Electrographic imaging of recognition memory in 34–38 week gestation intrauterine growth restricted newborns

Postnatal functional integrity of the brainstem auditory pathway in late preterm infants born of small-for-gestation age: how different from those born of appropriate-for-gestation

It is unclear whether there is any postnatal abnormality in brainstem auditory function in late preterm small-for-gestational-age (SGA) infants. We investigated the functional integrity of the brainstem auditory pathway at 4 months after term in late preterm SGA infants and defined differences from appropriate-for-gestational age (AGA) infants. The maximum length sequence brainstem evoked response (MLS BAER) was recorded and analyzed in 24 SGA (birthweight < 3rd centile) infants and 28 AGA infants (birthweight > 10th centile). All infants were born at 33-36-week gestation without major perinatal and postnatal problems. We found that I-V interval in SGA infants was shorter than in AGA infants at higher click rates and significantly shorter at the highest rate of 910/s. Of the two smaller intervals, I-III interval was significantly shorter in SGA infants than in AGA infants at higher click rates of 455 and 910/s clicks, whereas III-V interval was similar in the two groups. The III-V/I-III interval ratio in SGA infants tended to be greater than in AGA infants at all rates and was significantly greater at 455 and 910/s clicks. The slope of I-III interval-rate functions in SGA infants was moderately smaller than in AGA infants.  Conclusions: The main and fundamental difference between late preterm SGA and AGA infants was a significant shortening in the MLS BAER I-III interval in SGA infants at higher click rates, suggesting moderately faster neural conduction in the caudal brainstem regions. Postnatal neural maturation in the caudal brainstem regions is moderately accelerated in late preterm SGA infants. What is Known: • At 40 weeks of postconceptional age, late preterm SGA infants manifested a mild delay in neural conduction in the auditory brainstem. What is New: • At 56 weeks of postconceptional age, late preterm SGA infants manifested moderately faster neural conduction in the caudal brainstem regions. • Postnatal neural maturation is moderately accelerated in the caudal brainstem regions of late preterm SGA infants.

Infants exposed to antibiotics after birth have altered recognition memory responses at one month of age

BACKGROUND

Neonatal exposure to antibiotics, in the absence of infection, results in abnormal learning and memory in animals and is linked to changes in gut microbes. The relevance of early-life antibiotic exposure to brain function in humans is not known.

METHODS

Recognition memory was assessed at 1 month of age in 15 term-born infants exposed to antibiotics (with negative cultures) and 57 unexposed infants using event-related potentials (ERPs). Linear regression analysis, adjusting for covariates, was employed to compare groups with respect to ERP features representing early stimulus processing (P2 amplitude) and discrimination between mother and stranger voices.

RESULTS

Infants exposed to antibiotics exhibited smaller P2 amplitudes for both voice conditions (p = 0.001), with greatest reductions observed for mother's voice in frontal and central scalp regions (p < 0.04). Infants exposed to antibiotics showed larger P2 amplitudes to stranger's as compared to mother's voice, a reversal of the typical response exhibited by unexposed infants. Abnormal ERP responses did not consistently correlate with increased inflammatory cytokines within the antibiotic-exposed group.

CONCLUSIONS

Otherwise healthy infants exposed to antibiotics soon after birth demonstrated altered auditory processing and recognition memory responses, supporting the possibility of a microbiota-gut-brain axis in humans during early life.

IMPACT

Infants exposed to antibiotics after birth demonstrate altered auditory processing and recognition memory responses at 1 month of age. Preclinical models support a role for gut microbiomes in modulating brain function and behavior, particularly in developing brains. This study is one of the first to explore the relevance of these findings for human infants. The findings of this study have implications for the management and follow-up of at-risk infants with exposure to gut-microbiome disrupting factors and lay foundation for future studies to further characterize the short- and long-term effects of gut microbiome perturbation on brain development.

Intrauterine growth restriction and development of the hippocampus: implications for learning and memory in children and adolescents

Intrauterine growth restriction (IUGR) is often the result of compromised placental function and suboptimal uteroplacental blood flow. Children born with IUGR have impaired cognitive functioning and specific memory deficits, indicating long-lasting impairments in hippocampal functioning; indeed, hippocampal volume is reduced in infants with IUGR. Animal studies have provided valuable insight into the nature of deficits in hippocampal-dependent functions observed in children born with IUGR; outcomes of experimental IUGR reveal reduced neuron numbers and morphological alterations in the cornu ammonis fields 1 and 3 and dentate gyrus subregions of the hippocampus. However, whether such early and ongoing structural changes in the hippocampus could account for deficits in spatial memory reported in adolescent rats with IUGR is yet to be established. Understanding the association between hippocampal structural and functional alterations in IUGR will aid in the development of interventions to minimise the effect of IUGR on the hippocampus and long-term cognitive outcomes.

ERP evidence of preserved early memory function in term infants with neonatal encephalopathy following therapeutic hypothermia

BACKGROUND

Neonatal encephalopathy (NE) carries high risk for neurodevelopmental impairments. Therapeutic hypothermia (TH) reduces this risk, particularly for moderate encephalopathy (ME). Nevertheless, these infants often have subtle functional deficits, including abnormal memory function. Detection of deficits at the earliest possible time-point would allow for intervention during a period of maximal brain plasticity.

METHODS

Recognition memory function in 22 infants with NE treated with TH was compared to 23 healthy controls using event-related potentials (ERPs) at 2 wk of age. ERPs were recorded to mother's voice alternating with a stranger's voice to assess attentional responses (P2), novelty detection (slow wave), and discrimination between familiar and novel (difference wave). Development was tested at 12 mo using the Bayley Scales of Infant Development, Third Edition (BSID-III).

RESULTS

The NE group showed similar ERP components and BSID-III scores to controls. However, infants with NE showed discrimination at midline leads (P = 0.01), whereas controls showed discrimination in the left hemisphere (P = 0.05). Normal MRI (P = 0.05) and seizure-free electroencephalogram (EEG) (P = 0.04) correlated positively with outcomes.

CONCLUSION

Infants with NE have preserved recognition memory function after TH. The spatially different recognition memory processing after early brain injury may represent compensatory changes in the brain circuitry and reflect a benefit of TH.

Mild maturational delay of the brainstem at term in late preterm small-for-gestation age babies

AIMS

To detect any functional abnormality in the brainstem auditory pathway in late preterm babies born of small-for-gestational age (SGA) using maximum length sequence brainstem evoked response.

STUDY DESIGN

The response was recorded and analyzed at term in 38 SGA (birthweight <3rd centile) babies born at 33-36 week gestation. The results were compared with 40 age-matched babies born of appropriate-for-gestational age (AGA) (birthweight >10th centile). None of the subjects had major perinatal problems.

RESULTS

All wave latencies and interpeak intervals in the SGA group were slightly longer than those in the AGA group at most click rates. Wave III latency was significantly longer than that in the AGA group at 227/s (P < 0.05), and wave V latency was at 227 and 910/s (P < 0.05 and 0.05). Of the interpeak intervals, only the I-V interval in the SGA group was significantly longer than that in the AGA group at the highest rate 910/s (P < 0.05). The amplitudes of waves I, III and V in the SGA group all tended to be smaller than those in the AGA group at all click rates 91-910/s. The wave V amplitude was significantly smaller at most click rates (227-910/s, all P < 0.05). The slopes of all wave latency-, interval-, and amplitude-rate functions were similar in SGA and AGA groups.

CONCLUSIONS

There were marginal abnormalities in MLS BAER of low-risk late preterm SGA babies, suggesting a mild degree of maturational delay in the brainstem. Intrauterine growth retardation occurring in late preterm babies has a minor effect on neural maturation of the immature brainstem.

Spectral power differences in the brain activity of growth-restricted and normal fetuses

Using non-invasive fetal magnetoencephalography (fMEG), we investigated spontaneous brain activity in 28 fetuses diagnosed with intrauterine growth restriction (IUGR) and compared the results to 47 normal-growth fetuses. The fetal gestational age ranged from 28 to 39 weeks with post-natal recordings obtained on 17 of the IUGR fetuses. Power spectrum was computed and was divided into four frequency bands. A significant difference in the relative spectral power in delta, theta and beta bands (P<0.01) was observed only in the 28-32 week gestation age group with alpha band showing a similar trend (P=0.054). This observation suggests that growth restriction may have a more pronounced effect on the fetal brain in early gestation. Larger population studies could reveal the potential value of fMEG as an additional surveillance tool for growth-restricted fetuses.

Growth and nutrient intake among very-low-birth-weight infants fed fortified human milk during hospitalisation

Postnatal growth failure in preterm infants is due to interactions between genetic and environmental factors, which are not fully understood. We assessed dietary supply of nutrients in very-low-birth-weight (VLBW, < 1500 g) infants fed fortified human milk, and examined the association between nutrient intake, medical factors and growth during hospitalisation lasting on average 70 d. We studied 127 VLBW infants during the early neonatal period. Data were obtained from medical records on nutrient intake, growth and growth-related factors. Extra-uterine growth restriction was defined as body weight < 10th percentile of the predicted value at discharge. Using logistic regression, we evaluated nutrient intake and other relevant factors associated with extra-uterine growth restriction in the subgroup of VLBW infants with adequate weight for gestational age at birth. The proportion of growth restriction was 33 % at birth and increased to 58 % at discharge from hospital. Recommended values for energy intake (>500 kJ/kg per d) and intra-uterine growth rate (15 g/kg per d) were not met, neither in the period from birth to 28 weeks post-conceptional age (PCA), nor from 37 weeks PCA to discharge. Factors negatively associated with growth restriction were energy intake (Ptrend = 0.002), non-Caucasian ethnicity (P = 0.04) and weight/predicted birth weight at birth (Ptrend = 0.004). Extra-uterine growth restriction is common in VLBW infants fed primarily fortified human milk. Currently recommended energy and nutrient intake for growing preterm infants was not achieved. Reduced energy supply and non-Caucasian ethnicity were risk factors for growth restriction at discharge from hospital.

Early postnatal weight gain, intellectual performance, and body mass index at 7 years of age in term infants with intrauterine growth restriction

OBJECTIVE

To determine whether the postnatal growth rate of infants with intrauterine growth restriction (IUGR) is associated with later cognitive function and body mass index (BMI).

STUDY DESIGN

Infants with IUGR (<2211 g at > or =37 weeks' gestation) were identified in data from the Collaborative Perinatal Project, excluding those with diagnoses affecting cognition or growth. Wechsler Scale of Children's Intelligence (WISC) scores at age 7 years and data on postnatal growth at 16 weeks were available for 463 infants with IUGR. Linear regression relating postnatal growth and WISC score, adjusting for potential confounders, was performed for these infants. BMI at 7 years also was examined.

RESULTS

Weight gain at 16 postnatal weeks ranged from 1059 to 5119 g in the infants with IUGR, with lower achieved cognitive testing scores apparent at both extremes (ie, an inverted J-shape; P < .001). Infants gaining 1200 and 5000 g scored 15.5 and 2.4 fewer points, respectively, on the full scale compared with infants with score-maximizing growth. In contrast, BMI at 7 years was linearly related to postnatal weight gain (P < .001).

CONCLUSIONS

Growth in the first 4 postnatal months is an independent risk factor for cognitive outcome at age 7 years, with both extremes associated with negative effects.

Early behavioral intervention, brain plasticity, and the prevention of autism spectrum disorder

Advances in the fields of cognitive and affective developmental neuroscience, developmental psychopathology, neurobiology, genetics, and applied behavior analysis have contributed to a more optimistic outcome for individuals with autism spectrum disorder (ASD). These advances have led to new methods for early detection and more effective treatments. For the first time, prevention of ASD is plausible. Prevention will entail detecting infants at risk before the full syndrome is present and implementing treatments designed to alter the course of early behavioral and brain development. This article describes a developmental model of risk, risk processes, symptom emergence, and adaptation in ASD that offers a framework for understanding early brain plasticity in ASD and its role in prevention of the disorder.

Improved cognitive development among preterm infants attributable to early supplementation of human milk with docosahexaenoic acid and arachidonic acid

OBJECTIVE

The objective of our study was to evaluate the effect of supplementation with docosahexaenoic acid and arachidonic acid for human milk-fed preterm infants. The primary end point was cognitive development at 6 months of age.

METHODS

The study was a randomized, double-blind, placebo-controlled study among 141 infants with birth weights of <1500 g. The intervention with 32 mg of docosahexaenoic acid and 31 mg of arachidonic acid per 100 mL of human milk started 1 week after birth and lasted until discharge from the hospital (on average, 9 weeks). Cognitive development was evaluated at 6 months of age by using the Ages and Stages Questionnaire and event-related potentials, a measure of brain correlates related to recognition memory.

RESULTS

There was no difference in adverse events or growth between the 2 groups. At the 6-month follow-up evaluation, the intervention group performed better on the problem-solving subscore, compared with the control group (53.4 vs 49.5 points). There was also a nonsignificant higher total score (221 vs 215 points). The event-related potential data revealed that infants in the intervention group had significantly lower responses after the standard image, compared with the control group (8.6 vs 13.2). There was no difference in responses to novel images.

CONCLUSIONS

Supplementation with docosahexaenoic acid and arachidonic acid for very preterm infants fed human milk in the early neonatal period was associated with better recognition memory and higher problem-solving scores at 6 months.

Electrophysiological Evaluation of Human Brain Development

The complex development of the human brain during infancy can only be understood by convergent structural, functional, and behavioral measurements. The evaluation of event-related potentials (ERPs) is the most effective current way to look at infant brain function. ERP paradigms can be used to examine the simple transmission of sensory information to the cortex and the discrimination of this information within the cortex. The main developmental changes involve localization of function as the brain becomes tuned to the experienced world (related to synaptic pruning) and a speeding up of transmission as pathways become efficient (related to myelination). ERPs that occur in relation to different temporal aspects of a stimulus (onset-responses, offset-responses, sustained potentials and steady-state responses) and ERPs recorded at different stimulus rates may help track perceptual development from a temporal perspective. Particularly important in human development are the ERP changes that occur in the processing of speech sounds and human faces. At present, ERP studies can show differences between groups of subjects that can demonstrate developmental disorders or elucidate mechanisms of development. However, because of their variability, ERPs are less helpful in determining whether an individual infant is developing abnormally. Where possible, ERP measurements should be used in conjunction with behavioral tests so as to relate performance to mechanism, and with anatomical brain measurements to relate mechanism to structure.

Magnetoencephalography of the newborn brain

This paper reviews the use of event-related magnetic fields (ERFs) in infants; ERFs can be derived from magnetoencephalography by means of averaging. Basic perceptive skills are important prerequisites for the infant's later development. The automatic cortical processes related to processing auditory, somatosensory and visual stimuli can be addressed by using responses recorded directly from the brain. The traditional method, the event-related potential (ERP), has recently been accompanied by ERFs. Similarly to ERPs, higher processes related to short-term memory, stimulus comparisons, and attention allocation can also be studied with ERFs. Further, since addressing the neonatal higher cognitive and social capabilities is challenging using only behavioural means, ERFs provide information on these important functions at a very early stage immediately after birth or in some cases even before birth. The main advantage of ERFs, compared to ERPs, is detection of the signals with high accuracy both with respect to the noise level and estimation of the spatial location.

Cortical auditory event-related potentials in newborn infants

The possibility of recording changes in electroencephalography potentials following perception of sound was reported several decades ago. The recent expanding research on auditory cortical event-related potentials (AERPs) for assessing sound discrimination abilities in children and infants has indicated that several methodological issues need to be addressed before it can be implemented in clinical practice. Latencies, polarities, and amplitudes of the responses change with gestational age and during infancy. Thus, the maturation of the infant must be considered when designing stimulus paradigms and interpreting the responses. Of healthy newborn infants, only about 80% will show mismatch negativity, the automatic change detection of the auditory stimuli. Currently, the AERP method cannot be applied in clinical practice in the neonatal period, although the findings in healthy newborns at risk for dyslexia are promising. Further research will elucidate the possibility of developing AERPs as a possible early screening method during infancy for later dyslexia or cognitive dysfunction.

Memory functions of children born with asymmetric intrauterine growth restriction

OBJECTIVE

Learning difficulties are frequently diagnosed in children born with intrauterine growth restriction (IUGR). Models of various animal species with IUGR were studied and demonstrated specific susceptibility and alterations of the hippocampal formation and its related neural structures. The main purpose was to study memory functions of children born with asymmetric IUGR in a large-scale cohort using a long-term prospective paradigm.

METHODS

One hundred and ten infants diagnosed with IUGR were followed-up from birth to 9 years of age. Their performance was compared with a group of 63 children with comparable gestational age and multiple socioeconomic factors. Memory functions (short-term, super- and long-term spans) for different stimuli types (verbal and visual) were evaluated using Visual Auditory Digit Span tasks (VADS), Rey Auditory Verbal Learning Test (Rey-AVLT), and Rey Osterrieth Complex Figure Test (ROCF).

RESULTS

Children with IUGR had short-term memory difficulties that hindered both serial verbal processing system and simultaneous processing of high-load visuo-spatial stimuli. The difficulties were not related to prematurity, neonatal complications or growth catch-up, but were augmented by lower maternal education. Recognition skills and benefits from reiteration, typically affected by hippocampal dysfunction, were preserved in both groups.

CONCLUSIONS

Memory profile of children born with IUGR is characterized primarily by a short-term memory deficit that does not necessarily comply with a typical hippocampal deficit, but rather may reflect an executive short-term memory deficit characteristic of anterior hippocampal-prefrontal network. Implications for cognitive intervention are discussed.