic (EMG) activity of agonist muscles (tibialis anterior or gastrocnemius lateralis compared with masseter or digastricus pars anterior) and those between the onsets of movement acceleration at each joint. Despite the fact that subjects reported simultaneous jaw-foot movements, there was always a short time interval between the two movements as between the agonist EMG activities. When the subjects were asked to perform a jaw elevation movement simultaneously with an ankle movement (flexion or extension), the sign of the time interval was dependent on the situation of movement initiation. In the reaction-time situation, the jaw motor activity preceded that of the ankle, whereas the reverse temporal order was observed in the self-paced situation. This is consistent with a previous hypothesis suggesting that the simultaneity of two motor actions is centrally established through two separate central processes: reactive or predictive. When subjects tried to perform simultaneous jaw lowering and foot flexion or extension movements, the strict temporal order observed when considering jaw elevation and ankle movements disappeared. The jaw motor activity generally preceded that of ankle in the reactive situation, but, depending on the subjects, it preceded or followed the ankle motor activity during self-paced movements. It is likely that the specific spindle supply of jaw muscles accounts for these results. Indeed, the jaw depressor muscles, in contrast to the elevators, lack muscle spindles. Our results suggest that the kinesthetic inputs used by the upper central nervous system to synchronize two rapid voluntary movements are mainly those from spindles located in the muscles that accelerate the movement, suggesting a strong alpha-gamma linkage.

Acceleration↗
PubMed1998

Summation of elementary phonomyograms during isometric twitches in humans.

To study its summation principle, the phonomyogram (PMG) from the first interosseus dorsalis muscle was recorded in five subjects during single twitches evoked by electrical stimulation over the motor point. By increasing the current pulse from threshold to maximal intensity, PMG amplitude increased linearly with motor unit recruitment. The twitch amplitude-intensity relationship was also linear. The PMG amplitude was therefore linearly related to the external force. For all these relationships highly significant correlation coefficients were found. These relationships were interpreted as being a consequence of an orderly recruitment, although, contrary to what happens during voluntary contraction, the largest and strongest motor units were recruited before the smallest and weakest ones during axon electrical stimulation. The PMG onset always preceded twitch onsets as indicated by latency measurements [mean 3.2 (SD 1.3) ms versus 11.5 (SD 3.9) ms, respectively]. Moreover, PMG and twitch latencies may have been significantly reduced by recruitment, suggesting that orderly recruitment influenced both PMG amplitude and occurrence. These results were interpreted as being the result of the summation of elementary PMG from every contracting motor unit and the stiffness change of the muscle medium occurring with recruitment.

Acoustics↗
PubMed1997

The amygdala is critical for seizure propagation from brainstem to forebrain.

Audiogenic seizures, a model of brainstem epilepsy, are characterized by a tonic phase (sustained muscular contraction fixing the limbs in a flexed or extended position) associated with a short cortical electroencephalogram flattening. When sound-susceptible rats are exposed to repeated acoustic stimulations, kindled audiogenic seizures, characterized by a clonic phase (facial and forelimb repetitive jerks) associated with cortical spike-waves, progressively appear, suggesting that repetition of brainstem seizures causes a propagation of the epileptic discharge toward the forebrain. In order to determine the structures through which this propagation occurs, four kinds of experiments were performed in non-epileptic rats and in sound-susceptible rats exposed to single or repeated sound stimulations. The following results were obtained: (I) Electrical amygdalar kindling was similar in non-epileptic and naive-susceptible rats, but was facilitated in sound-susceptible rats submitted to 40 acoustic stimulations and presenting kindled audiogenic seizures. (2) Audiogenic seizures induced an increase in [(14)C]2-deoxyglucose concentration in the amygdala after a single seizure, and in the amygdala, hippocampus and perirhinal and piriform cortices after a kindled audiogenic seizure. (3) A single audiogenic seizure induced the expression of c-Fos protein mainly in the auditory nuclei. A few cells were stained in the amygdala. After 5-10 audiogenic seizures, a clear staining appeared in the amygdala, and perirhinal and piriform cortices. The hippocampus expressed c-Fos later, after 40 audiogenic seizures. (4) Injection of lidocaine into the amygdala did not modify single audiogenic seizures, but suppressed myoclonias and cortical spike-waves of kindled audiogenic seizures. Similar deactivation of the hippocampus failed to modify kindled audiogenic seizures. Taken together, these data indicate a critical role for the amygdala in the spread of audiogenic seizures from brainstem to forebrain.

Acoustic Stimulation↗
PubMed1997

Involvement of proprioceptive feedback in brainstem-triggered convulsions.

PURPOSE: In rodents, specific motor components of generalized convulsive seizures depend on two distinct anatomic substrates: (a) forebrain networks are responsible for facial and forelimb clonus with or without rearing and falling; and (b) brainstem networks are responsible for running-bouncing fits and tonic convulsions. To investigate the requirement of proprioceptive inputs in the generation of these two different types of seizures, we compared the effects of neuromuscular blockade by D-tubocurarine on the EEG expression of brainstem- and forebrain-triggered seizures. METHODS: Unilateral electrical stimulations were applied for 50 consecutive days in freely moving male adult rats through a bipolar electrode aimed at the dorsal hippocampus (n = 5), the occipital cortex (n = 4), the inferior colliculus (n = 6), or the midbrain reticular formation (n = 6). Two days after the last stimulation, rats were paralyzed with d-tubocurarine and stimulated in the same way. RESULTS: In brainstem structures, the first electrical stimulation induced tonic seizures concomitant with low-voltage cortical activity; repetition of daily stimulations progressively induced tonic-clonic seizures associated with high-amplitude cortical spike-wave discharges. After immobilization by d-tubocurarine, brainstem stimulations failed to induce any EEG paroxysm. In forebrain structures, repeated electrical stimulations produced a classic kindling with progressive occurrence of clonic seizures associated with large cortical discharges; d-tubocurarine left unchanged the EEG pattern of these latter seizures. CONCLUSIONS: These data suggest that proprioceptive reafferentation resulting from movement is necessary for the generation of self-sustained brainstem seizures but is not implicated in the elaboration of forebrain seizures.

Animals↗
PubMed1997

Discrepancies between HMPAO and ECD SPECT imaging in brain tumors.

Among several brain radiopharmaceuticals for SPECT imaging, 99mTc complexes of HMPAO and ECD are the most widely used. They are considered to be equal in their capacity to reflect regional cerebral blood flow; but discrepancies between HMPAO and ECD brain uptake have been reported in stroke patients. This paper reports our observations regarding discrepancies between HMPAO and ECD SPECT in 14 of 23 patients with suspected brain tumors or presumed metabolic cerebral abnormalities. We obtained similar conflicting results, namely focal HMPAO hyperactivities and isoactive ECD SPECT. The majority of these discrepancies were found in patients with brain tumors (10 of 13 patients), while only 4 of the 10 remaining patients with nontumoral process showed similar discrepant results. The physiopathology behind these observations is discussed here, and it is likely to be related to the specific response to cellular metabolic disorders rather than to perfusion disturbances.

Adult↗
PubMed1996

Responses of motor cortical cells to short trains of vibration.

The response discharges of precentral motor cortical cells to brief trains of vibration applied to the tendon of biceps brachii were analyzed in two alert but passive monkeys. The activity of 20 phasic-tonic and 6 tonic cells was analyzed. All had functional linkages with flexor muscles during a preceding flexion task and responded to passive movement of the elbow. Taking as a reference the stereotyped reflex response in the stretched muscle, the effect of changes in the amplitude of a constant frequency vibration (4 vibrations at 58 Hz) was quantified statistically in peristimulus histograms of the cortical cell discharges. All cells were transiently influenced by low vibration amplitudes. Most responses (71%) were excitatory and occurred at a mean latency of 24 ms, which is consistent with cells activated by input from stretch receptors. Excitatory, reproducible responses to the lowest vibration amplitudes were more frequent in phasic-tonic than in pure tonic cells. Large-amplitude vibrations always excited the motor cortical cells. The sign of the responses to vibration matched that to passive elbow movements for most cells. These findings show that elbow-related motor cortical cells are very sensitive to proprioceptive input from primary spindle afferents.

Animals↗
PubMed1996

Adaptation of the precentral cortical command to elbow muscle fatigue.

The control exerted by individual motor cortical cells on their fatigued target muscles was assessed by analyzing the discharge patterns and electromyographic (EMG) postspike effects of cortical cells in monkeys making repeated forceful, but submaximal, isometric flexions of the elbow to produce fatigue. Two monkeys were trained to perform self-paced isometric contractions (for longer than 2 s) at forces greater than 35% maximal contraction, with three sets of 20 consecutive contractions; the first and last sets were at the same force level. Pairs of EMG electrodes were implanted in the biceps brachii, brachioradialis, and triceps brachii. The cortical cell discharges were modulated with the active and passive movements of the elbow and produced consistent EMG postspike effects during isometric contraction. Muscle fatigue was assessed as a statistically significant (P < 0.05) drop in the mean power frequency of the EMG power spectrum in one or both flexors in the last set of contractions. Clear signs of muscular fatigue occurred in 20 different experimental sessions. Before fatigue, cortical cells were classified as phasic-tonic (18), phasi-cramp (three), or tonic (five). Twenty cells briskly fired to passive elbow extension, and 9 also responded to passive flexion. Only 6 cells showed a decreased discharge to passive extension. A 22-30% increase in the contraction force produced a higher discharge frequency in 13 cells, and a lower frequency in 5 cells. All cells exerted EMG postspike effects in their target muscles: 20 cells facilitated the flexors, and some of these also inhibited (3 cells) or cofacilitated (5 cells) the extensor; the other 6 cells had mixed effects: 5 of them inhibited at least one flexor, and 1 cell only facilitated the extensor. Most cells (24/26) still produced EMG postspike effects in their target muscles during fatigue, and the number of facilitated muscles increased: 21 cells facilitated the flexors, and 12 of them cofacilitated the extensor. Only 3 cells still inhibited the flexors and were tonic cells. The cortical cell firing frequency increased during fatigue in 13 cells and decreased in 8 cells. Increases involved 10 cells excited by passive elbow extension. Fourteen cells showed parallel changes in firing frequency with fatigue and force, and 9 of these cells facilitated both extensors and flexors in fatigue. Increases were found in 8 cells, decreases in 5 cells and no change in 1 cell. As muscle afferents provide substantial information to cortical cells, which in turn establish functional linkages with their target muscles before and during fatigue, the changes in cell firing frequencies during fatigue demonstrate the active participation of the motor cortex in the control of compensation for the peripheral adjustments concomitant with muscle fatigue.

Adaptation, Physiological↗
PubMed1995

Phonomyogram from single motor units during voluntary isometric contraction.

The purpose of this study was to determine the characteristics of the specific phonomyogram (PMG) of active motor units activated during voluntary isometric contractions. The electromyogram (EMG) and PMG were recorded from 87 anconeus motor units in 14 subjects. The elementary PMG from single motor units was analysed with a spike-triggered averaging technique. The electro-acoustical delay was 3.5 (SD 1.1) ms, which is within the range of values reported in the literature for PMG evoked by motor nerve stimulation. All motor units demonstrated a pattern of impulsive sounds with a duration of 87.2 (SD 10.7) ms. These results would imply that PMG is linked to the contractile activity of the motor units. These results also would suggest that PMG recorded from a contracting muscle in situ reflects the summation of elementary PMG during voluntary contraction more than the overall mechanical properties of the muscle.

Acoustics↗
PubMed1995

Biomechanical analysis of simple jaw movements in Friedreich's ataxia.

The jaw movement kinematics in relation to the EMG activity of two antagonistic jaw muscles (the masseter and the digastricus pars anterior) were examined in healthy subjects and patients with Friedreich's disease. Dysarthria and ataxia are the main characteristics of this disease. Jaw movement was monitored with a magnetometer system, and bipolar surface electrodes were used to record EMG activity. Unidirectional opening, unidirectional closing and opening-closing movements of the mandible were performed in a simple reaction time situation. The data were compared with those for normal control subjects. The kinematic and electromyographic characteristics were: (a) prolonged total movement duration resulting from increased acceleration and deceleration durations; (b) decreased maximum velocity, and a secondary peak in the velocity profile; (c) tonic EMG activity in muscles supposedly at rest; (d) prolonged EMG bursts. Premotor reaction time was also increased. These characteristics are similar to those, previously described, of limb movements in subjects with cerebellar dysfunctions and suggest that the alterations of jaw movement in Friedreich's ataxia could be due to a deficit in cerebellar control.

Adult↗
PubMed1995

Functional linkages between motor cortical cells and elbow flexor muscles. Evidence for and characteristics of postspike facilitation.

1. Two monkeys (Macaca fascicularis) making high-level but submaximal isometric flexions of the elbow were investigated for the output effect of motor cortical cells on the electromyogram (EMG) activity of two main elbow flexors using the method of spike-triggered averaging of rectified EMGs (STAs). 2. Monkeys were trained to perform individual isometric contractions for > 2 s, and two series of > or = 20 contractions, the second series being at a greater force. EMG electrodes pairs were implanted in the biceps brachii and brachioradialis. A total of 257 cortical cells were found that discharged with the active and passive movements of the elbow. We examined the EMG postspike facilitations (PSFs) produced in either one or the two flexors for only those cells that discharged during the isometric contraction, and provoked PSFs in the two series of contractions. 3. The main characteristics of the EMG isometric contractions in the agonists were analyzed. Spectral analysis showed that the increases in the EMG median frequency with force stabilized at the force levels performed by monkeys. Cross correlation methods showed no cross talk between agonists. 4. The 26 selected cortical cells had a regular discharge frequency. Ten cells did not change frequency with a 22-30% force increase, 14 cells discharged at a higher frequency, and 2 cells discharged at a lower frequency. For single-cell frequencies of 5-65 Hz, interspike intervals < 10 ms were rare: the median and modal intervals were 20-30 ms. 5. The significance of PSFs with respect to the EMG background noise was estimated statistically. STAs from successive epochs under identical load conditions, and STAs performed at a distance from the trigger, showed that PSFs were authentic postspike effects and not sudden EMG changes synchronized by chance with the triggering cell. The features distinguishing PSF from secondary postspike EMG changes or coactivation and task-related effects were studied in simultaneous STAs of flexors and autocorrelogram of cortical spikes. 6. The magnitude of the PSF was expressed as the percent peak amplitude above the mean EMG baseline. The mean percent amplitude of the 90 PSFs produced in both muscles and series was 4.0 +/- 2.4% (mean +/- SD). There was no difference in the average amplitude of PSFs in the two flexors, although the baseline voltages in the biceps brachii were higher. Neither was there any significant change with force while the baseline level increased by 29 +/- 10%, indicating that the absolute PSF amplitude increased in the same proportion as baseline.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Characteristics of muscle fatigue in patients with myofascial pain-dysfunction syndrome.

The purpose of this study was to compare the properties of muscle fatigue in the masseter and temporalis muscles of normal individuals and those with myofascial pain-dysfunction syndrome (MPD). The MPD muscle is presumed to have different characteristics of fatigue than its healthy counterpart; these characteristics can be quantitated using standard electromyogram (EMG) signal-processing techniques. A total of 18 patients diagnosed as having MPD comprised the experimental group and 15 adults with no history or present symptoms of temporomandibular joint pain and dysfunction served as controls. Surface EMG recordings were made for both the masseter and anterior temporalis muscles while the subject held an incisal bite force level of 10 N for as long as possible. The EMG data were transferred to a microcomputer where the power-density spectrum of the signals were calculated for 2-s samples at 10-s intervals. The mean power frequency (MPF) and power (root mean square, r.m.s.) of the signals were calculated from the power-density spectra. Results showed: (1) the endurance times were significantly shorter for the MPD patients; (2) the masseter was not active in three of 17 MPD patients; (3) decreases in MPF over time were significantly greater for the MPD patients than normal subjects; (4) increases in r.m.s. power were significantly greater over time for the MPD patients; (5) bandwidths of the power-density spectra were similar for the two groups. The implication of these results is the MPD muscle is not in a state of constant fatigue, as is currently believed, but rather demonstrates accelerated fatigue.

Adolescent↗
PubMed1994

Nocturnal paroxysmal dystonia: a clinical form of focal epilepsy.

Different paroxysmal movements occur during sleep. They correspond either to epileptic seizures of sleep, or to parasomnia. Recently, other nocturnal motor phenomena have been described in the literature as nocturnal or hypnogenic paroxysmal dystonia (NPD), paroxysmal arousal, episodic nocturnal wanderings, etc. The NPD are involuntary nocturnal movements characterized by the association of dystonic postures, tonic movements of the four limbs and the body axis, automatisms, affective mimicry, and vocalization. In certain patients, the EEG records show abnormalities characteristic of epilepsy; in others, the EEG appears normal. A large proportion of the patients present epileptic seizures as antecedents. Typical generalized tonic-clonic seizures can follow an NPD. The NPD are improved with anti-epileptics. The considerable similarity of the clinical and paraclinical signs and of the effects of anti-epileptic treatments do not seem to justify the individualization of different subgroups as a function of the EEG patterns: the NPD are always the result of focal epilepsy, and never of a pathology of movement or of parasomnia. Numerous arguments based on the symptoms and the EEG suggest that these seizures involve the mesial frontal regions.

Adult↗
PubMed1993

Electroclinical signs of benign neonatal familial convulsions.

Benign neonatal familial convulsions comprise a distinct epileptic syndrome with an autosomal mode of transmission. The electroclinical signs of seizures in this syndrome are not yet well defined. In 3 children from two families presenting with benign neonatal familial convulsions, 14 seizures were recorded during electroencephalographic (EEG)-video sessions. All seizures occurred during sleep, after a short arousal reaction. Seizures started with bilateral, symmetrical flattening of the EEG for 5 to 19 seconds; simultaneously there was apnea and tonic motor activity. The EEG flattening was followed by a long (1-2-minute) bilateral discharge of spikes and sharp waves; simultaneously, there were vocalizations, chewing, and focal or generalized clonic activity. The prominence of EEG and motor abnormalities varied between the left and the right from one seizure to the next in any given child. The seizures stopped without EEG or clinical postictal depression. These electroclinical observations suggest that the convulsions of benign neonatal familial convulsions are a form of generalized tonic-clonic seizure whose expression may be asymmetrical, probably because of the immaturity of the corpus callosum or other structures ensuring seizure synchronization.

Adult↗
PubMed1993

The influence of tonic neck reflexes on voluntary fatiguing elbow movements in humans.

Tonic neck reflexes (TNR) are often assumed to be included in the building of voluntary motor programmes. The present study was designed to test the importance of TNR in the performance by healthy human adults of high level dynamic exercise. The subjects were placed in an experimental situation similar to the original one used by previous authors, but in a fixed restrained posture. They repeatedly lifted weights by extending the elbow, with the head rotated either towards the side of the active upper limb or towards the opposite side. The rate of movement was 0.5 Hz, and the initial amplitude 60 degrees. Successive series of 15 movements separated by an equivalent period of rest were made by each subject until exhaustion. The mechanical work performed during each series of movements was calculated. Surface electromyograms (EMG) from triceps brachii, anconeus, and biceps brachii muscles were recorded simultaneously with the elbow rotation displacement and then integrated. The EMG from the sterno-cleïdo-mastoidei muscles were also recorded. With successive series of lifting, movement amplitude decreased progressively as a result of fatigue. Thus there was a decrease in the work performed. In agreement with the experimental data of the previous authors as well as with the expected effect of TNR, the decrease in work was less marked when the subjects kept their heads turned towards their moving limb. However, in contrast with the results from other authors, the facilitation was very low. From these results, we concluded that TNR can slightly influence the amount of work that a subject can produce.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Reciprocal positive transfer between kindling of audiogenic seizures and electrical kindling of inferior colliculus.

The behavioral and EEG concomitants of kindling produced by daily electrical stimulation of the inferior colliculus have been recorded in three series of Wistar rats: (1) non epileptic controls (NE), (2) rats susceptible to audiogenic seizures (AS), (3) acoustically susceptible rats with prior kindling of audiogenic seizures by repeated sound exposure (KAS). Repeated collicular stimulation produced behavioral and EEG changes which were similar in the AS and the NE rats. The tonic seizure without cortical discharges elicited by the first stimulation progressively changed into tonic-clonic seizures with sustained cortical EEG discharges after more than 20 stimulations. In the KAS group, the electrical collicular kindling was clearly accelerated: kindled tonic-clonic seizures and their EEG discharges already occurred after one to five electrical stimulations. Similarly, after completion of electrical collicular kindling in AS, sound stimulations immediately induced characteristic kindled audiogenic seizures. The immediate reciprocal positive transfer observed between kindling of audiogenic seizures and kindling of seizures induced by electrical stimulation of the inferior colliculus suggests that kindling of these two brain-stem seizures involves similar structures and mechanisms.

Acoustic Stimulation↗
PubMed1992

Dorsal tegmentum kindling in rats.

Electrical stimulations were applied daily for 40 days to the dorsal tegmentum in 9 rats through chronically implanted bipolar electrodes. The intensity of current (2 s trains of 50 Hz, 1 ms monophasic square waves) necessary to trigger a full tonic seizure was determined and applied for all further stimulations. Initial stimulations induced a tonic seizure with a low voltage fast electrocorticographic activity. After repeated stimulations, high amplitude spike and wave discharges developed over the cortex, their duration exceeding 50 s at the 40th stimulation. Simultaneously, the tonic seizures evolved into tonic-clonic fits with bilateral myoclonias following the tonic phase. These EEG and behavioral modifications persisted for 30 days after the last stimulus. These results demonstrate that kindling may be obtained from brainstem structures.

Animals↗