Between molecules and experience: role of early patterns of coordinated activity for the development of cortical maps and sensory abilities

Exploring the role of white matter connectivity in cortex maturation

The maturation of the cortical gray matter (GM) and white matter (WM) are described as sequential processes following multiple, but distinct rules. However, neither the mechanisms driving brain maturation processes, nor the relationship between GM and WM maturation are well understood. Here we use connectomics and two MRI measures reflecting maturation related changes in cerebral microstructure, namely the Apparent Diffusion Coefficient (ADC) and the T1 relaxation time (T1), to study brain development. We report that the advancement of GM and WM maturation are inter-related and depend on the underlying brain connectivity architecture. Particularly, GM regions and their incident WM connections show corresponding maturation levels, which is also observed for GM regions connected through a WM tract. Based on these observations, we propose a simple computational model supporting a key role for the connectome in propagating maturation signals sequentially from external stimuli, through primary sensory structures to higher order functional cortices.

Theta Oscillations during Active Sleep Synchronize the Developing Rubro-Hippocampal Sensorimotor Network

Neuronal oscillations comprise a fundamental mechanism by which distant neural structures establish and express functional connectivity. Long-range functional connectivity between the hippocampus and other forebrain structures is enabled by theta oscillations. Here, we show for the first time that the infant rat red nucleus (RN)-a brainstem sensorimotor structure-exhibits theta (4-7 Hz) oscillations restricted primarily to periods of active (REM) sleep. At postnatal day 8 (P8), theta is expressed as brief bursts immediately following myoclonic twitches; by P12, theta oscillations are expressed continuously across bouts of active sleep. Simultaneous recordings from the hippocampus and RN at P12 show that theta oscillations in both structures are coherent, co-modulated, and mutually interactive during active sleep. Critically, at P12, inactivation of the medial septum eliminates theta in both structures. The developmental emergence of theta-dependent functional coupling between the hippocampus and RN parallels that between the hippocampus and prefrontal cortex. Accordingly, disruptions in the early expression of theta could underlie the cognitive and sensorimotor deficits associated with neurodevelopmental disorders such as autism and schizophrenia.

Impact of thalamocortical input on barrel cortex development

The development of cortical maps requires the balanced interaction between genetically determined programs and input/activity-dependent signals generated spontaneously or triggered from the environment. The somatosensory pathway of mice provides an excellent scenario to study cortical map development because of its highly organized cytoarchitecture, known as the barrel field. This precise organization makes evident even small alterations in the cortical map layout. In this review, we will specially focus on the thalamic factors that control barrel field development. We will summarize the role of thalamic input integration and identity, neurotransmission and spontaneous activity in cortical map formation and early cross-modal plasticity.

Fast sleep spindle reduction in schizophrenia and healthy first-degree relatives: association with impaired cognitive function and potential intermediate phenotype

Several studies in patients with schizophrenia reported a marked reduction in sleep spindle activity. To investigate whether the reduction may be linked to genetic risk of the illness, we analysed sleep spindle activity in healthy volunteers, patients with schizophrenia and first-degree relatives, who share an enriched set of schizophrenia susceptibility genes. We further investigated the correlation of spindle activity with cognitive function in first-degree relatives and whether spindle abnormalities affect both fast (12-15 Hz) and slow (9-12 Hz) sleep spindles. We investigated fast and slow sleep spindle activity during non-rapid eye movement sleep in a total of 47 subjects comprising 17 patients with schizophrenia, 13 healthy first-degree relatives and 17 healthy volunteers. Groups were balanced for age, gender, years of education and estimated verbal IQ. A subsample of relatives received additional testing for memory performance. Compared to healthy volunteers, fast spindle density was reduced in patients with schizophrenia and healthy first-degree relatives following a pattern consistent with an assumed genetic load for schizophrenia. The deficit in spindle density was specific to fast spindles and was associated with decreased memory performance. Our findings indicate familial occurrence of this phenotype and thus support the hypothesis that deficient spindle activity relates to genetic liability for schizophrenia. Furthermore, spindle reductions predict impaired cognitive function and are specific to fast spindles. This physiological marker should be further investigated as an intermediate phenotype of schizophrenia. It could also constitute a target for drug development, especially with regard to cognitive dysfunction.

Visual-tactile processing in primary somatosensory cortex emerges before cross-modal experience

The presumptive unisensory neocortical areas process multisensory information by oscillatory entrainment of neuronal networks via direct cortico-cortical projections. While neonatal unimodal experience has been identified as necessary for setting up the neuronal networks of multisensory processing, it is still unclear whether early cross-modal experience equally controls the ontogeny of multisensory processing. Here, we assess the development of visual-somatosensory interactions and their anatomical substrate by performing extracellular recordings of network activity in primary sensory cortices in vivo and assessing the cortico-cortical connectivity in pigmented rats. Similar to adult animals, juvenile rats with minimal cross-modal experience display supra-additive augmentation of evoked responses, time-dependent modulation of power and phase reset of network oscillations in response to cross-modal light and whisker stimulation. Moreover, the neuronal discharge of individual neurons is stronger coupled to theta and alpha network oscillations after visual-tactile stimuli. The adult-like multisensory processing of juvenile rats relies on abundant direct visual-somatosensory connections and thalamocortical feedforward interactions. Thus, cellular and network interactions ensuring multisensory processing emerge before cross-modal experience and refine during juvenile development.

Layer-specific optogenetic activation of pyramidal neurons causes beta-gamma entrainment of neonatal networks

Coordinated activity patterns in the developing brain may contribute to the wiring of neuronal circuits underlying future behavioural requirements. However, causal evidence for this hypothesis has been difficult to obtain owing to the absence of tools for selective manipulation of oscillations during early development. We established a protocol that combines optogenetics with electrophysiological recordings from neonatal mice in vivo to elucidate the substrate of early network oscillations in the prefrontal cortex. We show that light-induced activation of layer II/III pyramidal neurons that are transfected by in utero electroporation with a high-efficiency channelrhodopsin drives frequency-specific spiking and boosts network oscillations within beta–gamma frequency range. By contrast, activation of layer V/VI pyramidal neurons causes nonspecific network activation. Thus, entrainment of neonatal prefrontal networks in fast rhythms relies on the activation of layer II/III pyramidal neurons. This approach used here may be useful for further interrogation of developing circuits, and their behavioural readout.

Oscillations in cortical activity during development are important for functional maturation. Here, the authors use optogenetics in neonatal mice to determine a causal role for pyramidal cell firing in different prelimbic cortex layers in generating beta–gamma range activity.

Tonotopic action potential tuning of maturing auditory neurons through endogenous ATP

KEY POINTS

Following the genetically controlled formation of neuronal circuits, early firing activity guides the development of sensory maps in the auditory, visual and somatosensory system. However, it is not clear whether the activity of central auditory neurons is specifically regulated depending on the position within the sensory map. In the ventral cochlear nucleus, the first central station along the auditory pathway, we describe a mechanism through which paracrine ATP signalling enhances firing in a cell-specific and tonotopically-determined manner. Developmental down-regulation of P2X2/3R currents along the tonotopic axis occurs simultaneously with an increase in AMPA receptor currents, suggesting a high-to-low frequency maturation pattern. Facilitated action potential (AP) generation, measured as higher firing rate, shorter EPSP-AP delay in vivo and shorter AP latency in slice experiments, is consistent with increased synaptic efficacy caused by ATP. The long lasting change in intrinsic neuronal excitability is mediated by the heteromeric P2X2/3 receptors.

ABSTRACT

Synaptic refinement and strengthening are activity-dependent processes that establish orderly arranged cochleotopic maps throughout the central auditory system. The maturation of auditory brainstem circuits is guided by action potentials (APs) arising from the inner hair cells in the developing cochlea. The AP firing of developing central auditory neurons can be modulated by paracrine ATP signalling, as shown for the cochlear nucleus bushy cells and principal neurons in the medial nucleus of the trapezoid body. However, it is not clear whether neuronal activity may be specifically regulated with respect to the nuclear tonotopic position (i.e. sound frequency selectivity). Using slice recordings before hearing onset and in vivo recordings with iontophoretic drug applications after hearing onset, we show that cell-specific purinergic modulation follows a precise tonotopic pattern in the ventral cochlear nucleus of developing gerbils. In high-frequency regions, ATP responsiveness diminished before hearing onset. In low-to-mid frequency regions, ATP modulation persisted after hearing onset in a subset of low-frequency bushy cells (characteristic frequency< 10 kHz). Down-regulation of P2X2/3R currents along the tonotopic axis occurs simultaneously with an increase in AMPA receptor currents, thus suggesting a high-to-low frequency maturation pattern. Facilitated AP generation, measured as higher firing frequency, shorter EPSP-AP delay in vivo, and shorter AP latency in slice experiments, is consistent with increased synaptic efficacy caused by ATP. Finally, by combining recordings and pharmacology in vivo, in slices, and in human embryonic kidney 293 cells, it was shown that the long lasting change in intrinsic neuronal excitability is mediated by the P2X2/3R.

Large Scale Cortical Functional Networks Associated with Slow-Wave and Spindle-Burst-Related Spontaneous Activity

Cortical sensory systems are active with rich patterns of activity during sleep and under light anesthesia. Remarkably, this activity shares many characteristics with those present when the awake brain responds to sensory stimuli. We review two specific forms of such activity: slow-wave activity (SWA) in the adult brain and spindle bursts in developing brain. SWA is composed of 0.5-4 Hz resting potential fluctuations. Although these fluctuations synchronize wide regions of cortex, recent large-scale imaging has shown spatial details of their distribution that reflect underlying cortical structural projections and networks. These networks are regulated, as prior awake experiences alter both the spatial and temporal features of SWA in subsequent sleep. Activity patterns of the immature brain, however, are very different from those of the adult. SWA is absent, and the dominant pattern is spindle bursts, intermittent high frequency oscillations superimposed on slower depolarizations within sensory cortices. These bursts are driven by intrinsic brain activity, which act to generate peripheral inputs, for example via limb twitches. They are present within developing sensory cortex before they are mature enough to exhibit directed movements and respond to external stimuli. Like in the adult, these patterns resemble those evoked by sensory stimulation when awake. It is suggested that spindle-burst activity is generated purposefully by the developing nervous system as a proxy for true external stimuli. While the sleep-related functions of both slow-wave and spindle-burst activity may not be entirely clear, they reflect robust regulated phenomena which can engage select wide-spread cortical circuits. These circuits are similar to those activated during sensory processing and volitional events. We highlight these two patterns of brain activity because both are prominent and well-studied forms of spontaneous activity that will yield valuable insights into brain function in the coming years.

Encoding of mechanical nociception differs in the adult and infant brain

Newborn human infants display robust pain behaviour and specific cortical activity following noxious skin stimulation, but it is not known whether brain processing of nociceptive information differs in infants and adults. Imaging studies have emphasised the overlap between infant and adult brain connectome architecture, but electrophysiological analysis of infant brain nociceptive networks can provide further understanding of the functional postnatal development of pain perception. Here we hypothesise that the human infant brain encodes noxious information with different neuronal patterns compared to adults. To test this we compared EEG responses to the same time-locked noxious skin lance in infants aged 0–19 days (n = 18, clinically required) and adults aged 23–48 years (n = 21). Time-frequency analysis revealed that while some features of adult nociceptive network activity are present in infants at longer latencies, including beta-gamma oscillations, infants display a distinct, long latency, noxious evoked 18-fold energy increase in the fast delta band (2–4 Hz) that is absent in adults. The differences in activity between infants and adults have a widespread topographic distribution across the brain. These data support our hypothesis and indicate important postnatal changes in the encoding of mechanical pain in the human brain.

Spontaneous Neuronal Activity in Developing Neocortical Networks: From Single Cells to Large-Scale Interactions

Neuronal activity has been shown to be essential for the proper formation of neuronal circuits, affecting developmental processes like neurogenesis, migration, programmed cell death, cellular differentiation, formation of local and long-range axonal connections, synaptic plasticity or myelination. Accordingly, neocortical areas reveal distinct spontaneous and sensory-driven neuronal activity patterns already at early phases of development. At embryonic stages, when immature neurons start to develop voltage-dependent channels, spontaneous activity is highly synchronized within small neuronal networks and governed by electrical synaptic transmission. Subsequently, spontaneous activity patterns become more complex, involve larger networks and propagate over several neocortical areas. The developmental shift from local to large-scale network activity is accompanied by a gradual shift from electrical to chemical synaptic transmission with an initial excitatory action of chloride-gated channels activated by GABA, glycine and taurine. Transient neuronal populations in the subplate (SP) support temporary circuits that play an important role in tuning early neocortical activity and the formation of mature neuronal networks. Thus, early spontaneous activity patterns control the formation of developing networks in sensory cortices, and disturbances of these activity patterns may lead to long-lasting neuronal deficits.

Spindle Activity Orchestrates Plasticity during Development and Sleep

Spindle oscillations have been described during early brain development and in the adult brain. Besides similarities in temporal patterns and involved brain areas, neonatal spindle bursts (NSBs) and adult sleep spindles (ASSs) show differences in their occurrence, spatial distribution, and underlying mechanisms. While NSBs have been proposed to coordinate the refinement of the maturating neuronal network, ASSs are associated with the implementation of acquired information within existing networks. Along with these functional differences, separate synaptic plasticity mechanisms seem to be recruited. Here, we review the generation of spindle oscillations in the developing and adult brain and discuss possible implications of their differences for synaptic plasticity. The first part of the review is dedicated to the generation and function of ASSs with a particular focus on their role in healthy and impaired neuronal networks. The second part overviews the present knowledge of spindle activity during development and the ability of NSBs to organize immature circuits. Studies linking abnormal maturation of brain wiring with neurological and neuropsychiatric disorders highlight the importance to better elucidate neonatal plasticity rules in future research.

Early development of synchrony in cortical activations in the human

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We study the early development of cortical activations synchrony index (ASI).

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Cortical activations become increasingly synchronized during the last trimester.

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Interhemispheric synchrony increases more than intrahemispheric synchrony.

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Our EEG metric ASI can be directly translated to experimental animal studies.

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ASI holds promise as an early functional biomarker of brain networks.

Early intermittent cortical activity is thought to play a crucial role in the growth of neuronal network development, and large scale brain networks are known to provide the basis for higher brain functions. Yet, the early development of the large scale synchrony in cortical activations is unknown. Here, we tested the hypothesis that the early intermittent cortical activations seen in the human scalp EEG show a clear developmental course during the last trimester of pregnancy, the period of intensive growth of cortico-cortical connections. We recorded scalp EEG from altogether 22 premature infants at post-menstrual age between 30 and 44 weeks, and the early cortical synchrony was quantified using recently introduced activation synchrony index (ASI). The developmental correlations of ASI were computed for individual EEG signals as well as anatomically and mathematically defined spatial subgroups. We report two main findings. First, we observed a robust and statistically significant increase in ASI in all cortical areas. Second, there were significant spatial gradients in the synchrony in fronto-occipital and left-to-right directions. These findings provide evidence that early cortical activity is increasingly synchronized across the neocortex. The ASI-based metrics introduced in our work allow direct translational comparison to in vivo animal models, as well as hold promise for implementation as a functional developmental biomarker in future research on human neonates.

Spindle Bursts in Neonatal Rat Cerebral Cortex

Spontaneous and sensory evoked spindle bursts represent a functional hallmark of the developing cerebral cortex in vitro and in vivo. They have been observed in various neocortical areas of numerous species, including newborn rodents and preterm human infants. Spindle bursts are generated in complex neocortical-subcortical circuits involving in many cases the participation of motor brain regions. Together with early gamma oscillations, spindle bursts synchronize the activity of a local neuronal network organized in a cortical column. Disturbances in spindle burst activity during corticogenesis may contribute to disorders in cortical architecture and in the activity-dependent control of programmed cell death. In this review we discuss (i) the functional properties of spindle bursts, (ii) the mechanisms underlying their generation, (iii) the synchronous patterns and cortical networks associated with spindle bursts, and (iv) the physiological and pathophysiological role of spindle bursts during early cortical development.

Early Detection of Preterm Intraventricular Hemorrhage From Clinical Electroencephalography

OBJECTIVES

Intraventricular hemorrhage is a common neurologic complication of extremely preterm birth and leads to lifelong neurodevelopmental disabilities. Early bedside detection of intraventricular hemorrhage is crucial to enabling timely interventions. We sought to detect early markers of brain activity that preempt the occurrence of intraventricular hemorrhage in extremely preterm infants during the first postnatal days.

DESIGN

Cross-sectional study.

SETTING

Level III neonatal ICU.

PATIENTS

Twenty-five extremely preterm infants (22-28 wk gestational age).

MEASUREMENTS AND MAIN RESULTS

We quantitatively assessed electroencephalography in the first 72 hours of postnatal life, focusing on the electrical burst activity of the preterm. Cranial ultrasound was performed on day 1 (0-24 hr) and day 3 (48-72 hr). Outcomes were categorized into three classes: 1) no intraventricular hemorrhage (grade 0); 2) mild-moderate intraventricular hemorrhage (grades 1-2, i.e., germinal matrix hemorrhages or intraventricular hemorrhage without ventricular dilatation, respectively); and 3) severe intraventricular hemorrhage (grades 3-4, i.e., intraventricular hemorrhage with ventricular dilatation or intraparenchymal involvement). Quantitative assessment of electroencephalography burst shapes was used to preempt the occurrence and severity of intraventricular hemorrhage as detected by ultrasound. The shapes of electroencephalography bursts found in the intraventricular hemorrhage infants were significantly sharper (F = 13.78; p < 0.0001) and less symmetric (F = 6.91; p < 0.015) than in preterm infants without intraventricular hemorrhage. Diagnostic discrimination of intraventricular hemorrhage infants using measures of burst symmetry and sharpness yielded high true-positive rates (82% and 88%, respectively) and low false-positive rates (19% and 8%). Conventional electroencephalography measures of interburst intervals and burst counts were not significantly associated with intraventricular hemorrhage.

CONCLUSIONS

Detection of intraventricular hemorrhage during the first postnatal days is possible from bedside measures of brain activity prior to ultrasound confirmation of intraventricular hemorrhage. Significantly, our novel automated assessment of electroencephalography preempts the occurrence of intraventricular hemorrhage in the extremely preterm. Early bedside detection of intraventricular hemorrhage holds promise for advancing individual care, targeted therapeutic trials, and understanding mechanisms of brain injury in neonates.

Neonatal Restriction of Tactile Inputs Leads to Long-Lasting Impairments of Cross-Modal Processing

Optimal behavior relies on the combination of inputs from multiple senses through complex interactions within neocortical networks. The ontogeny of this multisensory interplay is still unknown. Here, we identify critical factors that control the development of visual-tactile processing by combining in vivo electrophysiology with anatomical/functional assessment of cortico-cortical communication and behavioral investigation of pigmented rats. We demonstrate that the transient reduction of unimodal (tactile) inputs during a short period of neonatal development prior to the first cross-modal experience affects feed-forward subcortico-cortical interactions by attenuating the cross-modal enhancement of evoked responses in the adult primary somatosensory cortex. Moreover, the neonatal manipulation alters cortico-cortical interactions by decreasing the cross-modal synchrony and directionality in line with the sparsification of direct projections between primary somatosensory and visual cortices. At the behavioral level, these functional and structural deficits resulted in lower cross-modal matching abilities. Thus, neonatal unimodal experience during defined developmental stages is necessary for setting up the neuronal networks of multisensory processing.

Reducing unisensory experience during neonatal development causes permanent disruption of connectivity between primary sensory cortices, resulting in impaired multisensory abilities.

Our senses, working together, enable us to interact with the environment. To obtain a unified percept of the world, diverse sensory inputs need to be bound together within distributed but strongly interconnected neuronal networks. Many multisensory abilities emerge or mature late in life, long after the maturation of the individual senses, yet the factors and mechanisms controlling their development are largely unknown. Here, we provide evidence for the critical role of unisensory experience during early postnatal life for the development of multisensory integration. Focusing on visual-tactile interactions in pigmented rats with good visual acuity, we show that a transient reduction of tactile inputs during neonatal development leads to sparser direct connections between adult primary visual and somatosensory cortices. As a result, these animals showed reduced neuronal activation following co-occurring tactile and visual stimuli, as well as impaired communication within visual-somatosensory networks. The structural and functional deficits resulting from an early manipulation of tactile experience had major behavioral consequences, impairing the rats’ ability to transfer information about encountered objects between senses. Thus, unisensory experience during early development shapes the neuronal networks of multisensory processing and the ability to transfer cross-modal information.

Reduced Cortical Activity Impairs Development and Plasticity after Neonatal Hypoxia Ischemia

Survivors of preterm birth are at high risk of pervasive cognitive and learning impairments, suggesting disrupted early brain development. The limits of viability for preterm birth encompass the third trimester of pregnancy, a "precritical period" of activity-dependent development characterized by the onset of spontaneous and evoked patterned electrical activity that drives neuronal maturation and formation of cortical circuits. Reduced background activity on electroencephalogram (EEG) is a sensitive marker of brain injury in human preterm infants that predicts poor neurodevelopmental outcome. We studied a rodent model of very early hypoxic-ischemic brain injury to investigate effects of injury on both general background and specific patterns of cortical activity measured with EEG. EEG background activity is depressed transiently after moderate hypoxia-ischemia with associated loss of spindle bursts. Depressed activity, in turn, is associated with delayed expression of glutamate receptor subunits and transporters. Cortical pyramidal neurons show reduced dendrite development and spine formation. Complementing previous observations in this model of impaired visual cortical plasticity, we find reduced somatosensory whisker barrel plasticity. Finally, EEG recordings from human premature newborns with brain injury demonstrate similar depressed background activity and loss of bursts in the spindle frequency band. Together, these findings suggest that abnormal development after early brain injury may result in part from disruption of specific forms of brain activity necessary for activity-dependent circuit development.

SIGNIFICANCE STATEMENT

Preterm birth and term birth asphyxia result in brain injury from inadequate oxygen delivery and constitute a major and growing worldwide health problem. Poor outcomes are noted in a majority of very premature (<25 weeks gestation) newborns, resulting in death or life-long morbidity with motor, sensory, learning, behavioral, and language disabilities that limit academic achievement and well-being. Limited progress has been made to develop therapies that improve neurologic outcomes. The overall objective of this study is to understand the effect of early brain injury on activity-dependent brain development and cortical plasticity to develop new treatments that will optimize repair and recovery after brain injury.

Distinct calcium signals in developing cortical interneurons persist despite disorganization of cortex by Tbr1 KO

Cortical development involves the structuring of network features by genetically programmed molecular signaling pathways. Additionally, spontaneous ion channel activity refines neuronal connections. We examine Ca(2+) fluctuations in the first postnatal week of normal mouse neocortex and that expressing knockout of the transcription factor T-brain-1 (Tbr1): a signaling molecule in cortical patterning and differentiation of excitatory neurons. In cortex, glutamatergic neurons express Tbr1 just before the onset of population electrical activity that is accompanied by intracellular Ca(2+) increases. It is known that glutamatergic cells are disordered with Tbr1 KO such that normal laying of the cortex, with newer born cells residing in superficial layers, does not occur. However, the fate of cortical interneurons is not well studied, nor is the ability of Tbr1 deficient cortex to express normal physiological activity. Using fluorescent proteins targeted to interneurons, we find that cortical interneurons are also disordered in the Tbr1 knockout. Using Ca(2+) imaging we find that population activity in mutant cortex occurs at normal frequencies with similar sensitivity to GABAA receptor blockade as in nonmutant cortex. Finally, using multichannel fluorescence imaging of Ca(2+) indicator dye and interneurons labeled with red fluorescent protein, we identify an additional Ca(2+) signal in interneurons distinct from population activity and with different pharmacological sensitivities. Our results show the population activity described here is a robust property of the developing network that continues in the absence of an important signaling molecule, Tbr1, and that cortical interneurons generate distinct forms of activity that may serve different developmental functions. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 705-720, 2016.

Early network activity propagates bidirectionally between hippocampus and cortex

Spontaneous activity in the developing brain helps refine neuronal connections before the arrival of sensory-driven neuronal activity. In mouse neocortex during the first postnatal week, waves of spontaneous activity originating from pacemaker regions in the septal nucleus and piriform cortex propagate through the neocortex. Using high-speed Ca(2+) imaging to resolve the spatiotemporal dynamics of wave propagation in parasagittal mouse brain slices, we show that the hippocampus can act as an additional source of neocortical waves. Some waves that originate in the hippocampus remain restricted to that structure, while others pause at the hippocampus-neocortex boundary and then propagate into the neocortex. Blocking GABAergic neurotransmission decreases the likelihood of wave propagation into neocortex, whereas blocking glutamatergic neurotransmission eliminates spontaneous and evoked hippocampal waves. A subset of hippocampal and cortical waves trigger Ca(2+) waves in astrocytic networks after a brief delay. Hippocampal waves accompanied by Ca(2+) elevation in astrocytes are more likely to propagate into the neocortex. Finally, we show that two structures in our preparation that initiate waves-the hippocampus and the piriform cortex-can be electrically stimulated to initiate propagating waves at lower thresholds than the neocortex, indicating that the intrinsic circuit properties of those regions are responsible for their pacemaker function.

Structural damage in early preterm brain changes the electric resting state networks

A robust functional bimodality is found in the long-range spatial correlations of newborn cortical activity, and it likely provides the developmentally crucial functional coordination during the initial growth of brain networks. This study searched for possible acute effects on this large scale cortical coordination after acute structural brain lesion in early preterm infants. EEG recordings were obtained from preterm infants without (n=11) and with (n=6) haemorrhagic brain lesion detected in their routine ultrasound exam. The spatial cortical correlations in band-specific amplitudes were examined within two amplitude regimes, high and low amplitude periods, respectively. Technical validation of our analytical approach showed that bimodality of this kind is a genuine physiological characteristic of each brain network. It was not observed in datasets created from uniform noise, neither is it found between randomly paired signals. Hence, the observed bimodality arises from specific interactions between cortical regions. We found that significant long-range amplitude correlations are found in most signal pairs in both groups at high amplitudes, but the correlations are generally weaker in newborns with brain lesions. The group difference is larger during high mode, however the difference did not have any statistically apparent topology. Graph theoretical analysis confirmed a significantly larger weight dispersion in the newborns with brain lesion. Comparison of graph measures to a child's performance at two years showed that lower clustering coefficient and weight dispersion were both correlated to better neurodevelopmental outcomes. Our findings suggest that the common preterm brain haemorrhage causes diffuse changes in the functional long-range cortical correlations. It has been recently recognized that the high mode network activity is crucial for early brain development. The present observations may hence offer a mechanistic link between early lesion and the later emergence of complex neurocognitive sequelae.

Visual fixation in human newborns correlates with extensive white matter networks and predicts long-term neurocognitive development

Infants are well known to seek eye contact, and they prefer to fixate on developmentally meaningful objects, such as the human face. It is also known, that visual abilities are important for the developmental cascades of cognition from later infancy to childhood. It is less understood, however, whether newborn visual abilities relate to later cognitive development, and whether newborn ability for visual fixation can be assigned to early microstructural maturation. Here, we investigate relationship between newborn visual fixation (VF) and gaze behavior (GB) to performance in visuomotor and visual reasoning tasks in two cohorts with cognitive follow-up at 2 (n = 57) and 5 (n = 1410) years of age. We also analyzed brain microstructural correlates to VF (n = 45) by voxel-based analysis of fractional anisotropy (FA) in newborn diffusion tensor imaging. Our results show that newborn VF is significantly related to visual-motor performance at both 2 and 5 years, as well as to visual reasoning at 5 years of age. Moreover, good newborn VF relates to widely increased FA levels across the white matter. Comparison to motor performance indicated that early VF is preferentially related to visuocognitive development, and that early motor performance relates neither to white matter integrity nor to visuocognitive development. The present findings suggest that newborn VF is supported by brainwide subcortical networks and it represents an early building block for the developmental cascades of cognition.

Cortical burst dynamics predict clinical outcome early in extremely preterm infants

Intermittent bursts of electrical activity are a ubiquitous signature of very early brain activity. Previous studies have largely focused on assessing the amplitudes of these transient cortical bursts or the intervals between them. Recent advances in basic neuroscience have identified the presence of scale-free 'avalanche' processes in bursting patterns of cortical activity in other clinical contexts. Here, we hypothesize that cortical bursts in human preterm infants also exhibit scale-free properties, providing new insights into the nature, temporal evolution, and prognostic value of spontaneous brain activity in the days immediately following preterm birth. We examined electroencephalographic recordings from 43 extremely preterm infants (gestational age 22-28 weeks) and demonstrated that their cortical bursts exhibit scale-free properties as early as 12 h after birth. The scaling relationships of cortical bursts correlate significantly with later mental development-particularly within the first 12 h of life. These findings show that early preterm brain activity is characterized by scale-free dynamics which carry developmental significance, hence offering novel means for rapid and early clinical prediction of neurodevelopmental outcomes.

Critical periods for the neurodevelopmental processes of externalizing and internalizing

Research on neurobiological development is providing insight into the nature and mechanisms of human neural plasticity. These mechanisms appear to support two different forms of developmental learning. One form of learning could be described as externalizing, in which neural representations are highly responsive to environmental influences, as the child typically operates under a mode of hedonic approach. A second form of learning supports internalizing, in which motive control separates attention and self-regulation from the immediate influences of the context, particularly when the child faces conditions of avoidance and threat. The dorsal cortical networks of externalizing are organized around dorsal limbic (cingulate, septal, lateral hypothalamic, hippocampal, and ventral striatal) circuits. In contrast, the ventral cortical networks of internalizing are organized around ventral limbic (anterior temporal and orbital cortex, extended amygdala, dorsal striatal, and mediodorsal thalamic) circuits. These dual divisions of the limbic system in turn self-regulate their arousal levels through different brain stem and forebrain neuromodulator projection systems, with dorsal corticolimbic networks regulated strongly by locus coeruleus norepinephrine and brain stem raphe nucleus serotonin projection systems, and ventral corticolimbic networks regulated by ventral tegmental dopamine and forebrain acetylcholine projections. Because the arousal control systems appear to regulate specific properties of neural plasticity in development, an analysis of these systems explains differences between externalizing and internalizing at multiple levels of neural and psychological self-regulation. In neuroscience, the concept of critical periods has been applied to times when experience is essential for the maturation of sensory systems. In a more general neuropsychological analysis, certain periods of the child's development require successful self-regulation through the differential capacities for externalizing and internalizing.

A valuable and promising method for recording brain activity in behaving newborn rodents

Neurophysiological recording of brain activity has been critically important to the field of neuroscience, but has contributed little to the field of developmental psychobiology. The reasons for this can be traced largely to methodological difficulties associated with recording neural activity in behaving newborn rats and mice. Over the last decade, however, the evolution of methods for recording from head-fixed newborns has heralded a new era in developmental neurophysiology. Here, we review these recent developments and provide a step-by-step primer for those interested in applying the head-fix method to their own research questions. Until now, this method has been used primarily to investigate spontaneous brain activity across sleep and wakefulness, the contributions of the sensory periphery to brain activity, or intrinsic network activity. Now, with some ingenuity, the uses of the head-fix method can be expanded to other domains to benefit our understanding of brain-behavior relations under normal and pathophysiological conditions across early development.

Early Brain Activity Relates to Subsequent Brain Growth in Premature Infants

Recent experimental studies have shown that early brain activity is crucial for neuronal survival and the development of brain networks; however, it has been challenging to assess its role in the developing human brain. We employed serial quantitative magnetic resonance imaging to measure the rate of growth in circumscribed brain tissues from preterm to term age, and compared it with measures of electroencephalographic (EEG) activity during the first postnatal days by 2 different methods. EEG metrics of functional activity were computed: EEG signal peak-to-peak amplitude and the occurrence of developmentally important spontaneous activity transients (SATs). We found that an increased brain activity in the first postnatal days correlates with a faster growth of brain structures during subsequent months until term age. Total brain volume, and in particular subcortical gray matter volume, grew faster in babies with less cortical electrical quiescence and with more SAT events. The present findings are compatible with the idea that (1) early cortical network activity is important for brain growth, and that (2) objective measures may be devised to follow early human brain activity in a biologically reasoned way in future research as well as during intensive care treatment.

Unsupervised classification of neocortical activity patterns in neonatal and pre-juvenile rodents

Flexible communication within the brain, which relies on oscillatory activity, is not confined to adult neuronal networks. Experimental evidence has documented the presence of discontinuous patterns of oscillatory activity already during early development. Their highly variable spatial and time-frequency organization has been related to region specificity. However, it might be equally due to the absence of unitary criteria for classifying the early activity patterns, since they have been mainly characterized by visual inspection. Therefore, robust and unbiased methods for categorizing these discontinuous oscillations are needed for increasingly complex data sets from different labs. Here, we introduce an unsupervised detection and classification algorithm for the discontinuous activity patterns of rodents during early development. For this, in a first step time windows with discontinuous oscillations vs. epochs of network “silence” were identified. In a second step, the major features of detected events were identified and processed by principal component analysis for deciding on their contribution to the classification of different oscillatory patterns. Finally, these patterns were categorized using an unsupervised cluster algorithm. The results were validated on manually characterized neonatal spindle bursts (SB), which ubiquitously entrain neocortical areas of rats and mice, and prelimbic nested gamma spindle bursts (NG). Moreover, the algorithm led to satisfactory results for oscillatory events that, due to increased similarity of their features, were more difficult to classify, e.g., during the pre-juvenile developmental period. Based on a linear classification, the optimal number of features to consider increased with the difficulty of detection. This algorithm allows the comparison of neonatal and pre-juvenile oscillatory patterns in their spatial and temporal organization. It might represent a first step for the unbiased elucidation of activity patterns during development.

Taurine activates GABAergic networks in the neocortex of immature mice

Although it has been suggested that taurine is the main endogenous neurotransmitter acting on glycine receptors, the implications of glycine receptor-mediated taurine actions on immature neocortical networks have not been addressed yet. To investigate the influence of taurine on the excitability of neuronal networks in the immature neocortex, we performed whole-cell patch-clamp recordings from visually identified pyramidal neurons and interneurons in coronal slices from C57Bl/6 and GAD67-green fluorescent protein (GFP) transgenic mice (postnatal days 2–4). In 46% of the pyramidal neurons bath-application of taurine at concentrations ≥ 300 μM significantly enhanced the frequency of postsynaptic currents (PSCs) by 744.3 ± 93.8% (n = 120 cells). This taurine-induced increase of PSC frequency was abolished by 0.2 μM tetrodotoxin (TTX), 1 μM strychnine or 3 μM gabazine, but was unaffected by the glutamatergic antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (±) R(-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP), suggesting that taurine specifically activates GABAergic network activity projecting to pyramidal neurons. Cell-attached recordings revealed that taurine enhanced the frequency of action potentials (APs) in pyramidal neurons, indicating an excitatory action of the GABAergic PSCs. In order to identify the presynaptic targets of taurine we demonstrate that bath application of taurine induced in GAD67-GFP labeled interneurons an inward current that is mainly mediated by glycine receptors and can generate APs in these cells. We conclude from these results that taurine can enhance network excitability in the immature neocortex by selectively activating GABAergic interneurons via interactions with glycine receptors.

Resonance properties of GABAergic interneurons in immature GAD67-GFP mouse neocortex

Subthreshold resonance is a characteristic membrane property of different neuronal classes, is critically involved in the generation of network oscillations, and tunes the integration of synaptic inputs to particular frequency ranges. In order to investigate whether neocortical GABAergic interneurons show resonant behavior already during early postnatal development, we performed whole-cell patch-clamp recordings from visually identified interneurons in supragranular layers of parietal regions in coronal neocortical slices from postnatal day (P) P6-P13 GAD67-GFP knock-in mice. Subthreshold resonance was analyzed by injection of sinusoidal current with varying frequency. About 50% of the investigated GABAergic interneurons showed subthreshold resonance with an average frequency of 2.0±0.2 Hz (n=38). Membrane hyperpolarization to -86 mV attenuated the frequency and strength of subthreshold resonance. In the presence of 1 mM Ni(2+) subthreshold resonance was virtually abolished, suggesting that T-type Ca(2+) currents are critically involved in the generation of resonance. In contrast, subthreshold resonance was not affected by ZD7288, a blocker of HCN channels. Application of TTX suppressed subthreshold resonance at depolarized, but not hyperpolarized membrane potential, suggesting that persistent Na(+) current contribute to the amplification of membrane resonance. In summary, these results demonstrate that GABAergic interneurons express subthreshold resonance at low frequencies, with T-type Ca(2+) and persistent Na(+) currents underlying the generation of membrane resonance. The membrane resonance of immature interneurons may contribute to the generation of slow oscillatory activity pattern in the immature neocortex and enhance the temporal precision of synaptic integration in developing cortical neurons.

Decoding the language of epigenetics during neural development is key for understanding development as well as developmental neurotoxicity

Neural development is a delicate process that can be disrupted by pollution that exerts detrimental impact on neural signaling. This commentary highlights recent discoveries in the arena of research at the interface of environmental toxicology and developmental neuroscience relating to toxicity mechanisms of bisphenol A (BPA), a ubiquitous chemical used in manufacturing of plastics and epoxy resins that is known to bind to and interfere with estrogen receptors, estrogen-receptor-related receptors and other receptors for gonadal steroids. It was recently observed that BPA disrupts the perinatal chloride shift, a key neurodevelopmental mechanism that brings down neuronal chloride from ~100 mM to ~20 mM within weeks. The chloride shift happens in all central nervous systems of vertebrates around parturition. High neuronal chloride supports neuron precursors' migrations, low neuronal chloride is the prerequisite for inhibitory action of neurotransmitters GABA and glycine, and thus an absolute requisite for normal functioning of the mature CNS. One critical contributor to the neuronal chloride shift is the concomitant upregulation of expression of the chloride-extruding transporter molecule, KCC2. We highlight recent findings including our discovery that BPA disrupts the chloride shift in a sex-specific manner by recruiting epigenetics mechanisms. These could be relevant for childhood neuropsychiatric disorders as well as for liability to develop chronic neuropsychiatric diseases later in life.

Oscillatory coupling within neonatal prefrontal-hippocampal networks is independent of selective removal of GABAergic neurons in the hippocampus

GABAergic neurons have been proposed to control oscillatory entrainment and cognitive processing in prefrontal-hippocampal networks. Co-activation of these networks emerges already during neonatal development, with hippocampal theta bursts driving prefrontal oscillations via axonal projections. The cellular substrate of neonatal prefrontal-hippocampal communication and in particular, the role of GABAergic neurons, is still unknown. Here, we used saporin-conjugated anti-vesicular GABA transporter antibodies to cause selective immunotoxic lesion of GABAergic neurons in the CA1 area of the hippocampus during the first postnatal week. Without affecting the somatic development of rat pups, the lesion impaired the generation of hippocampal sharp waves, but not of theta bursts during neonatal development. Moreover, the oscillatory entrainment and firing of neonatal prefrontal cortex as well as the early prefrontal-hippocampal synchrony were largely independent of GABAergic neurotransmission in the hippocampus. Thus, hippocampal interneurons are critical elements for the ontogeny of hippocampal sharp waves, but seem to not control the directed oscillatory coupling between the neonatal prefrontal cortex and hippocampus.

Sleep Spindles: Where They Come From, What They Do

Sleep spindles are extensively studied electroencephalographic rhythms that recur periodically during non-rapid eye movement sleep and that are associated with rhythmic discharges of neurons throughout the thalamocortical system. Their occurrence thus constrains many aspects of the communication between thalamus and cortex, ranging from sensory transmission, to cortical plasticity and learning, to development and disease. I review these functional aspects in conjunction with novel findings on the cellular and molecular makeup of spindle-pacemaking circuits. A highlight in the search of roles for sleep spindles is the repeated finding that spindles correlate with memory consolidation in humans and animals. By illustrating that spindles are at the forefront understanding on how the brain might benefit from sleep rhythms, I hope to stimulate further experimentation.

Voltage-sensitive dye imaging reveals dynamic spatiotemporal properties of cortical activity after spontaneous muscle twitches in the newborn rat

Spontaneous activity in the developing brain contributes to its maturation, but how this activity is coordinated between distinct cortical regions and whether it might reflect developing sensory circuits is not well understood. Here, we address this question by imaging the spread and synchronization of cortical activity using voltage-sensitive dyes (VSDs) in the developing rat in vivo. In postnatal day 4-6 rats (n = 10), we collected spontaneous changes in VSD signal that reflect underlying membrane potential changes over a large craniotomy (50 mm2) that encompassed both the sensory and motor cortices of both hemispheres. Bursts of depolarization that occurred approximately once every 12 s were preceded by spontaneous twitches of the hindlimbs and/or tail. The close association with peripheral movements suggests that these bursts may represent a slow component of spindle bursts, a prominent form of activity in the developing somatosensory cortex. Twitch-associated cortical activity was synchronized between subregions of somatosensory cortex, which reflected the synchronized twitching of the limbs and tail. This activity also spread asymmetrically, toward the midline of the brain. We found that the spatial and temporal structure of such spontaneous cortical bursts closely matched that of sensory-evoked activity elicited via direct stimulation of the periphery. These data suggest that spontaneous cortical activity provides a recurring template of functional cortical circuits within the developing cortex and could contribute to the maturation of integrative connections between sensory and motor cortices.

Neonatal whisker clipping alters behavior, neuronal structure and neural activity in adult rats

Early experience plays critical roles during the development of sensory systems. For example, neonatal surgical manipulations of the whiskers in rodents lead to altered neural activity and behaviors later in life. However, while surgical procedures damage the sensory pathway; it is hard to examine the impact of whisker deprivation on adult animals. To address this issue, we performed a neonatal whisker clipping (WC0-3) paradigm, a non-invasive procedure, from the day of birth (P0) to postnatal day (P) 3, and examined behavioral performances in their adult age. With fully regrown whiskers, the WC0-3 rats exhibited shorter crossable distance than controls in a gap-crossing task, suggesting a defect in their whisker-specific tactile function. In their somatosensory cortex, the layer IV spiny stellate neurons had reduced dendritic complexity and spine density. After exploration in a novel environment, the expression of an activity-dependent immediate early gene, c-fos, increased dramatically in the somatosensory cortex. However, in WC0-3 rats, the number of c-Fos positive cells was less than those in control rats, indicating a fault in transducing sensory-related neural activity between cortical layers in WC0-3 rats. Together, our results demonstrate the roles of early tactile experience on the establishment of layer-specific excitatory connection in the barrel cortex. Early sensory insufficiency would leave long-lasting functional deficits in the sensory system.

Rapid whisker movements in sleeping newborn rats

Spontaneous activity in the sensory periphery drives infant brain activity and is thought to contribute to the formation of retinotopic and somatotopic maps. In infant rats during active (or REM) sleep, brainstem-generated spontaneous activity triggers hundreds of thousands of skeletal muscle twitches each day; sensory feedback from the resulting limb movements is a primary activator of forebrain activity. The rodent whisker system, with its precise isomorphic mapping of individual whiskers to discrete brain areas, has been a key contributor to our understanding of somatotopic maps and developmental plasticity. But although whisker movements are controlled by dedicated skeletal muscles, spontaneous whisker activity has not been entertained as a contributing factor to the development of this system. Here we report in 3- to 6-day-old rats that whiskers twitch rapidly and asynchronously during active sleep; furthermore, neurons in whisker thalamus exhibit bursts of activity that are tightly associated with twitches but occur infrequently during waking. Finally, we observed barrel-specific cortical activity during periods of twitching. This is the first report of self-generated, sleep-related twitches in the developing whisker system, a sensorimotor system that is unique for the precision with which it can be experimentally manipulated. The discovery of whisker twitching will allow us to attain a better understanding of the contributions of peripheral sensory activity to somatosensory integration and plasticity in the developing nervous system.

Development of coherent neuronal activity patterns in mammalian cortical networks: common principles and local hetereogeneity

Many mammals are born in a very immature state and develop their rich repertoire of behavioral and cognitive functions postnatally. This development goes in parallel with changes in the anatomical and functional organization of cortical structures which are involved in most complex activities. The emerging spatiotemporal activity patterns in multi-neuronal cortical networks may indeed form a direct neuronal correlate of systemic functions like perception, sensorimotor integration, decision making or memory formation. During recent years, several studies--mostly in rodents--have shed light on the ontogenesis of such highly organized patterns of network activity. While each local network has its own peculiar properties, some general rules can be derived. We therefore review and compare data from the developing hippocampus, neocortex and--as an intermediate region--entorhinal cortex. All cortices seem to follow a characteristic sequence starting with uncorrelated activity in uncoupled single neurons where transient activity seems to have mostly trophic effects. In rodents, before and shortly after birth, cortical networks develop weakly coordinated multineuronal discharges which have been termed synchronous plateau assemblies (SPAs). While these patterns rely mostly on electrical coupling by gap junctions, the subsequent increase in number and maturation of chemical synapses leads to the generation of large-scale coherent discharges. These patterns have been termed giant depolarizing potentials (GDPs) for predominantly GABA-induced events or early network oscillations (ENOs) for mostly glutamatergic bursts, respectively. During the third to fourth postnatal week, cortical areas reach their final activity patterns with distinct network oscillations and highly specific neuronal discharge sequences which support adult behavior. While some of the mechanisms underlying maturation of network activity have been elucidated much work remains to be done in order to fully understand the rules governing transition from immature to mature patterns of network activity.

Long-term potentiation in the neonatal rat barrel cortex in vivo

Long-term potentiation (LTP) is important for the activity-dependent formation of early cortical circuits. In the neonatal rodent barrel cortex, LTP has been studied only in vitro. We combined voltage-sensitive dye imaging with extracellular multielectrode recordings to study whisker stimulation-induced LTP in the whisker-to-barrel cortex pathway of the neonatal rat barrel cortex in vivo. Single whisker stimulation at 2 Hz for 10 min induced an age-dependent expression of LTP in postnatal day (P) 0 to P14 rats, with the strongest expression of LTP at P3-P5. The magnitude of LTP was largest in the activated barrel-related column, smaller in the surrounding septal region, and no LTP could be observed in the neighboring barrel. Current source density analyses revealed an LTP-associated increase of synaptic current sinks in layer IV/lower layer II/III at P3-P5 and in the cortical plate/upper layer V at P0-P1. Our study demonstrates for the first time an age-dependent and spatially confined LTP in the barrel cortex of the newborn rat in vivo.

Resonance properties of different neuronal populations in the immature mouse neocortex

In vivo recordings in the immature neocortex revealed spontaneous and sensory-driven oscillatory activity from delta (0.5-4 Hz) to gamma (30-100 Hz) frequencies. In order to investigate whether the resonance properties of distinct neuronal populations in the immature neocortex contribute to these network oscillations, we performed whole-cell patch-clamp recordings from visually identified neurons in tangential and coronal neocortical slices from postnatal day (P)0-P7 C57Bl/6 mice. Subthreshold resonance was analysed by sinusoidal current injection of varying frequency. All Cajal-Retzius cells showed subthreshold resonance, with an average frequency of 2.6 ± 0.1 Hz (n = 60), which was massively reduced by ZD7288, a blocker of hyperpolarization-activated cation currents. Approximately 65.6% (n = 61) of the supragranular pyramidal neurons showed subthreshold resonance, with an average frequency of 1.4 ± 0.1 Hz (n = 40). Application of Ni(2+) suppressed subthreshold resonance, suggesting that low-threshold calcium currents contribute to resonance in these neurons. Approximately 63.6% (n = 77) of the layer V pyramidal neurons showed subthreshold resonance, with an average frequency of 1.4 ± 0.2 Hz (n = 49), which was abolished by ZD7288. Only 44.1% (n = 59) of the subplate neurons showed subthreshold resonance, with an average frequency of 1.3 ± 0.2 Hz (n = 26) and a small resonance strength. In summary, these results demonstrate that neurons in all investigated layers show resonance behavior, with either hyperpolarization-activated cation or low-threshold calcium currents contributing to the subthreshold resonance. The observed resonance frequencies are in the range of slow activity patterns observed in the immature neocortex, suggesting that subthreshold resonance may support the generation of this activity.

Development of Fetal Movement between 26 and 36-Weeks' Gestation in Response to Vibro-Acoustic Stimulation

BACKGROUND

Ultrasound observation of fetal movement has documented general trends in motor development and fetal age when motor response to stimulation is observed. Evaluation of fetal movement quality, in addition to specific motor activity, may improve documentation of motor development and highlight specific motor responses to stimulation.

AIM

The aim of this investigation was to assess fetal movement at 26 and 36-weeks gestation during three conditions (baseline, immediate response to vibro-acoustic stimulation (VAS), and post-response).

DESIGN

A prospective, longitudinal design was utilized.

SUBJECTS

Twelve normally developing fetuses, eight females and four males, were examined with continuous ultrasound imaging.

OUTCOME MEASURES

The fetal neurobehavioral coding system (FENS) was used to evaluate the quality of motor activity during 10-s epochs over the three conditions.

RESULTS

Seventy-five percent of the fetuses at the 26-week assessment and 100% of the fetuses at the 36-week assessment responded with movement immediately following stimulation. Significant differences in head, fetal breathing, general, limb, and mouthing movements were detected between the 26 and 36-week assessments. Movement differences between conditions were detected in head, fetal breathing, limb, and mouthing movements.

CONCLUSION

Smoother and more complex movement was observed with fetal maturation. Following VAS stimulation, an immediate increase of large, jerky movements suggests instability in fetal capabilities. Fetal movement quality changes over gestation may reflect sensorimotor synaptogenesis in the central nervous system, while observation of immature movement patterns following VAS stimulation may reflect movement pattern instability.

Language development after cochlear implantation: an epigenetic model

Growing evidence supports the notion that dynamic gene expression, subject to epigenetic control, organizes multiple influences to enable a child to learn to listen and to talk. Here, we review neurobiological and genetic influences on spoken language development in the context of results of a longitudinal trial of cochlear implantation of young children with severe to profound sensorineural hearing loss in the Childhood Development after Cochlear Implantation study. We specifically examine the results of cochlear implantation in participants who were congenitally deaf (N = 116). Prior to intervention, these participants were subject to naturally imposed constraints in sensory (acoustic-phonologic) inputs during critical phases of development when spoken language skills are typically achieved rapidly. Their candidacy for a cochlear implant was prompted by delays (n = 20) or an essential absence of spoken language acquisition (n = 96). Observations thus present an opportunity to evaluate the impact of factors that influence the emergence of spoken language, particularly in the context of hearing restoration in sensitive periods for language acquisition. Outcomes demonstrate considerable variation in spoken language learning, although significant advantages exist for the congenitally deaf children implanted prior to 18 months of age. While age at implantation carries high predictive value in forecasting performance on measures of spoken language, several factors show significant association, particularly those related to parent-child interactions. Importantly, the significance of environmental variables in their predictive value for language development varies with age at implantation. These observations are considered in the context of an epigenetic model in which dynamic genomic expression can modulate aspects of auditory learning, offering insights into factors that can influence a child's acquisition of spoken language after cochlear implantation. Increased understanding of these interactions could lead to targeted interventions that interact with the epigenome to influence language outcomes with intervention, particularly in periods in which development is subject to time-sensitive experience.

pUNISHER: a high-level expression cassette for use with recombinant viral vectors for rapid and long term in vivo neuronal expression in the CNS

Fast onset and high-level neurospecific transgene expression in vivo is of importance for many areas in neuroscience, from basic to translational, and can significantly reduce the amount of vector load required to maintain transgene expression in vivo. In this study, we tested various cis elements to optimize transgene expression at transcriptional, posttranscriptional, and posttranslational levels and combined them together to create the high-level neuronal transgene expression cassette pUNISHER. Using a second-generation adenoviral vector system in combination with the pUNISHER cassette, we characterized its rate of onset of detectable expression and levels of expression compared with a neurospecific expression cassette driven by the 470-bp human synapsin promoter in vitro and in vivo. Our results demonstrate in primary neurons that the pUNISHER cassette, in a recombinant adenovirus type 5 background, led to a faster rate of onset of detectable transgene expression and higher level of transgene expression. More importantly, this cassette led to highly correlated neuronal expression in vivo and to stable transgene expression up to 30 days in the auditory brain stem with no toxicity on the characteristics of synaptic transmission and plasticity at the calyx of Held synapse. Thus the pUNISHER cassette is an ideal high-level neuronal expression cassette for use in vivo for neuroscience applications.

Developmental programming of early brain and behaviour development and mental health: a conceptual framework

The Developmental Origins of Health and Disease (DOHaD) hypothesis studies the short- and long-term consequences of the conditions of the developmental environment for phenotypic variations in health and disease. Central to this hypothesis is the idea of interdependence of developmental influences, genes, and environment. Developmental programming effects are mediated by alterations in fundamental life functions, and the most enduring effects seem to occur if the main regulatory instances of the organ - the (epi)genome and the brain - are affected. Some new insights in the role of chromatin, in cellular development and differentiation, and neural plasticity from the field of epigenetics are introduced, followed by a section on epigenetics and brain development. It is proposed to extend the DOHaD hypothesis into the 'Developmental Origins of Behaviour, Health, and Disease' (DOBHaD) concept. Pregnancy and the early postnatal period are times of both great opportunity and considerable risk, and their influence can extend over a lifetime. The DOBHaD hypothesis opens fundamental new perspectives on preventing diseases and disorders.