Motor patterns of herbivorous feeding: electromyographic analysis of biting in the parrotfishes Cetoscarus bicolor and Scarus iseri

The motor patterns of the herbivorous feeding bite were investigated in two species of parrotfish (Cetoscarus bicolor and Scarus iseri) with functionally distinct biting modes using electromyographic recordings. Behavioral data revealed that S. iseri utilized faster bites, took more bites per feeding bout, and bit at a higher frequency than did C. bicolor. EMGs recorded from the epaxialis (EP), levator operculi (LOP), 3 subdivisions of the adductor mandibulae (A1-A3), and the sternohyoideus (SH) muscles displayed a high degree of within-individual variance. Duration of muscle activity and onset time relative to LOP were shorter in S. iseri than in C. bicolor and S. iseri displayed a greater EMG amplitude in the LOP and SH muscles than did C. bicolor. We calculated the duty factors of the muscles as the relative timing of EMG variables divided by the total feeding cycle time. Patterns of duty factors of the feeding muscles were similar in both species, though muscles were active for a longer portion of the total bite cycle in S. iseri. In addition to its typical bite, S. iseri employed additional motor patterns when taking particularly hard bites. A multivariate comparison of EMGs from biting and suction feeding taxa revealed that the biting motor pattern was significantly different from suction feeding, although there was a high degree of overlap among all feeding strikes. The activity of the sternohyoideus muscle was significantly different between suction feeders and biters. Despite strong similarities of the general motor pattern in a wide range of teleost fishes, components of this pattern are shown to be evolutionarily plastic.     

Morphology, behavior, and evolution: comparative kinematics of aquatic feeding in salamanders.

The kinematics of aquatic prey capture were studied in species representing six salamander families (Ambystomatidae, Amphiumidae, Cryptobranchidae, Dicamptodontidae, Proteidae, and Sirenidae) to test the hypothesis that the process of aquatic prey capture is similar in these families. Seven variables were digitized from high-speed video records of prey capture, and a nested analysis of variance was performed to test for both significant individual within taxon and among taxa effects. The time-to-peak head angle and gape variables showed no taxon effect, while the other five variables exhibited highly significant differences among taxa. Cryptobranchus and Siren showed the most divergent kinematic pattern from the other taxa in a multivariate analysis of all variables, while Ambystoma, Dicamptodon, and Amphiuma tended to have similar overall patterns of head movement. These results show that kinematic patterns during aquatic feeding are not conserved across salamander taxa, and that phylogenetic differentiation in head morphology has been accompanied by novelties in feeding function. The feeding mechanisms of Cryptobranchus and Amphiuma have a bidirectional hydrodynamic design with kinematic correlates that are similar to kinematic characteristics of aquatic feeding in turtles and transformed ambystomatid salamanders. A general framework is presented as an aid to understanding the interrelationships among muscle activity patterns, morphology, and behavior (kinematic patterns). By considering the distribution of taxa in three multivariate spaces, corresponding to three of the levels at which one might analyze a behavior (kinematics, morphology, and motor pattern), it is possible to identify patterns of correspondence among the levels, which aid in understanding the evolution of behavior.     

Effect of teeth clenching on swallowing motor patterns in humans

The purpose of this study was to investigate the effect of teeth clenching on swallowing motor patterns. Seven healthy humans participated in this study. Electromyograms (EMGs) were recorded from the right masseter muscle, the suprahyoid muscles, and the right infrahyoid muscles. Three motor tasks were performed while the EMGs were recorded: swallowing without teeth clenching, and two tasks of swallowing with teeth clenching, one with masseter EMG activity at 20% of maximum, and one with masseter EMG activity at 40% of maximum. The duration of suprahyoid EMG activity with teeth clenching was significantly longer than that without teeth clenching. The duration of infrahyoid EMG activity with teeth clenching was significantly shorter than that without teeth clenching. The whole duration of swallowing with teeth clenching was significantly shorter than that without teeth clenching. Teeth clenching changes the swallowing motor pattern, indicating that activity of the masticatory center affects activity of the swallowing center.     

EFFECT OF TEETH CLENCHING ON SWALLOWING MOTOR PATTERNS IN HUMANS

The purpose of this study was to investigate the effect of teeth clenching on swallowing motor patterns. Seven healthy humans participated in this study. Electromyograms (EMGs) were recorded from the right masseter muscle, the suprahyoid muscles, and the right infrahyoid muscles. Three motor tasks were performed while the EMGs were recorded: swallowing without teeth clenching, and two tasks of swallowing with teeth clenching, one with masseter EMG activity at 20% of maximum, and one with masseter EMG activity at 40% of maximum. The duration of suprahyoid EMG activity with teeth clenching was significantly longer than that without teeth clenching. The duration of infrahyoid EMG activity with teeth clenching was significantly shorter than that without teeth clenching. The whole duration of swallowing with teeth clenching was significantly shorter than that without teeth clenching. Teeth clenching changes the swallowing motor pattern, indicating that activity of the masticatory center affects activity of the swallowing center.     

Evolution of vertebrate motor systems for acoustic and electric communication: peripheral and central elements

Among vertebrates, there are a number of different neuromuscular systems specialized for the production of acoustic and electric social communication signals. Each system involves distinct sets of striated muscles that are derived from paraxial mesodermal somites and are components of a peripheral effector or 'communication organ': the larynx and syrinx of tetrapods, the sonic swim bladder and electric organ of fishes. Each of these systems further exhibits species-typical characters ranging from the number of muscles involved to myofibrillar architecture. Given that communication uses striated muscle, its circuitry is seen to represent a modification of existing motor systems. Thus, it is not surprising that these systems share several features suggesting that common mechanical or developmental factors influence their evolution. Of prime importance in comparing central communication circuitry between fishes and tetrapods is that among tetrapods the sound-generating organs are a part of the ventilatory system and so their activity must be coordinated with other sets of neuromuscular units. Differences in the central pattern of circuitry are thus expected between fishes and tetrapods, as well as among tetrapods themselves, since ventilation mechanisms differ between taxa. Moreover, birds have independently evolved a vocal syrinx which is distinctly separate from their larynx.     

A regional histochemical and electromyographic analysis of the cat respiratory diaphragm

We analyzed the fiber type composition and pattern of electromyogram (EMG) activity in selected regions of the cat diaphragm. The muscles were composed of three basic fiber types. The percentages of each type varied markedly between and within the different regions. The muscle bordering the esophageal hiatus was highest in slow-twitch oxidative (SO) fibers, which appeared specialized to constrict the esophagus and help prevent gastroesophageal reflux. The hiatal muscle was also unique because it received bilateral phrenic motor innervation. Fiber type composition and EMG activity patterns correlated in a consistent manner, i.e., the areas highest in SO fibers yielded patterns of activity characteristic of low-threshold, tonic motor units and the regions lowest in SO and highest in fast glycolytic fibers generated patterns of activity distinctive of high-threshold, phasic motor units. All areas were electrically silent during expiration. Thus, our findings further substantiate the striking nonhomogeneous composition of the diaphragm and indicate that this heterogeneity is a consequence of regional specialization of function.     

Reliability of EMG determinism to detect changes in motor unit synchrony and coherence during submaximal contraction

The determinism (DET) is a parameter used in nonlinear analysis to quantify the occurrence of recurrent patterns in a signal. Applied to the electromyographic activity (EMG), DET has been proposed as an index of motor unit synchrony in human. We have recently shown that the amount of motor unit synchronous firings above chance level was enhanced with stronger submaximal muscle contraction. Using these data, we aimed at determining if (1) EMG DET and motor unit synchrony varied in the same way and (2) EMG DET was more specifically related to the degree of oscillatory coupling between motor unit discharges. Cross-correlation and coherence analyses were applied to the discharges of 30 motor unit pairs tested at various force levels to assess the amount of synchronous impulses and the strength of oscillatory coupling in the time and frequency domains, respectively. Recurrent quantification analysis was applied to EMG activity to extract its DET. Overall, changes in EMG DET were poorly explained by changes in motor unit synchronous impulse probability (6%) and frequency (5%), and by changes in motor unit coherence in the 6-12Hz (5%) and 25-40Hz (8%) bands. Moreover, the comparison of the data obtained at the weakest and the strongest contraction levels tested with each motor unit pair showed that EMG DET remained unaltered with stronger contraction despite the occurrence of consistent changes in motor unit synchrony in both time and frequency domains. This speaks strongly against the reliability of DET in evaluating changes in motor unit synchronization during submaximal muscle contraction.     

Circadian variation and intermuscular correlation of rabbit jaw muscle activity

The activation of jaw muscles varies with different tasks and must be coordinated to ensure proper function of the masticatory system. The activation patterns might differ in various muscles or over the time course. In order to evaluate the activation patterns and the intermuscular correlation during normal daily activity the electromyograms (EMG) of the superficial and deep masseter, medial pterygoid and digastric muscles were continuously recorded in rabbits and related to activity levels. Muscle use was assessed as the relative time per hour (duty time) during which predefined levels of the peak-EMG of the day were exceeded. Pearson's correlation of duty times was calculated for 6 muscle pairs at various activity levels. The duty times of the muscles differed significantly at levels exceeding 50% of the peak-EMG. The animals exhibited apparent intraday variations of duty times revealing a circadian covariant pattern of muscle use. These variations, however, were different in each individual animal. The activation of pairs of jaw-closing muscles was more highly correlated than that of pairs consisting of a jaw-closing and a jaw-opening muscle. The mutual dependence of hourly muscle activity among jaw-closers and among jaw-closers and jaw-openers varied with the activity level suggesting that those muscle groups might be independently controlled during non-powerful and powerful motor behaviors.     

Reaction times recording methods: reliability and EMG analysis of patterns of motor commands.

Different methods for estimating reaction times (RTs) from either finger flexion or finger extension responses have been evaluated. The onset of finger movement was recorded with a photoelectric method and the results are compared with RT measures based on microswitch closure or onset of electromyographic (EMG) activity in the prime move muscle. EMG analysis showed the voluntary motor commands to present a characteristic ballistic pattern in RTs. However, this was not true for a number of trials with unusually long RTs which involved ramp or double burst EMG patterns that were interpreted as reflecting errors in the force calibration of motor commands. RTs based on photoelectric recording of onset of finger extension were consistently related to the RTs estimated from EMG onset in the prime mover muscle. It is concluded that the EMG onset or the finger lift photoelectric method is best suited for reliable RT recording.     

Comparative scanning electron microscopic investigations of the sensory epithelia in the teleost sacculus and lagena

Scanning electron microscopic studies were conducted on the sensory epithelia of the auditory portions of the ears in teleost species representing wide taxonomic diversity. A number of the features of the ears investigated resembled features found in other teleost species, although some major exceptions to earlier patterns were found, particularly in the saccular sensory epithelium. The saccular maculae of all but one species contained basically similar ciliary bundles on the sensory hair cells while there was some significant variation on the lagenar maculae. Hair cell orientation patterns on the sacculus contained four orientation groups in all of the species, other than the mormyrid, Gnathonemus, which only had two groups. Lagenar maculae had two orientation groups, and the orientation patterns were similar to one another. The most divergent form of lagenar macula was found in gnathonemus. These data, combined with data from earlier investigations, provide a broad overview of the surface features of the ear in teleost fishes. Most significantly, it now appears that there are at least five different saccular hair cell orientation patterns among teleost fishes, and all of these patterns are found spread through many major teleost taxa. While there is some similarity in ear structures among some groups of closely related species, such as the Elopomorpha and the Gadiformes, it is becoming more apparent that there is extensive convergence in a number of features of he teleost ear that most likely reflect similar selective pressures during the evolution of the ear. The nature of these selective pressures, however, are not well understood.     

Relation between muscle and brain activity during isometric contractions of the first dorsal interosseus muscle

We studied the relationship between muscle activity (electromyography, EMG), force, and brain activity during isometric contractions of the index finger, on a group and individual level. Ten subjects contracted their right or left index finger at 5, 15, 30, 50, and 70% of their maximal force. Subjects received visual feedback of the produced force. We focused our analysis on brain activation that correlated with EMG. Brain activity of specific anatomical areas (region-of-interest analysis, ROI) was quantified and correlated with EMG activity. Furthermore, we tried to distinguish between brain areas in which activity was modulated by the amount of EMG and areas that were active during the task but in which the activity was not modulated. Therefore, we used two regressors simultaneously: (1) the produced EMG and (2) the task (a categorical regressor). As expected, activity in the motor areas (contralateral sensorimotor cortex, premotor areas, and ipsilateral cerebellum) strongly correlated with the amount of EMG. In contrast, activity in frontal and parietal areas (inferior part of the right precentral sulcus, ipsilateral supramarginal gyrus, bilateral inferior parietal lobule, bilateral putamen, and insular cortex) correlated with activation per se, independently of the amount of EMG. Activity in these areas was equal during contractions of the right or left index finger. We suppose that these areas are more involved in higher order motor processes during the preparatory phase or monitoring feedback mechanisms. Furthermore, our ROI analysis showed that muscle and brain activity strongly correlate in traditional motor areas, both at group and at subject level.     

Spontaneously changing muscular activation pattern in patients with cervical dystonia.

The objective of this study was to determine stability of the neck muscle activation pattern in a given dystonic head position in patients with cervical dystonia (CD). We assessed 26 patients with CD and botulinum toxin (BT) treatment failure before surgical denervation. None of them had received BT injections for at least 4 months. To relate dystonic head position to underlying neck muscle activity, we used synchronised video and poly-electromyographic (EMG) recording over a period of 10 minutes. The muscle activation pattern during constant ("stable") maximal dystonic excursions was analysed. EMG data of nine patients was excluded from the analysis, as these patients had a constantly changing head position or marked head tremor. In the remaining 17 patients, who had a fairly stable dystonic position, muscular activation patterns during the recording spontaneously changed in nine (Group A) while in eight it remained stable (Group B). There was no significant difference in demographic variables between the two groups other than a male predominance in Group A. However, the retrospectively determined initial response to BT treatment (before BT treatment failure had occurred) was significantly worse in Group A as compared with Group B. Neck muscle activation patterns can spontaneously change in CD patients despite constant dystonic head position, implying an inherent variability of the underlying central motor program in some patients. This should be considered when BT treatment response is unsatisfactory, and should also be taken into account when interpreting results of EMG recordings of neck muscles in these patients.     

Intensity modulation of TMS-induced cortical excitation: primary motor cortex

The intensity dependence of the local and remote effects of transcranial magnetic stimulation (TMS) on human motor cortex was characterized using positron-emission tomography (PET) measurements of regional blood flow (BF) and concurrent electromyographic (EMG) measurements of the motor-evoked potential (MEP). Twelve normal volunteers were studied by applying 3 Hz TMS to the hand region of primary motor cortex (M1(hand)). Three stimulation intensities were used: 75%, 100%, and 125% of the motor threshold (MT). MEP amplitude increased nonlinearly with increasing stimulus intensity. The rate of rise in MEP amplitude was greater above MT than below. The hemodynamic response in M1(hand) was an increase in BF. Hemodynamic variables quantified for M1(hand) included value-normalized counts (VNC), intensity (z-score), and extent (mm(3)). All three hemodynamic response variables increased nonlinearly with stimulus intensity, closely mirroring the MEP intensity-response function. VNC was the hemodynamic response variable which showed the most significant effect of TMS intensity. VNC correlated strongly with MEP amplitude, both within and between subjects. Remote regions showed varying patterns of intensity response, which we interpret as reflecting varying levels of neuronal excitability and/or functional coupling in the conditions studied.     

Divergent synaptic influences affecting discharge patterning of genioglossus motor units

Discharge patterns of single motor units were recorded from 5 inframandibular muscles in acutely prepared adult rhesus monkeys and cats. The alterations in interspike interval patterns were studied in genioglossus motor units during respiration, swallowing, laryngeal, and precentral cortex stimulation in animals anesthetized with urethane. Genioglossus motor units were active in both inspiration and swallowing with 87% of the units demonstrating a significant difference in distributions of their first order interspike interval histograms in swallowing as compared to their respiratory pattern. Interaction between several swallows and the prolonged inhibition of respiration (1–7 sec) altered the discharge pattern of a genioglossus unit from its activity during normal respiration. This significant change in the distribution of the interspike intervals of the motor unit in both first order and autocorrelation histograms occurred during the marked increase in intensity and duration of the gross EMG of the genioglossus muscle during the return of respiration. Stimulation of the precentral cortex of the rhesus monkey indicated a third central synaptic influence on the genioglossus motoneurons with a given motor unit discharging in masticatory movements and swallowing. A first order latency histogram demonstrated a fourth synaptic influence with a correlation between the stimulus pulse to the superior laryngeal nerve innervating the laryngeal region and the latency to when a genioglossus motor unit discharged. The latency analysis suggested a vago-hypoglossal reflex from sensory input of the laryngeal region synaptically affecting genioglossus motoneurons by a polysynaptic pathway.     

Transient decrease in number of motor units after immobilisation in man.

On the day after the removal of a long leg cast, when the patient could just bend his knee, the electrical activity in the disused quadriceps muscle showed changes that indicated a reduction in the number of motor units. At 10 to 75% of maximum force the number of turns and the mean amplitude of the needle-recorded EMG were reduced in the disused muscle. Eight days later, when half the initial loss of force had been regained, the electrical activity was normal. The electrical activity produced during a constant force of 5 kg did not differ in the disused and in the contralateral muscle. From the findings in normal subjects it was deduced that the compensatory increase in turns in the EMG pattern to be expected from the decrease in cross-sectional area of the muscle fibres was within the error of the method. The transient decrease in the number of turns and in mean amplitude of the EMG of the disused muscle are an indication of the plasticity of the motor system.     

Evolutionary convergence in nervous systems: insights from comparative phylogenetic studies

Over the past 20 years, cladistic analyses have revolutionized our understanding of brain evolution by demonstrating that many structures, some of which had previously been assumed to be homologous, have evolved many times independently. These and other studies demonstrate that evolutionary convergence in brain anatomy and function is widespread. Although there are relatively few neuroethological studies in which brain and behavior have be studied within an evolutionary framework, three relatively well studied cases are reviewed here: electric communication among gymnotiform and mormyriform fishes, prey capture among frogs, and sound localization among owls. These three examples reveal similar patterns of brain evolution. First, it is clear that novel abilities have evolved many times independently in taxa whose common ancestors lack these abilities. Second, it is apparent that small changes in neural pathways can lead to dramatic changes in an organism's abilities. Brain evolution at this small scale is quite common. The behavioral importance of small scale changes on one hand, and the pervasiveness of convergent evolution on the other, have several implications for understanding brain evolution. First, similar abilities may be conferred by convergent rather than homologous circuits, even among closely related species. Furthermore, closely related species may use the same information in different ways, or they may use different means to obtain the same information. One reason that convergence is so common in the biological world may be that the evolutionary appearance of novel functions is associated with constraints, for example in the algorithms used for a given neural computation. Convergence in functional organization may thus reveal basic design features of neural circuits in species that possess unique evolutionary histories but use similar algorithms to solve basic computational problems.     

Quantification of peripherally induced reciprocal activation during voluntary muscle contraction

A new method was developed to compare patterns of coactivation and reciprocal activation of antagonistic muscles during different experimental conditions. Pure coactivation was defined as a muscle activity pattern where there was never a difference between the slope of the agonist EMG record and the slope of the antagonist EMG record. The degree of reciprocal activation was defined as being proportional to the average absolute value of the difference between these two slope values. Use of this method for the comparison of muscle activity patterns during isometric contractions and unexpected movements showed that peripheral input related to agonist unloading and antagonist stretch significantly increased reciprocal activity.     

Early ictal speech and motor inhibition in fronto-mesial epileptic seizures: a polygraphic study in one patient.

OBJECTIVE: To investigate ictal motor inhibition occurring during seizures in a patient with a tumor located in the left fronto-mesial pre-central cortex. METHODS: Awake and sleep video-polygraphic monitoring, recording scalp EEG and EMG activities from several cranial, trunk and limbs muscles, was performed in a patient with drug-resistant recurrent focal motor seizures before surgical treatment. Speech/motor tasks were repeatedly administered to the patient during the recording sessions in order to evaluate the occurrence of early ictal motor inhibition. RESULTS: Thirty-four seizures were recorded during wakefulness showing a stereotyped pattern of inhibition of speech and voluntary movements followed by sequential activation of upper limb-trunk-lower limb muscles contralateral to the tumor. Polygraphic recordings showed that: (1) initial speech and motor arrest were associated with the EMG evidence of progressive muscle tone suppression in cranial and right distal upper limb muscles; (2) tonic contraction of right deltoid, biceps brachii, intercostalis and paraspinalis muscles appeared after motor inhibition; (3) tonic-clonic activity in the right tibialis anterior muscle occurred at the end of seizures. Eleven subclinical seizures were recorded during sleep showing mild focal tonic EMG activity in right side trunk muscles. CONCLUSIONS: Our findings evidenced early and somatotopically organized inhibition of voluntary movement at the beginning of epileptic seizures with fronto-mesial onset. The demonstration that speech and motor arrest were associated with progressive EMG suppression in cranial and limb muscles supports the hypothesis of motor inhibitory seizures originating in the mesial aspect of pre-motor frontal cortex.     

Characteristics of the locomotor-like muscle activity during orthotic gait in paraplegic persons

We previously found that orthotic gait training can induce 'locomotor-like' coordinated muscle activity of the paralyzed lower limb in persons with spinal cord injury (SCI). The purpose of the present study was to characterize the locomotor-like muscle activity based on data obtained from electromyographic recordings and motion analysis during orthotic gait in nine motor complete SCI subjects. Seven of nine subjects showed a common EMG activation pattern mainly in the ankle (soleus: Sol) and hip extensor (biceps femoris: BF) muscles. The locomotor-like muscle activity was well synchronized with the gait cycle, namely, the EMG amplitude of both Sol and BF muscle had common temporal relationships with the ground reaction force, and hip and ankle joint motions. While the presence or absence of the EMG activity during orthotic gait was consistent with those of mechanically-induced stretch reflex, the duration and amount area of the locomotor-like muscle activity were significantly longer than those of the stretch reflex in the Sol muscle. Moreover, the Sol EMG magnitude had strong relevance to hip as well as ankle angular velocities. These results indicate that the locomotor-like muscle activity during orthotic gait is not a mere reflex response, but includes an activity of the central pattern generator (CPG) and its interaction with afferent inputs. Orthotic gait training for complete SCI persons might have a potential to activate the spinal locomotor center.     

Ontogeny of leg motor output in the chick embryo: a neural analysis.

The motor output of the leg of the chick embryo during hatching (20 days of incubation) was characterized using electromyographic (EMG) recordings from identified knee and ankle muscles. A highly coordinated pattern of motor output was found. It was therefore used as a standard against which to compare the motor output from younger embryos (7, 9, 13, 17 and 19 days of incubation). Despite large differences in some aspects of the EMG records from embryos of different ages, consistent patterns of muscle activation were observed. Quantitative analysis of phase and latency relationships between pairs of muscles indicated that at least some elements of the neural circuitry involved in generating the hatching motor output may be laid down very early in development. Duration vs. latency plots revealed that there is a gradual refinement in the temporal pattern of alternation between antagonist muscles during development.