Hippocampal volume and everyday memory in children of very low birth weight

Relationship between white matter apparent diffusion coefficients in preterm infants at term-equivalent age and developmental outcome at 2 years

OBJECTIVE

The aim of this study was to develop a simple reproducible method for the measurement of apparent diffusion coefficient values in the white matter of preterm infants using diffusion-weighted imaging to test the hypothesis that elevated mean apparent diffusion coefficient values are associated with lower developmental quotient scores at 2 years' corrected age.

METHODS

We obtained diffusion-weighted imaging in 38 preterm infants at term-equivalent age who had no evidence of overt cerebral pathology on conventional MRI. Mean apparent diffusion coefficient values at the level of the centrum semiovale were determined. The children were assessed using a standardized neurologic examination, and the Griffiths Mental Development Scales were administered to obtain a developmental quotient at 2 years' corrected age. The relationship between mean apparent diffusion coefficient values and developmental quotient was examined. Clinical data relating to postnatal sepsis, antenatal steroid exposure, supplemental oxygen, gender, patent ductus arteriosus, and inotrope requirement were collected, and the mean apparent diffusion coefficient values for each group were compared.

RESULTS

The mean (+/-SD) apparent diffusion coefficient value in the white matter was 1.385 +/- 0.07 x 10(-3) mm2/second, and the mean developmental quotient was 108.9 +/- 11.5. None of the children had a significant neurologic problem. There was a significant negative correlation between mean apparent diffusion coefficient and developmental quotient.

CONCLUSION

These findings suggest that higher white matter apparent diffusion coefficient values at term-equivalent age in preterm infants without overt lesions are associated with poorer developmental performance in later childhood. Consequently, apparent diffusion coefficient values at term may be of prognostic value for neurodevelopmental outcome in infants who are born preterm and who have no other imaging indicators of abnormality.

Executive functions in school-age children born very prematurely

BACKGROUND

School-age preterm children are at risk for cognitive difficulties including Executive Dysfunction and low average IQ.

AIM

The aim of this study was to determine the performance of very preterm, school-age children on three components of Executive Function (EF), two components of Executive Attention and a measure of IQ.

STUDY DESIGN

Cross-sectional, independent samples comparison.

METHODS

A UK sample of 40 very preterm (<32 weeks gestational age, Mean 28.43, SD 2.41) children and 41 term born control children aged between 6 and 12 years (mean ages 8 years 5 months in both groups) was assessed on IQ, EF (inhibition, working memory and set shifting) and attention (sustained and selective). Between group comparisons were made using multivariate analysis of variance and covariance.

RESULTS

Multivariate analyses indicated that preterm children scored significantly lower than their term born peers across Executive Function and executive attention tasks. As expected, the preterm group achieved IQ scores at the low end of the average range. Univariate analyses indicated some difficulties with shifting and inhibition components of EF, although covariate analysis revealed that only shifting was independent of IQ.

CONCLUSIONS

Preterm children showed mild executive function and executive attention difficulties in the context of average IQ scores. The findings highlight the benefit of using multivariate assessments of executive skills rather than general intellectual outcome alone, to obtain a better distinction of the specific cognitive weaknesses associated with preterm birth.

Memory Performance in a Sample of Very Low Birth Weight Adolescents

Prematurely born participants with very low birth weight (VLBW) are at high risk of brain injury in the perinatal period and of later cognitive impairment. Studies of long-term memory sequelae in VLBW participants are scarce and focus on verbal and visual memory assessed by standard clinical memory tests. There is even less research into everyday memory, and the results obtained are contradictory. This study explores long-term memory deficits in VLBW adolescents using 2 standard clinical memory tests and 1 everyday memory test. Results show impairment only in everyday memory. These memory deficits are not specific; they are related to an impaired general cognitive performance. Unlike birth weight, gestational age is a good predictor of intelligence.

Differences in behavioral outcome and motor development at school age after neonatal treatment for chronic lung disease with dexamethasone versus hydrocortisone

Neonatal dexamethasone (DEX) for chronic lung disease is associated with adverse outcome. We compared behavioral and motor development at school age of children who neonatally received DEX to children neonatally treated with hydrocortisone (HC) in a retrospective matched cohort study. DEX- and HC-treated groups matched for gestational age, birth weight and year, gender, and severity of respiratory distress syndrome were compared with a reference group (REF) and a group treated only antenatally with betamethasone (BMETH). REF and BMETH groups had a higher gestational age and less severe respiratory distress syndrome. From 192 children (DEX, n = 46; HC, n = 52; REF, n = 43; BMETH, n = 51), the Child Behavioral Checklists from parents and teachers (Teacher's Report Form) and the Movement Assessment Battery for Children to assess neuromotor function were analyzed. DEX girls had a poorer performance on nearly all behavioral scales of the Teacher's Report Form compared with HC girls. DEX boys did not differ from HC boys. The HC boys or girls did not differ from the REF or BMETH groups. Neuromotor development was poorer in DEX than the BMETH and REF groups. The HC group did not differ from REF and BMETH groups. We suggest that neonatal HC may be a "safer" alternative for DEX for the treatment of CLD.

Cortical recruitment patterns in children born prematurely compared with control subjects during a passive listening functional magnetic resonance imaging task

OBJECTIVES

To use functional magnetic resonance imaging (fMRI) to test the hypothesis that subjects who were born prematurely develop alternative systems for processing language.

STUDY DESIGN

Subjects who were born prematurely (n = 14; 600-1250 g birthweight) without neonatal brain injury and 10 matched term control subjects were examined with a fMRI passive listening task of language, the Clinical Evaluation of Language Fundamentals (CELF) and portions of the Comprehensive Test of Phonological Processing (CTOPP). The fMRI task was evaluated for both phonologic and semantic processing.

RESULTS

Although there were differences in CELF scores between the subjects born prematurely and control subjects, there were no significant differences in the CTOPP measures in the 2 groups. fMRI studies demonstrated that the groups differentially engaged neural systems known to process language. Children born at term were significantly more likely to activate systems for the semantic processing of language, whereas subjects born prematurely preferentially engaged regions that subserve phonology.

CONCLUSIONS

At 12 years of age, children born prematurely and children born at term activate neural systems for the auditory processing of language differently. Subjects born prematurely engage different networks for phonologic processing; this strategy is associated with phonologic language scores that are similar to those of control subjects. These biologically based developmental strategies may provide the substrate for the improving language skills noted in children who are born prematurely.

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.

A functional magnetic resonance imaging study of the long-term influences of early indomethacin exposure on language processing in the brains of prematurely born children

BACKGROUND

Previous studies have demonstrated that indomethacin lowers the incidence and decreases the severity of intraventricular hemorrhage, as well as improves the cognitive outcome, in prematurely born male infants.

OBJECTIVE

The purpose of this work was to use functional magnetic resonance imaging to test the hypothesis that neonatal indomethacin treatment would differentially affect brain activation across genders in school-aged, prematurely born children during performance of a language task.

METHODS

Forty-seven prematurely born children (600-1250-g birth weight) and 24 matched term control subjects were evaluated using a functional magnetic resonance imaging passive language task and neurodevelopmental assessments that included the Wechsler Intelligence Scale for Children-III and the Peabody Picture Vocabulary Test-Revised. Neural activity was assessed during both phonologic and semantic processing in the functional magnetic resonance imaging protocol.

RESULTS

Neurodevelopmental assessments demonstrated significant differences in full-scale, verbal, and performance intelligence quotient, as well as Peabody Picture Vocabulary Test scores, between the preterm and term control subjects. Rates of perinatal complications did not differ significantly across preterm treatment groups, but male preterm subjects randomly assigned to saline tended to have lower Peabody Picture Vocabulary Test-Revised scores than did all of the other preterm groups. During phonological processing, a significant treatment-by-gender effect was demonstrated in 3 brain regions: the left inferior parietal lobule, the left inferior frontal gyrus (Broca's area), and the right dorsolateral prefrontal cortex.

CONCLUSIONS

These data demonstrate a differential effect of indomethacin administration early in postnatal life on the subsequent development of neural systems that subserve language functioning in these male and female preterm infants.

Développement cognitif et performances attentionnelles de l'ancien prématuré « normal » à l'âge scolaire

OBJECTIVE

A preterm birth can exert an influence on cognitive development. The aim of this study was to determine whether preterm birth may impact on attention executive processes, at school age, in children without neurological sequelae.

DESIGN AND METHODS

Prematurely born children admitted in the level III NICU of the Maternité régionale of Nancy between 1992 and 1994, underwent at 8 to 10 years 8 subtests of the mental processing scales of the K-ABC, which assess process categories involved in learning. The children were also submitted to 3 tests that evaluate attention mechanisms efficiency (category fluency task, backward digits span, Tower of London). The controls were children born at term recruted in schools of the same area.

RESULTS

The 124 children were born with birth weight appropriate for gestational age, and were in the school grades expected for their ages, in 3rd, 4rth, and 5fth grades. Fifty-three children were born at term, 29 were prematurely born (33-36 w), and 42 were very prematurely born (28-32 w). Birth term was significantly correlated (P < 0.001) with scores at sequential processing scale, at simultaneous processing scale and at the mental processing composite scale. At this scale, the children born at term obtained a median score of 112, the children prematurely born of 101, and the children very prematurely born of 98.5. For 40 third grade children (18 born at term, 10 prematurely born, and 12 very prematurely born), birth term was significantly correlated with performances at the 3 tests of attention. In all cases, preterm was inversely correlated with performances.

CONCLUSION

The results are consistent with a lower efficiency in attention executive processes which may be related to the higher frequency of learning disabilities associated with prematurity.

Brain and cognitive-behavioural development after asphyxia at term birth

Perinatal asphyxia occurs in approximately 1-6 per 1000 live full-term births. Different patterns of brain damage can result, though the relation of these patterns to long-term cognitive-behavioural outcome remains under investigation. The hippocampus is one brain region that can be damaged (typically not in isolation), and this site of damage has been implicated in two different long-term outcomes, cognitive memory impairment and the psychiatric disorder schizophrenia. Factors in addition to the acute episode of asphyxia likely contribute to these specific outcomes, making prediction difficult. Future studies that better document long-term cognitive-behavioural outcome, quantitatively identify patterns of brain injury over development and consider additional variables that may modulate the impact of asphyxia on cognitive and behavioural function will forward the goals of predicting long-term outcome and understanding the mechanisms by which it unfolds.

Long-term consequences of pain in human neonates

The low tactile threshold in preterm infants when they are in the neonatal intensive care unit (NICU), while their physiological systems are unstable and immature, potentially renders them more vulnerable to the effects of repeated invasive procedures. There is a small but growing literature on pain and tactile responsivity following procedural pain in the NICU, or early surgery. Long-term effects of repeated pain in the neonatal period on neurodevelopment await further research. However, there are multiple sources of stress in the NICU, which contribute to inducing high overall 'allostatic load', therefore determining specific effects of neonatal pain in human infants is challenging.

Abnormal cortical development after premature birth shown by altered allometric scaling of brain growth

BACKGROUND

We postulated that during ontogenesis cortical surface area and cerebral volume are related by a scaling law whose exponent gives a quantitative measure of cortical development. We used this approach to investigate the hypothesis that premature termination of the intrauterine environment by preterm birth reduces cortical development in a dose-dependent manner, providing a neural substrate for functional impairment.

METHODS AND FINDINGS

We analyzed 274 magnetic resonance images that recorded brain growth from 23 to 48 wk of gestation in 113 extremely preterm infants born at 22 to 29 wk of gestation, 63 of whom underwent neurodevelopmental assessment at a median age of 2 y. Cortical surface area was related to cerebral volume by a scaling law with an exponent of 1.29 (95% confidence interval, 1.25-1.33), which was proportional to later neurodevelopmental impairment. Increasing prematurity and male gender were associated with a lower scaling exponent (p < 0.0001) independent of intrauterine or postnatal somatic growth.

CONCLUSIONS

Human brain growth obeys an allometric scaling relation that is disrupted by preterm birth in a dose-dependent, sexually dimorphic fashion that directly parallels the incidence of neurodevelopmental impairments in preterm infants. This result focuses attention on brain growth and cortical development during the weeks following preterm delivery as a neural substrate for neurodevelopmental impairment after premature delivery.

A controlled trial of skin-to-skin contact in extremely preterm infants

BACKGROUND

Extremely preterm birth, even in the absence of significant neurological impairment, is associated with altered pain responses and impaired memory and behaviour. Preterm birth increases the risk of maternal depression and may impede the development of the mother-infant relationship, factors that in turn are also associated with impaired infant outcome. Mother-infant skin-to-skin contact has been recommended as a simple means of ameliorating these effects.

METHODS

We conducted a pragmatic, prospective, controlled, intention-to-treat trial in two neonatal intensive care units. Infants born below 32 weeks gestation were recruited within the first week after birth and assigned to a control group receiving standard care, or an intervention group in which mothers were encouraged to provide a session of skin-to-skin contact once daily for 4 weeks. We assessed infant behaviour at time of discharge from hospital, responses to immunisation at 4 and 12 months of age, and memory, behaviour and development at 1 year corrected (postmenstrual) age. Indices of maternal depression, stress, anxiety, lactation performance and infant interaction were assessed at time of infant discharge, 4 months and 1 year.

RESULTS

No significant difference was identified in any infant or maternal measure at any time point.

CONCLUSIONS

Mother-infant skin-to-skin contact after extremely preterm birth results in neither benefit nor adverse consequences. Although there is no reason to dissuade mothers who wish to provide STS contact, we are unable to recommend resource allocation for the implementation of STS programmes for extremely preterm infants in a neonatal intensive care unit setting.

White matter volume and concentration reductions in adolescents with history of very preterm birth: a voxel-based morphometry study

Very preterm birth (VPTB) is an important risk factor for white matter (WM) damage. We used voxel-based morphometry (VBM) to examine regional WM brain abnormalities in 50 adolescents with antecedents of very preterm birth (VPTB) without evidence of WM damage on T2-weighted MRI. This group was compared with a group of 50 subjects born at term and matched for age, handedness and socio-cultural status. We also examined the relationship between WM changes and gestational age (GA) and weight (GW) at birth in VPTB subjects. Both modulated and unmodulated VBM analyses showed significant abnormalities in several WM brain regions in the VPTB group, involving all the cerebral lobes. However, density analyses (unmodulated data) mainly identified periventricular damage and the involvement of the longitudinal fascicles while volume analyses (modulated data) detected WM decreases in regions distant from the ventricular system, located at the origin and end of the long fascicles. A significant correlation was found between WM decreases and both GA and GW in various brain regions: the lower the GA and GW, the lower the WM integrity. This study supports the current view that widespread white matter impairment is associated with immature birth.

Chronic endotoxin exposure causes brain injury in the ovine fetus in the absence of hypoxemia

OBJECTIVE

Intrauterine infection has been linked to brain injury in human infants, although the mechanisms are not fully understood. We recently showed that repeated acute exposure of preterm fetal sheep to bacterial endotoxin (lipopolysaccharide [LPS]) results in fetal hypoxemia, hypotension, increased systemic proinflammatory cytokines, and brain damage, including white matter injury. However, it is not clear whether this injury is caused by reduced cerebral oxygen delivery or inflammatory pathways independent of hypoxia. The aim of the present study was to determine the effects on the fetal brain and placenta of a chronic intrauterine inflammatory state, induced by LPS infusion into the fetal circulation, a model that did not cause hypoxia.

METHODS

At 0.65 of term, eight catheterized fetal sheep received intravenous infusions of LPS (5 to 15 mug) over 5 days; control fetuses received saline. Fetal physiologic responses were monitored throughout the infusion. Fetal brain and placental tissues were examined histologically 6 days after the conclusion of the infusion.

RESULTS

LPS infusions did not result in physiologically significant alterations to fetal blood gases or mean arterial pressure; however, plasma proinflammatory cytokine levels were elevated. Following LPS exposure there was no difference in fetal body or brain weights (P >.05); placental weight was reduced (P <.05), consistent with reduced placentome cross-sectional area (P <.05). In the cerebral hemispheres subcortical white matter injury was present in six LPS-exposed fetuses and included axonal damage, microgliosis, oligodendrocyte injury, and increased beta amyloid precursor protein (beta-APP) expression.

CONCLUSIONS

Chronic, systemic exposure of the fetus to LPS resulted in fetal brain damage in the absence of hypoxemia or hypotension, although the resulting injury was less severe than following repeated acute exposure.

Modes of imprinted gene action in learning disability

BACKGROUND

It is now widely acknowledged that there may be a genetic contribution to learning disability and neuropsychiatric disorders, stemming from evidence provided by family, twin and adoption studies, and from explicit syndromic conditions. Recently it has been recognized that in some cases the presentation of genetic syndromes (or discrete aspects of disorders) is dependent on the sex of the transmitting parent. Such 'parent-of-origin effects' can be explained by a number of genetic mechanisms, a predominant one of which is genomic imprinting. Genomic imprinting refers to the parent of origin-specific epigenetic marking of an allele of a gene, such that for some genes it is mainly the maternally inherited allele only that is expressed, whereas for others expression occurs mainly from the paternal copy.

METHODS

Here we discuss the contribution of imprinted genes to mental dysfunction and learning disability, using clinical examples of association studies and explicit imprinting disorders (with particular emphasis to Angelman and Prader-Willi syndromes), and evidence from animal work.

RESULTS

Clinical and animal studies strongly suggest that imprinted genes contribute to brain functioning, and when the genes or epigenetic processes are disrupted, this can give rise to neuropsychiatric problems. Another system to which imprinted genes provide a large contribute is the placenta and foetal development. Epidemiological studies suggest that this is also a key area in which dysregulation can give rise to learning difficulties.

CONCLUSIONS

Disruption of imprinted genes, or the epigenetic processes controlling them, can contribute to learning disability. These effects can be divided into two types: direct effects, such as those seen in explicit imprinting disorders such as Angelman and Prader-Willi syndromes, and indirect effects as manifest via changes in foetal programming.

Memory in Early Adolescents Born Prematurely: A Functional Magnetic Resonance Imaging Investigation

This study employed functional magnetic resonance imaging to examine the functional neuroanatomy of the hippocampus and head of the caudate nucleus during 2 different types of memory tasks in a sample of 9 early adolescent children who were born preterm (neonatal intensive care unit [NICU] sample) and a group of 9 age-matched control children who were born at term. The investigation employed delayed match to sample (DMS), delayed nonmatch to sample (DNMS), and spatial memory span tasks, as well as 2 analogous perceptuomotor tasks that placed no demands on memory. The general question examined was whether preterm children show different levels of hippocampal and caudate activation during these tasks when compared to children born at term. The findings indicated that the 2 groups did not differ in functional activation of the hippocampus during the DMS and DNMS tasks. During the encoding phase of the spatial memory span task, the DMS perceptuomotor task, and the spatial memory span perceptuomotor task, the NICU sample showed greater activation change in the right caudate nucleus, and less right caudate activation change during the test phase. During the spatial span perceptuomotor task, the preterm group showed reduced activation change in the left caudate nucleus during both the encoding and test phase. Also, during the DMS perceptuomotor task, the NICU group showed increased activation change in the left caudate nucleus during encoding and decreased activation change at test. The implications of these findings for understanding the functional neuroanatomy of memory deficits are discussed, as is the potential for distinguishing the effects of neural plasticity from those of typical brain maturational processes.

Perinatal corticosteroid effect on amygdala and hippocampus volume during brain development in the rat model

Exposure of the fetus to corticosteroid during brain development has been suggested to cause permanent change in brain structure and has been associated with long term cognitive, behavioral and emotional impairment. We evaluated the effect of perinatal corticosteroid, at a dose similar to that which human fetuses are exposed, on cerebral cortex, corpus collosum, hippocampus, dentate gyrus and amygdala in a rat model. Rat pups were given betamethasone at day 1 (P1). Brain sections from the rat pups at postnatal day 45 (P45) were then analyzed. No differences were noted in the volumes of cerebral cortex, corpus collosum, hippocampus, dentate gyrus, or three nuclei of the amygdala compared to the control and sham groups. We concluded that a single course of betamethasone, at a comparable dose to that which the human fetus is exposed in clinical practice, had no effect on these regional brain volumes at this stage of development.

Brain Injury from Cardiac Arrest in Children

This article reviews the important differences between children and adults suffering brain injury following cardiac arrest. The differences in etiology, pathophysiology, neuronal vulnerability, and repair in the context of the developing brain are reviewed. The available clinical data are reviewed, and selected treatment priori-ties are declared. The article includes a discussion of knowledge gaps and future directions.

Neonatal hydrocortisone treatment related to 1H-MRS of the hippocampus and short-term memory at school age in preterm born children

Animal studies have shown that corticosteroids (dexamethasone) cause neuronal loss in the hippocampus and deficits in short term memory. Proton magnetic resonance spectroscopy can measure brain metabolites in vivo and give an indication of neuronal integrity. We investigated whether prolonged administration of hydrocortisone during the neonatal period for bronchopulmonary dysplasia (BPD) in preterm born children changes the metabolism in the hippocampus, measured at school age. Secondly, we investigated whether hippocampal metabolism and short-term memory and neurodevelopmental outcome are related. In this observational study 37 preterm born children (< or = 32 wk (range 25.0-33.0) and/or a birth weight < or = 1500 g) underwent proton spectroscopy of the hippocampus at school age. Eighteen children were treated with hydrocortisone for BPD (starting dose 5 mg/kg/d tapered over a minimum period of 22 d, median duration 28 d) and 19 never received corticosteroids during the perinatal period. N-acetyl aspartate/ Choline + Creatine/phosphocreatine (NAA/(Cho + Cr)) ratios were determined. A 15-word recall memory test and an IQ measurement were obtained on the same day. Hydrocortisone treated children were younger, lighter and sicker than their nonsteroid treated counterparts. Mean NAA/(Cho + Cr) ratios in the hippocampus were not significantly different in the hydrocortisone group compared with the non-steroid group. Performance on the 15-word memory test and IQ were similar in the two groups. There was no relation between NAA/(Cho + Cr) ratios and memory nor between NAA/(Cho + Cr) ratios and IQ. We conclude that hydrocortisone in the mentioned dose, administered in the neonatal period for BPD, does not appear to have any long-term effects on memory and/or hippocampal metabolism.

Patterns of cerebral injury in a primate model of preterm birth and neonatal intensive care

Very preterm birth is associated with significant neurodevelopmental morbidity, with 10% to 15% of these infants later developing cerebral palsy and up to 50% experiencing learning disabilities. The nature of the cerebral lesion predisposing these infants to such impairments is not fully understood but is likely related to both cerebral injury and alterations in cerebral development associated with neonatal intensive care. To study the impact of both preterm birth and neonatal intensive care on the immature brain, we are studying a preterm primate model delivered at 125 days of a 184-day gestational period and cared for in a neonatal intensive care unit for 2 to 4 weeks in a fashion highly similar to that for human preterm infants. The most common neuropathology in this model is white-matter damage manifested by reactive astrogliosis or activated microglia and enlarged ventricular size. Subarachnoid, germinal matrix, and intraventricular hemorrhages are also common. These preliminary results support the similarity of this model to both the alterations in cerebral developmental and the pattern of cerebral injury found in human preterm infants. We are now investigating the impact of randomized respiratory therapies on the pattern of cerebral injury. The prematurely born baboon appears to be an accurate and relevant model for the study of preterm human birth.

Neurodevelopmental outcomes of infants born prematurely

Long-term follow-up of infants born prematurely is necessary to determine neurodevelopmental outcomes, particularly with the expansion of interest from major disabilities to high prevalence/low severity dysfunctions. Models of pathogenesis include changes due to developmental disruptions and to injury, the magnitude and type of change influenced by the infant's age, and central nervous system recovery and reorganization. Alterations in neurogenesis, migration, myelination, cell death, and synaptogenesis occur even in the absence of insult. Despite increased knowledge regarding these processes, the functional significance of brain abnormalities is unclear. Because of methodologic problems in follow-up studies, it is difficult to characterize outcome definitively. Nonetheless, an acceptable degree of agreement across studies is found with regard to specific neurodevelopmental outcomes: motor/neurologic function, visuomotor integrative skills, IQ, academic achievement, language, executive function, and attention-deficit hyperactivity disorder/behavioral issues. In general, children born prematurely have more problems in these areas than do their normal birth weight counterparts. Suggestions for improved analyses and clarification of outcomes include use of cluster analysis, structural equation modeling, growth curve analysis, developmental epidemiologic approaches, and better control of background variables using risk indexes and factor scores. Better assessment techniques measuring functions documented to be at higher risk of problems are discussed.

Cognitive development in low risk preterm infants at 3-4 years of life

BACKGROUND

Major neurological handicaps and neuropsychological disturbances are more common in ex-preterm children than their counterparts born at term.

OBJECTIVE

To establish in a prospective study whether a characteristic neuropsychological profile exists in ex-preterm children who do not exhibit neurodevelopmental deficits on routine clinical examination.

METHODS

Thirty intellectually normal children born preterm (30-34 weeks gestation) without major neurological disabilities and a control group of term children matched for age, sex, and parental educational and occupational status were assessed at 3-4 years of age to obtain a complete neuropsychological profile. Intellectual ability, language comprehension and expression, perceptual and visual motor function, working memory, and attention and behavioural problems were investigated.

RESULTS

Even in the absence of major neurological signs, children born preterm achieved lower mean scores than controls on the Stanford-Binet intelligence scale (110.8 v 121, p<0.001), visual perception test (33.8 v 42.7, p<0.001), visual motor integration test (42.6 v 47.4, p = 0.049), memory for location test (8.4 v 9.5, p = 0.007), sustained attention test (41.6 v 51.5, p = 0.009), and the picture vocabulary test (33.3 v 44.7, p = 0.021).

CONCLUSIONS

Neuropsychological abnormalities can be detected early in childhood in apparently normal ex-preterm children and are consistent with a growing body of evidence that prematurity may be associated with long term neuropsychological morbidity in childhood and adolescence.

Executive control of learning and memory in children with bilateral spastic cerebral palsy

Executive control of learning and memory was examined in children with bilateral spastic cerebral palsy (SCP). We hypothesized that SCP-related brain damage would disrupt executive but not associative aspects of learning and memory. To test this hypothesis, the California Verbal Learning Test-Children's Version was administered to 16 children with bilateral SCP and 19 control children ranging from 6 to 18 years of age. Controlling for general verbal ability, the groups did not differ in initial learning and retention of information over time, suggesting that associative learning and memory processes subserved by medial temporal brain regions were relatively intact in children with SCP. In contrast, impairments in learning over repeated trials, strategic processing, and inhibition in the SCP group pointed to disruptions in prefrontally-mediated executive aspects of learning and memory. The inhibitory deficit was more pronounced in younger children with SCP, suggesting a developmental delay in this ability.

How do specific memory disorders present in the school classroom?

Childhood memory disorders have received increasing empirical investigation over recent years and reviews of the dissociations within the developmental memory system are now available. However, there are few descriptions within the literature of children's consequent behavioural and learning difficulties within an educational context. This paper reviews the growing evidence that links specific memory disorders to academic skills and then provides clinical descriptions of the day-to-day behaviour and learning often observed following the identification of such children. It is anticipated that such descriptions will allow professionals to understand the range of consequences possible and alert health and educational staff to children at risk of suffering unidentified memory difficulties. A clinical description of the behavioural repertoire associated with different childhood memory disorders is also necessary to consider how professionals may design rehabilitative support.

Differential brain growth in the infant born preterm: current knowledge and future developments from brain imaging

Preterm birth is associated with a high prevalence of neuropsychiatric impairment in childhood and adolescence, but the neural correlates underlying these disorders are not fully understood. Quantitative magnetic resonance imaging techniques have been used to investigate subtle differences in cerebral growth and development among children and adolescents born preterm or with very low birth weight. Diffusion tensor imaging and computer-assisted morphometric techniques (including voxel-based morphometry and deformation-based morphometry) have identified abnormalities in tissue microstructure and cerebral morphology among survivors of preterm birth at different ages, and some of these alterations have specific functional correlates. This chapter reviews the literature reporting differential brain development following preterm birth, with emphasis on the morphological changes that correlate with neuropsychiatric impairment.

Object working memory deficits predicted by early brain injury and development in the preterm infant

Children born preterm and of very low birth weight are at increased risk of learning difficulties and educational under-achievement. However, little is known about the specific neuropsychological problems facing these children or their neurological basis. Using prospective longitudinal data from a regional cohort of 92 preterm and 103 full-term children, this study examined relations between term MRI measures of cerebral injury and structural brain development and children's subsequent performance on an object working memory task at the age of 2 years. Results revealed clear between-group differences, with preterm children having greater difficulty encoding new information in working memory than term control children. Within the preterm group, task performance at the age of 2 years was related to both qualitative MRI measures of white matter (WM) injury and quantitative measures of total and regional brain volumes assessed at term equivalent. Bilateral reductions in total tissue volumes (%region) of the following cerebral regions were specifically related to subsequent working memory performance: dorsolateral prefrontal cortex, sensorimotor, parietooccipital and premotor. Associations between total cerebral tissue volumes at term (adjusted and unadjusted for intracranial volume) persisted even after the effects of WM injury were taken into account. This suggests that early disturbance in cerebral development may have an independent adverse impact on later working memory function in the preterm infant. These findings add to our understanding of the neuropathological pathways associated with later executive dysfunction in the very preterm infant.

Deficits in spatial orientation of children with intrauterine growth retardation

The spatial orientation of intrauterine growth retarded (IUGR) children versus age-matched controls was examined using two spatial tests. The first test was the radial arm maze (RAM), a navigational test frequently used in animal models. The second test was a subtest from the Kaufman assessment battery for children (K-ABC). The IUGR group comprised 28 children aged 6 years. The control group comprised 29 appropriate-for-gestational age children. The performance of the IUGR children was significantly inferior to controls in both tests. In the RAM test, the ratio between the correct entrances to the total entrances was significantly lower in the IUGR group than in the control group (P<0.001). In the K-ABC, the IUGR group could not perform as well as control children (P<0.001). These results suggest that spatial orientation in IUGR children is inferior to their age-matched controls, possibly contributing to their potential learning difficulties. The present results also suggest that the RAM can be potentially used to test spatial orientation of children at-risk.

Investigation of cerebral development and injury in the prematurely born primate by magnetic resonance imaging and histopathology

We summarize the preliminary results of brain histopathology and magnetic resonance imaging applied to a premature baboon model developed for evaluation of the pathogenesis and treatment of bronchopulmonary dysplasia. Cerebral development was assessed in 10 gestational control animals at time points of 125, 140 and 160 days of gestation (dg). On the basis of histopathology, conventional MRI and diffusion MRI, 125 dg is equivalent to 26-28 weeks of human gestation, 140 dg is equivalent to 30-32 weeks, and 160 dg is equivalent to term. Preliminary data are also presented for 33 experimental cases delivered at 125 dg, nursed for 2 weeks in an intensive care facility, and sacrificed at 139-140 dg. The commonest neuropathology in this cohort is white matter damage, manifest by reactive astrogliosis or activated microglia, and enlarged ventricular size. Subarachnoid, germinal matrix and intraventricular hemorrhages are also common. These preliminary results support the similarity of this model to the human preterm infant for both cerebral development and the pattern of cerebral injury. The prematurely born baboon appears an important model for the study of preterm human birth.

The role of the medial temporal lobe in autistic spectrum disorders

The neural basis of autistic spectrum disorders (ASDs) is poorly understood. Studies of mnemonic function in ASD suggest a profile of impaired episodic memory with relative preservation of semantic memory (at least in high-functioning individuals). Such a pattern is consistent with developmental hippocampal abnormality. However, imaging evidence for abnormality of the hippocampal formation in ASD is inconsistent. These inconsistencies led us to examine the memory profile of children with ASD and the relationship to structural abnormalities. A cohort of high-functioning individuals with ASD and matched controls completed a comprehensive neuropsychological memory battery and underwent magnetic resonance imaging for the purpose of voxel-based morphometric analyses. Correlations between cognitive/behavioural test scores and quantified results of brain scans were also carried out to further examine the role of the medial temporal lobe in ASD. A selective deficit in episodic memory with relative preservation of semantic memory was found. Voxel-based morphometry revealed bilateral abnormalities in several areas implicated in ASD including the hippocampal formation. A significant correlation was found between parental ratings reflecting autistic symptomatology and the measure of grey matter density in the junction area involving the amygdala, hippocampus and entorhinal cortex. The data reveal a pattern of impaired and relatively preserved mnemonic function that is consistent with a hippocampal abnormality of developmental origin. The structural imaging data highlight abnormalities in several brain regions previously implicated in ASD, including the medial temporal lobes.

Structural and functional brain development after hydrocortisone treatment for neonatal chronic lung disease

OBJECTIVE

There is much concern about potential neurodevelopmental impairment after neonatal corticosteroid treatment for chronic lung disease. Dexamethasone is the corticosteroid most often used in this clinical setting, and it has been shown to impair cortical growth among preterm infants. This study evaluated long-term effects of prematurity itself and of neonatal hydrocortisone treatment on structural and functional brain development using three-dimensional MRI with advanced image-processing and neurocognitive assessments.

METHODS

Sixty children born preterm, including 25 children treated with hydrocortisone and 35 children not treated with hydrocortisone, and 21 children born at term were evaluated, at a mean age of 8 years, with quantitative MRI and neurocognitive assessments (Wechsler Intelligence Scales for Children-Revised [WISC-R]). Automatic image segmentation was used to determine the tissue volumes of cerebral gray matter, white matter, and cerebrospinal fluid. In addition, the volume of the hippocampus was determined manually. WISC-R scores were recorded as mean intelligence scores at evaluation. Neonatal hydrocortisone treatment for chronic lung disease consisted of a starting dose of 5 mg/kg per day tapered over a minimum of 3 weeks.

RESULTS

Cerebral gray matter volume was reduced among preterm children (regardless of hydrocortisone treatment), compared with children born at term (preterm: 649 +/- 4.4 mL; term: 666 +/- 7.3 mL). Birth weight was shown to correlate with gray matter volume at 8 years of age in the preterm group (r = 0.421). Cerebrospinal fluid volume was increased among children born preterm, compared with children born at term (preterm: 228 +/- 4.9 mL; term: 206 +/- 8.2 mL). Total hippocampal volume tended to be lower among children born preterm, with a more pronounced reduction of hippocampal volume among boys (preterm: 6.1 +/- 0.13 mL; term: 6.56 +/- 0.2 mL). The WISC-R score was lower for children born preterm, compared with children born at term (preterm: 99.4 +/- 12.4; term: 109.6 +/- 8.8). Children treated with neonatal hydrocortisone had very similar volumes of gray matter (preterm with hydrocortisone: 650 +/- 7.0 mL; preterm without hydrocortisone: 640 +/- 5.6 mL), white matter (preterm with hydrocortisone: 503 +/- 6.1 mL; preterm without hydrocortisone: 510 +/- 4.9 mL), and cerebrospinal fluid (preterm with hydrocortisone: 227 +/- 7.4 mL; preterm without hydrocortisone: 224 +/- 6.0 mL), compared with untreated infants. The hippocampal volumes were similar in the 2 groups (preterm with hydrocortisone: 5.92 +/- 0.15 mL; preterm without hydrocortisone: 5.81 +/- 0.12 mL). The WISC-R score assessments were within the normal range for both groups, with no difference between the groups (preterm with hydrocortisone: 100.8 +/- 13; preterm without hydrocortisone: 98.6 +/- 12.3).

CONCLUSIONS

Prematurity is associated with mild brain structural differences that persist at 8 years of age, with associated lower scores in neurocognitive assessments. The data suggest that perinatal hydrocortisone given at the described dosage has no long-term effects on either neurostructural brain development or neurocognitive outcomes.

Increased temporal lobe gyrification in preterm children

Preterm birth often results in significant learning disability, and previous magnetic resonance imaging (MRI) studies of preterm children have demonstrated reduction in overall cortical tissue with particular vulnerability in the temporal lobe. We measured cortical gyrification in 73 preterm and 33 term control children at 8 years of age and correlated these findings with tests of language ability to determine the associations among preterm birth, neurodevelopment and functional outcome. Preterm children demonstrated significantly increased bilateral temporal lobe gyrification index compared to term controls. Left temporal gyrification index was significantly negatively correlated with left temporal lobe gray matter volume as well as reading recognition scores in the preterm group. Cortical development in the temporal lobe appears to be differentially vulnerable to preterm birth.

Practitioner review: early adversity and developmental disorders

BACKGROUND

Knowledge of genetic influences, on developmental disorders such as autism spectrum, attention deficit/hyperactivity disorder and learning disabilities, has increased the opportunities for understanding the influences of the early environment.

METHODS

This paper provides a selective, narrative review for clinicians of the effects of factors such as exposure to toxins and stresses in utero and in postnatal life; brain injuries and perinatal compromise; neglect, malnutrition and selective food deficiencies. It also considers what is known about the mechanisms through which early adversities operate.

RESULTS

Gaps in the research are identified and suggestions made about clinical investigations. Several types of environmental adversity have associations with later disorders that suggest a causal role. The effects are often on a broad range of psychological processes, and are not always quickly reversible. Several adversities often coexist, calling for skilled judgement about priorities in treatment.

CONCLUSIONS

Individuals vary considerably in their exposure to adversity and their vulnerability to its effects, and genetic inheritance can influence both.

A “deficient environment” in prenatal life may compromise systems important for cognitive function by affecting BDNF in the hippocampus

The intrauterine environment has the capacity to mold the prenatal nervous system. Particularly, recent findings show that an adverse prenatal environment produces structural defects of the hippocampus, a critical area sub-serving learning and memory functions. These structural changes are accompanied by a disruption in the normal expression pattern of brain-derived neurotrophic factor (BDNF) and its cognate tyrosine kinase B (TrkB) receptor. The important role that the BDNF system plays in neural modeling and learning and memory processes suggests that fetal exposure to unfavorable intrauterine conditions may compromise proper cognitive function in adult life. These findings have implications for disorders that involve a dysfunction in the BDNF system and are accompanied by cognitive deficits.

Predictors of internalizing symptoms among very low birth weight young women

As part of a longitudinal study of the outcomes of very low birth weight children (<1.5 kg), we sought to examine the perinatal, childhood, and young adult predictors of internalizing symptoms among very low birth weight young women and their normal birth weight controls. The cohort included 125 very low birth weight and 124 normal birth weight 20-year-old subjects. Perinatal, childhood, and young adult predictors were examined via stepwise multivariate analyses. Results revealed very low birth weight to be a significant predictor of parent-reported internalizing symptoms of their daughters but only among white subjects who had mothers with high levels of psychological distress. Additional significant predictors of 20-year internalizing symptoms included child I.Q. and internalizing symptoms at age 8 years and family expressiveness. When the results were analyzed according to the young adult self-report, additional predictors of internalizing symptoms included a history of asthma and exposure to violence. Perinatal risk factors were not found to be predictive of internalizing symptoms at age 20 years. Future studies should prospectively examine social and environmental factors associated with the neonatal intensive care experience that might explain the effect of very low birth weight on later psychopathology.

The primate hippocampus: ontogeny, early insult and memory

Recent evidence suggests that in primates, as in rodents, the hippocampus shows a developmental continuum that affects memory abilities from infancy to adulthood. In primates relatively few hippocampal-dependent abilities (e.g. some aspects of recognition memory) are present in early infancy, whereas others (e.g. relational memory) begin to show adult-like characteristics around 2 years of age in monkeys and 5-7 years in humans. Profound and persistent memory loss resulting from insult to the hippocampus in infancy becomes evident in everyday behavior only later in childhood. This pattern of results suggests a maturational gradient within the medial temporal lobe memory system, with most abilities crucially dependent upon the hippocampus emerging in later stages of development, supporting a model of hierarchical organization of memory within the medial temporal lobe.

Prior pain induces heightened motor responses during clustered care in preterm infants in the NICU

BACKGROUND

Acute pain is a significant stressor for preterm infants in neonatal intensive care units (NICU); however, little is known about the effects of acute pain on subsequent motor responses during clusters of tactile handling.

AIMS

(1) To compare facial, body and heart rate reactivity in preterm infants at 32 weeks gestational age (GA) during routine care-giving tasks following a rest period (RCC: diapering, measuring abdominal girth and axillary temperature, mouth care) with their responses to Clustered Care following blood collection (PCC). (2) To examine how GA at birth affects patterns of stress and self-regulatory behaviors during RCC and PCC.

STUDY DESIGN

Within-group crossover design (random order).

SUBJECTS

Preterm infants, N=54 (mean GA at birth 29.3 +/- 2.2 weeks; mean birth weight 1257 +/- 423 g) were assessed at 32 weeks GA in the NICU.

OUTCOME MEASURES

The Newborn Developmental Care and Assessment Program (NIDCAP) and Neonatal Facial Coding System (NFCS) were coded from continuous bedside video recordings. Changes in mean heart rate (HR) were computed using custom physiologic software.

RESULTS

All infants had heightened facial, body and HR responses when CC followed a painful procedure compared to when they had not been handled prior to CC. Infants born at earlier GA (<30 weeks) had equal numbers of stress cues during RCC and PCC, but dampened self-regulatory behaviors during PCC.

CONCLUSION

Prior pain induces heightened biobehavioral reactivity in preterm infants during subsequent tactile procedures. In addition, clustering care is particularly stressful for infants born at earlier GA.

Abnormal cerebral structure is present at term in premature infants

BACKGROUND

Long-term studies of the outcome of very prematurely born infants have clearly documented that the majority of such infants have significant motor, cognitive, and behavioral deficits. However, there is a limited understanding of the nature of the cerebral abnormality underlying these adverse neurologic outcomes.

AIM

The overall aim of this study was to define quantitatively the alterations in cerebral tissue volumes at term equivalent in a large longitudinal cohort study of very low birth weight premature infants in comparison to term-born infants by using advanced volumetric 3-dimensional magnetic resonance imaging (MRI) techniques. We also aimed to define any relationship of such perinatal lesions as white matter (WM) injury or other potentially adverse factors to the quantitative structural alterations. Additionally, we wished to identify the relationship of the structural alterations to short-term neurodevelopmental outcome.

METHODS

From November 1998 to December 2000, 119 consecutive premature infants admitted to the neonatal intensive care units at Christchurch Women's Hospital (Christchurch, New Zealand) and the Royal Women's Hospital (Melbourne, Australia) were recruited (88% of eligible) after informed parental consent to undergo an MRI scan at term equivalent. Twenty-one term-born infants across both sites were recruited also. Postacquisition advanced 3-dimensional tissue segmentation with 3-dimensional reconstruction was undertaken to estimate volumes of cerebral tissues: gray matter (GM; cortical and deep nuclear structures), WM (myelinated and unmyelinated), and cerebrospinal fluid (CSF).

RESULTS

In comparison to the term-born infants, the premature infants at term demonstrated prominent reductions in cerebral cortical GM volume (premature infants [mean +/- SD]: 178 +/- 41 mL; term infants: 227 +/- 26 mL) and in deep nuclear GM volume (premature infants: 10.8 +/- 4.1 mL; term infants: 13.8 +/- 5.2 mL) and an increase in CSF volume (premature infants: 45.6 +/- 22.1 mL; term infants: 28.9 +/- 16 mL). The major predictors of altered cerebral volumes were gestational age at birth and the presence of cerebral WM injury. Infants with significantly reduced cortical GM and deep nuclear GM volumes and increased CSF volume volumes exhibited moderate to severe neurodevelopmental disability at 1 year of age.

CONCLUSIONS

This MRI study of prematurely born infants further defines the nature of quantitative cerebral structural abnormalities present as early as term equivalent. The abnormalities particularly involve cerebral neuronal regions including both cortex and deep nuclear structures. The pattern of cerebral alterations is related most significantly to the degree of immaturity at birth and to concomitant WM injury. The alterations are followed by abnormal short-term neurodevelopmental outcome.

Hippocampal functional magnetic resonance imaging during a face-name learning task in adolescents with antecedents of prematurity

Functional magnetic resonance imaging (fMRI) was used to map hippocampal activation during a declarative memory task in a sample of 14 adolescents with antecedents of prematurity (AP). The sample with AP was matched by age, sex and handedness with 14 full-term controls with no history of neurological or psychiatric illness. The target task consisted in learning 16 novel face-name pairs, and the control task involved the examination of two repeated face-name pairs. Stereological methods were also used to quantify hippocampal volumes. In both groups, we observed increased activation in the learning condition compared to the control task in the right fusiform gyrus and the left inferior occipital gyrus, but only premature subjects activated the hippocampus. Group comparison of the activation versus control conditions showed that prematures had greater activity in the right hippocampus than controls during the encoding of the word-face association. Volumetric analyses showed a significant left hippocampal volume loss in adolescents with AP. In addition, we found a significant positive correlation in the premature group between right hippocampal activation and face-name recognition. Functional MRI data also correlated with structural MRI data: right hippocampal activation correlated positively with right hippocampal volume. Our findings are consistent with previous studies of brain plasticity after focal lesions. Left hippocampal tissue loss may be related to an increase in contralateral brain activity, probably reflecting a compensatory mechanism. Our data also suggest that this plasticity is not enough to achieve normal performance.

Spatial working memory deficits in children at ages 3-4 who were low birth weight, preterm infants

The aim of this study was to investigate attention and perceptual and spatial working memory abilities in preterm, low birth weight preschool children without evident brain disorders as determined by normal cerebral ultrasound findings and normal motor development. The authors evaluated 19 preterm and 19 typically developing children who were matched for IQ and chronological age. Results indicated that children born prematurely without major neurological deficits and with a normal cognitive level may have specific difficulty in sustained attention, visuospatial processing, and spatial working memory when evaluated at ages 3-4. This finding is relevant for understanding the qualitative aspects of cognitive development in preterm children and the neurobiological substrate underlying this development.

Neurophysiologic evaluation of early cognitive development in high-risk infants and toddlers

New knowledge of the perceptual, discriminative, and memory capabilities of very young infants has opened the door to further evaluation of these abilities in infants who have risk factors for cognitive impairments. A neurophysiologic technique that has been very useful in this regard is the recording of event-related potentials (ERPs). The event-related potential (ERP) technique is widely used by cognitive neuroscientists to study cognitive abilities such as discrimination, attention, and memory. This method has many attractive attributes for use in infants and children as it is relatively inexpensive, does not require sedation, has excellent temporal resolution, and can be used to evaluate early cognitive development in preverbal infants with limited behavioral repertories. In healthy infants and children, ERPs have been used to gain a further understanding of early cognitive development and the effect of experience on brain function. Recently, ERPs have been used to elucidate atypical memory development in infants of diabetic mothers, difficulties with perception and discrimination of speech sounds in infants at risk for dyslexia, and multiple areas of cognitive differences in extremely premature infants. Atypical findings seen in high-risk infants have correlated with later cognitive outcomes, but the sensitivity and specificity of the technique has not been studied, and thus evaluation of individual infants is not possible at this time. With further research, this technique may be very useful in identifying children with cognitive deficits during infancy. Because even young infants can be examined with ERPs, this technique is likely to be helpful in the development of focused early intervention programs used to improve cognitive function in high-risk infants and toddlers.

The Pattern of Cerebral Injury in a Primate Model of Preterm Birth and Neonatal Intensive Care

Survivors of very premature birth face an increased risk of adverse motor, cognitive, and behavior sequelae. In order to understand the pathogenesis of these adverse outcomes, an animal model of premature birth and neonatal care in a species with a close similarity to the human infant is sought. In this histological and immunohistochemical study we have defined the pattern of cerebral injury in a premature baboon model undergoing similar neonatal intensive care to that of the human premature infant. Sixteen baboons were delivered at 125 days gestation (dg; term approximately184 dg) with 14 days neonatal intensive care and were compared with gestational control brains at 125, 140, and 160 dg. The premature baboons undergoing neonatal intensive care sustained a spectrum of neuropathologies including white matter injury, hemorrhage, and ventriculomegaly, which resemble lesions frequently observed in the human premature infant. These data suggest that the premature baboon is a model with similarities in maturation and pattern of cerebral injury to the human infant that may provide useful insights of relevance to the human preterm infant.

Non-human primate models of neonatal brain injury

Nonhuman primate species have been selectively used in the scientific investigation of adult and newborn neurological diseases. The rhesus monkey has been utilized in models of term asphyxial insults, accurately reflecting the mechanisms and neuropathology demonstrated in the newborn human infant. More recently, a premature baboon model developed for evaluation of bronchopulmonary dysplasia has been applied to the investigation of cerebral development and injury, revealing high similarity in neuropathology to the premature human infant. Given the differences in the outcomes of neuroprotective therapies between lower order species, such as the rat, and human trials in disorders such as stroke, nonhuman primate models may provide an invaluable resource for safety and efficacy testing before trials in human newborns. This article summarizes both models of brain injury. The histologic findings from the models are compared with neuropathological studies in human infants.

Fetal and neonatal inflammatory response and adverse outcome

This article will define the concept of fetal/neonatal inflammatory response, and examine the complex interaction between inflammation and neurotoxicity. There appear to be important interactions between infection/inflammation and hypoxia-ischaemia leading to cytokine release and subsequent brain injury. This article will also define adverse outcome and summarize the complexities inherent to neurodevelopmental assessment. Finally, this article will investigate the currently available evidence suggesting a link between inflammatory response and adverse neurodevelopmental outcome, and focus on those variables that need further study: timing and nature of the infectious/inflammatory process; established and new anti-insult strategies; morbidity in organs other than the brain; genetic influences; and environmental factors.

Hippocampal gray matter reduction associates with memory deficits in adolescents with history of prematurity

Using optimized voxel-based morphometry (VBM), we compared the relationship between hippocampal and thalamic gray matter loss and memory impairment in 22 adolescents with history of prematurity (HP) and 22 normal controls. We observed significant differences between groups in verbal learning and verbal recognition, but not in visual memory. VBM analysis showed significant left hippocampal and bilateral thalamic reductions in HP subjects. Using stereological methods, we also observed a reduction in hippocampal volume, with left posterior predominance. We found correlations between left hippocampal gray matter reductions (assessed by VBM) and verbal memory (learning and percentage of memory loss) in the premature group. The stereological analysis showed a correlation between verbal learning and the left posterior hippocampus. Our results suggest that left hippocampal tissue loss may be responsible for memory impairment and is probably related to the learning disabilities that HP subjects present during schooling.

Volumetric analysis of regional cerebral development in preterm children

Preterm birth is frequently associated with both neuropathologic and cognitive sequelae. This study examined cortical lobe, subcortical, and lateral ventricle development in association with perinatal variables and cognitive outcome. High-resolution volumetric magnetic resonance imaging scans were acquired and quantified using advanced image processing techniques. Seventy-three preterm and 33 term control children ages 7.3-11.4 years were included in the study. Results indicated disproportionately enlarged parietal and frontal gray matter, occipital horn, and ventricular body, as well as reduced temporal and subcortical gray volumes in preterm children compared with control subjects. Birth weight was negatively correlated with parietal and frontal gray, as well as occipital horn volumes. Intraventricular hemorrhage was associated with reduced subcortical gray matter. Ventricular cerebrospinal fluid was negatively correlated with subcortical gray matter volumes but not with white matter volumes. Maternal education was the strongest predictor of cognitive function in the preterm group. Preterm birth appears to be associated with disorganized cortical development, possibly involving disrupted synaptic pruning and neural migration. Lower birth weight and the presence of intraventricular hemorrhage may increase the risk for neuroanatomic abnormality.