Error-related brain potentials elicited by vocal errors.

Error-related negativity (ERN) is observed immediately after an error in choice reaction time tasks performed by hand response. We examined whether the ERN occurs in relation to slips of vocalization in the Stroop color word task. In one condition, the subject's vocal responses were masked by continuous pink noise in order to prevent vocalization-related cortical potentials from contaminating the ERN time window. This masking procedure was successful in inhibiting the vocalization-related cortical potential. More importantly, vocalization errors elicited a frontocentral negative-going deflection followed by a positive component immediately after the error response regardless of the masking condition. The present results suggest that the error detection mechanism may also elicit an ERN-like component in response to vocal slips.     

Neural correlates of the lombard effect in primate auditory cortex

Speaking is a sensory-motor process that involves constant self-monitoring to ensure accurate vocal production. Self-monitoring of vocal feedback allows rapid adjustment to correct perceived differences between intended and produced vocalizations. One important behavior in vocal feedback control is a compensatory increase in vocal intensity in response to noise masking during vocal production, commonly referred to as the Lombard effect. This behavior requires mechanisms for continuously monitoring auditory feedback during speaking. However, the underlying neural mechanisms are poorly understood. Here we show that when marmoset monkeys vocalize in the presence of masking noise that disrupts vocal feedback, the compensatory increase in vocal intensity is accompanied by a shift in auditory cortex activity toward neural response patterns seen during vocalizations under normal feedback condition. Furthermore, we show that neural activity in auditory cortex during a vocalization phrase predicts vocal intensity compensation in subsequent phrases. These observations demonstrate that the auditory cortex participates in self-monitoring during the Lombard effect, and may play a role in the compensation of noise masking during feedback-mediated vocal control.     

Vocalization and stapedius muscle activity evoked by local electrical stimulation of midbrain in the chicken (Gallus gallus)

The organization of chicken mesencephalic areas from which stapedius muscle activity and vocalization can be differently elicited was studied. Our results show the existence of an area, around the mesencephalic ‘calling area’, from which stapedius muscle activity can be evoked independently of vocalization. Furthermore, low threshold ‘vocalization loci’ stimulation evokes field potentials in the stapedius-controlling area, due to the activation of stapedius-controlling neurons by vocalization neurons.     

Vocalization and stapedius muscle activity evoked by local electrical stimulation of midbrain in the chicken (Gallus gallus)

The organization of chicken mesencephalic areas from which stapedius muscle activity and vocalization can be differently elicited was studied. Our results show the existence of an area, around the mesencephalic ‘calling area’, from which stapedius muscle activity can be evoked independently of vocalization. Furthermore, low threshold ‘vocalization loci’ stimulation evokes field potentials in the stapedius-controlling area, due to the activation of stapedius-controlling neurons by vocalization neurons.     

On the search for the vocal pattern generator. A single-unit recording study

In the squirrel monkey (Saimiri sciureus), single-unit activity was compared between the midbrain periaqueductal grey and the parvocellular and central nuclei of the medullary reticular formation during the production of species-specific vocalization. It was found that all three areas contain neurones with vocalization-related activity. The relative number of specific reactions types differed between areas, however. While the majority of periaqueductal cells fired just before, but not during vocalization, most cells in the reticular formation fired before and during vocalization. Modulation of discharge rate with changing fundamental frequency was only found in the reticular formation, not the periaqueductal grey. It is concluded that the parvocellular and central nuclei of the reticular formation, but not the periaqueductal grey are involved in vocal pattern generation.     

Laryngeal afferent inputs during vocalization in the cat.

To reveal the kind of information about the larynx which is transmitted to the central nervous system during vocalization, we studied discharge patterns of single fibers of the laryngeal afferent nerve during electrically induced vocalization in ketamine-anesthetized cats. Recorded fibers were classified into four types based on their discharge patterns. Type A fibers responded to vocal fold vibration during vocalization. Type B fibers increased their activity during vocalization without synchronization with vocal fold vibration. Type C fibers decreased their activity during vocalization. Type D fibers discharged only at the onset of vocal fold adduction and abduction. We discuss the functional properties of these afferents and the possibility that these afferent inputs participate in the feedback control of vocalization.     

Changes in muscle activity determine progression of clinical symptoms in patients with chronic spine-related muscle pain. A complex clinical and neurophysiological approach

Spine-related muscle pain can affect muscle strength and motor unit activity. This study was undertaken to investigate whether surface electromyographic (sEMG) recordings performed during relaxation and maximal contraction reveal differences in the activity of muscles with or without trigger points (TRPs). We also analyzed the possible coexistence of characteristic spontaneous activity in needle electromyographic (eEMG) recordings with the presence of TRPs. Thirty patients with non-specific cervical and back pain were evaluated using clinical, neuroimaging and electroneurographic examinations. Muscle pain was measured using a visual analog scale (VAS), and strength using Lovett's scale; trigger points were detected by palpation. EMG was used to examine motor unit activity. Trigger points were found mainly in the trapezius muscles in thirteen patients. Their presence was accompanied by increased pain intensity, decreased muscle strength, increased resting sEMG amplitude, and decreased sEMG amplitude during muscle contraction. eEMG revealed characteristic asynchronous discharges in TRPs. The results of EMG examinations point to a complexity of muscle pain that depends on progression of the myofascial syndrome.     

Not paralysis, but dystonia causes stridor in multiple system atrophy

Electromyography (EMG) was performed in 10 patients with multiple system atrophy, laryngeal or pharyngeal symptoms, or both. In patients with stridor, EMG during quiet breathing revealed persistent tonic activity in both abductor and adductor vocal cord muscles. In patients with dysphagia, the cricopharyngeal muscle showed persistent EMG activity throughout all phases of swallowing. Botulinum toxin injection into the adductor muscle determined subjective improvement and reduced tonic EMG activity. Therefore, the cause of stridor in multiple system atrophy is dystonia of the vocal cords.     

Repetitive vocalizations evoked by electrical stimulation of avian brains. IV. Evoked and spontaneous activity in expiratory and inspiratory nerves and muscles of the chicken (Gallus gallus).

The activity in respiratory nerves and muscles in response to electrical stimulation of vocal substrates in the brain and to CO2 stimulation of the respiratory centers was studied in 28 adult chickens. It was found that the same nerves and muscles were active during both vocalization and respiration. Stimulation of vocal substrates resulted in short latency bursting in the expiratory nerves and muscles. As stimulation intensity increased, progressively longer duration bursts composed of numerous subbursts were produced. By relating muscle activity with sound production , such bursting was shown to underlie evoked vocalizations. Background activity in inspiratory nerves and muscles continued uninterruptedly past stimulus onset only stopping when expiratory activity began. Thereafter inspiratory bursting reciprocated with expiratory bursting and was shown to underlie the intervals between vocalizations. The pattern of activity which was evoked by stimulating vocal substrates was found to strongly interact with the pattern of activity evoked by CO2 stimulation of the respiratory system. Simultaneous records of respiratory and tracheal muscles demonstrated that the same information was sent to both groups of muscles during evoked vocalization. Activity in the respiratory muscles was recorded during spontaneous vocalization of a free-moving bird and was found to resemble that recorded from anesthetized birds. Finally the activity of single units in the obex region of the medulla was recorded during electrical stimulation of vocal substrates and during CO2 stimulation of the respiratory system. Rhythmically active units were found only in the medulla. Unit activity paralleled that found in the nerves and muscles. On the basis on the data accumulated, two models of the chicken vocal system are presented. The first is a model of the sound-producing structures of the chicken. The second is a model of the neural machinery which controls the sound-producing structures. The two models are used as a basis for an explanation of the production of voclizations by the chick of the same species.     

Electromechanical changes during electrically induced and maximal voluntary contractions: Surface and intramuscular EMG responses during sustained maximal voluntary contraction

Changes in the electrical activity of the human gastrocnemius and soleus muscles during fatiguing maximal plantar flexions were studied with computer-aided EMG frequency power spectral analysis and intramuscular spike amplitude-frequency histogram analysis. In some experiments, brief supramaximal nerve stimulations of 80 Hz were given at 15-s intervals during sustained maximal voluntary contractions (MVCs). Multiple muscle biopsy samples were also obtained from the gastrocnemius muscle for fiber type determination. The surface EMG frequency spectral analysis showed a highly significant reduction in mean power frequency and root mean square EMG amplitude during sustained MVCs. The intramuscular spike amplitude-frequency histograms showed that the gastrocnemius muscle had a progressive reduction in the motor unit discharge frequency, particularly those with a relatively high amplitude, whereas the soleus muscle hardly showed a reduction in motor unit activity. Reduction in motor unit activity was also found to be more pronounced in gastrocnemius muscles with higher proportions of type II fibers. Brief maximal tetanic stimulations initially matching the MVC failed to increase the contraction force. Similarly, the evoked compound mass action potentials showed little change in the amplitude in subjects with different muscle fiber compositions. Results of this study suggest that during sustained MVCs, force fatigue could not be attributed to a failure of muscle membrane electrical propagation; a progressive reduction in motor unit activation does not result in a functional disadvantage, but may optimize excitation-contraction coupling by avoiding a muscle electrical conduction failure; and the extent of the reduction in motor unit activation seems to be muscle-fiber-type-dependent which may account for the reduction in amplitude and frequency of the surface EMG.     

Vocalization-induced enhancement of the auditory cortex responsiveness during voice F0 feedback perturbation

ObjectiveThe present study investigated whether self-vocalization enhances auditory neural responsiveness to voice pitch feedback perturbation and how this vocalization-induced neural modulation can be affected by the extent of the feedback deviation.MethodsEvent-related potentials (ERPs) were recorded in 15 subjects in response to +100, +200 and +500 cents pitch-shifted voice auditory feedback during active vocalization and passive listening to the playback of the self-produced vocalizations.ResultsThe amplitude of the evoked P₁ (latency: 73.51 ms) and P₂ (latency: 199.55 ms) ERP components in response to feedback perturbation were significantly larger during vocalization than listening. The difference between P₂ peak amplitudes during vocalization vs. listening was shown to be significantly larger for +100 than +500 cents stimulus.ConclusionsResults indicate that the human auditory cortex is more responsive to voice F₀ feedback perturbations during vocalization than passive listening. Greater vocalization-induced enhancement of the auditory responsiveness to smaller feedback perturbations may imply that the audio–vocal system detects and corrects for errors in vocal production that closely match the expected vocal output.SignificanceFindings of this study support previous suggestions regarding the enhanced auditory sensitivity to feedback alterations during self-vocalization, which may serve the purpose of feedback-based monitoring of one’s voice.     

Amplitude changes in the 8-12, 20-25, and 40 Hz oscillations in finger tremor.

OBJECTIVE: The study examined the amplitude and frequency modulation of the 8-12, 20-25, and 40 Hz frequencies of tremor to determine the degree to which increments of load affect the amplitude of these neural rhythms. METHODS: Finger acceleration from the middle phalange and electromyographic (EMG) activity of the extensor digitorum communis (EDC) muscle were recorded on 10 normal adult subjects. Two experiments are reported that manipulated loads ranging from 0 to 40 and 0 to 200 g that were attached to the distal portion of the outstretched middle phalange. RESULTS: There were 8-12, 20-25, and 40 Hz oscillations in the EMG recording but only the 8-12 and 20-25 Hz rhythms were present in the tremor and tremor-EMG coherence. Adding load to the finger reliably decreased the 20-25 Hz band of acceleration, reduced the relative power within the 20-25 Hz EMG band, increased the relative power of the 40 Hz band, but had no effect on the relative power within the 8-12 Hz EMG frequency band. The tremor-EMG coherence in the 8-12 and 40 Hz regions was independent of load, but was markedly reduced with load in the 20-25 Hz band. CONCLUSIONS: The 8-12, 20-25, and 40 Hz neural rhythms of physiological tremor have a stable frequency consistent with central oscillations. There is an increase in the relative power of the 40 Hz EMG band with force, but only the amplitude of the 20-25 Hz band is modulated by mechanical-reflex feedback.     

Depression of human electromyographic activity by fatigue of a synergistic muscle

In human volunteers, lateral gastrocnemius muscles were stimulated electrically under ischemic conditions so as to produce fatigue. Recordings of electromyographic (EMG) activity were then made from those muscles and simultaneously from untreated medial gastrocnemius muscles during maximal voluntary efforts. In the lateral gastrocnemius the mean amount of EMG activity declined by 52% and was associated with a 35% reduction in the mean amplitude of the M wave (muscle compound action potential) and an insignificant change in M-wave area. In the medial gastrocnemius the EMG was also diminished, by 29%, but there were no significant changes in M-wave amplitude or area. The findings in the medial gastrocnemius are consistent with the existence of an inhibitory reflex effect which originates in the fatigued lateral gastrocnemius muscle and serves to depress excitation in motoneurons supplying that muscle and also in those innervating synergists. The inhibitory effect appears to be long-lasting, in that a significant reduction of the EMG could still be demonstrated 10 min after release of the arterial cuff. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20, 710–717, 1997.     

Leg muscle activation during gait in Parkinson's disease: adaptation and interlimb coordination

Adaptation in leg muscle activity and coordination between lower limbs were studied during walking on a treadmill with split belts in one group of parkinsonian patients and one of age-matched healthy subjects. Four different belt speeds (0.25/0.5/0.75/1.0 m/sec) were applied in selected combinations to the left and right leg. While these walking conditions were easily tolerated by the healthy subjects, the parkinsonian patients usually reached the limits of their walking capabilities. Both groups adapted automatically to a change in belt speed within approximately 20 stride cycles. Healthy subjects adapted by reorganizing their stride cycle with a relative shortening of duration of support and lengthening of the swing phase of the “fast” leg and vice versa on the “slow” leg. The patients showed a restricted range of stride frequencies for the. various belt speeds during normal and split-belt walking with consequent deviations in the reorganization of the stride cycle. In both healthy subjects and patients, ipsilateral gastrocnemius and contralateral tibialis anterior electromyographic (EMG) activity increased predominantly with an ipsilateral increase in belt speed. Two main differences were observed in the EMG patterns: (1) In the patients leg muscle EMG activity was less modulated and gastrocnemius EMG amplitude was small during normal and split-belt walking. However, there was no significant difference between the two groups in respect to the reorganization of the EMG pattern required for the various split-belt walking conditions. (2) The amount of co-activation of antagonistic leg muscles during the support phase of the stride cycle was greater in the patients compared to the healthy subjects during normal and split-belt walking. It is suggested that reduced EMG modulation and recruitment in the leg extensors may contribute to the impaired walking of the patients. This in turn is a result of an irepaired proprioceptive feedback from extensor load receptors. This defective control is partially compensated for in parkinsonian patients by a greater amount of leg flexor activation which leads to a higher degree of co-activation. Visual input plays a role in the control of this increased activation.     

Investigating the use of coherence analysis on mandibular electromyograms to investigate neural control of early oromandibular behaviours: A pilot study

An empirical method for investigating differences in neural control of jaw movement across oromandibular behaviours is to compute the coherence function for electromyographic signals obtained from mandibular muscle groups. This procedure has been used with adults but not extended to children. This pilot study investigated if coherence analysis could reveal task-related differences in control for children by measuring mandibular electromyograms obtained from an infant and adult. Electromyographic signals were obtained from bilateral masseter and temporalis muscle groups during chewing and babble from a typically developing infant from 8–22 months, and chewing and speech were obtained from an adult. Coherence functions were computed. Measures obtained from the infant and adult exhibited a significant main effect for task, with peak coherence values within 20–60 Hz being significantly greater for chewing than vocalization. This pilot study suggests that coherence analysis of mandibular EMG is a sensitive measure for distinguishing task-related differences in neural organization for children.     

Audio-vocal interaction in the pontine brainstem during self-initiated vocalization in the squirrel monkey

The adjustment of the voice by auditory input happens at several brain levels. The caudal pontine brainstem, though rarely investigated, is one candidate area for such audio-vocal integration. We recorded neuronal activity in this area in awake, behaving squirrel monkeys (Saimiri sciureus) during vocal communication, using telemetric single-unit recording techniques. We found audio-vocal neurons at locations not described before, namely in the periolivary region of the superior olivary complex and the adjacent pontine reticular formation. They showed various responses to external sounds (noise bursts) and activity increases (excitation) or decreases (inhibition) to self-produced vocalizations, starting prior to vocal onset and continuing through vocalizations. In most of them, the responses to noise bursts and self-produced vocalizations were similar, with the only difference that neuronal activity started prior to vocal onset. About one-third responded phasically to noise bursts, independent of whether they increased or decreased their activity to vocalization. The activity of most audio-vocal neurons correlated with basic acoustic features of the vocalization, such as call duration and/or syllable structure. Auditory neurons near audio-vocal neurons showed significantly more frequent phasic response patterns than those in areas without audio-vocal activity. Based on these findings, we propose that audio-vocal neurons showing similar activity to external acoustical stimuli and vocalization play a role in olivocochlear regulation. Specifically, audio-vocal neurons with a phasic response to external auditory stimuli are candidates for the mediation of basal audio-vocal reflexes such as the Lombard reflex. Thus, our findings suggest that complex audio-vocal integration mechanisms exist in the ventrolateral pontine brainstem.     

Power spectrum and turns analysis of EMG at different voluntary efforts in normal subjects

The power spectrum and the number of turns of the needle EMG were analysed at different degrees of voluntary contraction in the brachial biceps muscle or the first dorsal interosseus muscle of 23 normal subjects. During a stepwise increase in force HF/LF amplitude ratio showed a slight decrease with increasing force from 10% to 80% maximal voluntary contraction (MVC). At moderate to high force (i.e., 30-80% MVC) the HF/LF amplitude ratio increased with increasing turns at the individual site of the muscle. This relation probably reflects that both the HF/LF amplitude ratio and the number of turns are influenced by the degree of summation in the electrical activity. There was no correlation between HF/LF amplitude ratio and mean amplitude. The finding of a relation between HF/LF amplitude ratio and turns suggests that power spectrum analysis may differentiate between controls and patients with neuromuscular diseases.     

Spontaneous electrical activity in muscles of dystrophic (dy/dy) mice

Spontaneous electrical activity of tibialis anterior (TA) muscles was recorded using extracellular electrodes in dystrophic and phenotypically normal mice. Abnormal levels of spontaneous activity were recorded in the muscles of adult dystrophic mice. The activity was reduced by more than 75% after sciatic nerve section in anaesthetised dystrophic mice suggesting that most of the activity was neurally mediated. No abnormal activity was seen in the biceps brachii muscles of adult dystrophic mice. No abnormal spontaneous activity was seen in young (2-3-week-old) dystrophic mice. As degeneration of muscle fibres begins at about 7 days of age in dystrophic hindlimb muscles, the onset of the abnormal spontaneous EMG activity could not be considered causally related to muscle fibre degeneration.     

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.     

Sound-induced laryngeal and respiratory reflexes originate from vestibular afferents

To determine whether the auditory or vestibular system causes the sound-induced laryngeal reflex, which has been considered to participate in the auditory feedback control of vocalization, click-induced laryngeal responses were compared before and after sectioning of the cochlear and/or vestibular nerves in cats. The sound-induced reflex modulation of respiratory muscle activity was also investigated, because respiratory movement is important for vocal control. Sectioning of the cochlear nerves had little influence on these responses. In contrast, sectioning of the vestibular nerves abolished these responses. It was concluded that the sound-induced laryngeal and respiratory reflexes are attributed to the vestibular system.