Visual activation in infants and young children studied by functional magnetic resonance imaging

Development of human visual cortical function: A scoping review of task- and naturalistic-fMRI studies through the interactive specialization and maturational frameworks

Overarching theories such as the interactive specialization and maturational frameworks have been proposed to describe human functional brain development. However, these frameworks have not yet been systematically examined across the fMRI literature. Visual processing is one of the most well-studied fields in neuroimaging, and research in this area has recently expanded to include naturalistic paradigms that facilitate study in younger age ranges, allowing for an in-depth critical appraisal of these frameworks across childhood. To this end, we conducted a scoping review of 94 developmental visual fMRI studies, including both traditional experimental task and naturalistic studies, across multiple sub-domains (early visual processing, category-specific higher order processing, naturalistic visual processing). We found that across domains, many studies reported progressive development, but few studies describe regressive or emergent changes necessary to fit the maturational or interactive specialization frameworks. Our findings suggest a need for the expansion of developmental frameworks and clearer reporting of both progressive and regressive changes, along with well-powered, longitudinal studies.

Clinical Usefulness of Simultaneous Electroencephalography and Functional Magnetic Resonance Imaging in Children With Focal Epilepsy

Background and Purpose

The current study analyzed the interictal epileptiform discharge (IED)-related hemodynamic response and aimed to determine the clinical usefulness of simultaneous electroencephalography and functional magnetic resonance imaging (EEG-fMRI) in defining the epileptogenic zone (EZ) in children with focal epilepsy.

Methods

Patients with focal epilepsy showing IEDs on conventional EEG were evaluated using EEG-fMRI. Statistical analyses were performed using the times of spike as events modeled with multiple hemodynamic response functions. The area showing the most significant t-value for blood-oxygen-level-dependent (BOLD) changes was compared with the presumed EZ. Moreover, BOLD responses between -9 and +9 s around the spike times were analyzed to track the hemodynamic response patterns over time.

Results

Half (n=13) of 26 EEG-fMRI investigations of 19 patients were successful. Two patients showed 2 different types of spikes, resulting in 15 analyses. The maximum BOLD response was concordant with the EZ in 11 (73.3%) of the 15 analyses. In 10 (66.7%) analyses, the BOLD response localized the EZs more specifically. Focal BOLD responses in the EZs occurred before IEDs in 11 analyses and were often widespread after IEDs. Hemodynamic response patterns were consistent in the same epilepsy syndrome or when repeating the investigation in the same patients.

Conclusions

EEG-fMRI can provide additional information for localizing the EZ in children with focal epilepsy, and also reveal the pathogenesis of pediatric epilepsy by evaluating the patterns in the hemodynamic response across time windows of IEDs.

Imaging the rapidly developing brain: Current challenges for MRI studies in the first five years of life

Rapid and widespread changes in brain anatomy and physiology in the first five years of life present substantial challenges for developmental structural, functional, and diffusion MRI studies. One persistent challenge is that methods best suited to earlier developmental stages are suboptimal for later stages, which engenders a trade-off between using different, but age-appropriate, methods for different developmental stages or identical methods across stages. Both options have potential benefits, but also biases, as pipelines for each developmental stage can be matched on methods or the age-appropriateness of methods, but not both. This review describes the data acquisition, processing, and analysis challenges that introduce these potential biases and attempts to elucidate decisions and make recommendations that would optimize developmental comparisons.

Neurovascular coupling in the developing neonatal brain at rest

The neonatal brain is an extremely dynamic organization undergoing essential development in terms of connectivity and function. Several functional imaging investigations of the developing brain have found neurovascular coupling (NVC) patterns that contrast with those observed in adults. These discrepancies are partly due to that NVC is still developing in the neonatal brain. To characterize the vascular response to spontaneous neuronal activations, a multiscale multimodal noninvasive approach combining simultaneous electrical, hemodynamic, and metabolic recordings has been developed for preterm infants. Our results demonstrate that the immature vascular network does not adopt a unique strategy to respond to spontaneous cortical activations. NVC takes on different forms in the same preterm infant during the same recording session in response to very similar types of neural activation. This includes (a) positive stereotyped hemodynamic responses (increases in HbO, decreases in HbR together with increases in rCBF and rCMRO2), (b) negative hemodynamic responses (increases in HbR, decreases in HbO together with decreases in rCBF and rCMRO2), and (c) Increases and decreases in both HbO‐HbR and rCMRO2 together with no changes in rCBF. Age‐related NVC maturation is demonstrated in preterm infants, which can contribute to a better understanding/prevention of cerebral hemodynamic risks in these infants.

Cerebral hemodynamic responses in preterm-born neonates to visual stimulation: classification according to subgroups and analysis of frontotemporal-occipital functional connectivity

How neurovascular coupling develops in preterm-born neonates has been largely neglected in scientific research. We measured visually evoked (flicker light) hemodynamic responses (HRs) in preterm-born neonates ( n = 25 , gestational age: 31.71 ± 3.37 weeks, postnatal age: 25.48 ± 23.94 days) at the visual cortex (VC) and left frontotemporal lobe (FTL) using functional near-infrared spectroscopy (fNIRS) neuroimaging. We found that the HR characteristics show a large intersubject variability but could be classified into three groups according to the changes of oxyhemoglobin concentration at the VC [(A) increase, (B) decrease, or (C) inconclusive]. In groups A and B, the HRs at the left FTL were correlated with those at the VC, indicating the presence of a frontotemporal-occipital functional connectivity. Neonates in group A had a higher weight at measurement compared to those in group B, and had the lowest baseline total hemoglobin concentration and hematocrit compared to group C. To the best of our knowledge, this is the first fNIRS study showing (1) that the HRs of preterm-born neonates need to be classified into subgroups, (2) that the subgroups differed in terms of weight at measurement, and (3) that HRs can be observed also at the FTL during visual stimulation. These findings add insights into how neurovascular coupling develops in preterm-born neonates.

Measurement of Neurovascular Coupling in Neonates

Neurovascular coupling refers to the mechanism that links the transient neural activity to the subsequent change in cerebral blood flow, which is regulated by both chemical signals and mechanical effects. Recent studies suggest that neurovascular coupling in neonates and preterm born infants is different compared to adults. The hemodynamic response after a stimulus is later and less pronounced and the stimulus might even result in a negative (hypoxic) signal. In addition, studies both in animals and neonates confirm the presence of a short hypoxic period after a stimulus in preterm infants. In clinical practice, different methodologies exist to study neurovascular coupling. The combination of functional magnetic resonance imaging or functional near-infrared spectroscopy (brain hemodynamics) with EEG (brain function) is most commonly used in neonates. Especially near-infrared spectroscopy is of interest, since it is a non-invasive method that can be integrated easily in clinical care and is able to provide results concerning longer periods of time. Therefore, near-infrared spectroscopy can be used to develop a continuous non-invasive measurement system, that could be used to study neonates in different clinical settings, or neonates with different pathologies. The main challenge for the development of a continuous marker for neurovascular coupling is how the coupling between the signals can be described. In practice, a wide range of signal interaction measures exist. Moreover, biomedical signals often operate on different time scales. In a more general setting, other variables also have to be taken into account, such as oxygen saturation, carbon dioxide and blood pressure in order to describe neurovascular coupling in a concise manner. Recently, new mathematical techniques were developed to give an answer to these questions. This review discusses these recent developments.

Neonatal brain injury and aberrant connectivity

Brain injury sustained during the neonatal period may disrupt development of critical structural and functional connectivity networks leading to subsequent neurodevelopmental impairment in affected children. These networks can be characterized using structural (via diffusion MRI) and functional (via resting state-functional MRI) neuroimaging techniques. Advances in neuroimaging have led to expanded application of these approaches to study term- and prematurely-born infants, providing improved understanding of cerebral development and the deleterious effects of early brain injury. Across both modalities, neuroimaging data are conducive to analyses ranging from characterization of individual white matter tracts and/or resting state networks through advanced 'connectome-style' approaches capable of identifying highly connected network hubs and investigating metrics of network topology such as modularity and small-worldness. We begin this review by summarizing the literature detailing structural and functional connectivity findings in healthy term and preterm infants without brain injury during the postnatal period, including discussion of early connectome development. We then detail common forms of brain injury in term- and prematurely-born infants. In this context, we next review the emerging body of literature detailing studies employing diffusion MRI, resting state-functional MRI and other complementary neuroimaging modalities to characterize structural and functional connectivity development in infants with brain injury. We conclude by reviewing technical challenges associated with neonatal neuroimaging, highlighting those most relevant to studying infants with brain injury and emphasizing the need for further targeted study in this high-risk population.

Rapid Eye Movements in Sleep Furnish a Unique Probe Into Consciousness

The neural correlates of rapid eye movements (REMs) in sleep are extraordinarily robust; including REM-locked multisensory-motor integration and accompanying activation in the retrosplenial cortex, the supplementary eye field and areas encompassing cholinergic basal nucleus (Hong et al., 2009). The phenomenology of REMs speaks to the notion that perceptual experience in both sleep and wakefulness is a constructive process - in which we generate predictions of sensory inputs and then test those predictions through actively sampling the sensorium with eye movements. On this view, REMs during sleep may index an internalized active sampling or 'scanning' of self-generated visual constructs that are released from the constraints of visual input. If this view is correct, it renders REMs an ideal probe to study consciousness as "an exclusively internal affair" (Metzinger, 2009). In other words, REMs offer a probe of active inference - in the sense of predictive coding - when the brain is isolated from the sensorium in virtue of the natural blockade of sensory afferents during REM sleep. Crucially, REMs are temporally precise events that enable powerful inferences based on time series analyses. As a natural, task-free probe, (REMs) could be used in non-compliant subjects, including infants and animals. In short, REMs constitute a promising probe to study the ontogenetic and phylogenetic development of consciousness and perhaps the psychopathology of schizophrenia and autism, which have been considered in terms of aberrant predictive coding.

Investigation of the Pattern of the Hemodynamic Response as Measured by Functional Near-Infrared Spectroscopy (fNIRS) Studies in Newborns, Less Than a Month Old: A Systematic Review

It has been 20 years since functional near-infrared spectroscopy (fNIRS) was first used to investigate the evoked hemodynamic response to a stimulus in newborns. The hemodynamic response to functional activation is well-established in adults, with an observed increase in concentration change of oxygenated hemoglobin (Δ[HbO2]) and decrease in deoxygenated hemoglobin (Δ[HHb]). However, functional studies in newborns have revealed a mixed response, particularly with Δ[HHb] where an inconsistent change in direction is observed. The reason for this heterogeneity is unknown, with potential explanations arising from differing physiology in the developing brain, or differences in instrumentation or methodology. The aim of this review is to collate the findings from studies that have employed fNIRS to monitor cerebral hemodynamics in term newborn infants aged 1 day-1 month. A total of 46 eligible studies were identified; some studies investigated more than one stimulus type, resulting in a total of 51 reported results. The NIRS parameters reported varied across studies with 50/51 cases reporting Δ[HbO2], 39/51 reporting Δ[HHb], and 13/51 reporting total hemoglobin concentration Δ[HbT] (Δ[HbO2] + Δ[HHb]). However, of the 39 cases reporting Δ[HHb] in graphs or tables, only 24 studies explicitly discussed the response (i.e., direction of change) of this variable. In the studies where the fNIRS responses were discussed, 46/51 cases observed an increase in Δ[HbO2], 7/51 observed an increase or varied Δ[HHb], and 2/51 reported a varied or negative Δ[HbT]. An increase in Δ[HbO2] and decrease or no change in Δ[HHb] was observed in 15 studies. By reviewing this body of literature, we have identified that the majority of research articles reported an increase in Δ[HbO2] across various functional tasks and did not report the response of Δ[HHb]. Confirming the normal, healthy hemodynamic response in newborns will allow identification of unhealthy patterns and their association to normal neurodevelopment.

Imaging structural and functional brain development in early childhood

In humans, the period from term birth to ∼2 years of age is characterized by rapid and dynamic brain development and plays an important role in cognitive development and risk of disorders such as autism and schizophrenia. Recent imaging studies have begun to delineate the growth trajectories of brain structure and function in the first years after birth and their relationship to cognition and risk of neuropsychiatric disorders. This Review discusses the development of grey and white matter and structural and functional networks, as well as genetic and environmental influences on early-childhood brain development. We also discuss initial evidence regarding the usefulness of early imaging biomarkers for predicting cognitive outcomes and risk of neuropsychiatric disorders.

Development of the macaque face-patch system

Face recognition is highly proficient in humans and other social primates; it emerges in infancy, but the development of the neural mechanisms supporting this behaviour is largely unknown. We use blood-volume functional MRI to monitor longitudinally the responsiveness to faces, scrambled faces, and objects in macaque inferotemporal cortex (IT) from 1 month to 2 years of age. During this time selective responsiveness to monkey faces emerges. Some functional organization is present at 1 month; face-selective patches emerge over the first year of development, and are remarkably stable once they emerge. Face selectivity is refined by a decreasing responsiveness to non-face stimuli.

Hemoglobin phase of oxygenation and deoxygenation in early brain development measured using fNIRS

A crucial issue in neonatal medicine is the impact of preterm birth on the developmental trajectory of the brain. Although a growing number of studies have shown alterations in the structure and function of the brain in preterm-born infants, we propose a method to detect subtle differences in neurovascular and metabolic functions in neonates and infants. Functional near-infrared spectroscopy (fNIRS) was used to obtain time-averaged phase differences between spontaneous low-frequency (less than 0.1 Hz) oscillatory changes in oxygenated hemoglobin (oxy-Hb) and those in deoxygenated hemoglobin (deoxy-Hb). This phase difference was referred to as hemoglobin phase of oxygenation and deoxygenation (hPod) in the cerebral tissue of sleeping neonates and infants. We examined hPod in term, late preterm, and early preterm infants with no evidence of clinical issues and found that all groups of infants showed developmental changes in the values of hPod from an in-phase to an antiphase pattern. Comparison of hPod among the groups revealed that developmental changes in hPod in early preterm infants precede those in late preterm and term infants at term equivalent age but then, progress at a slower pace. This study suggests that hPod measured using fNIRS is sensitive to the developmental stage of the integration of circular, neurovascular, and metabolic functions in the brains of neonates and infants.

Contribution of Neuroimaging Studies to Understanding Development of Human Cognitive Brain Functions

Humans experience significant physical and mental changes from birth to adulthood, and a variety of perceptual, cognitive and motor functions mature over the course of approximately 20 years following birth. To deeply understand such developmental processes, merely studying behavioral changes is not sufficient; simultaneous investigation of the development of the brain may lead us to a more comprehensive understanding. Recent advances in noninvasive neuroimaging technologies largely contribute to this understanding. Here, it is very important to consider the development of the brain from the perspectives of “structure” and “function” because both structure and function of the human brain mature slowly. In this review, we first discuss the process of structural brain development, i.e., how the structure of the brain, which is crucial when discussing functional brain development, changes with age. Second, we introduce some representative studies and the latest studies related to the functional development of the brain, particularly for visual, facial recognition, and social cognition functions, all of which are important for humans. Finally, we summarize how brain science can contribute to developmental study and discuss the challenges that neuroimaging should address in the future.

Functional and structural connectivity of the visual system in infants with perinatal brain injury

BACKGROUND

Infants with perinatal brain injury are at risk of later visual problems. Advanced neuroimaging techniques show promise to detect functional and structural alterations of the visual system. We hypothesized that infants with perinatal brain injury would have less brain activation during a visual functional magnetic resonance imaging (fMRI) task and reduced task-based functional connectivity and structural connectivity as compared with healthy controls.

METHODS

Ten infants with perinatal brain injury and 20 control infants underwent visual fMRI and diffusion tensor imaging (DTI) during natural sleep with no sedation. Activation maps, functional connectivity maps, and structural connectivity were analyzed and compared between the two groups.

RESULTS

Most infants in both groups had negative activation in the visual cortex during the fMRI task. Infants with brain injury showed reduced activation in the occipital cortex, weaker connectivity between visual areas and other areas of the brain during the visual task, and reduced fractional anisotropy in white matter tracts projecting to visual regions, as compared with control infants.

CONCLUSION

Infants with brain injury sustained in the perinatal period showed evidence of decreased brain activity and functional connectivity during a visual task and altered structural connectivity as compared with healthy term neonates.

Auditory functional magnetic resonance in awake (nonsedated) and propofol-sedated children

BACKGROUND

Functional Magnetic Resonance Imaging (fMRI) is often used in preoperative assessment before epilepsy surgery, tumor or cavernous malformation resection, or cochlear implantation. As it requires complete immobility, sedation is needed for uncooperative patients.

OBJECTIVE

The aim of this study was to compare the fMRI cortical activation pattern after auditory stimuli in propofol-sedated 5- to 8-year-old children with that of similarly aged nonsedated children.

METHODS

When possible, children underwent MRI without sedation, otherwise it was induced with i.v. propofol 2 mg·kg(-1) and maintained with i.v. propofol 4-5 mg·kg(-1) ·h(-1) . Following diagnostic MRI, fMRi was carried out, randomly alternating two passive listening tasks (a fairy-tale and nonsense syllables).

RESULTS

We studied 14 awake and 15 sedated children. During the fairy-tale task, the nonsedated children's blood-oxygen-level-dependent (BOLD) signal was bilaterally present in the posterior superior temporal gyrus (STG), Wernicke's area, and Broca's area. Sedated children showed similar activation, with lesser extension to Wernicke's area, and no activation in Broca's area. During the syllable task, the nonsedated children's BOLD signal was bilaterally observed in the STG and Wernicke's area, in Broca's area with leftward asymmetry, and in the premotor area. In sedated children, cortical activation was present in the STG, but not in the frontal lobes. BOLD signal change areas in sedated children were less extended than in nonsedated children during both the fairy-tale and syllable tasks. Modeling the temporal derivative during both the fairy-tale and syllable tasks, nonsedated children showed no response while sedated children did.

CONCLUSIONS

After auditory stimuli, propofol-sedated 5- to 8-year-old children exhibit an fMRI cortical activation pattern which is different from that in similarly aged nonsedated children.

Hemodynamic signals in fNIRS

Near-infrared spectroscopy (NIRS) was originally designed for clinical monitoring of tissue oxygenation, and it has also been developed into a useful tool in neuroimaging studies, with the so-called functional NIRS (fNIRS). With NIRS, cerebral activation is detected by measuring the cerebral hemoglobin (Hb), where however, the precise correlation between NIRS signal and neural activity remains to be fully understood. This can in part be attributed to the situation that NIRS signals are inherently subject to contamination by signals arising from extracerebral tissue. In recent years, several approaches have been investigated to distinguish between NIRS signals originating in cerebral tissue and signals originating in extracerebral tissue. Selective measurements of cerebral Hb will enable a further evolution of fNIRS. This chapter is divided into six sections: first a summary of the basic theory of NIRS, NIRS signals arising in the activated areas, correlations between NIRS signals and fMRI signals, correlations between NIRS signals and neural activities, and the influence of a variety of extracerebral tissue on NIRS signals and approaches to this issue are reviewed. Finally, future prospects of fNIRS are described.

Neurovascular coupling and energy metabolism in the developing brain

In the adult brain, increases in local neural activity are almost always accompanied by increases in local blood flow. However, many functional imaging studies of the newborn and developing human brain have observed patterns of hemodynamic responses that differ from adult responses. Among the proposed mechanisms for the observed variations is that neurovascular coupling itself is still developing in the perinatal brain. Many of the components thought to be involved in actuating and propagating this hemodynamic response are known to still be developing postnatally, including perivascular cells such as astrocytes and pericytes. Both neural and vascular networks expand and are then selectively pruned over the first year of human life. Additionally, the metabolic demands of the newborn brain are still evolving. These changes are highly likely to affect early postnatal neurovascular coupling, and thus may affect functional imaging signals in this age group. This chapter will discuss the literature relating to neurovascular development. Potential effects of normal and aberrant development of neurovascular coupling on the newborn brain will also be explored, as well as ways to effectively utilize imaging techniques that rely on hemodynamic modulation such as fMRI and NIRS in younger populations.

BOLD Response Selective to Flow-Motion in Very Young Infants

In adults, motion perception is mediated by an extensive network of occipital, parietal, temporal, and insular cortical areas. Little is known about the neural substrate of visual motion in infants, although behavioural studies suggest that motion perception is rudimentary at birth and matures steadily over the first few years. Here, by measuring Blood Oxygenated Level Dependent (BOLD) responses to flow versus random-motion stimuli, we demonstrate that the major cortical areas serving motion processing in adults are operative by 7 wk of age. Resting-state correlations demonstrate adult-like functional connectivity between the motion-selective associative areas, but not between primary cortex and temporo-occipital and posterior-insular cortices. Taken together, the results suggest that the development of motion perception may be limited by slow maturation of the subcortical input and of the cortico-cortical connections. In addition they support the existence of independent input to primary (V1) and temporo-occipital (V5/MT+) cortices very early in life.

Although 7-wk-old infants do not perceive motion with fine sensitivity, this study shows that their brains have a well-established network of associative cortical areas selective to visual flow-motion.

While it is known that the visual brain is immature at birth, there is little firm information about the developmental timeline of the visual system in humans. Despite this, it is commonly assumed that the cortex matures slowly, with primary visual areas developing first, followed by higher associative regions. Here we use fMRI in very young infants to show that this isn’t the case. Adults are highly sensitive to moving objects, and to the spurious flow projected on their retinas while they move in the environment. Flow perception is mediated by an extensive network of areas involving primary and associative visual areas, but also vestibular associative cortices that mediate the perception of body motion (vection). Our data demonstrate that this complex network of higher associative areas is established and well developed by 7 wk of age, including the vestibular associative cortex. Interestingly, the maturation of the primary visual cortex lags behind the higher associative cortex; this suggests the existence of independent cortical inputs to the primary and the associative cortex at this stage of development, explaining why infants do not yet perceive motion with the same sensitivity as adults.

Pediatric applications of functional magnetic resonance imaging

Pediatric functional MRI has been used for the last 2 decades but is now gaining wide acceptance in the preoperative workup of children with brain tumors and medically refractory epilepsy. This review covers pediatrics-specific difficulties such as sedation and task paradigm selection according to the child's age and cognitive level. We also illustrate the increasing uses of functional MRI in the depiction of cognitive function, neuropsychiatric disorders and response to pharmacological agents. Finally, we review the uses of resting-state fMRI in the evaluation of children and in the detection of epileptogenic regions.

Optimizing stimulation and analysis protocols for neonatal fMRI

The development of brain function in young infants is poorly understood. The core challenge is that infants have a limited behavioral repertoire through which brain function can be expressed. Neuroimaging with fMRI has great potential as a way of characterizing typical development, and detecting abnormal development early. But, a number of methodological challenges must first be tackled to improve the robustness and sensitivity of neonatal fMRI. A critical one of these, addressed here, is that the hemodynamic response function (HRF) in pre-term and term neonates differs from that in adults, which has a number of implications for fMRI. We created a realistic model of noise in fMRI data, using resting-state fMRI data from infants and adults, and then conducted simulations to assess the effect of HRF of the power of different stimulation protocols and analysis assumptions (HRF modeling). We found that neonatal fMRI is most powerful if block-durations are kept at the lower range of those typically used in adults (full on/off cycle duration 25-30s). Furthermore, we show that it is important to use the age-appropriate HRF during analysis, as mismatches can lead to reduced power or even inverted signal. Where the appropriate HRF is not known (for example due to potential developmental delay), a flexible basis set performs well, and allows accurate post-hoc estimation of the HRF.

Using fMRI to Investigate Memory in Young Children Born Small for Gestational Age

Objectives

Intrauterine growth restriction (IUGR) can lead to infants being born small for gestational age (SGA). SGA is associated with differences in brain anatomy and impaired cognition. We investigated learning and memory in children born SGA using neuropsychological testing and functional Magnetic Resonance Imaging (fMRI).

Study Design

18 children born appropriate for gestational age (AGA) and 34 SGA born children (18 with and 16 without postnatal catch-up growth) participated in this study. All children were between 4 and 7 years old. Cognitive functioning was assessed by IQ and memory testing (Digit/Word Span and Location Learning). A newly developed fMRI picture encoding task was completed by all children in order to assess brain regions involved in memory processes.

Results

Neuropsychological testing demonstrated that SGA children had IQ’s within the normal range but lower than in AGA and poorer performances across measures of memory. Using fMRI, we observed memory related activity in posterior parahippocampal gyrus as well as the hippocampus proper. Additionally, activation was seen bilaterally in the prefrontal gyrus. Children born SGA showed less activation in the left parahippocampal region compared to AGA.

Conclusions

This is the first fMRI study demonstrating different brain activation patterns in 4-7 year old children born SGA, suggesting that intrauterine growth restriction continues to affect neural functioning in children later-on.

Use of resting-state functional MRI to study brain development and injury in neonates

Advances in methodology have led to expanded application of resting-state functional MRI (rs-fMRI) to the study of term and prematurely born infants during the first years of life, providing fresh insight into the earliest forms of functional cerebral development. In this review, we detail our evolving understanding of the use of rs-fMRI for studying neonates. We initially focus on the biological processes of cortical development related to resting-state network development. We then review technical issues principally affecting neonatal investigations, including the effects of subject motion during acquisition and image distortions related to magnetic susceptibility effects. We next summarize the literature in which rs-fMRI is used to study normal brain development during the early postnatal period, the effects of prematurity, and the effects of cerebral injury. Finally, we review potential future directions for the field, such as the use of complementary imaging modalities and advanced analysis techniques.

Technology-aided assessment of sensorimotor function in early infancy

There is a pressing need for new techniques capable of providing accurate information about sensorimotor function during the first 2 years of childhood. Here, we review current clinical methods and challenges for assessing motor function in early infancy, and discuss the potential benefits of applying technology-assisted methods. We also describe how the use of these tools with neuroimaging, and in particular functional magnetic resonance imaging (fMRI), can shed new light on the intra-cerebral processes underlying neurodevelopmental impairment. This knowledge is of particular relevance in the early infant brain, which has an increased capacity for compensatory neural plasticity. Such tools could bring a wealth of knowledge about the underlying pathophysiological processes of diseases such as cerebral palsy; act as biomarkers to monitor the effects of possible therapeutic interventions; and provide clinicians with much needed early diagnostic information.

Technology-aided assessment of sensorimotor function in early infancy

There is a pressing need for new techniques capable of providing accurate information about sensorimotor function during the first 2 years of childhood. Here, we review current clinical methods and challenges for assessing motor function in early infancy, and discuss the potential benefits of applying technology-assisted methods. We also describe how the use of these tools with neuroimaging, and in particular functional magnetic resonance imaging (fMRI), can shed new light on the intra-cerebral processes underlying neurodevelopmental impairment. This knowledge is of particular relevance in the early infant brain, which has an increased capacity for compensatory neural plasticity. Such tools could bring a wealth of knowledge about the underlying pathophysiological processes of diseases such as cerebral palsy; act as biomarkers to monitor the effects of possible therapeutic interventions; and provide clinicians with much needed early diagnostic information.

A multi-methodological MR resting state network analysis to assess the changes in brain physiology of children with ADHD

The purpose of this work was to highlight the neurological differences between the MR resting state networks of a group of children with ADHD (pre-treatment) and an age-matched healthy group. Results were obtained using different image analysis techniques. A sample of n = 46 children with ages between 6 and 12 years were included in this study (23 per cohort). Resting state image analysis was performed using ReHo, ALFF and ICA techniques. ReHo and ICA represent connectivity analyses calculated with different mathematical approaches. ALFF represents an indirect measurement of brain activity. The ReHo and ICA analyses suggested differences between the two groups, while the ALFF analysis did not. The ReHo and ALFF analyses presented differences with respect to the results previously reported in the literature. ICA analysis showed that the same resting state networks that appear in healthy volunteers of adult age were obtained for both groups. In contrast, these networks were not identical when comparing the healthy and ADHD groups. These differences affected areas for all the networks except the Right Memory Function network. All techniques employed in this study were used to monitor different cerebral regions which participate in the phenomenological characterization of ADHD patients when compared to healthy controls. Results from our three analyses indicated that the cerebellum and mid-frontal lobe bilaterally for ReHo, the executive function regions in ICA, and the precuneus, cuneus and the clacarine fissure for ALFF, were the “hubs” in which the main inter-group differences were found. These results do not just help to explain the physiology underlying the disorder but open the door to future uses of these methodologies to monitor and evaluate patients with ADHD.

Brain development in preterm infants assessed using advanced MRI techniques

Infants who are born preterm have a high incidence of neurocognitive and neurobehavioral abnormalities, which may be associated with impaired brain development. Advanced magnetic resonance imaging (MRI) approaches, such as diffusion MRI (d-MRI) and functional MRI (fMRI), provide objective and reproducible measures of brain development. Indices derived from d-MRI can be used to provide quantitative measures of preterm brain injury. Although fMRI of the neonatal brain is currently a research tool, future studies combining d-MRI and fMRI have the potential to assess the structural and functional properties of the developing brain and its response to injury.

Imaging of an inflammatory injury in the newborn rat brain with photoacoustic tomography

Background

The precise assessment of cerebral saturation changes during an inflammatory injury in the developing brain, such as seen in periventricular leukomalacia, is not well defined. This study investigated the impact of inflammation on locoregional cerebral oxygen saturation in a newborn rodent model using photoacoustic imaging.

Methods

1 mg/kg of lipopolysaccharide(LPS) diluted in saline or saline alone was injected under ultrasound guidance directly in the corpus callosum of P3 rat pups. Coronal photoacoustic images were carried out 24 h after LPS exposure. Locoregional oxygen saturation (SO₂) and resting state connectivity were assessed in the cortex and the corpus callosum. Microvasculature was then evaluated on cryosection slices by lectin histochemistry.

Results

Significant reduction of SO₂ was found in the corpus callosum; reduced SO₂ was also found in the cortex ipsilateral to the injection site. Seed-based functional connectivity analysis showed that bilateral connectivity was not affected by LPS exposure. Changes in locoregional oxygen saturation were accompanied by a significant reduction in the average length of microvessels in the left cortex but no differences were observed in the corpus callosum.

Conclusion

Inflammation in the developing brain induces marked reduction of locoregional oxygen saturation, predominantly in the white matter not explained by microvascular degeneration. The ability to examine regional saturation offers a new way to monitor injury and understand physiological disturbance non-invasively.

Inferences about infants’ visual brain mechanisms

We discuss hypotheses that link the measurements we can make with infants to inferences about their developing neural mechanisms. First, we examine evidence from the sensitivity to visual stimulus properties seen in infants’ responses, using both electrophysiological measures (transient and steady-state recordings of visual evoked potentials/visual event-related potentials) and behavioral measures and compare this with the sensitivity of brain processes, known from data on mammalian neurophysiology and human neuroimaging. The evidence for multiple behavioral systems with different patterns of visual sensitivity is discussed. Second, we consider the analogies which can be made between infants’ behavior and that of adults with identified brain damage, and extend these links to hypothesize about the brain basis of visual deficits in infants and children with developmental disorders. Last, we consider how these lines of data might allow us to form “inverse linking hypotheses” about infants’ visual experience.

Simultaneous EEG and fMRI recordings (EEG-fMRI) in children with epilepsy

By combining electroencephalography (EEG) with functional magnetic resonance imaging (fMRI) it is possible to describe blood oxygenation level-dependent (BOLD) signal changes related to EEG patterns. This way, EEG-pattern-associated networks of hemodynamic changes can be detected anywhere in the brain with good spatial resolution. This review summarizes EEG-fMRI studies that have been performed in children with epilepsy. EEG-fMRI studies in focal epilepsy (structural and nonlesional cases, benign epilepsy with centrotemporal spikes), generalized epilepsy (especially absence epilepsy), and epileptic encephalopathies (West syndrome, Lennox-Gastaut syndrome, continuous spike and waves during slow sleep, and Dravet syndrome) are presented. Although EEG-fMRI was applied mainly to localize the region presumably generating focal interictal discharges in focal epilepsies, EEG-fMRI identified underlying networks in patients with generalized epilepsies and thereby contributed to a better understanding of these epilepsies. In epileptic encephalopathies a specific fingerprint of hemodynamic changes associated with the particular syndrome was detected. The value of the EEG-fMRI technique for diagnosis and investigation of pathogenetic mechanisms of different forms of epilepsy is discussed.

Functional magnetic resonance imaging of the visual cortex performed in children under sedation to assist in presurgical planning

OBJECT

Advances in brain imaging have allowed for more sophisticated mapping of crucial neural structures. Functional MRI (fMRI) measures local changes in blood oxygenation associated with changes in neural activity and is useful in mapping cortical activation. Applications of this imaging modality have generally been restricted to cooperative patients; however, fMRI has proven successful in localizing the motor cortex for neurosurgical planning in uncooperative children under sedation. The authors demonstrate that the use of fMRI to localize the visual cortex in sedated children can be safely and effectively performed, allowing for more accurate presurgical planning to spare visual structures.

METHODS

Between 2007 and 2009, 11 children (age range 1-11 years) underwent fMRI for neurosurgical planning while under sedation. Blood oxygen level-dependent fMRI was performed to detect visual cortex activation during stimulation through closed eyelids. Visual stimulation was presented in block design with periods of flashing light alternated with darkness.

RESULTS

Functional MRI was successful in identifying visual cortex in each of the 11 children tested. There were no complications with propofol sedation or the fMRI. All children suffered from epilepsy, 5 had brain tumors, and 1 had tuberous sclerosis. After fMRI was performed, 6 patients underwent surgery. Frameless stereotactic guidance was synchronized with fMRI data to design an approach to spare visual structures during resection. There were no cases where a false negative led to unexpected visual field deficits or other side effects of surgery. In 2 cases, the fMRI results demonstrated that the tracts were already disrupted: in one case from a prior tumor operation and in another from dysplasia.

CONCLUSIONS

Functional MRI for evaluation of visual pathways can be safely and reproducibly performed in young or uncooperative children under light sedation. Identification of primary visual cortex aids in presurgical planning to avoid vision loss in appropriately selected patients.

Resolving the transition from negative to positive blood oxygen level-dependent responses in the developing brain

The adult brain exhibits a local increase in cortical blood flow in response to external stimulus. However, broadly varying hemodynamic responses in the brains of newborn and young infants have been reported. Particular controversy exists over whether the "true" neonatal response to stimulation consists of a decrease or an increase in local deoxyhemoglobin, corresponding to a positive (adult-like) or negative blood oxygen level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI), respectively. A major difficulty with previous studies has been the variability in human subjects and measurement paradigms. Here, we present a systematic study in neonatal rats that charts the evolution of the cortical blood flow response during postnatal development using exposed-cortex multispectral optical imaging. We demonstrate that postnatal-day-12-13 rats (equivalent to human newborns) exhibit an "inverted" hemodynamic response (increasing deoxyhemoglobin, negative BOLD) with early signs of oxygen consumption followed by delayed, active constriction of pial arteries. We observed that the hemodynamic response then matures via development of an initial hyperemic (positive BOLD) phase that eventually masks oxygen consumption and balances vasoconstriction toward adulthood. We also observed that neonatal responses are particularly susceptible to stimulus-evoked systemic blood pressure increases, leading to cortical hyperemia that resembles adult positive BOLD responses. We propose that this confound may account for much of the variability in prior studies of neonatal cortical hemodynamics. Our results suggest that functional magnetic resonance imaging studies of infant and child development may be profoundly influenced by the maturing neurovascular and autoregulatory systems of the neonatal brain.

Functional activation of the infant cortex during object processing

A great deal is known about the functional organization of the neural structures that mediate visual object processing in the adult observer. These findings have contributed significantly to our conceptual models of object recognition and identification and provided unique insight into the nature of object representations extracted from visual input. In contrast, little is known about the neural basis of object processing in the infant. The current research used near-infrared spectroscopy (NIRS) as a neuroimaging tool to investigate functional activation of the infant cortex during an object processing task that has been used extensively with infants. The neuroimaging data revealed that the infant cortex is functionally specialized for object processing (i.e., individuation-by-feature) early in the first year but that patterns of activation also change between 3 and 12 months. These changes may reflect functional reorganization of the immature cortex or age-related differences in the cognitive processes engaged during the task.

Mapping fetal brain development in utero using magnetic resonance imaging: the Big Bang of brain mapping

The development of tools to construct and investigate probabilistic maps of the adult human brain from magnetic resonance imaging (MRI) has led to advances in both basic neuroscience and clinical diagnosis. These tools are increasingly being applied to brain development in adolescence and childhood, and even to neonatal and premature neonatal imaging. Even earlier in development, parallel advances in clinical fetal MRI have led to its growing use as a tool in challenging medical conditions. This has motivated new engineering developments encompassing optimal fast MRI scans and techniques derived from computer vision, the combination of which allows full 3D imaging of the moving fetal brain in utero without sedation. These promise to provide a new and unprecedented window into early human brain growth. This article reviews the developments that have led us to this point, examines the current state of the art in the fields of fast fetal imaging and motion correction, and describes the tools to analyze dynamically changing fetal brain structure. New methods to deal with developmental tissue segmentation and the construction of spatiotemporal atlases are examined, together with techniques to map fetal brain growth patterns.

Functional connectivity MRI in infants: exploration of the functional organization of the developing brain

Advanced neuroimaging techniques have been increasingly applied to the study of preterm and term infants in an effort to further define the functional cerebral architecture of the developing brain. Despite improved understanding of the complex relationship between structure and function obtained through these investigations, significant questions remain regarding the nature, location, and timing of the maturational changes which occur during early development. Functional connectivity magnetic resonance imaging (fcMRI) utilizes spontaneous, low frequency (< 0.1 Hz), coherent fluctuations in blood oxygen level dependent (BOLD) signal to identify networks of functional cerebral connections. Due to the intrinsic characteristics of its image acquisition and analysis, fcMRI offers a novel neuroimaging approach well suited to investigation of infants. Recently, this methodology has been successfully applied to examine neonatal populations, defining normative patterns of large-scale neural network development in the maturing brain. The resting-state networks (RSNs) identified in these studies reflect the evolving cerebral structural architecture, presumably driven by varied genetic and environmental influences. Principal features of these investigations and their role in characterization of the tenets of neural network development during this critical developmental period are highlighted in this review. Despite these successes, optimal methods for fcMRI data acquisition and analysis for this population have not yet been defined. Further, appropriate schemes for interpretation and translation of fcMRI results remain unknown, a matter of increasing importance as functional neuroimaging findings are progressively applied in the clinical arena. Notwithstanding these concerns, fcMRI provides insight into the earliest forms of cerebral connectivity and therefore holds great promise for future neurodevelopmental investigations.

The physiology of developmental changes in BOLD functional imaging signals

BOLD fMRI (blood oxygenation level dependent functional magnetic resonance imaging) is increasingly used to detect developmental changes of human brain function that are hypothesized to underlie the maturation of cognitive processes. BOLD signals depend on neuronal activity increasing cerebral blood flow, and are reduced by neural oxygen consumption. Thus, developmental changes of BOLD signals may not reflect altered information processing if there are concomitant changes in neurovascular coupling (the mechanism by which neuronal activity increases blood flow) or neural energy use (and hence oxygen consumption). We review how BOLD signals are generated, and explain the signalling pathways which convert neuronal activity into increased blood flow. We then summarize in broad terms the developmental changes that the brain's neural circuitry undergoes during growth from childhood through adolescence to adulthood, and present the changes in neurovascular coupling mechanisms and energy use which occur over the same period. This information provides a framework for assessing whether the BOLD changes observed during human development reflect altered cognitive processing or changes in neurovascular coupling and energy use.

Functional neuroimaging to characterize visual system development in children with retinoblastoma

PURPOSE

To use functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) to investigate visual system development in children being treated for retinoblastoma.

METHODS

Informed consent was obtained for all participants (N = 42) in this institutional review board-approved study. Participants were imaged with a 1.5-T scanner while under propofol sedation. Diagnostic brain and orbital imaging was followed by investigational functional neuroimaging, which included fMRI during photic stimulation through closed eyelids, to measure functional activation in the visual cortex, and DTI, to evaluate diffusion parameters of white matter tracts in the corpus callosum and the periventricular optic radiations. Analysis included 115 examinations of 39 patients with a median age of 16.4 months and age range from 1.5 to 101.5 months at first evaluation.

RESULTS

The blood oxygen level-dependent signal was predominantly negative and located in the anterior visual cortex. Activation was affected by tumor lateralization (unilateral or bilateral), macular involvement, and retinal detachment. Patients who had undergone unilateral enucleation showed cortical dominance corresponding to the projection from the nasal hemiretina in the unaffected eye. Diffusion parameters followed a normal developmental trajectory in the optic radiations and corpus callosum, but variability was greater in the splenium than in the genu of the corpus callosum.

CONCLUSIONS

Longitudinal functional neuroimaging demonstrated important effects of disease and treatment. Therefore, fMRI and DTI may be useful for characterizing the impact of retinoblastoma on the developing visual system and improving the prediction of visual outcome in survivors.

Development of human visual function

By 1985 newly devised behavioral and electrophysiological techniques had been used to track development of infants' acuity, contrast sensitivity and binocularity, and for clinical evaluation of developing visual function. This review focus on advances in the development and assessment of infant vision in the following 25 years. Infants' visual cortical function has been studied through selectivity for orientation, directional motion and binocular disparity, and the control of subcortical oculomotor mechanisms in fixation shifts and optokinetic nystagmus, leading to a model of increasing cortical dominance over subcortical pathways. Neonatal face processing remains a challenge for this model. Recent research has focused on development of integrative processing (hyperacuity, texture segmentation, and sensitivity to global form and motion coherence) in extra-striate visual areas, including signatures of dorsal and ventral stream processing. Asynchronies in development of these two streams may be related to their differential vulnerability in both acquired and genetic disorders. New methods and approaches to clinical disorders are reviewed, in particular the increasing focus on paediatric neurology as well as ophthalmology. Visual measures in early infancy in high-risk children are allowing measures not only of existing deficits in infancy but prediction of later visual and cognitive outcome. Work with early cataract and later recovery from blinding disorders has thrown new light on the plasticity of the visual system and its limitations. The review concludes with a forward look to future opportunities provided by studies of development post infancy, new imaging and eye tracking methods, and sampling infants' visual ecology.

Neuroimaging of cortical development and brain connectivity in human newborns and animal models

Significant human brain growth occurs during the third trimester, with a doubling of whole brain volume and a fourfold increase of cortical gray matter volume. This is also the time period during which cortical folding and gyrification take place. Conditions such as intrauterine growth restriction, prematurity and cerebral white matter injury have been shown to affect brain growth including specific structures such as the hippocampus, with subsequent potentially permanent functional consequences. The use of 3D magnetic resonance imaging (MRI) and dedicated postprocessing tools to measure brain tissue volumes (cerebral cortical gray matter, white matter), surface and sulcation index can elucidate phenotypes associated with early behavior development. The use of diffusion tensor imaging can further help in assessing microstructural changes within the cerebral white matter and the establishment of brain connectivity. Finally, the use of functional MRI and resting-state functional MRI connectivity allows exploration of the impact of adverse conditions on functional brain connectivity in vivo. Results from studies using these methods have for the first time illustrated the structural impact of antenatal conditions and neonatal intensive care on the functional brain deficits observed after premature birth. In order to study the pathophysiology of these adverse conditions, MRI has also been used in conjunction with histology in animal models of injury in the immature brain. Understanding the histological substrate of brain injury seen on MRI provides new insights into the immature brain, mechanisms of injury and their imaging phenotype.

Neonatal hemodynamic response to visual cortex activity: high-density near-infrared spectroscopy study

The neurodevelopmental outcome of neonatal intensive care unit (NICU) infants is a major clinical concern with many infants displaying neurobehavioral deficits in childhood. Functional neuroimaging may provide early recognition of neural deficits in high-risk infants. Near-infrared spectroscopy (NIRS) has the advantage of providing functional neuroimaging in infants at the bedside. However, limitations in traditional NIRS have included contamination from superficial vascular dynamics in the scalp. Furthermore, controversy exists over the nature of normal vascular, responses in infants. To address these issues, we extend the use of novel high-density NIRS arrays with multiple source-detector distances and a superficial signal regression technique to infants. Evaluations of healthy term-born infants within the first three days of life are performed without sedation using a visual stimulus. We find that the regression technique significantly improves brain activation signal quality. Furthermore, in six out of eight infants, both oxy- and total hemoglobin increases while deoxyhemoglobin decreases, suggesting that, at term, the neurovascular coupling in the visual cortex is similar to that found in healthy adults. These results demonstrate the feasibility of using high-density NIRS arrays in infants to improve signal quality through superficial signal regression, and provide a foundation for further development of high-density NIRS as a clinical tool.

The role of functional magnetic resonance imaging in the study of brain development, injury, and recovery in the newborn

Development of brain functions and the structural-functional correlates of brain injury remain difficult to evaluate in the young infant. Thus, new noninvasive methods capable of early functional diagnosis are needed. This review describes the use of functional magnetic resonance imaging (fMRI) for studying localization of brain function in the developing brain when standard clinical investigations are not available or conclusive. This promising neuroimaging technique has been successfully used in healthy newborns and in newborns with brain injury using different paradigms, including passive visual, somato-sensorial, and auditory stimulation. We summarize the major findings of previous fMRI studies in young infants, describe ongoing methodological challenges, and propose exciting future developments in using resting-state protocols and functional connectivity techniques to assist in evaluating early life brain function and its recovery from injury.

Long-term outcome of preterm infants and the role of neuroimaging

Preterm birth has been defined as one of the major public health problems of this decade, preterm neonates being at high risk for neurodevelopmental disabilities. As preterm survival rates increase, the next great imperative for perinatal medicine is to understand and prevent the serious adverse neurodevelopmental outcomes of preterm birth. The challenge for neonatologists and neurologists alike is identifying early markers of outcome in the prematurely born. This article reviews current trends in prevalence, mortality, and morbidity, and the present status of outcome data for cognitive and neurosensory neurodevelopmental dysfunctions in preterm infants. New neuroimaging modalities and analysis tools are contributing to the understanding of neurologic sequelae of preterm birth by providing microstructural evidence of injury sustained by the preterm brain.

Somatosensory cortical activation identified by functional MRI in preterm and term infants

Functional MRI (fMRI) has not previously been used systematically to investigate brain function in preterm infants. We here describe statistically robust and reproducible fMRI results in this challenging subject group using a programmable somatosensory stimulus synchronized with MR image acquisition which induced well-localized positive blood oxygen level dependent (BOLD) responses contralateral to the side of the stimulation in: 11 preterm infants (median post menstrual age 33 weeks and 4 days, range 29+1 to 35+3); 6 control infants born at term gestational age; and 18 infants born preterm (median gestational age at birth 30 weeks and 5 days, range 25+4 to 36+0) but studied at term corrected gestational age. Bilateral signals were identified in 8 of the ex-preterm infants at term age. Anatomical confirmation of appropriate activations was provided with diffusion tensor imaging (DTI) based tractography which identified connecting pathways from the regions of activation through the ipsilateral corticospinal tracts and posterior limb of the internal capsule. These results demonstrate that it is possible to reliably identify positive BOLD signals in the infant brain and that fMRI techniques can also be applied in the study of preterm infants.

Resting-state functional connectivity in the human brain revealed with diffuse optical tomography

Mapping resting-state networks allows insight into the brain's functional architecture and physiology and has rapidly become important in contemporary neuroscience research. Diffuse optical tomography (DOT) is an emerging functional neuroimaging technique with the advantages, relative to functional magnetic resonance imaging (fMRI), of portability and the ability to simultaneously measure both oxy- and deoxyhemoglobin. Previous optical studies have evaluated the temporal features of spontaneous resting brain signals. Herein, we develop techniques for spatially mapping functional connectivity with DOT (fc-DOT). Simultaneous imaging over the motor and visual cortices yielded robust correlation maps reproducing the expected functional neural architecture. The localization of the maps was confirmed with task-response studies and with subject-matched fc-MRI. These fc-DOT methods provide a task-less approach to mapping brain function in populations that were previously difficult to research. Our advances may permit new studies of early childhood development and of unconscious patients. In addition, the comprehensive hemoglobin contrasts of fc-DOT enable innovative studies of the biophysical origin of the functional connectivity signal.

Functional magnetic resonance imaging of the sensorimotor system in preterm infants

OBJECTIVE

Preterm birth at <32 weeks' gestational age has a specific predilection for periventricular white matter injury. Early prediction of concomitant motor sequelae is a fundamental clinical issue. Recently, functional MRI was introduced as a noninvasive method for investigating the functional integrity of the neonatal brain. We aimed at implementing a unilateral passive forearm extension/flexion functional MRI paradigm in a routine clinical MRI setup to allow noninvasive mapping of the sensorimotor system in preterm infants and to relate the functional data to structural and behavioral data.

PATIENTS AND METHODS

Eight patients (median gestational age: 26.5 weeks; median birth weight: 885 g) were included. The functional MRI was performed at term-equivalent age (median: 39 weeks' postconceptional age) under chloral hydrate (50 mg/kg) sedation. In 5 of 8 patients, functional MRI data acquisition was successful. This resulted in 10 functional data sets (5 for passive stimulation of each forearm).

RESULTS

Unilateral stimulation was associated with mainly bilateral activation of the primary sensorimotor cortex (n = 7 of 10 data sets), the prevailing hemodynamic response being a negative blood oxygenation level-dependent signal. Positive blood oxygenation level-dependent response or failure to activate the sensorimotor cortex (n = 3 of 10 data sets) were seen in those patients with aberrant structural/behavioral indices.

CONCLUSIONS

Our data show the feasibility of passive unilateral sensorimotor stimulation during neonatal clinical MRI protocols. The bilateral activation pattern observed at this age is compatible with a bilaterally distributed sensorimotor system. Our data validate initial accounts for a raised incidence of negative blood oxygenation level-dependent responses in the primary sensorimotor cortex at this developmental stage. The negative blood oxygenation level-dependent response is likely to reflect a reduction of the oxy/deoxy-hemoglobin ratio during a maturational stage characterized by rapid formation of synapses, yet ineffective processing. Positive blood oxygenation level-dependent responses or failure to activate the sensorimotor cortex may be an early indicator of abnormal development and will have to be followed up carefully.

Cerebrovascular injury in premature infants: current understanding and challenges for future prevention

Cerebrovascular insults are a leading cause of brain injury in premature infants, contributing to the high prevalence of motor, cognitive, and behavioral deficits. Understanding the complex pathways linking circulatory immaturity to brain injury in premature infants remains incomplete. These mechanisms are significantly different from those causing injury in the mature brain. The gaps in knowledge of normal and disturbed cerebral vasoregulation need to be addressed. This article reviews current understanding of cerebral perfusion, in the sick premature infant in particular, and discusses challenges that lie ahead.