Sensitive periods in the development of the brain and behavior

NR2B subunit-dependent long-term potentiation enhancement in the rat cortical auditory system in vivo following masking of patterned auditory input by white noise exposure during early postnatal life

The composition of N-methyl-D-aspartate (NMDA) receptor subunits influences the degree of synaptic plasticity expressed during development and into adulthood. Here, we show that theta-burst stimulation of the medial geniculate nucleus reliably induced NMDA receptor-dependent long-term potentiation (LTP) of field postsynaptic potentials recorded in the primary auditory cortex (A1) of urethane-anesthetized rats. Furthermore, substantially greater levels of LTP were elicited in juvenile animals (30-37 days old; approximately 55% maximal potentiation) than in adult animals (approximately 30% potentiation). Masking patterned sound via continuous white noise exposure during early postnatal life (from postnatal day 5 to postnatal day 50-60) resulted in enhanced, juvenile-like levels of LTP (approximately 70% maximal potentiation) relative to age-matched controls reared in unaltered acoustic environments (approximately 30%). Rats reared in white noise and then placed in unaltered acoustic environments for 40-50 days showed levels of LTP comparable to those of adult controls, indicating that white noise rearing results in a form of developmental arrest that can be overcome by subsequent patterned sound exposure. We explored the mechanisms mediating white noise-induced plasticity enhancements by local NR2B subunit antagonist application in A1. NR2B subunit antagonists (Ro 25-6981 or ifenprodil) completely reversed white noise-induced LTP enhancement at concentrations that did not affect LTP in adult or age-matched controls. We conclude that white noise exposure during early postnatal life results in the maintenance of juvenile-like, higher levels of plasticity in A1, an effect that appears to be critically dependent on NR2B subunit activation.

Two functions of early language experience

The unique human ability of linguistic communication, defined as the ability to produce a practically infinite number of meaningful messages using a finite number of lexical items, is determined by an array of "linguistic" genes, which are expressed in neurons forming domain-specific linguistic centers in the brain. In this review, I discuss the idea that infants' early language experience performs two complementary functions. In addition to allowing infants to assimilate the words and grammar rules of their mother language, early language experience initiates genetic programs underlying language production and comprehension. This hypothesis explains many puzzling characteristics of language acquisition, such as the existence of a critical period for acquiring the first language and the absence of a critical period for the acquisition of additional language(s), a similar timetable for language acquisition in children belonging to families of different social and cultural status, the strikingly similar timetables in the acquisition of oral and sign languages, and the surprisingly small correlation between individuals' final linguistic competence and the intensity of their training. Based on the studies of microcephalic individuals, I argue that genetic factors determine not only the number of neurons and organization of interneural connections within linguistic centers, but also the putative internal properties of neurons that are not limited to their electrophysiological and synaptic properties.

Brain maturation in adolescence and young adulthood: regional age-related changes in cortical thickness and white matter volume and microstructure

The development of cortical gray matter, white matter (WM) volume, and WM microstructure in adolescence is beginning to be fairly well characterized by structural magnetic resonance imaging (sMRI) and diffusion tensor imaging (DTI) studies. However, these aspects of brain development have rarely been investigated concurrently in the same sample and hence the relations between them are not understood. We delineated the age-related changes in cortical thickness, regional WM volume, and diffusion characteristics and investigated the relationships between these properties of brain development. One hundred and sixty-eight healthy participants aged 8-30 years underwent sMRI and DTI. The results showed regional age-related cortical thinning, WM volume increases, and changes in diffusion parameters. Cortical thickness was the most strongly age-related parameter. All classes of measures showed unique associations with age. The results indicate that cortical thinning in adolescence cannot be explained by WM maturation in underlying regions as measured by volumetry or DTI. Moderate associations between cortical thickness and both volume and diffusion parameters in underlying WM regions were also found, although the relationships were not strong. It is concluded that none of the measures are redundant and that the integration of the 3 will yield a more complete understanding of brain maturation.

Effects of prenatal androgens on rhesus monkeys: a model system to explore the organizational hypothesis in primates

After proposing the organizational hypothesis from research in prenatally androgenized guinea pigs (Phoenix, C.H., Goy, R.W., Gerall, A.A., Young, W.C., 1959. Organizational action of prenatally administered testosterone propionate on the tissues mediating mating behavior in the female guinea pig. Endocrinology 65, 369-382.), the same authors almost immediately extended the hypothesis to a nonhuman primate model, the rhesus monkey. Studies over the last 50 years have verified that prenatal androgens have permanent effects in rhesus monkeys on the neural circuits that underlie sexually dimorphic behaviors. These behaviors include both sexual and social behaviors, all of which are also influenced by social experience. Many juvenile behaviors such as play, mounting, and vocal behaviors are masculinized and/or defeminized, and aspects of adult sexual behavior are both masculinized (e.g. approaches, sex contacts, and mounts) and defeminized (e.g. sexual solicits). Different behavioral endpoints have different periods of maximal susceptibility to the organizing actions of prenatal androgens. Aromatization is not important, as both testosterone and dihydrotestosterone are equally effective in rhesus monkeys. Although the full story of the effects of prenatal androgens on sexual and social behaviors in the rhesus monkey has not yet completely unfolded, much progress has been made. Amazingly, a large number of the inferences drawn from the original 1959 study have proved applicable to this nonhuman primate model.

Back to the future: The organizational-activational hypothesis adapted to puberty and adolescence

Phoenix, Goy, Gerall, and Young first proposed in 1959 the organizational-activational hypothesis of hormone-driven sex differences in brain and behavior. The original hypothesis posited that exposure to steroid hormones early in development masculinizes and defeminizes neural circuits, programming behavioral responses to hormones in adulthood. This hypothesis has inspired a multitude of experiments demonstrating that the perinatal period is a time of maximal sensitivity to gonadal steroid hormones. However, recent work from our laboratory and others demonstrates that steroid-dependent organization of behavior also occurs during adolescence, prompting a reassessment of the developmental time-frame within which organizational effects are possible. In addition, we present evidence that adolescence is part of a single protracted postnatal sensitive period for steroid-dependent organization of male mating behavior that begins perinatally and ends in late adolescence. These findings are consistent with the original formulation of the organizational/activational hypothesis, but extend our notions of what constitutes "early" development considerably. Finally, we present evidence that female behaviors also undergo steroid-dependent organization during adolescence, and that social experience modulates steroid-dependent adolescent brain and behavioral development. The implications for human adolescent development are also discussed, especially with respect to how animal models can help to elucidate the factors underlying the association between pubertal timing and adult psychopathology in humans.

Developmental contributions to motor sequence learning

Little is known about how children acquire new motor sequences. In particular, it is not clear if the same learning progression observed in adults is also present in childhood nor whether motor skills are acquired in a similar fashion across development. In the present study we used the multi-finger sequencing task (MFST), a variant of the serial reaction time (SRT) task, to study motor sequence learning, across two consecutive days, in three cross-sectional samples of children aged 6, 8, and 10 years, and a control sample of adults. In the MFST, participants reproduced 10-element sequences of key presses on an electronic keyboard, using four fingers of the right hand. Each block of practice included 10 intermixed trials of a Repeated (REP) sequence and four trials of Random (RAN) sequences. Performance was assessed by examining changes in accuracy, a component of the task that requires the association of the visual stimulus with the motor response, and response synchronization, a component that requires fine-grained sensorimotor integration and timing. Additionally, participants completed Recognition and Recall tests, to assess explicit knowledge of the repeated sequence. Overall, results showed a developmental progression in motor sequence learning within and across days of practice. Interestingly, the two behavioral measures showed different developmental trajectories. For accuracy, differences were greatest for the two youngest groups early in learning, and these groups also showed the greatest rate of improvement. However, by the end of Day 2, only the 6-year-olds still lagged behind all other groups. For response synchronization, all child groups differed from adults early in learning, but both child and adult groups showed similar rates of improvement across blocks of practice. By the end of Day 2, 10-year-olds reached adult levels of performance, whereas 6- and 8-year-olds did not. Taken together, the dissociation observed with our two behavioral measures of sequence learning is consistent with the hypothesis that accuracy or finger-stimulus association may rely on cortical pathways that show the greatest maturation between ages 6 and 10; whereas motor timing and sensorimotor integration may rely on subcortical pathways that continue to develop into young adulthood. Despite developmental differences across blocks of practice on both behavioral measures, there were no significant group differences for either the Recognition or Recall tests. We suggest that explicit knowledge of the MFST is not directly linked to task performance, thus challenging the implicit-explicit distinction in pediatric SRT studies assessing the developmental invariance model.

The genetic and neurobiologic compass points toward common signaling dysfunctions in autism spectrum disorders

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder with high heritability. Here, we discuss data supporting the view that there are at least two distinct genetic etiologies for ASD: rare, private (de novo) single gene mutations that may have a large effect in causing ASD; and inherited, common functional variants of a combination of genes, each having a small to moderate effect in increasing ASD risk. It also is possible that a combination of the two mechanisms may occur in some individuals with ASD. We further discuss evidence from individuals with a number of different neurodevelopmental syndromes, in which there is a high prevalence of ASD, that some private mutations and common variants converge on dysfunctional ERK and PI3K signaling, which negatively impacts neurodevelopmental events regulated by some receptor tyrosine kinases.

Honeybees can learn the relationship between the solar ephemeris and a newly-experienced landscape

Many species learn the sun's daily pattern of azimuthal movement (the solar ephemeris function) for use in sun-compass orientation. In honeybees, this learning is accomplished with much innate guidance and yields stubborn, imprinting-like retention of certain aspects of the stored information. One such case involves the failure of transplanted bees to update their memories of the relationship between the solar ephemeris and a new landscape, even after many days' experience at the new site. In the present study, I ask whether the bees in previous transplantation experiments failed to update their memories of the relationship between the sun and landscape because the source and recipient landscapes were (rotated) panoramic twins of each other, each dominated by a conspicuous treeline. To test this hypothesis, I transplanted bees from their natal site at the bottom of a valley to a panoramically different, treelined site and later tested the bees' knowledge of the sun's course in relation to the treeline. The test involved observing the bees' communicative dances under overcast skies at a second treeline that was a mirror image of the first. The cloudy-day dances show that the bees had indeed learned the relationship between sun's pattern of movement and the (panoramically novel) treelined site, indicating that the bees' memory of the relationship between the ephemeris function and the landscape is not incapable of revision as the earlier results had suggested. I discuss these results in the context of a brief summary of our current understanding of solar ephemeris learning in bees.

A critical review of the empirical literature on the relation between anxiety and puberty

The current paper critically reviews the empirical literature focused on the association between puberty and anxiety. A detailed review of more than 45 empirical articles is provided. There is some evidence that among girls, but not boys, a more advanced pubertal status (controlling for age) is associated with higher reported anxiety symptoms. Also among girls, earlier pubertal timing is linked to higher anxiety scores. It is unclear whether early puberty may lead to increased anxiety or if high anxiety influences pubertal timing. With respect to hormones, there were relatively few significant associations for girls, although this literature is very small. Among boys, several studies reported positive associations between both gonadal and adrenal hormones and anxiety. The direction of effect for these finding is also unstudied. The primary limitation of the hormone-anxiety literature pertains to the absence of pubertal measures in samples of youth in which hormones are measured. The paper concludes with a comprehensive examination of the methodological strengths and weaknesses of the literature and recommendations for future work.

A parallel and distributed-processing model of joint attention, social cognition and autism

The impaired development of joint attention is a cardinal feature of autism. Therefore, understanding the nature of joint attention is central to research on this disorder. Joint attention may be best defined in terms of an information-processing system that begins to develop by 4-6 months of age. This system integrates the parallel processing of internal information about one's own visual attention with external information about the visual attention of other people. This type of joint encoding of information about self and other attention requires the activation of a distributed anterior and posterior cortical attention network. Genetic regulation, in conjunction with self-organizing behavioral activity, guides the development of functional connectivity in this network. With practice in infancy the joint processing of self-other attention becomes automatically engaged as an executive function. It can be argued that this executive joint attention is fundamental to human learning as well as the development of symbolic thought, social cognition and social competence throughout the life span. One advantage of this parallel and distributed-processing model of joint attention is that it directly connects theory on social pathology to a range of phenomena in autism associated with neural connectivity, constructivist and connectionist models of cognitive development, early intervention, activity-dependent gene expression and atypical ocular motor control.

Presence of beta-follicle-stimulating hormone and beta-luteinizing hormone transcripts in the brain of Cichlasoma dimerus (Perciformes: Cichlidae): effect of brain-derived gonadotropins on pituitary hormone release

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play key roles in vertebrate gametogenesis and steroidogenesis. They are mainly synthesized in the pituitary gland. While investigating the ontogeny of FSH and LH cells in the cichlid fish Cichlasoma dimerus by immunohistochemistry (IHC), we unexpectedly found immunoreactive neurons in the preoptic area, sending their projections through different brain areas and neurohypophysis. Our previous work using Western blot and IHC techniques applied to the adult brain confirmed these findings. To further demonstrate the extrapituitary expression of these hormones, we performed RT-PCR detecting sequences coding for beta-FSH and beta-LH subunits in the C. dimerus pituitary and brain (preoptic-hypothalamic area). The expression of these transcripts in both organs was consistent with their peptide expression showing a high sequence homology when compared with other phylogenetically related fish. An individual pituitary in vitro culture system was utilized to study the possible modulatory effect of brain-derived gonadotropins on pituitary hormone secretion. Pituitary explants were cultured with different concentrations of LH or FSH, and the culture media were analyzed by Western blot. Exogenous LH produced a dose-dependent increase in pituitary beta-LH, beta-FSH and somatolactin (SL) releases. No effect was observed on growth hormone (GH). The effect on prolactin (PRL) was not consistent among treatments. Exogenous FSH produced an inhibition in beta-LH release, dose-dependent increases in beta-FSH and SL releases, and no effect on PRL and GH releases. These findings support the concept of regulation of pituitary trophic hormones by brain-derived gonadotropins.

Plasticity in the adult human auditory brainstem following short-term linguistic training

Peripheral and central structures along the auditory pathway contribute to speech processing and learning. However, because speech requires the use of functionally and acoustically complex sounds which necessitates high sensory and cognitive demands, long-term exposure and experience using these sounds is often attributed to the neocortex with little emphasis placed on subcortical structures. The present study examines changes in the auditory brainstem, specifically the frequency following response (FFR), as native English-speaking adults learn to incorporate foreign speech sounds (lexical pitch patterns) in word identification. The FFR presumably originates from the auditory midbrain and can be elicited preattentively. We measured FFRs to the trained pitch patterns before and after training. Measures of pitch tracking were then derived from the FFR signals. We found increased accuracy in pitch tracking after training, including a decrease in the number of pitch-tracking errors and a refinement in the energy devoted to encoding pitch. Most interestingly, this change in pitch-tracking accuracy only occurred in the most acoustically complex pitch contour (dipping contour), which is also the least familiar to our English-speaking subjects. These results not only demonstrate the contribution of the brainstem in language learning and its plasticity in adulthood but also demonstrate the specificity of this contribution (i.e., changes in encoding only occur in specific, least familiar stimuli, not all stimuli). Our findings complement existing data showing cortical changes after second-language learning, and are consistent with models suggesting that brainstem changes resulting from perceptual learning are most apparent when acuity in encoding is most needed.

Brain development: anatomy, connectivity, adaptive plasticity, and toxicity

The developing brain is inherently more vulnerable to injury than the adult brain because brain development is extraordinarily complex, with periods of unique susceptibility. When brain developmental processes are suspended or delayed by any external influence, virtually no potential exists for subsequent regeneration and repair. This inevitably leads to long-lasting or permanent consequences. Recent genetic studies have contributed to a better understanding of the dynamic adaptive changes that occur in the developing brain as a consequence of genetic and environmental processes. Many industrial and environmental chemicals such as lead, methyl-mercury, polychlorinated biphenyls, arsenic, and toluene are recognized causes of neurodevelopmental disorders that lead to clinical or subclinical brain dysfunction. A number of these developmental disabilities arise from interactions between environmental factors and individual gene susceptibility. In addition, neurodevelopmental disorders of unknown origin, such as mental retardation, attention deficit disorder, cerebral palsy, and autism are becoming increasingly prevalent, with costly consequences for the family and society. The aim of this review is examine brain developmental anatomy, connectivity, adaptive plasticity, and toxicity in the context of current knowledge and future trends.

Top-down regulation of plasticity in the birdsong system: "premotor" activity in the nucleus HVC predicts song variability better than it predicts song features

We studied real-time changes in brain activity during active vocal learning in the zebra finch songbird. The song nucleus HVC is required for the production of learned song. To quantify the relationship of HVC activity and behavior, HVC population activity during repeated vocal sequences (motifs) was recorded and temporally aligned relative to the motif, millisecond by millisecond. Somewhat surprisingly, HVC activity did not reliably predict any vocal feature except amplitude and, to a lesser extent, entropy and pitch goodness (sound periodicity). Variance in "premotor" HVC activity did not reliably predict variance in behavior. In contrast, HVC activity inversely predicted the variance of amplitude, entropy, frequency, pitch, and FM. We reasoned that, if HVC was involved in song learning, the relationship of HVC activity to learned features would be developmentally regulated. To test this hypothesis, we compared the HVC song feature relationships in adults and juveniles in the sensorimotor "babbling" period. We found that the relationship of HVC activity to variance in FM was developmentally regulated, with the greatest difference at an HVC vocalization lag of 50 ms. Collectively, these data show that, millisecond by millisecond, bursts in HVC activity predict song stability on-line during singing, whereas decrements in HVC activity predict plasticity. These relationships between neural activity and plasticity may play a role in vocal learning in songbirds by enabling the selective stabilization of parts of the song that match a learned tutor model.

Use of the Screening Tool for Autism in Two-Year-Olds (STAT) for children under 24 months

The study examined the properties of the Screening Tool for Autism in Two-Year-Olds (STAT) for children under 24 months. The STAT provides a standard context for observing social-communicative behavior in play, imitation, and communication. Seventy-one children received the STAT between 12 and 23 months of age and a follow-up diagnostic evaluation after 24 months. All had an older sibling with an autism spectrum diagnosis ( n = 59) or had been referred for evaluation for concerns about autism ( n = 12). Signal detection analysis resulted in a cut score of 2.75 for this sample, which yielded a sensitivity of 0.95, specificity of 0.73, positive predictive value of 0.56, and negative predictive value of 0.97. False positives were highest for the 12- to 13-month-old age group; STAT screening properties were improved when the sample was limited to children 14 months and older. Implications for using the STAT with children under 24 months are discussed.

Pleiotropic effects of neurotransmission during development: modulators of modularity

The formation and function of the mammalian cerebral cortex relies on the complex interplay of a variety of genetic and environmental factors through protracted periods of gestational and postnatal development. Biogenic amine systems are important neuromodulators, both in the adult nervous system, and during critical epochs of brain development. Abnormalities in developmental programming likely contribute to developmental delays and multiple neurological and psychiatric disorders, often with symptom onset much later than the actual induction of pathology. We review several genetic and pharmacological models of dopamine, norepinephrine and serotonin modulation during development, each of which produces permanent changes in cerebral cortical structure and function. These models clearly illustrate the ability of these neurotransmitters to function beyond their classic roles and show their involvement in the development and modulation of fine brain circuitry that is sensitive to numerous effectors. Furthermore, these studies demonstrate the need to consider not only gene by environment interactions, but also gene by environment by developmental time interactions.

Embryonically expressed GABA and glutamate drive electrical activity regulating neurotransmitter specification

Neurotransmitter signaling in the mature nervous system is well understood, but the functions of transmitters in the immature nervous system are less clear. Although transmitters released during embryogenesis regulate neuronal proliferation and migration, little is known about their role in regulating early neuronal differentiation. Here, we show that GABA and glutamate drive calcium-dependent embryonic electrical activity that regulates transmitter specification. The number of neurons expressing different transmitters changes when GABA or glutamate signaling is blocked chronically, either using morpholinos to knock down transmitter-synthetic enzymes or applying pharmacological receptor antagonists during a sensitive period of development. We find that calcium spikes are triggered by metabotropic GABA and glutamate receptors, which engage protein kinases A and C. The results reveal a novel role for embryonically expressed neurotransmitters.

Neurodevelopmental trajectories of the human cerebral cortex

Understanding the organization of the cerebral cortex remains a central focus of neuroscience. Cortical maps have relied almost exclusively on the examination of postmortem tissue to construct structural, architectonic maps. These maps have invariably distinguished between areas with fewer discernable layers, which have a less complex overall pattern of lamination and lack an internal granular layer, and those with more complex laminar architecture. The former includes several agranular limbic areas, and the latter includes the homotypical and granular areas of association and sensory cortex. Here, we relate these traditional maps to developmental data from noninvasive neuroimaging. Changes in cortical thickness were determined in vivo from 764 neuroanatomic magnetic resonance images acquired longitudinally from 375 typically developing children and young adults. We find differing levels of complexity of cortical growth across the cerebrum, which align closely with established architectonic maps. Cortical regions with simple laminar architecture, including most limbic areas, predominantly show simpler growth trajectories. These areas have clearly identified homologues in all mammalian brains and thus likely evolved in early mammals. In contrast, polysensory and high-order association areas of cortex, the most complex areas in terms of their laminar architecture, also have the most complex developmental trajectories. Some of these areas are unique to, or dramatically expanded in primates, lending an evolutionary significance to the findings. Furthermore, by mapping a key characteristic of these development trajectories (the age of attaining peak cortical thickness) we document the dynamic, heterochronous maturation of the cerebral cortex through time lapse sequences ("movies").

Phonetic learning as a pathway to language: new data and native language magnet theory expanded (NLM-e)

Infants' speech perception skills show a dual change towards the end of the first year of life. Not only does non-native speech perception decline, as often shown, but native language speech perception skills show improvement, reflecting a facilitative effect of experience with native language. The mechanism underlying change at this point in development, and the relationship between the change in native and non-native speech perception, is of theoretical interest. As shown in new data presented here, at the cusp of this developmental change, infants' native and non-native phonetic perception skills predict later language ability, but in opposite directions. Better native language skill at 7.5 months of age predicts faster language advancement, whereas better non-native language skill predicts slower advancement. We suggest that native language phonetic performance is indicative of neural commitment to the native language, while non-native phonetic performance reveals uncommitted neural circuitry. This paper has three goals: (i) to review existing models of phonetic perception development, (ii) to present new event-related potential data showing that native and non-native phonetic perception at 7.5 months of age predicts language growth over the next 2 years, and (iii) to describe a revised version of our previous model, the native language magnet model, expanded (NLM-e). NLM-e incorporates five new principles. Specific testable predictions for future research programmes are described.

The effect of early human diet on caudate volumes and IQ

Early nutrition in animals affects both behavior and brain structure. In humans, randomized trials show that early nutrition affects later cognition, notably in males. We hypothesized that early nutrition also influences brain structure, measurable using magnetic resonance imaging. Prior research suggested that the caudate nucleus may be especially vulnerable to early environment and that its size relates to IQ. To test the hypothesis that the caudate nucleus could be a neural substrate for cognitive effects of early nutrition, we compared two groups of adolescents, assigned a Standard- or High-nutrient diet in the postnatal weeks after preterm birth. Groups had similar birth status and neonatal course. Scans and IQ data were obtained from 76 adolescents and volumes of several subcortical structures were calculated. The High-nutrient group had significantly larger caudate volumes and higher Verbal IQ (VIQ). Caudate volumes correlated significantly with VIQ in the Standard-nutrient group only. Caudate volume was influenced by early nutrition and related selectively to VIQ in males, but not in females. Our findings may partly explain the effects of early diet on cognition and the predominant effects in males. They are among the first to show that human brain structure can be influenced by early nutrition.

The effect of early musical training on adult motor performance: evidence for a sensitive period in motor learning

Developmental changes in the human brain coincide with and underlie changes in a wide range of motor and cognitive abilities. Neuroimaging studies have shown that musical training can result in structural and functional plasticity in the brains of musicians, and that this plasticity is greater for those who begin training early in life. However, previous studies have not controlled for differences between early-trained (ET) and late-trained (LT) musicians in the total number of years of musical training and experience. In the present experiment, we tested musicians who began training before and after the age of 7 on learning of a timed motor sequence task. The groups were matched for years of musical experience, years of formal training and hours of current practice. Results showed that ET musicians performed better than LT musicians, and that this performance advantage persisted after 5 days of practice. Performance differences were greatest for a measure of response synchronization, suggesting that early training has its greatest effect on neural systems involved in sensorimotor integration and timing. These findings support the idea that there may be a sensitive period in childhood where enriched motor training through musical practice results in long-lasting benefits for performance later in life. These results are also consistent with the results of studies showing structural changes in motor-related regions of the brain in musicians that are specifically related to training early in life.

Anxiety as a developmental disorder

There is increasing recognition that many psychiatric disorders including anxiety disorders are neurodevelopmental in their origins. Here, we review and integrate data from human studies and from animal models that point to a critical period during which neural circuits that mediate anxiety develop. We then postulate that this highly plastic critical period is a time of heightened responsiveness that is particularly susceptible to adverse events. We discuss these concepts in the context the current heightened interest in gene by environment interactions in psychiatric illness emphasizing the importance of the temporal relationship between gene action and environmental milieu.

Brain neuroplasticity in healthy, hyperactive and psychotic children: insights from neuroimaging

Noninvasive brain imaging permits longitudinal studies of anatomic brain development in healthy and psychiatrically ill children. The time course for gray matter maturation varies by region and parallels earlier histological studies, indicating dynamic patterns of overproduction and regression. Developmental trajectories vary in relation to gender, intelligence, and overall functioning. Twin studies show high heritability for brain volumes, which varies with region and with age. Diagnostically specific, illness-related changes as well as outcome-associated plastic response are observed as illustrated for two pediatric populations, childhood-onset schizophrenia and attention-deficit/hyperactivity disorder, conditions which may be, in part, disorders of brain plasticity.

Vision and cortical map development

Functional maps arise in developing visual cortex as response selectivities become organized into columnar patterns of population activity. Recent studies of developing orientation and direction maps indicate that both are sensitive to visual experience, but not to the same degree or duration. Direction maps have a greater dependence on early vision, while orientation maps remain sensitive to experience for a longer period of cortical maturation. There is also a darker side to experience: abnormal vision through closed lids produces severe impairments in neuronal selectivity, rendering these maps nearly undetectable. Thus, the rules that govern their formation and the construction of the underlying neural circuits are modulated-for better or worse-by early vision. Direction maps, and possibly maps of other properties that are dependent upon precise conjunctions of spatial and temporal signals, are most susceptible to the potential benefits and maladaptive consequences of early sensory experience.

Effects of aerobic exercise on overweight children's cognitive functioning: a randomized controlled trial

The study tested the effect of aerobic exercise training on executive function in overweight children. Ninety-four sedentary, overweight but otherwise healthy children (mean age = 9.2 years, body mass index 85th percentile) were randomized to a low-dose (20 min/day exercise), high-dose (40 min/day exercise), or control condition. Exercise sessions met 5 days/week for 15 weeks. The Cognitive Assessment System (CAS), a standardized test of cognitive processes, was administered individually before and following intervention. Analysis of covariance on posttest scores revealed effects on executive function. Group differences emerged for the CAS Planning scale (p = .03). Planning scores for the high-dose group were significantly greater than those of the control group. Exercise may prove to be a simple, yet important, method of enhancing aspects of children's mental functioning that are central to cognitive and social development.

Intelligence and the developing human brain

Determining the brain properties that make people 'brainier' has moved well beyond early demonstrations that increasing intelligence correlates with increasing grey and white matter volumes. Both structural and functional in vivo neuroimaging techniques delineate a distributed network of brain regions, perhaps with a focus in the lateral prefrontal cortex, which varies in extent and connectivity with individual differences in intelligence. Longitudinal studies further show that the neuroanatomic correlates of intelligence are dynamic, changing most rapidly in early childhood. Several promising candidate genes affecting neuronal development and neurotransmission have been proposed that might begin to explain the marked genetic overlap between cortical morphology and intelligence. A major future challenge is to determine the cellular events that underpin the neuroanatomic differences correlated with intelligence.

Attention-deficit/hyperactivity disorder is characterized by a delay in cortical maturation

There is controversy over the nature of the disturbance in brain development that underpins attention-deficit/hyperactivity disorder (ADHD). In particular, it is unclear whether the disorder results from a delay in brain maturation or whether it represents a complete deviation from the template of typical development. Using computational neuroanatomic techniques, we estimated cortical thickness at >40,000 cerebral points from 824 magnetic resonance scans acquired prospectively on 223 children with ADHD and 223 typically developing controls. With this sample size, we could define the growth trajectory of each cortical point, delineating a phase of childhood increase followed by adolescent decrease in cortical thickness (a quadratic growth model). From these trajectories, the age of attaining peak cortical thickness was derived and used as an index of cortical maturation. We found maturation to progress in a similar manner regionally in both children with and without ADHD, with primary sensory areas attaining peak cortical thickness before polymodal, high-order association areas. However, there was a marked delay in ADHD in attaining peak thickness throughout most of the cerebrum: the median age by which 50% of the cortical points attained peak thickness for this group was 10.5 years (SE 0.01), which was significantly later than the median age of 7.5 years (SE 0.02) for typically developing controls (log rank test chi(1)(2) = 5,609, P < 1.0 x 10(-20)). The delay was most prominent in prefrontal regions important for control of cognitive processes including attention and motor planning. Neuroanatomic documentation of a delay in regional cortical maturation in ADHD has not been previously reported.

Learning to hear: plasticity of auditory cortical processing

Sensory experience and auditory cortex plasticity are intimately related. This relationship is most striking during infancy when changes in sensory input can have profound effects on the functional organization of the developing cortex. But a considerable degree of plasticity is retained throughout life, as demonstrated by the cortical reorganization that follows damage to the sensory periphery or by the more controversial changes in response properties that are thought to accompany perceptual learning. Recent studies in the auditory system have revealed the remarkably adaptive nature of sensory processing and provided important insights into the way in which cortical circuits are shaped by experience and learning.

Nature and strength of epidemiological evidence for origins of childhood and adulthood obesity in the first year of life

Increased interest in early life origins of chronic disease, a concept often referred to as programming, has resulted in several studies investigating the origins of childhood or adulthood obesity during infancy. Rapid infancy weight gain as a risk factor and breastfeeding as a protective factor for later obesity have been most thoroughly studied. The association between rapid infancy weight gain and later obesity is supported by several observational studies, but not by the two, relatively small, randomized trials. This association is strong, suggests a dose-response effect and has biological plausibility, but is not consistent between study designs. Rapid infancy weight gain as a risk factor for later obesity has been experimentally reproduced in animal models, but not in humans. The protective effect of breastfeeding on obesity is also supported by several observational studies, but randomized trials are not available. Considering the potential for residual confounding factors, current evidence is insufficient to demonstrate origins of obesity during infancy or to change public health recommendations, but the potential for obesity prevention during infancy is promising.

Vibrotactile activation of the auditory cortices in deaf versus hearing adults

Neuroplastic changes in auditory cortex as a result of lifelong perceptual experience were investigated. Adults with early-onset deafness and long-term hearing aid experience were hypothesized to have undergone auditory cortex plasticity due to somatosensory stimulation. Vibrations were presented on the hand of deaf and normal-hearing participants during functional MRI. Vibration stimuli were derived from speech or were a fixed frequency. Higher, more widespread activity was observed within auditory cortical regions of the deaf participants for both stimulus types. Life-long somatosensory stimulation due to hearing aid use could explain the greater activity observed with deaf participants.

Adaptive auditory plasticity in developing and adult animals

Enormous progress has been made in our understanding of adaptive plasticity in the central auditory system. Experiments on a range of species demonstrate that, in adults, the animal must attend to (i.e., respond to) a stimulus in order for plasticity to be induced, and the plasticity that is induced is specific for the acoustic feature to which the animal has attended. The requirement that an adult animal must attend to a stimulus in order for adaptive plasticity to occur suggests an essential role of neuromodulatory systems in gating plasticity in adults. Indeed, neuromodulators, particularly acetylcholine (ACh), that are associated with the processes of attention, have been shown to enable adaptive plasticity in adults. In juvenile animals, attention may facilitate plasticity, but it is not always required: during sensitive periods, mere exposure of an animal to an atypical auditory environment can result in large functional changes in certain auditory circuits. Thus, in both the developing and mature auditory systems substantial experience-dependent plasticity can occur, but the conditions under which it occurs are far more stringent in adults. We review experimental results that demonstrate experience-dependent plasticity in the central auditory representations of sound frequency, level and temporal sequence, as well as in the representations of binaural localization cues in both developing and adult animals.

Attention and sensory interactions within the occipital cortex in the early blind: an fMRI study

Visual deprivation early in life results in occipital cortical responsiveness across a broad range of perceptual and cognitive tasks. In the reorganized occipital cortex of early blind (EB) individuals, the relative lack of specificity for particular sensory stimuli and tasks suggests that attention effects may play a prominent role in these areas. We wished to establish whether occipital cortical areas in the EB were responsive to stimuli across sensory modalities (auditory, tactile) and whether these areas maintained or altered their activity as a function of selective attention. Using a three-stimulus oddball paradigm and event-related functional magnetic resonance imaging, auditory and tactile tasks presented separately demonstrated that several occipital regions of interest (ROIs) in the EB, but not sighted controls (SCs), responded to targets and task-irrelevant distracter stimuli of both modalities. When auditory and tactile stimuli were presented simultaneously with subjects alternating attention between sensory streams, only the calcarine sulcus continued to respond to stimuli in both modalities. In all other ROIs, responses to auditory targets were as large or larger than those observed in the auditory-alone condition, but responses to tactile targets were attenuated or abolished by the presence of unattended auditory stimuli. Both auditory and somatosensory cortices responded consistently to auditory and tactile targets, respectively. These results reveal mechanisms of orienting and selective attention within the visual cortex of EB individuals and suggest that mechanisms of enhancement and suppression interact asymmetrically on auditory and tactile streams during bimodal sensory presentation.

Resilience and developmental psychopathology

Humans vary to a great extent in their ability to adapt to adverse experiences. Resilience reflects the positive end of this spectrum of adaptation and maladaptation in response to risk exposure. Some individuals, despite being faced with the most pernicious of adversities, manage to avoid psychologic collapse and to maintain healthy adjustment. For decades, researchers and clinicians have searched for the correlates and causes of resilience, and several comprehensive reviews of these efforts are available. This article provides an overview of resilience research and selectively summarizes recent advances in the field, with a particular focus on a developmental psychopathology perspective. This article highlights some of the challenges to resilience research and uses the example of maltreatment to illustrate some of these issues.

The development of intellectual abilities in pediatric temporal lobe epilepsy

PURPOSE

The aim of this study was to examine the impact of clinical variables, particularly age at onset of epilepsy, on intellectual function in a group of children with temporal lobe epilepsy (TLE).

METHODS

We reviewed the preoperative neuropsychological test results of 79 children with unilateral TLE who subsequently underwent surgical resection. The impact of age at onset and duration of epilepsy, pathology type, and side of resection on full-scale intelligence quotient (IQ) scores was examined.

RESULTS

Intellectual dysfunction (defined as IQ < 79) was present in 57% of children, and age at onset of epilepsy was the best predictor of intellectual function. Children with epilepsy onset in the first year of life had a particularly high incidence of intellectual impairment (82.4%).

CONCLUSION

These data suggest a critical period during the first year of life for the subsequent development of intellectual abilities and highlight the importance of early treatment in this population.

Reproducing inequalities: luck, wallets, and the enduring effects of childhood health

In this article, I argue that research on social stratification, on intergenerational transmission of inequalities, and on the theory of factor payments and wage determination will be strengthened by studying the role played by early childhood health. I show that the inclusion of such a factor requires researchers to integrate theories in each of these fields with new theories linking early childhood health conditions and events that occur at later stages in the life course of individuals, particularly physical and mental health as well as disability and mortality. The empirical evidence I gather shows that early childhood health matters for the achievement of or social accession to, adult social class positions. Even if the magnitude of associations is not overwhelming, it is not weaker than that found between adult social accession and other, more conventional and better-studied individual characteristics, such as educational attainment. It is very likely that the evidence presented in this article grossly underplays the importance of early childhood health for adult socioeconomic achievement.

Autism spectrum disorders: developmental disconnection syndromes

Autism is a common and heterogeneous childhood neurodevelopmental disorder. Analogous to broad syndromes such as mental retardation, autism has many etiologies and should be considered not as a single disorder but, rather, as 'the autisms'. However, recent genetic findings, coupled with emerging anatomical and functional imaging studies, suggest a potential unifying model in which higher-order association areas of the brain that normally connect to the frontal lobe are partially disconnected during development. This concept of developmental disconnection can accommodate the specific neurobehavioral features that are observed in autism, their emergence during development, and the heterogeneity of autism etiology, behaviors and cognition.

A role for eukaryotic translation initiation factor 2B (eIF2B) in taste memory consolidation and in thermal control establishment during the critical period for sensory development

All species exhibit critical periods for sensory development, yet very little is known about the molecules involved in the changes in the network wiring that underlies this process. Here the role of transcription regulation of the translation machinery was determined by evaluating the expression of eIF2Bepsilon, an essential component of translation initiation, in both taste-preference development and thermal control establishment in chicks. Analysis of the expression pattern of this gene after passive-avoidance training revealed clear induction of eIF2Bepsilon in both the mesopallium intermediomediale (IMM) and in the striatum mediale (StM). In addition, a correlation was found between the concentration of methylanthranilate (MeA), which was the malaise substrate in the passive-avoidance training procedure, the duration of memory, and the expression level of eIF2Bepsilon. Training chicks on a low concentration of MeA induced short-term memory and low expression level of eIF2Bepsilon, whereas a high concentration of MeA induced long-term memory and a high expression level of eIF2Bepsilon in both the IMM and StM. Furthermore, eIF2Bepsilon-antisense "knock-down" not only reduced the amount of eIF2Bepsilon but also attenuated taste memory formation. In order to determine whether induction of eIF2Bepsilon is a general feature of neuronal plasticity, we checked whether it was induced in other forms of neuronal plasticity, with particular attention to its role in temperature control establishment, which represents hypothalamic-related plasticity. It was established that eIF2Bepsilon-mRNA was induced in the preopotic anterior hypothalamus during heat conditioning. Taken together, these results correlate eIF2Bepsilon with sensory development.

“Scientific roots” of dualism in neuroscience

Although the dualistic concept is unpopular among neuroscientists involved in experimental studies of the brain, neurophysiological literature is full of covert dualistic statements on the possibility of understanding neural mechanisms of human consciousness. Particularly, the covert dualistic attitude is exhibited in the unwillingness to discuss neural mechanisms of consciousness, leaving the problem of consciousness to psychologists and philosophers. This covert dualism seems to be rooted in the main paradigm of neuroscience that suggests that cognitive functions, such as language production and comprehension, face recognition, declarative memory, emotions, etc., are performed by neural networks consisting of simple elements. I argue that neural networks of any complexity consisting of neurons whose function is limited to the generation of electrical potentials and the transmission of signals to other neurons are hardly capable of producing human mental activity, including consciousness. Based on results obtained in physiological, morphological, clinical, and genetic studies of cognitive functions (mainly linguistic ones), I advocate the hypothesis that the performance of cognitive functions is based on complex cooperative activity of "complex" neurons that are carriers of "elementary cognition." The uniqueness of human cognitive functions, which has a genetic basis, is determined by the specificity of genes expressed by these "complex" neurons. The main goal of the review is to show that the identification of the genes implicated in cognitive functions and the understanding of a functional role of their products is a possible way to overcome covert dualism in neuroscience.