VEP development in infancy and early childhood. A longitudinal study

Coregistration of EEG and eye-tracking in infants and developing populations

Infants cannot be instructed where to look; therefore, infant researchers rely on observation of their participant's gaze to make inferences about their cognitive processes. They therefore started studying infant attention in the real world from early on. Developmental researchers were early adopters of methods combining observations of gaze and behaviour with electroencephalography (EEG) to study attention and other cognitive functions. However, the direct combination of eye-tracking methods and EEG to test infants is still rare, as it includes specific challenges. The current article reviews the development of co-registration research in infancy. It points out specific challenges of co-registration in infant research and suggests ways to overcome them. It ends with recommendations for implementing the co-registration of EEG and eye-tracking in infant research to maximise the benefits of the two measures and their combination and to orient on Open Science principles while doing so. In summary, this work shows that the co-registration of EEG and eye-tracking in infant research can be beneficial to studying natural and real-world behaviour despite its challenges.

Developmental trajectory of transmission speed in the human brain

The structure of the human connectome develops from childhood throughout adolescence to middle age, but how these structural changes affect the speed of neuronal signaling is not well described. In 74 subjects, we measured the latency of cortico-cortical evoked responses across association and U-fibers and calculated their corresponding transmission speeds. Decreases in conduction delays until at least 30 years show that the speed of neuronal communication develops well into adulthood.

Impact of hematopoietic stem cell transplant on VEP and ABR values of the patients with malignant infantile osteopetrosis

OBJECTIVES

Malignant Infantile Osteopetrosis (MIOP) is a rare inherited disorder with neurological complications, notably visual impairment and decrease of hearing level. Although Hematopoietic Stem Cell Transplantation (HSCT) has been approved as the only curative treatment for these patients, the exact impact of it on visual and hearing level is still unclear.

STUDY DESIGN

We analyzed the P2 latency and amplitude from Visual Evoked Potentials (VEP) of 10 patients (20 eyes) and the threshold of wave V from Auditory Brainstem Response (ABR) of 15 patients (30 ears) with MIOP before, 6 and 12 months after HSCT.

RESULTS

Before the HSCT, 10/30 ears demonstrated some degree of hearing loss; while only 3/20 eyes had P2 wave latencies in normal range for age. Using GEE models, it was shown that 12 months after HSCT, wave V threshold of ABR of the patients was significantly lower compared to its value from before the transplant (p value: 0.04). The analysis of latency and amplitude of P2 wave of VEPs showed no significant difference between before and after the transplant.

CONCLUSION

This study clearly showed that HSCT can improve the hearing level of the patients in terms of ABR threshold. Although HSCT made no significant improvement in latency of P2 in VEP of the patients, it can be concluded that transplant can halt visual regression in these patients. Early diagnosis of MIOP with this objective tools and subsequently early HSCT in these patients can decrease the rate of neurological complications of MIOP and improve the quality of life in them.

Auditory and Visual Electrophysiology of Deaf Children with Cochlear Implants: Implications for Cross-modal Plasticity

Deaf children who receive a cochlear implant early in life and engage in intensive oral/aural therapy often make great strides in spoken language acquisition. However, despite clinicians' best efforts, there is a great deal of variability in language outcomes. One concern is that cortical regions which normally support auditory processing may become reorganized for visual function, leaving fewer available resources for auditory language acquisition. The conditions under which these changes occur are not well understood, but we may begin investigating this phenomenon by looking for interactions between auditory and visual evoked cortical potentials in deaf children. If children with abnormal auditory responses show increased sensitivity to visual stimuli, this may indicate the presence of maladaptive cortical plasticity. We recorded evoked potentials, using both auditory and visual paradigms, from 25 typical hearing children and 26 deaf children (ages 2-8 years) with cochlear implants. An auditory oddball paradigm was used (85% /ba/ syllables vs. 15% frequency modulated tone sweeps) to elicit an auditory P1 component. Visual evoked potentials (VEPs) were recorded during presentation of an intermittent peripheral radial checkerboard while children watched a silent cartoon, eliciting a P1-N1 response. We observed reduced auditory P1 amplitudes and a lack of latency shift associated with normative aging in our deaf sample. We also observed shorter latencies in N1 VEPs to visual stimulus offset in deaf participants. While these data demonstrate cortical changes associated with auditory deprivation, we did not find evidence for a relationship between cortical auditory evoked potentials and the VEPs. This is consistent with descriptions of intra-modal plasticity within visual systems of deaf children, but do not provide evidence for cross-modal plasticity. In addition, we note that sign language experience had no effect on deaf children's early auditory and visual ERP responses.

Auditory- and visual-evoked potentials in Mexican infants are not affected by maternal supplementation with 400 mg/d docosahexaenoic acid in the second half of pregnancy

The evidence relating prenatal supplementation with DHA to offspring neurological development is limited. We investigated the effect of prenatal DHA supplementation on infant brainstem auditory-evoked responses and visual- evoked potentials in a double-blind, randomized controlled trial in Cuernavaca, Mexico. Pregnant women were supplemented daily with 400 mg DHA or placebo from gestation wk 18-22 through delivery. DHA and placebo groups did not differ in maternal characteristics at randomization or infant characteristics at birth. Brainstem auditory-evoked responses were measured at 1 and 3 mo in 749 and 664 infants, respectively, and visual-evoked potentials were measured at 3 and 6 mo in 679 and 817 infants, respectively. Left-right brainstem auditory-evoked potentials were moderately correlated (range, 0.26-0.43; all P < 0.001) and left-right visual-evoked potentials were strongly correlated (range, 0.79-0.94; all P < 0.001) within any assessment. Correlations across visits were modest to moderate (range, 0.09-0.38; all P < 0.01). The offspring of DHA-supplemented women did not differ from those of control women with respect to any outcome measure (all comparisons P > 0.10). We conclude that DHA supplementation during pregnancy did not influence brainstem auditory-evoked responses at 1 and 3 mo or visual-evoked potentials at 3 and 6 mo.

Abnormal flash visual evoked potentials in malnourished infants: an evaluation using principal component analysis

OBJECTIVE

To characterize the morphology of flash visual evoked potentials (fVEPs) obtained from infants hospitalized with severe, chronic malnutrition (marasmus).

METHODS

A covariance-based principal component analysis with Promax factor rotation was applied to fVEPs obtained from malnourished infants and age-matched control subjects.

RESULTS

The analysis suggests the presence of a late positive complex in the fVEP, with at least one of its components being significantly diminished in marasmic infants. The N3 component was also diminished in marasmic infants. Following remediation, the marasmic group no longer differed with respect to these components. However, an abnormally large late, positive deflection was evident at discharge.

CONCLUSIONS

The fVEP morphology of infants hospitalized with severe malnutrition was found to be significantly different from age-matched controls. Moreover, although there was evidence of recovery following remediation, fVEPs continued to show abnormality at discharge, suggesting the possibility that nutritional rehabilitation did not fully eliminate the physiological deficit.

SIGNIFICANCE

Malnourishment during early infancy results in altered neurophysiological functioning, possibly in cortical areas responsible for higher order visual processing.

Development of visual texture segregation during the first year of life: a high-density electrophysiological study

There are important developmental changes occurring during infancy in visual cortical structures that underlie higher-order perceptual abilities. Using high-density electrophysiological recording techniques, the present study aimed to examine the development of visual mechanisms, during the first year of life, associated with texture segregation. Forty-two normal full term infants were tested at 1, 3, 6 or 12 months of age. Visual-evoked potentials to low-level stimuli varying in orientation (oriVEP) and higher-level textured stimuli (texVEP) were recorded from 128 scalp electrodes. Difference potentials were obtained to extract the VEP component associated specifically with texture segregation (tsVEP). Results show a clear developmental pattern regarding amplitude, latency and scalp distribution of tsVEP, which appears at around 3 months but does not reach maturity by 12 months of age. A reduction in latency is particularly evident between 3 and 6 months, whereas amplitude shows a gradual increase with a marked increment between 3 and 6 months for low-level orientation stimuli and between 6 and 12 months for higher-level textured stimuli. These developmental patterns are attributed to neural maturational processes such as myelination and synaptogenesis. The differential developmental rates can be explained by delayed maturational processes of brain regions involved in more complex visual processing.

Flash visually evoked potentials in the newborn and their maturation during the first six months of life

The aim of this paper has been to obtain normative data for the major components of the visually evoked potentials obtained by flash stimulus (F-PEV) in the newborn, and to analyse the evolution of these responses during the first 24 weeks of life. In order to do so, F-VEP were recorded in 109 normal full-term newborn infants. Fifty-five of these infants were also studied longitudinally at 4, 8, 12 and 24 weeks. We recorded responses in all newborns. A great morphological variability was observed. P2 was the only component present in all of these infants. Early components, which were always present from the fourth week of life on, were recorded in 34% of the newborns. There were significant differences according to waking/sleep state. At 24 weeks the most characteristic response was a triphasic waveform with clear negative-positive-negative components at 67.9, 110 and 158.3 ms. The morphological variability observed in the F-PEV of the newborn and the presence of early components in some cases, suggest differences in the maturation of the specific and unspecific visual system at birth. The study of these responses provides us with information about certain aspects of visual maturation. The relative stability of P2 response of the newborn and of the early negative components later on, made them the most useful components to be used in paediatric clinical work . The latency of P2 in the newborn is the parameter that showed lower variability, and therefore the most suitable one to establish normative data.

Auditory and visual refractory period effects in children and adults: An ERP study

OBJECTIVE

This developmental study was designed to investigate event-related potential (ERP) refractory period effects in the auditory and visual modalities in children and adults and to correlate these electrophysiological measures with standard behavioral measures.

METHODS

ERPs, accuracy, and reaction time were recorded as school-age children and adults monitored a stream of repetitive standard stimuli and detected occasional targets. Standards were presented at various interstimulus intervals (ISIs) in order to measure refractory period effects on early sensory components.

RESULTS

As has been reported previously in adults, larger components for standards with longer ISIs were observed for an auditory N1 and the visual occipital P1 and P2 in adults. Remarkably similar effects were observed in children. However, only children showed refractory effects on the amplitude of the visual N1 and P2 measured at anterior sites. Across groups, behavioral accuracy and reaction time were correlated with latencies of auditory N1 and visual P2 across ISI conditions.

CONCLUSIONS

The results establish a normal course of development for auditory and visual ERP refractory period effects across the 6- to 8-year-old age range and indicate similar refractoriness in the neural systems indexed by ERPs in these paradigms in typically developing children and adults. Further, the results suggest that electrophysiological measures and standard behavioral measures may at least in part index similar processing in the present paradigms.

SIGNIFICANCE

These findings provide a foundation for further investigation into atypical development, particularly in those populations for which processing time deficits have been implicated such as children with specific language impairment or dyslexia.

Visual evoked potentials in disproportionately growth-retarded human neonates

To study brain function in the neonatal period, disproportionately growth-retarded (n = 33) and appropriately grown (n = 21) infants were examined using Doppler flow velocities prenatally and visual evoked potentials postnatally. Visual evoked potentials recordings were made at gestation of 40 and 46 weeks. The group of growth-retarded infants had significantly prolonged latencies to both of the two major peaks (designated P and N), most pronounced for the P peak. This result was observed at both ages investigated and corresponds to a developmental delay of 3 weeks. For individuals, the increase in P latency correlated to prenatal flow indices and to neonatal anthropometric parameters indicative of growth retardation. We conclude that in utero growth retardation affects brain development as assessed by visual evoked potentials in the neonatal period. This developmental delay may be produced by intracerebral factors during the process of growth retardation, and these alterations may have a prognostic value.

Magnocellular and parvocellular developmental course in infants during the first year of life

The visual system undergoes major modifications during the first year of life. We wanted to examine whether the magnocellular (M) and parvocellular (P) pathways mature at the same rate or if they follow a different developmental course. A previous study carried out in our laboratory had shown that the N1 and P1 components of pattern visual evoked potentials (PVEPs) were preferentially related to the activity of P and M pathways, respectively. In the present study, PVEPs were recorded at Oz in 33 infants aged between 0 and 52 weeks, in response to two spatial frequencies (0.5 and 2.5 c deg(-1)) presented at four contrast levels (4, 12, 28 and 95%). Results indicate that the P1 component appeared before the N1 component in the periods tested and was unambiguously present at birth. The P1 component showed a rapid gain in amplitude in the following months, to reach a ceiling around 4-6 months. Conversely, the N1 component always appeared later and then gained in amplitude until the end of the first year without reaching a plateau. Latencies were also computed but no developmental dissociation was revealed. Results obtained on amplitude are interpreted as demonstrating a developmental dissociation between the underlying M and P pathways, suggesting that the former is functional earlier and matures faster than the latter during the first year of life.

Age-related changes in the dynamics of human albino visual pathways

A deficiency of melanin in the retinal pigment epithelium, which regulates the development of neural retina, leads to chiasmal misrouting such that the uncrossed pathway (to the ipsilateral hemisphere) is reduced relative to the crossed pathway (to the contralateral hemisphere). This study examines age-related changes in the flash and pattern appearance visual evoked potentials (VEP) of human albinos. Scalp recorded cortical VEPs to flash (FVEP) and pattern appearance stimulation were recorded in 58 albino (8 months to 60 years) and 34 normal subjects (4-55 years). VEPs were analysed by amplitude and latency. The contralateral hemisphere FVEP amplitude decreased with age in albino subjects, as in both hemispheres in normals. However, the ipsilateral hemisphere FVEP amplitude was significantly lower in young albino subjects, initially giving a marked interhemispheric asymmetry, but this normalized with age. Significant interhemispheric FVEP latency asymmetries were not observed. The contralateral pattern appearance VEP latency in albino subjects decreased with age, as in both hemispheres in normals; the ipsilateral latency increased significantly with age. Significant interhemispheric pattern appearance VEP amplitude asymmetries were not observed. These novel and unexpected observations indicate significant age-related changes in the retinocortical pathways of the human albino. These changes have implications for our understanding of development and plasticity of the central visual pathways.

Menkes' syndrome: ophthalmic findings

PURPOSE

To report the prevalence and clinical significance of ocular findings in 20 patients with Menkes' syndrome recruited for a clinical trial at the National Institute of Child Health and Human Development (NICHHD).

DESIGN

Retrospective observational case series.

PARTICIPANTS

Twenty patients with Menkes' syndrome enrolled in a clinical trial at the NICHHD, who underwent ophthalmic evaluation at the National Eye Institute from 1990 through 1997.

METHODS

Review of clinical ophthalmic examination records, photographs, and visual evoked potential recordings.

MAIN OUTCOME MEASURES

Prevalence of ophthalmic signs of unusual frequency in patients with Menkes' syndrome.

RESULTS

There was a high prevalence of very poor visual acuity (8 patients), myopia at 21 months old or younger (5 of 9 patients this age who underwent cycloplegic refraction), strabismus (11 of 18 patients whose motility was evaluated), blue irides (15 of 16 patients whose iris color was documented), iris stromal hypoplasia and bilateral peripheral transillumination (7 and 3 patients, respectively), peripheral retinal hypopigmentation (7 of 18 patients whose retinal periphery was noted at the initial examination), and aberrant eyelashes (5 patients).

CONCLUSIONS

Patients with Menkes' syndrome exhibit a high prevalence of several ocular findings, including some (very poor visual acuity, myopia, strabismus) that may warrant special care. Early ocular examination is thus indicated for patients with Menkes' syndrome, particularly those with mild variants of the disease, whose neurologic status is better and lifespan is longer.

Effect of sleep state on the flash visual evoked potential. A case study

Controversy exists regarding the influence of sleep state on the flash visual evoked potential. This study recorded the visual evoked potential in a new-born infant in four different sleep states; wakefulness. drowsiness, active sleep and quiet sleep over a five hour period. The infant's heart rate, breathing rate and breathing regularity were also recorded. It was clear that when this subject was awake the VEPs recorded differed substantially from those recorded when sleeping. Two of the four main components had shorter peak latencies, one component was prolonged and one of the peak to trough amplitudes was consistently smaller when alert. This study highlights an important and often overlooked aspect of developmental research that the state of the infant may affect developmental measures.

The neonatal development of the light flash visual evoked potential

AIMS

To follow visual development longitudinally in the normal neonate using the flash visual evoked potential (VEP) and to find indications for a relationship between potential development and visual development.

METHODS

Twenty healthy infants, born at term, were included in the study. Flash and patterned flash VEPs were used. The first VEP was recorded the day of birth or just postnatally, and succeeding recordings were performed the following weeks and months.

RESULTS

The data revealed different types of VEP in the neonatal period suggesting great variability in visual function on the day of birth. In the early development a potential of long latency and duration preceded the development of a more compound potential of shorter latency. The two types of responses seemed to coalesce during early development; the first late response was attenuated and was eventually integrated in the more mature VEP. At approximately five weeks of age changes in the VEP were simultaneous with the development of responsive smiling and another visual behaviour of the infants.

CONCLUSIONS

The results showed many similarities between the VEP development in infants and in immature animals. In developing animals geniculo-cortical and extra-geniculate visual afferent pathways evoke two types of VEPs similar to those recorded in the present study. The early responses were also similar to previous recordings from children with lesions in the geniculo-striatal pathway or primary cortex. Our interpretation of the results was that the human VEP also consists of responses evoked by afferents running both in geniculo-cortical and extra-geniculate pathways and that the two types of responses could be separated in the VEP in the neonatal period. These findings are important for our understanding of conditions with a delay in visual maturation, for example intracranial haemorrhages, hydrocephalus, pre/dys-maturity and 'idiopathic' delayed visual maturation.

Near ultraviolet radiation elicits visual evoked potentials in children

OBJECTIVE

Ultraviolet radiation can be transmitted through the ocular media, as well as stimulate the retina, in some invertebrate, vertebrate and mammalian species. This study sought to determine if near ultraviolet radiation (UV-A) can elicit visual evoked potentials (VEPs) in young humans.

METHODS

VEP responses to 10 nm half-peak bandwidths of 340, 360 and 500 nm stimuli were measured in 8 children aged 7-10 years. Each VEP was based on an averaged response to 200 flashes and was recorded using a sensitivity of 250 microV (full scale) with the International 10-20 electrode placements Fz, O1, Oz, O2, and A1. Peak latencies (ms) were measured for the second negative peak, N2, third positive peak, P3, and third negative peak, N3. The amplitude (microV) between N2 and P3 was also measured.

RESULTS

Each child demonstrated a VEP response to both visible and UV-A stimuli. Most VEP parameters relative to the 340 and 360 nm stimuli (P < 0.05 to P < 0.001) were significantly different from the VEP responses to the 500 nm stimulus.

CONCLUSION

The results indicate that the near ultraviolet stimuli were indeed visible to the young human eye.

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.

Visual evoked potentials and dietary long chain polyunsaturated fatty acids in preterm infants

The influence of dietary long chain polyunsaturated fatty acid (LCP) supply, and especially of docosahexaenoic acid (DHA), on evoked potential maturation, was studied in 58 healthy preterm infants using flash visual evoked potentials (VEPs), flash electroretinography (ERG), and brainstem acoustic evoked potentials (BAEPs) at 52 weeks of postconceptional age. At the same time, the fatty acid composition of red blood cell membranes was examined. The infants were fed on breast milk (n = 12), a preterm formula supplemented with LCP (PF-LCP) (n = 21), or a traditional preterm formula (PF) (n = 25). In the breast milk and PF-LCP groups the morphology and latencies of the waves that reflect the visual projecting system were similar; in the PF group the morphology was quite different and the wave latencies were significantly longer. This could mean that the maturation pattern of VEPs in preterm infants who did not receive LCP was slower. Moreover, a higher level of erythrocyte LCP, especially DHA, was found in breast milk and PF-LCP groups compared with the PF group. ERG and BAEP recordings were the same in all three groups. These results suggest that a well balanced LCP supplement in preterm formulas can positively influence the maturation of visual evoked potentials in preterm infants when breast milk is not available.

Event-related potentials of 4-7-week-old infants in a visual recognition memory task

Event-related brain potentials were recorded from 4-7-week-old infants viewing a visual oddball task. During the task the duration of the infant's visual fixations of the stimuli was recorded. The latency of a frontally predominant negative component (Nc) and magnitude of an early slow wave (NSW) changed as a function of stimulus experience, thereby indicating a sensitivity to the infant's attention, stimulus discrimination and, perhaps, recognition memory. Nc latencies were faster and NSW magnitude was larger to the oddball stimulus than to the frequent stimulus. In addition, the latency of a component over occipital scalp. (N378) was faster to the oddball stimulus and may reflect the first perceptual registration of stimulus change. The latencies of the components allow an analysis of the infant's chronometry of processing. Analysis of looking behavior indicated that the infants also gave longer oddball looks than frequent looks. The relation of the ERP data to the infant's looking behavior suggests that fixation duration and the ERP components can be used as complementary measures of different aspects of the infant's attentional-cognitive processes.

Temporal frequency responsivity shows multiple maturational phases: state-dependent visual evoked potential luminance flicker fusion from birth to 9 months

Maturation of temporal resolution was investigated in a visual evoked potential study in 77 infants from birth to 9 months of age. Luminance evoked potential measures in response to homogeneous sinusoidal flickering light (1-64 Hz) were recorded under behavioral state-defined conditions. Behavioral state was determined by direct observation and by polygraphic recording of the electroencephalogram (EEG), eye movements (EOG), muscle activity (EMG), heart rate (ECG), and respiration. Temporal-frequency functions of the amplitude of the fundamental response across the temporal-frequency range were recorded during sleep and wakefulness. The highest temporal-frequency response recorded during wakefulness was accepted as a measure for inclusion in a growth function of temporal-frequency responsiveness. The resulting temporal resolution frequency vs. age function showed three separate maturational phases. Maturational phases were defined as (1) an initial slow phase from 1-32 days postnatal during which maturation of temporal vision is unremarkable; (2) an intermediate rapid phase of improvement from age 26 to 170 days; and (3) an overlapping but final slow phase from 151 to at least 270 days during which adult-like flicker resolution is approximated. This study suggests that the multiple maturational phases of the infant's responses to flickering light are due to maturational differences, which correspond with maturation of structural factors of brain function. Finally, across the age span tested, high-frequency responsivity was influenced significantly by the degree of infant arousal.

Infant malnutrition affects cortical auditory evoked potentials

Auditory evoked potentials (AEPs) to click and name stimuli were recorded for 23 malnourished infants on admission to and 17 on discharge from hospital, together with those from age-matched controls. The number of peaks on the AEPs and the amplitude were examined. The malnourished infants' AEPs to click stimuli differed from the controls' on admission but not on discharge. The malnourished infants had smaller AEP amplitudes to name than to click stimuli on discharge while the controls did not. The data show that cortical AEPs in infants are affected by malnutrition.

Detection and maturation of VEP albino asymmetry: an overview and a longitudinal study from birth to 54 weeks

The genetic anomaly in albinism prevents adequate melanin metabolism within the fetal eye cup and stalk. This results in severe disruption of pre- and postnatal retinal development and the condition of abnormal temporal retinal projections. The obligate misrouting of retinal-geniculate-cortical projections in albinism can be detected in the topographical representation across the occiput of the visual evoked potential (VEP). Age-dependent misrouting detection methods are described which yield 100% detection rates with zero false positives across the life span. By combining appropriate state-defined neonatal recording procedures with the albino infant VEP test paradigm, the presence of aberrant optic pathway projections was observed in a 5-day-old full-term infant. Maximum asymmetry was observed within a long-latency window of the response which shifted during the postpartum period to shorter latencies. Longitudinal studies show two specific latency regions of significant VEP asymmetry. The first occurs within 40-70 ms after stimulus onset and remains constant across the age range. The second, more robust, cluster of asymmetry occurs within a longer latency window and shows an age-related shift towards shorter latencies. The decreasing latency of this asymmetry is concomitant with normal maturational changes of the evoked response. These results show that VEP misrouting can be extended to reliable albino diagnosis within the neonatal period and to the assessment of visual maturation.

Electrophysiological assessment of visual pathway function in infants

The flash ERG and VEP have conspicuous immature features during the first 4 months following birth. The most marked maturational changes occur in ERG amplitude and VEP latency. Concurrent recording of the skin ERG and VEP provides information which is very useful in helping to arrive at a diagnosis in the young infant with nystagmus who appears to be blind and has a fundus of normal appearance. ERG and VEP features associated with Leber's Amaurosis, congenital cone dysfunction, albinism, optic nerve hypoplasia and unilateral hemisphere dysfunction are described.

Constancy of central conduction delays during development in man: investigation of motor and somatosensory pathways

1. A cross-sectional study has been performed on 457 normal subjects to determine changes in conduction delays with age in central and peripheral motor and somatosensory pathways to the upper limb. 2. Electromagnetic stimulation was used to investigate central and peripheral conduction in motor pathways from the cortex to biceps brachii and hypothenar muscles in 308 normal human subjects aged from 32 weeks gestation to 55 years. The responses were recorded in the surface electromyogram. 3. Somatosensory potentials evoked by electrical stimulation of the median nerve have been recorded at Erb's point and over the somatosensory cortex in 149 normal subjects aged from 34 weeks gestation to 52 years to determine central and peripheral somatosensory conduction delays. 4. The conduction delays in the central components of both motor and somatosensory pathways rapidly decrease over the first 2 years after birth and thereafter remain constant at adult values. 5. The conduction delays in the peripheral components of both motor and somatosensory pathways also decrease initially but then from the age of 5 years progressively increase in proportion to arm length. 6. The threshold stimulus intensity for evoking muscle responses following electromagnetic stimulation of the cortex is high initially and falls progressively until the age of 16 years. A linear relationship exists between the threshold intensity and height for the height range 70-180 cm. 7. The threshold stimulus intensities for exciting peripheral motor and somatosensory nerves decrease up to the age of 5 years and then reach a plateau. 8. The results support the conclusion, already reported in the literature that peripheral nerves attain maximum value for fibre diameter and conduction velocity at approximately 5 years of age. 9. In contrast, it is concluded that the maximum fibre diameters in both motor and somatosensory central pathways increase in proportion to height, leading to constant central conduction delays with growth.

The development of auditory and visual evoked potentials in early treated phenylketonuric children

Brain-stem auditory evoked potentials (BAEPs) and flash visual evoked potentials (F-VEPs) were gathered from 8 early treated phenylketonuric (PKU) children in a prospective longitudinal investigation during the 1st to the 12th months after birth. No consistent differences were found in the wave morphology of evoked potentials in PKU children from that of age-matched controls. Studying the latency of some components showed that in BAEPs, wave I latency was similar to control values for the whole year, but that the I-V interpeak mean latency (I-V IPL) was always significantly longer than in controls. In F-VEPs wave N1 latency was significantly longer than in controls only at 1-2 months of age, but returned to control values at 3-4 months (when all children were on dietary therapy) and remained in this range up to the 12th month. The mean latency of the P2 wave of flash VEPs was always significantly longer in PKU children than in controls. These results show that relevant alterations in evoked potentials may be found in PKU children several months after starting dietary therapy. This suggests that information processing in the brain may be impaired for a long time, due to abnormal metabolic conditions between birth and the onset of dietary therapy.

The effect of electrode position on flash visual evoked potentials in the newborn

We examined how changes in electrode position affected the visual evoked potential in 74 high-risk newborns using a multiple electrode technique. The variation in the visual evoked potential across the occiput was documented. Visual evoked potentials that were visible at one occipital electrode position were absent at a different electrode position in 21 of 87 recordings (24%). Changes of greater than 20 msec between electrodes in latency of waves P1 or N2 occurred in 34% and 29% of recordings, respectively. The amplitude of response varied by a factor of 2.36 between mid occipital and lateral occipital electrodes. The results demonstrated that large changes in morphologic characteristics, latency, and amplitude in the visual evoked potential of the newborn result from small changes in the position of recording electrodes. These findings underscored the importance of electrode position and accurate electrode placement. Our observations also indicated that recordings from a single electrode are inadequate in providing an accurate representation of the neonatal visual evoked potential.

Delayed visual maturation. A longitudinal clinical and electrophysiological assessment

Delayed visual maturation is an idiopathic condition characterized by visual inattention during infancy. The authors followed longitudinally nine children with an initial diagnosis of delayed visual maturation and compared their electroretinograms (ERGs) and visual evoked potentials with those of age-matched controls. Eight of the nine patients consistently had normal visual evoked potentials to flash and to pattern stimulation. All of the children had normal ERGs. Visually mediated behavior gradually developed in all of these children when they were between 3 and 8 months of age (mean, 5.5 months). Five patients also were delayed in other spheres of development. Visual evoked potentials are helpful in formulating a visual prognosis for children with delayed visual maturation.

Is the geniculostriate system a prerequisite for nystagmus?

The time of onset of congenital horizontal nystagmus is usually known. We present a group of infants in whom this was determined objectively. In two, vertical nystagmus in the neonatal period became horizontally directed, at 4 months in one, and between 7 and 9 months of age in the second. Two infants (one an oculocutaneous albino) had no visual response initially but subsequently developed horizontal nystagmus as the vision improved at 5 and 6 1/2 months: Type III delayed visual maturation. An infant totally blind due to Norrie's disease was examined in the first week of life but did not develop nystagmus for a further 3 months. Two children with cortical visual impairment never developed nystagmus. In early infancy, vision is thought to be predominantly subcortical. Therefore the development of nystagmus at a time when the geniculostriate system is emerging functionally (around 3 months), and its absence in cortical visual impairment, has led us to propose a hypothesis suggesting that a functioning geniculostriate system is a prerequisite for the development of horizontal nystagmus.

Rate and filter dependence of the middle-latency response in infants

Auditory evoked-potential activity in the 0 to 100-ms latency range was explored using wide-band filtering and a range of stimulus rates, in 8 babies ranging in age from 2 to 6 months. We observed both a stable early positive peak, in the 10 to 15-ms region, and a rate-dependent, positive peak at about 50 ms in all 8 babies. The latter response was best observed at rates of 1-2.5 stimuli/s and seldom observed at rates above 4/s. This peak may represent a developmentally early version of the Pa peak of the adult middle-latency response.

Visual evoked responses to light emitting diode (LED) photostimulation in newborn infants

The use of a Xenon discharge stroboscope to elicit VERs in a neonatal intensive care unit has several disadvantages. To overcome these a photostimulator has been developed which consists of an array of 25 red light emitting diodes (LEDs). The LEDs are driven by pulses of fixed length and current and the output intensity is controlled by the pulse repetition rate. Such a photostimulator is compact and can be hand-held inside a cot or incubator. Using this method VERs have been recorded in healthy full-term and pre-term infants which are comparable in wave form and latency to those elicited by a stroboscope.

Developmental changes in the human visual system as reflected by the latency of the pattern reversal VEP

Pattern reversal visually evoked potentials (VEPs) were recorded from 439 infants and young children ranging in age from 1 month to 5 years in response to large and small checks. Qualitative analysis of the VEP wave form showed that the first major positive component, P1, is consistently present at all ages, while the frequency of occurrence of later positive components is more variable. The proportion of infants showing late positive components increases with age; by 1 year, the frequency of occurrence of late components for large checks is more adult-like than for small checks. The latency of P1 was analyzed quantitatively. Results showed that P1 latency decreases rapidly during the first year of life for both large and small checks and that the time course of the latency change differs as a function of check size. VEPs to large checks attain adult-like P1 latency values by about 1 year of age, while the P1 latency of VEPs to small checks has still not reached adult levels by 5 years of age. Data from 12 infants tested longitudinally between 1 and 7 months of age using both checkerboards and square wave gratings show no difference in P1 latency between checkerboards and gratings comprised of large (30-240 min) pattern elements, but for patterns with small (7.5 and 15 min) elements, P1 latency to checks is significantly longer than P1 latency to stripes. These results are explained on the basis of the difference in the fundamental spatial frequency between checks and stripes.

Maturational sequence of the visual system: serial measurements of visual evoked potential and electroretinogram in the healthy neonatal lamb

The value of measurements of visual evoked potential (VEP) for neurological assessment of the adult is widely accepted. Its use for neonatal evaluation following birth asphyxia has been limited by our knowledge of developmental changes occurring in the newborn brain. VEPs and electroretinograms (ERGs) were simultaneously recorded from five healthy newborn lambs from birth until 30 days of life. Newborn age was then compared with amplitude (height of the signal) and latency (time from stimulus to a specific wave deflection) measurements from these neuroelectrical signals. Latencies to A wave (photoreceptor activity) and B wave (bipolar and ganglion cells) of the ERG declined in a small but significant manner, while the latency interval from A to B wave did not change with age. Latency to wave N1 of the VEP remained stable while latency to P2 declined from birth to 30 days. The ERG and VEP signals exhibited linear increases in amplitude as the lambs became older. We conclude from these observations that ganglion and bipolar cells (B wave of the ERG) within the retina and primary nerve tracts (N1 of the VEP) along the visual system are mature at birth. In contrast, photoreceptor activity within the retina (A wave of the ERG) and nerve conduction through the visual cortex (P2 of the VEP) exhibit changes which are consistent with ongoing maturation of these more specialized areas through the early newborn period.

Lateralization of visual cognitive potentials

Pairs of stimuli containing either the same or different visual patterns were presented separately to the right and left brain hemispheres. Ten adult males were trained before the formal experiment to perform the task automatically and without verbal control. A verbal control task was arranged at the end of the experiment. Reaction times and P3P4, C3C4 brain evoked potentials were recorded. The N2 (180-290 msecs) and P3 (290-380 msecs) components were found to be lateralized over the right side of the scalp for nonverbal conditions. Slightly larger P3 was found over the left side for the verbal control test. The results are discussed in relation to the present evidence about the nature of N2 and P3 in the single act of perception and in the ontogenetic development.