Prognostic value of electrically elicited blink reflex in neonates

The electrically elicited blink reflex (BR) was evaluated in 80 normal neonates and 12 neonates with neurologic abnormalities. In normal subjects, R1 and bilateral R2 responses were elicited both while awake and in a quiet sleep state. Whereas the R1 response was consistently elicited in the active sleep state, as well as while awake, the ipsilateral R2 response was markedly suppressed and the contralateral R2 response was almost absent. The BR in neonates with neurologic abnormalities showed the following variable results: normal, prolonged latency, or suppressed response at initial recording. Abnormal BRs were detected in most neonates with respiratory or sucking problems. While neonates in whom a suppressed response or prolonged latency persisted for over three months had a poor prognosis, those with normal BRs or early correction of the BR abnormality had almost normal development. The BR appears to be useful not only to evaluate brain-stem function in the neonatal period but also to predict subsequent outcome.     

Developmental changes in electrically elicited blink reflex in infancy and childhood

Developmental changes in electrically elicited blink reflex (BR) in 118 normal subjects, aged from 32 weeks of conceptional age to 14 years of age. During the waking state, R1 and bilateral R2 responses were always elicited. The latency of R1 shortened rapidly during the neonatal period, reaching the adult value at 3 months of age. The latency of R2 and contralateral R2 (CR2), which were elicited synchronously after 3 years of age, shortened slowly during childhood and reached the adult value at 6 years of age. The conduction indexes of R1, R2 and CR2, which were calculated as head circumference/latency (m/sec), increased rapidly during the neonatal period and reached the adult values at 6 years of age. The influence of NREM sleep on BR in neonates was different from those in infants and children. While BR of neonates in NREM sleep showed similar to that seen in wakefulness, BR of infants and children after one month of age was suppressed during NREM sleep. BR pattern in NREM sleep in infants and children after 6 months of age was similar to that seen in adults.     

Electrically and mechanically elicited blink reflexes in infants and children--maturation and recovery curves of blink reflex.

We studied the electrically and mechanically elicited blink reflexes in 2 groups of subjects, i.e., 237 newborn infants, 25-41 weeks of conceptional age, and 74 children, 1 month-12 years of age. In infants after 25 weeks of conceptional age we could usually induce the early response (R1) and ipsilateral late response (R2), while the contralateral late response (R2') of the electrical blink reflex became apparent after 33 weeks of conceptional age and the frequency of the appearance of R2' reached more than 60% after 38 weeks of conceptional age. After 7 months of age, R2' was usually observed. The R1 latency in full-term newborns was close to adult values, while the R2 and R2' latencies reached adult values at 7-12 years. After 1 year of age the latency of the R2 mechanical blink reflex had a tendency to be shorter than that of the electrical blink reflex. Under 35 weeks of conceptional age, the recovery curves of the blink reflex were considerably different from those of full-term infants, and premature infants showed little or no evidence of inhibition. These results indicate the absence of inhibitory interneurones in premature infants.     

Maturation of blink reflex in children

The blink reflex was examined in 57 subjects aged from neonate to adult in the alert state. The ipsilateral late response (R2) was elicited in all subjects and considered most suitable to evaluate maturational changes of the blink reflex. In a few subjects older than 3 years and of adults, the ipsilateral early response (R1) was difficult to observe. The contralateral late response (R2') could not be obtained in 32% of neonates and infants. From the observation about developmental change of an interference pattern, a latency shortening of R2 and a latency difference between R2' and R2, the blink reflex in children may be considered as mature at no later than 5 years of age. In addition, the R2 latency tended to increase temporarily through 1 or 2 years from late infancy. The reflex circuit evaluated by the blink reflex in children may partially change its makeup after the early infantile period and is almost fully mature at no later than 5 years.     

Lower limb cutaneous polysynaptic reflexes in the child, according to age and state of waking or sleeping.

An electromyographic study of reflex responses elicited by stimulation of an area of skin in the lower limb was undertaken in awake or sleeping children from 3 days to 3 years of age. Recordings were made on the tibialis anterior and the short head of the femoral biceps. In the awake child, electrical stimulation of the cutaneous area around the toes evoked polysynaptic discharges (R II and R III) in both muscles. From birth to one year of age, the threshold for the tibialis anterior was much lower than for the short head of biceps, and the flexion reflex pattern predominated. After 20 months of age, the recruitment pattern for polysynaptic responses was different: the threshold for tibialis anterior increased and became higher than for the short head of biceps, as in the adult. In sleeping children, the most striking feature was the depression of R II responses. In non-REM sleep, R III responses also were depressed, with a similar threshold in both muscles, and even disappeared during deep sleep. In REM sleep, R III responses were present in babies, but seemed to be abolished in older children.     

Maturation of the blink reflex in infants

The blink reflex was elicited in 50 children from birth to 3 years of age. In the awake state, the R1 response was always obtained; R2 responses, especially contralateral ones, were more difficult to elicit under 9 months of age. R1 latency and VIIth motor nerve conduction variations were a good witness of the peripheral nervous system maturation. The influence of the different states of waking and sleeping on these reflex responses was studied. These results and some of the mechanisms that underlie these changes are discussed.     

Middle latency auditory evoked responses in normal term infants: a longitudinal study

Middle latency auditory evoked responses (MLAERs) were measured in 21 normal term infants, three to five days after birth and then at 6 weeks, 7 months and 1 year of age. A polyphasic waveform was elicited during natural sleep in all infants at each recording session by monaural click stimulation at a rate of 9 per second. A 70 dBHL stimulus was found to be optimal as the MLAER became less well defined when the stimulus intensity approached the threshold hearing level. The first 60 to 70 msec of the waveform was found to be most stable, with decreasing detectability of peaks at longer latencies. There was no change in wave latency or reproducibility of MLAERs recorded during different sleep states. Waves Po and Na showed a significant decrease in latency with increasing stimulus intensity at term and/or 6 weeks of age. This was not evident for the remainder of the waveform. Waves Po, Na, Pa, Nb, Pb and Nc exhibited significant decreases in latency with age, attaining values indistinguishable from adults by 7 months of age.     

Preconditioning and excitability of the human orbicularis oculi reflex as a function of state

Reflex excitability and unstimulated activity of orbicularis oculi were found to vary as a function of state but the effects of weak conditioning stimuli, preceding reflex stimulation by 30--210 msec, were independent of state. Electromyographic activity was recorded from 23 young adults: 12 subjects with eyes closed during quiet wakefulness, 3 subjects during all-night sleep, 8 subjects during an afternoon nap. Stimulation with a 50 msec, 105 dB(A) white noise burst elicited a reflex response in 92% of waking trials and 87% of trials during REM sleep, but responses occurred in only 54% of trials during NREM sleep. Further, response latency was longer and magnitude less during the NREM state. Despite the differences in reflex excitability associated with state, state did not affect the modifications of reflex activity produced by a 20 msec, 70 dB(A) conditioning tone. At all lead intervals, reflex magnitude was reduced by the weak prestimulation even though, at the shortest interval, reflex activity was initiated more rapidly. The discordant changes in reflex size and latency have been seen in previous waking studies and appear to be mediated by different mechanisms. The persistence of both effects during sleep suggests that neither effect depends on high-level central processes.     

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.     

Corneal reflex in normal and pathological subjects

The orbicularis oculi response can be evoked both by mechanical stimulation of the cornea (corneal reflex) and by electrical stimulation of the skin overlying the supraorbital nerve (blink reflex). Mechanical stimuli to the cornea activate A delta and C free nerve endings of the corneal mucosa. Electrical stimuli to the supraorbital nerve activate A beta, A delta and C fibers of the nerve trunk. Both reflexes present a bilateral late response, but the blink reflex shows in addition an early ipsilateral component (R1), which has never been observed with the corneal stimulation in man. We have developed a simple technique of electrical stimulation of the cornea which provides stable responses and allows precise measurements of threshold and latency of the reflex. In normal subjects, the threshold ranged from 50 to 350 microA, and the maximal stimulus that the subject could bear (tolerance level) ranged from 1000 to 2500 microA. The minimal latency to tolerance level stimuli was 39 +/- 3 msec. The latency difference between the direct responses evoked from the two opposite corneas never exceeded 8 msec and the difference between the direct and consensual responses elicited from the same cornea never exceeded 5 msec. An early ipsilateral component similar to the R1 response of the blink reflex was not observed, even with supramaximal stimulation. The electrically evoked corneal reflex was normal in 10 cases of essential trigeminal neuralgia, while the responses showed significant abnormalities in 18 subjects submitted to thermocoagulation of the Gasserian ganglion as a treatment of neuralgic pain, as well as in 2 cases of symptomatic neuralgia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blink reflex elicited by auditory stimulation: clinical study in newborn infants

Blink reflex can be elicited by sudden strong auditory stimulation. Using a special transducer wer recorded this reflex which appears as a microvibration of the eyelid, and named it auditory-evoked eyelid microvibration (AMV). As the reflex pathway of AMV exists in the brainstem, AMV is an easy and useful way of knowing the function of the brainstem, especially in newborn periods. AMV was studied in infants from 25 to 43 weeks in conceptional age, to establish the normal value and to analyse the change of AMV in cases of neonatal asphyxia and intracranial hemorrhage. The mean latency of AMV in full-term infants was 31.0 +/- 67. msec. After 33 weeks in conceptional age, AMV was observed constantly with almost the same latency and amplitude as adult values. AMV appeared during both waking and sleep stages, except in active sleep. Marked change in AMV was noted such as delayed latency or disappearance of the response in neonatal asphyxia or intracranial hemorrhage. Infants who continued to have these abnormalities for a certain period, died or exhibited neurological sequelae.     

Masseter reflex in childhood and adolescence

We report normative data of masseter reflex from a group of 54 children 2-16 years of age. For statistical analysis, the patients were divided into five age groups: 2-4, 5-7, 8-10, 11-13, and 14-16 years of age. A tap to the chin, using a hammer with a trigger device, elicited the masseter reflex. The response was recorded by surface electrodes. The onset latency and peak-to-peak amplitude of the averaged curve of eight reflex responses were measured. The reflex response could be recorded in all children and adolescents of all groups. The mean latency shortened from age 2 to 7 and was stable at the age of 8 years. As a sign of maturation, the increase of amplitude corresponded to the shortening of latency and was also stable at the age of 8 years. Abnormal side differences in latency of 0.9 ms (age group 2-4 years), 1.1 ms (age group 5-7 years), and 0.8 ms (age group 8-16 years) were evaluated. An amplitude ratio (lower amplitude divided by higher one) above 0.33 was calculated as normal.     

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.     

Hemispheric asymmetry of late auditory evoked response induced by pitch changes in infants: influence of sleep stages

Late auditory evoked potentials (LAEPs) have been recorded in response to a 1000 Hz standard (occurrence 80%) or a 2000 Hz deviant (occurrence 20%) tone on the left (T3) and right (T4) temporal scalp in 6-week-old full-term newborns during pure quiet or active sleep states. Sleep states were permanently controlled by polygraphic recording including EEG, EOG, EMG, EKG and respiratory movements. During quiet sleep LAEPs consisted of a clear polygraphic response: N1-P2-N2. Mean latencies ranges in T3 and T4 were: N1 = 28–70 ms; P2 = 343–407 ms;N2 = 966–1178 ms; and P3 = 1461–1492 ms. During active sleep LAEPs consisted of a N1-P2-N2 response. Mean latency ranges on T3 and T4 were: N1 = 36–79 ms; P2 =278–304 ms; N2 = 555–620 ms. N2 latency was significantly shorter in AS than in QS. Amplitude of the N1-P2-N2 complex was significantly lower during active sleep. In response to standard stimuli, mean amplitudes and latencies of the LAEP were similar on T3 and T4 during active or quiet sleep states. In response to deviant stimuli mean amplitude of the N1-P2-N2 complex was significantly higher and mean latencies of N1 and N2 were significantly shorter on T3 during quiet sleep. No significant difference was observed during active sleep. These results confirm that sleep stages have a considerable influence on cortical auditory pathways. The auditory message is amplified during quiet sleep and inhibited during active sleep. Therefore sleep states need to be controlled to analyze LAEPs in young children. Furthermore our results show that unexpected auditory stimuli are differentiated in the temporal area of the left hemisphere of 6-week-old infants. This represents a functional correlate of the known hemispherical asymmetry in the speech region of the temporal cortex.     

Electrophysiological evidence for crossed oligosynaptic trigemino-facial connections in normal man.

A crossed short latency component (R1) of the human blink reflex could be elicited in orbicularis oculi muscles to stimulation of the contralateral supraorbital nerve, when infraliminal conditioning stimuli were applied to various cutaneous afferents of the body (facial, upper and lower limbs). The crossed R1 responses appeared when the time interval between the conditioning and the test stimuli was of 30 to 40 ms, 50 to 65 ms and 95 to 110 ms for facial, upper and lower limbs afferents respectively. For the same time intervals, these conditioning volleys also exerted a facilitatory effect on the ipsilateral R1 responses. Furthermore, crossed R1 responses were also obtained during supraspinal facilitation induced by a voluntary contraction of the eyelids. These data show that crossed oligosynaptic trigemino-facial reflex connections exist in normal subjects, which become functional when adequate conditioning stimuli are available.     

Auditory evoked potentials during sleep in normal children from ten days to three years of age.

Auditory evoked potentials (AEPs) to clicks of moderate intensity were studied in 130 normal sleeping children from 10 days to 3 years of age. Latencies of the principal response components were found to decrease with log age, i.e., change was most rapid during the first year of life. From 15 days of age to 3 years, mean latencies decreased as follows: P2 from 230 to 150, N2 from 535 to 320 and P3 from 785 to 625 msec. Variance was quite high, especially at younger ages. The fact that decreases in the latencies of the various components proceeded at different rates suggest that the components reflect quasi-independent neural substrates. The components of shortest latency displayed the weakest relationship to age. Findings with respect to latency for the subset of data obtained during stage 2 sleep were similar to those for the total population which contained responses recorded during several sleep stages. The amplitude of AEP components increased with age with the exception of N1P2 which decreased. Observations with regard to amplitude held both for the overall data recorded during several sleep stages and stage 2 data for components N0P1, N1P2 and N2P3. The amplitude trends for P1N1 and P2N2 were, however, not significant for the stage 2 subset. The maturation of the morphology of the AEP was characterized by a relative increase in the prominence of long latency components. The most striking change was the development of P3. High amplitude, V shaped P3 waves were also associated with stage 3-4 sleep. The changes which were delineated by this study for infancy and early childhood appear to be continuations of developmental trends reported for premature infants and neonates. AEPs are a reliable elicited measure which correlate well with maturation. They, therefore, can be a useful tool both in the study of central nervous system development and in the diagnosis of sensory and neurologic abnormalities.     

Further evidence for a central reorganisation of synaptic connectivity in patients with hypoglossal-facial anastomosis in man

In normal subjects, electrical stimulation of trigeminal mucosal afferents (lingual nerve - V3) can elicit a short latency (12.5+/-0. 3 ms; mean+/-S.D.) reflex response in the ipsilateral genioglossus muscle (Maisonobe et al., Reflexes elicited from cutaneous and mucosal trigeminal afferents in normal human subjects. Brain Res. 1998;810:220-228). In the present study on patients with hypoglossal-facial (XII-VII) nerve anastomoses, we were able to record similar R1-type blink reflex responses in the orbicularis oculi muscles, following stimulation of either supraorbital nerve (V1) or lingual nerve (V3) afferents. However, these responses were not present in normal control subjects. Voluntary swallowing movements produced clear-cut facilitations of the R1 blink reflex response elicited by stimulation of V1 afferents. In a conditioning-test procedure with a variable inter-stimulus interval, the R1 blink reflex response elicited by supraorbital nerve stimulation was facilitated by an ipsilateral mucosal conditioning stimulus in the V3 region. This facilitatory effect was maximal when the two stimuli (conditioning and test) were applied simultaneously. This effect was not observed on the R1 component of the blink reflex in the normal control subjects. These data strongly suggest that in patients with XII-VII anastomoses, but not in normal subjects, both cutaneous (V1) and mucosal (V3) trigeminal afferents project onto the same interneurones in the trigeminal principal sensory nucleus. This clearly supports the idea that peripheral manipulation of the VIIth and the XIIth nerves induces a plastic change within this nucleus.     

Long-lasting modification of reflexes after neonatal nerve injury in the rat

The reflex activity of motoneurones to the extensor digitorum longus (EDL) muscle following sciatic nerve crush during the first 5 days after birth (neonatal crush) or in the adult (adult crush) was studied 3-6 months later, when the axons had reinnervated their target muscles. Electromyograms (EMG) and muscle tension were recorded from the EDL muscle (a physiological flexor) on the injured and uninjured sides. Reflex responses were evoked by stimulation of the common peroneal (CP), the tibial (T) and the sural (S) nerves, ipsilateral and contralateral to the side of injury. In animals which had sustained a neonatal crush, stimulation of branches of the injured sciatic nerve elicited ipsilateral reflex responses that were about 3 times larger than those recorded from the uninjured side or in normal animals. Stimulation of the CP nerve on the uninjured side invariably elicited a contralateral reflex response from the reinnervated muscles, while stimulation of the CP nerve on the injured side either failed to produce a response or produced a very weak reflex response from the control muscles. Reflexes recorded from the reinnervated muscles by stimulation of the tibial and sural branches of the uninjured sciatic nerve were 3-7 times greater than those recorded from the uninjured side or in normal animals. The reflex responses obtained from reinnervated muscles of animals with nerve injury in adulthood were similar to those obtained from control, unoperated adult rats. These results indicate that sciatic nerve injury during a critical development period leads to a permanent enhancement of reflex responses from reinnervated fast flexor muscles not seen after similar injury in adults.     

Clinicophysiological studies of orbicularis oculi reflex in brain stem diseases]

Orbicularis oculi reflex is consisted of two components; one is early reflex response (R1) which is 14.1 +/- 2.2 msec in latency, and the other is late reflex response (R2) that is 35.0 +/- 8.6 msec in latency (mean +/- 2SD). R1 is observed on the ipsilateral side of stimulation and R2 is visible bilaterally on ipsiand contralateral sides of stimulation. Clinically orbicularis oculi reflex can be recorded easily, however, its clinical and physiological significance has not been clearly solved. Orbicularis oculi reflex was tested on patients with the brain stem lesions of various kinds, and the factors influencing to the reflex pathways were examined, such as the site and the type of lesions, sleep, several anesthetics and the level of consciousness. Results obtained were as follows; 1) both R1 and R2 disappeared or prolonged in latencies by nuclear as well as peripheral facial nerve palsy, since the facial nerve was the final common pathway. 2) on cases of facial sensory disturbance R1 prolonged in latency with concomitant delay of R2 response. 3) both R1 and were attenuated as soon as the alpha rhythmicity of the EEG was disappeared. Administration of thiamylal also attenuated both the R1 and R2, however, ketamine (a dissociative anesthetic) enhanced the R1 in amplitude and suppressed R2. These findings indicated that the R1 and R2 were in some extent regulated from brain stem reticular formation and the orbicularis oculi reflex should be an useful diagnostic measure to detect imparied consciousness. 4) also the reflex should be used to know the extent of neoplastic process in the cerebellar hemisphere to the brain stem. 5) recovery curve of R1 from double shock stimuli (conditioned and test) indicated that this reflex was different from H wave of the spinal cord because of absent refractory period and shorter facilitatory period ranging between 40 to 60 msec.