Modulation of mechanically evoked perioral reflexes during active force.

Mechanically evoked activity in orbicularis oris inferior and mentalis muscles was studied in humans during active lip force generation. A specially designed multipoint array skin contactor, coupled to a position servo-controlled linear motor, was used to deliver precise mechanical imputs to the lip vermilion. The array size of the skin contactor was systematically varied to quantify the effects of spatial summation on the amplitude and time course of the early component (R1) of the perioral reflex. For normal young adults, significant positive trends were found for the amplitude of R1 sampled from orbicularis oris inferior and mentalis muscle recording sites as contactor array size increased. Increasing skin contactor size from 2 to 16 points was also effective in shortening the latency of R1 by 3-5 ms.     

The orbicularis oculi reflexes in healthy premature and full-term newborns

Blink reflexes were evoked both by mechanical tapping and electrical current delivered to the skin of the periorbital region in 62 healthy babies distributed in 2 groups: 29 full-term newborns and 33 prematures. The electrical activity of the orbicularis oculi muscle was recorded by means of bipolar surface electrodes in all cases. Both ipsilateral R1 and R2 electrically evoked responses were obtained. Occasionally we also observed a late R3 ipsilateral response. The R2 contralateral electrically evoked response was never observed in premature babies; it was present in about 80% of the full-term newborns. The R1 recovery curves obtained by delivering two successive shocks are similar in our two groups of babies to those observed in adults. The R1 latency decreases from 18 msec (27 weeks of post-conceptional age) to 12.4 msec (37 weeks). The average value for the full-term newborns was 12.1 +/- 1.1 msec. Whatever the age mechanical stimulation evokes bilateral R1, R2 and occasionally R3 responses. The existence of central crossed connections is possible. The maturation of the blink reflex occurs essentially during the last months of pregnancy. Indeed the R1 latency measured in full-term newborns is similar to that given for adults.     

Patients with spastic hemiplegia at different recovery stages: evidence of reciprocal modulation of early/late reflex responses.

Reflex electromyographic (EMG) muscle responses were recorded from abductor pollicis brevis (APB) and tibialis anterior (TA) muscles of fifty patients with spastic hemiplegia. Responses in the muscles were evoked during voluntary muscle contraction (about 20% of maximum voluntary effort) by submaximal but suprathreshold electrical stimulation of the median (at the wrist) and common peroneal (at the neck of the fibula) nerves respectively. Three EMG peaks (R1, R2 and R3) could be recorded after the direct muscle response (M). There was only a slight difference in R1-R2 latency interval of about 5 ms between upper and lower limbs on the unaffected side of the patients making it unlikely that this late response of the lower limb involves a long loop pathway, although this possibility cannot be discounted for the later, R3, response. Reflex behaviour was analysed for three clinical identifiable recovery stages of voluntary movements in the spastic limbs (synergistic, isolated and useful movements). The major finding was that an increase in the amplitude of the early response "R1" was associated with a decreased amplitude and delayed latency of the late response "R2" on the spastic side. The amplitude of R1 in the three different recovery stages decreased significantly, whereas the amplitude of R2 increased significantly with improvement of the functional stage of the limb. A significant negative linear correlation was found between R1 and R2 amplitude changes in upper as well as lower limbs. A refractoriness of the motor neuron pool as a possible explanation for the decreased R2 amplitude could be discounted. These findings together with recent work on reflex development in children support the hypothesis of reciprocal modulation of early and late reflex signals by supraspinal motor centers.     

Contribution of the corticospinal tract to motor impairment in spina bifida

We aimed to disentangle the proportional contributions of upper and lower motor neuron dysfunction to motor impairment in children with spina bifida. We enrolled 42 children (mean age, 11.2 years; standard deviation, 2.8 years) with spina bifida and 36 control children (mean age, 11.4 years; standard deviation, 2.6 years). Motor impairment was graded to severity scales in children with spina bifida. We recorded motor evoked potentials after transcranial and lumbosacral magnetic stimulation and compound muscle action potentials after electric nerve stimulation. Regarding lower motor neuron function, severely impaired children with spina bifida demonstrated smaller compound muscle action potential areas and lumbosacral motor evoked potential areas than control children; mildly impaired children hardly differed from control children. Compound muscle action potential latencies and lumbosacral motor evoked potential latencies did not differ between children with spina bifida and control children. Regarding upper motor neuron function, children with spina bifida demonstrated smaller transcranial motor evoked potential areas and longer central motor conduction times than control children. The smallest motor evoked potential areas and longest central motor conduction times were observed in severely impaired children. In children with spina bifida, the contribution of upper motor neuron dysfunction to motor impairment is more considerable than expected from clinical neurologic examination.     

Somatotopic organization of perioral musculature innervation within the pig facial motor nucleus

The orbicularis oris and buccinator muscles of mammals form an important subset of the facial musculature, the perioral muscles. In many taxa, these muscles form a robust muscular hydrostat capable of highly manipulative fine motor movements, likely accompanied by a specialized pattern of innervation. We conducted a retrograde nerve-tracing study of cranial nerve (CN) VII in pigs (Sus scrofa) to: (1) map the motor neuron pool distributions of the superior and inferior orbicularis oris, and the buccinator, to test the hypothesis that perioral muscle motor neuron pools exhibit a somatotopic organization within the facial motor nucleus; and (2) test the hypothesis that portions of the superior orbicularis oris (SOO) motor neuron pool also exhibit a somatotopic organization, reflecting a potential compartmentalization of function of the rostral, middle, and caudal segments of this muscle. Cresyl violet histological staining showed that the pig facial motor nucleus was comprised of 7 well-defined subnuclei. Neuroanatomical tracers injected into these perioral muscles transported to the motor neuron pools of the lateral 4 of the 7 subnuclei of the facial motor nucleus. The motor neuron pools of the perioral muscles were generally segregated from motoneurons innervating other facial muscles of the rostrum. However, motor neuron pools were not confined to single nuclei but instead spanned across 3-4 subnuclei. Perioral muscle motor neuron pools overlapped but were organized somatotopically. Motor neuron pools of portions of the SOO overlapped greatly with each other but exhibited a crude somatotopy within the SOO motor neuron pool. The large and somatotopically organized SOO motor neuron pool in pigs suggests that the upper lip might be more richly innervated than the other perioral muscles and functionally divided.     

Sympathetic skin response and emotional changes of visual stimuli

We studied sympathetic skin response (SSR) to visual emotional stimuli in 11 normal children and 13 normal adults. The arousal and valence levels of original pictures were previously assessed by 20 normal children and adults. SSR appearance ratio tended to be high for pictures with high arousal and those with either high or low valence, and was higher in children than in adults. The response for pictures with high arousal and low valence was different between children and adults. These pictures were classified into 2 groups; one consisted of disgusting creatures such as worms and roaches, and another of violent scenes, symbolizing physiological and social unpleasure, respectively. In children, SSRs were evoked with the same ratio for these two groups of pictures. In adults, however, SSRs for social unpleasure pictures were evoked with a significantly higher ratio compared to those for physiological ones. These results indicate that children are more susceptible to emotional stimuli and that this susceptibility diminishes with development, suggesting the association between emotional signal and moral development.     

Facial motor cortex plasticity in patients with unilateral peripheral facial paralysis

Hand motor representation area expands towards the area of the perioral facial motor cortex in patients with peripheral facial paralysis (PFP) and in hemifacial spasm cases treated with botulinum toxin. In this current study, we aimed to investigate the changes both in the ipsilateral and contralateral facial motor cortex areas in patients with PFP with transcranial magnetic stimulation (TMS). Thirty healthy individuals and 41 patients with unilateral PFP with partial or total axonal degeneration participated in this study. Motor evoked potentials (MEPs) of perioral muscles elicited by TMS of the intracranial portion of the facial nerve and motor cortex, were recorded. TMS was delivered through a figure-of-eight coil. Mapping of the cortical representation of perioral muscles were also studied in 13 of 41 patients and in 10 of control subjects. Mean amplitude of the intact perioral MEPs elicited by the ipsilateral hemisphere TMS, was significantly higher in patients than the control subjects. There was also a mild enlargement of the mean cortical representation area of intact perioral muscles on both hemispheres though it was not significant. We have concluded that there was a cortical reorganization in the hemisphere contralateral to the paralytic side resulting in an increase at corticofugal output related to intact perioral muscles.     

Different responses to auditory and somaesthetic stimulation in patients with an excessive startle: a report of pediatric experience.

OBJECTIVES: Children with cerebral injury often exhibit brief muscle contraction to a variety of stimuli. However, it remains to be determined whether or not the pattern of the reaction is stereotypical irrespective of the site stimulated. To answer this question, we studied electromyographic (EMG) responses to three types of stimuli in children. METHODS: The EMG responses of cranial and limb muscles were recorded after acoustic or somaesthetic stimulation in 6 patients and 23 control subjects. RESULTS: Acoustic stimuli evoked patterned motor activity with a rostrocaudal progression. Nose-tapping stimuli elicited reflex EMG activity in the VIIth cranial muscles that was similar to the R1 component of the electrical blink reflex. Sternum-tap stimuli evoked motor activity in the sternocleidomastoid and arm muscles, and this reflex was probably mediated through the cervical cord (H-reflex). Moreover, late reflexes were evoked following these early reflexes in the patients. In particular, atypical forms of myoclonic jerks were evoked on sternum-tap stimuli. CONCLUSIONS: Many types of primitive reflexes were evoked following three types of stimuli. These reflexes included startle reflex, trigeminomotor reflex, H-reflex and atypical forms of myoclonus, and they were enhanced in the patient group. There are many startle-mimicking reflexes.     

A new method for measuring compound muscle action potentials in facial palsy: a preliminary study

To establish a simple, reproducible procedure for studying facial motor nerve conduction (MNC), we determined the optimal electrode position to record evoked compound muscle action potentials (CMAPs) from perioral muscles in normal subjects. We examined three new electrode positions in which the electrode connected to the one input of the amplifier was placed on the mental protuberance, and the one connected to the other input was placed on the skin over the orbicularis oris muscle (the philtrum, mouth angle, or lower lip). We then compared the morphology and amplitudes of the CMAPs, right-left differences, and the reproducibility of CMAP amplitudes with recordings taken from the standard electrode position in which one electrode was placed on the nasolabial fold closely lateral to the ala nasi, and the other was placed on the skin over the orbicularis oris. Percutaneous supramaximal electrical stimulation was applied to the main trunk of the facial nerve. All three of the new recording positions showed greater amplitudes and more obvious biphasic CMAPs than the standard method. Positioning the electrode connected to the negative input on the philtrum was optimal in terms of right-left differences and the reproducibility of CMAP amplitudes. Therefore, this midline recording is a simple, reproducible method for calculating the CMAP amplitude ratio. However, prior to clinical use of this procedure, analyses of patients with facial palsy are required.     

A silent period in orbicularis oculi muscles of humans.

Surface electromyographic activity was recorded bilaterally from orbicularis oculi muscles when subjects relaxed and contracted eyelid muscles. Cutaneous reflex responses were evoked during both the relaxed and contraction states. Following reflex elicitation periods of muscle silence in orbicularis oculi were observed for about 10 to 15 ms after the ipsilateral R1 response and for up to 100 ms after the bilateral R2 responses. Reflex responses appeared to be enhanced when elicited during contractions. Possible physiological mechanisms are discussed regarding the presence of silent periods in a motor system that is presumably devoid of spindles, Golgi tendon organs, and Renshaw-like interneurons.     

Mechanically evoked perioral reflexes in premature and term human infants

Neurophysiological assessment of the preterm human neonatal oromotor system has been limited due to their fragile medical state, and methodological limitations. A new, noninvasive technology known as the actifier was developed and used to evoke perioral motor unit activity during non-nutritive suck in preterm infants. A significant ontologic trend for the early component of the perioral reflex (R1) was discovered in the context of spontaneous, centrally-patterned oromotor behavior.     

Interfering cutaneous stimulation and the muscle afferent contribution to cortical potentials

Cerebral potentials were recorded in response to selective stimulation using microelectrodes of muscle afferents in motor fascicles innervating the intrinsic muscles of the foot or at the motor point of abductor hallucis. The early components of these potentials (P40, N50 and P60) were consistently attenuated by continuous tactile stimulation of related skin areas and by electrical stimulation of digital nerves, timed so that the digital volley reached cortex approximately 5 msec before the muscle afferent volley. The same conditioning cutaneous inputs also attenuated the cerebral potentials evoked by selective stimulation of cutaneous afferents. These findings confirm that there are intermodality and intramodality interactions between low-threshold cutaneous and muscle afferents and between cutaneous afferents, respectively. The findings indicate that 'interference phenomena' (Kakigi and Jones 1986) can occur between different afferent modalities, and within any one modality, and cannot be used to determine the afferent species responsible for the test evoked potential.     

Does cross-innervation occur after facial palsy?

When the unaffected facial nerve was stimulated in 30 patients with facial palsy, evoked action potentials could be recorded from the contralateral (paralysed) perioral muscles. Similarly, in four normal subjects responses were evoked contralateral to the stimulated facial nerve. The latency of these responses in the patients remained unchanged over several months, and they were conducted at a rate compatible with conduction along muscle fibres. The contralateral responses are suggested to be due to conduction along muscle fibres crossing the midline rather than to cross-innervation.     

Intracortical motor inhibition and facilitation in adults with attention deficit/hyperactivity disorder

Using transcranial magnetic stimulation (TMS), disturbed facilitatory and inhibitory motor functions were recently found to correlate with motor hyperactivity in children with ADHD. Since hyperactivity seems to become reduced in ADHD during the transition to adulthood, a normalization of motor cortical excitability might be assumed. Therefore, we investigated the same inhibitory and facilitatory TMS paradigms in ADHD adults as we had previously examined in children. Motor cortical excitability was tested with TMS paired-pulse protocols in 21 ADHD adults and 21 age- and gender-matched healthy controls. In contrast to our results in ADHD children, no group-specific differences in amplitude changes of motor evoked potentials for inhibitory inter-stimulus intervals (ISI) (3, 100, 200 and 300 ms) or for facilitatory ISIs (13, 50 ms) could be detected. In ADHD adults, disturbed facilitatory and inhibitory motor circuits as found in ADHD children could not be shown, probably due to a development-dependent normalization of motor cortical excitability.     

Is Ross syndrome a dysautonomic disorder only? An electrophysiologic and histologic study.

OBJECTIVE: To define the involvement of peripheral nerve fibers in Ross syndrome. METHODS: Mechanical pain perception, tactile and thermal thresholds on hand, foot dorsum, thigh, median nerve orthodromic sensory conduction velocity (SCV) and motor conduction velocity (MCV), sural nerve antidromic SCV, peroneal nerve MCV, H-reflex, F-wave, median, tibial nerve somatosensory evoked potentials (SSEPs), perioral, hand CO(2) laser late (LEPs) and ultralate evoked potentials, sympathetic skin response (SSRs), cardiovascular, Minor sweat, silastic imprint, histamine, photopletysmographic and pupil pilocarpine tests, cutaneous innervation immunohistochemical techniques were studied in 3 patients with Ross syndrome. RESULTS: Quantitative sensory testing showed altered results in patients 1 and 2, and patient 3 had a slight impairment of mechanical pain perception. Nerve conduction, except for a median nerve distal reduction of sensory conduction in patient 1, F-wave and SSEP findings were normal; H-reflex was absent at rest in all patients. Hand LEPs were absent in patient 2, ultralate potentials were absent in patients 1 and 2. Skin biopsy showed a disease duration related reduction of unmyelinated and myelinated sensory fibers and a lack of unmyelinated autonomic fibers in all patients. CONCLUSIONS: Our data suggest that Ross syndrome is a degenerative disorder involving progressive sudomotor fibers, and then epidermal sensory unmyelinated and myelinated fibers.     

Related timing for peripheral and central plasticity in hypoglossal-facial nerve anastomosis

The aim of this work was to determine the role of peripheral facial muscle reinnervation in the central reorganization of the blink reflex (BR) after hypoglossal-facial anastomosis (HFA). An electrophysiological study was performed on seven patients who underwent HFA after facial nerve transection during surgery for acoustic neuroma. HFA was performed within 15 days after surgery in five patients (group 1) and later for the two others (group 2). We studied the motor responses (MR) and the BR evoked on the affected side, before and over 3 years after the HFA. The MR appeared by the third month for the first group, and by the sixth and twelfth for the second group. After 36 months, the amplitude of MR was significantly higher than its control value, showing hyperinnervation of the facial muscles. Study of the BR evoked only an R1-type blink response that was observed 4 and 6 months after the MR for groups 1 and 2, respectively. This central reorganization appeared closely correlated with muscle reinnervation and its related timing. The occurrence of peripheral nerve-muscle contacts seems to be a necessary condition for reorganization of the trigemino-hypoglossal-facial reflex.     

Neurophysiologic intraoperative monitoring in children with Down syndrome

Objective

Neurophysiological monitoring during complex spine procedures may reduce risk of injury by providing feedback to the operating surgeon. This tool is a well-established and important surgical adjunct in adults, but clinical data in children are not well described. Moreover, to the best of our knowledge, neurophysiologic intraoperative monitoring data have not been reported in children with neurodevelopmental disorders, such as Down syndrome, who commonly present with craniocervical instability requiring internal fixation. The purpose of this study is to determine the reliability and safety of neurophysiologic intraoperative monitoring in a group of children with Down syndrome undergoing neurosurgical spine procedures.

Methods

A total of six consecutive spinal procedures in six children with Down syndrome (three boys and three girls; mean age 10 years, range 4–16 years) were analyzed between January 1, 2008 and June 31, 2011. Somatosensory evoked potentials were stimulated at the ulnar nerve and tibial nerve for upper and lower extremities, respectively, and recorded at Erb’s point and the scalp. Motor evoked potentials were elicited by transcranial electrical stimulation and recorded at the extensor carpi ulnaris muscle and tibialis anterior muscle for upper and lower extremities, respectively. A standardized anesthesia protocol for monitoring consisted of a titrated propofol drip combined with bolus dosing of fentanyl or sufentanil.

Results

Somatosensory and motor evoked potentials were documented at the beginning and end of the procedure in all six patients. Changes during the surgery were recorded. Five patients maintained somatosensory potentials throughout surgery. One patient demonstrated a >10 % increase in latency or >50 % decrease in amplitude suggesting spinal cord dysfunction. A mean baseline stimulation threshold for motor evoked potentials of 485?+?85 V (range 387–600 V) was used. Four patients maintained motor evoked potentials throughout surgery. One patient had loss of left lower somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) after rod placement; upon removal of the rod, SSEPs returned but not MEPs. Another patient did not have consistent MEPs on one side and had absent MEPs on the contralateral side throughout the case. Loss of MEPs in these two patients did not correlate with postoperative neurological status. There were no complications directly related to neurophysiologic intraoperative monitoring technique.

Conclusions

Neurophysiologic intraoperative monitoring during neurosurgical procedures in children with Down syndrome may be reliably and safely implemented. Changes in neurophysiologic parameters during surgery must be carefully interpreted, and discussed with the neurosurgeon, neurophysiologist, and neuroanesthesiologist, and may not correlate with postoperative clinical changes. These changes may be related to abnormal physiology rather than an insult at the time of surgery. Nonetheless, the authors advocate routine neurophysiologic intraoperative monitoring in this special group of children undergoing neurosurgical spine procedures.     

Normal maximal and minimal motor nerve conduction velocities in adults determined by a collision method

Using a new collision method, we measured motor nerve conduction velocities of the ulnar nerve in the forearm and the action potential amplitude of the abductor digiti minimi muscle on 60 adults, ages 20 to 82 years and apparently free from diseases of the peripheral nervous system. Both maximal and minimal motor nerve conduction velocities were linear functions of age; 64.42-0.05 age and 60.45-0.12 age, respectively. The percentage of the minimal to the maximal motor nerve conduction velocities was expressed as 94.45-0.13 age. The maximum amplitude of evoked muscle action potentials was also correlated with age. This novel method may be useful in detecting pathology of motor nerve fibers which results in a decrease in submaximal conduction velocities.     

Corticonuclear innervation to facial muscles in normal controls and in patients with central facial paresis

Recently it has been proposed that corticobulbar innervation of the lower facial muscles is bilateral, that is from both right and left sides of the motor cortex. The objectives of this study were, i) to evaluate the corticonuclear descending fibers to the perioral muscles and, ii) to determine how central facial palsy (CFP) occurs and often recovers rapidly following a stroke. Eighteen healthy volunteers and 28 patients with a previous history of a stroke and CFP (mean ages: 51 and 61 years) were investigated by TMS (transcranial magnetic stimulation) with a figure of eight coil. Intracranial facial nerve and cortical motor evoked potentials (MEPs) were recorded from the perioral muscles. The periorbital MEPs were also studied. The absence of MEPs in both perioral muscles with TMS of the affected hemisphere was the most obvious abnormality. Also, central conduction time was significantly prolonged in the remaining patients. The mean amplitude of the affected hemisphere MEPs was diminished. The amplitudes of the unaffected hemisphere MEPs recorded from the intact side were enhanced especially in the first week following the stroke. During TMS, only the blink reflexes were elicited from the periorbital muscles due to stimulus spreading to trigeminal afferent nerve fibers. It is concluded that perioral muscles are innervated by the corticobulbar tract bilaterally. CFP caused by a stroke is generally incomplete and mild because of the ipsilateral cortical and multiple innervations out of the infarction area, and recovers fast through cortical reorganisation.     

Effects of fatigue on the stretch reflex in a human muscle.

The effects of fatigue on the electromyographic (EMG) reflex activities were compared during sustained voluntary contractions and contractions evoked by electrical stimulation (30 Hz) in the human first dorsal interosseus (FDI). Short latency (SL), medium latency (ML) and long latency (LL) reflex responses to a ramp-and-hold stretch of the muscle were recorded and analysed in 27 healthy subjects of both sexes. The amplitude of the reflex components was normalized as function of the amplitude of the surface action potential (SAP) recorded in response to the supramaximal stimulation of the motor nerve. The results indicate that for a similar reduction of force, SL and ML are significantly reduced after fatigue induced by voluntary contractions but they are not when the fatigue test is performed by electrical stimulation at the motor point. In voluntary fatigue experiments, the LL component showed no significant decrease below control values, but an enhancement was observed during electrically evoked contraction. This enhancement remained above control values for at least 15 min during the recovery period, whereas SL and ML decreases returned to control within 5 min after the fatigue tests. The electrical stimulation applied to the skin overlying the FDI at an intensity lower than the motor threshold did not affect SL and ML, but enhanced LL for about 15 min. On the contrary, the anaesthesia of the skin overlying the FDI induced a decrease in LL without significant change of SL and ML. It is concluded that muscle reflex fatigue is present during sustained voluntary contractions and decreases SL and ML responses to quick stretches.(ABSTRACT TRUNCATED AT 250 WORDS)