Subcortical regulation of cortical development: some effects of early, selective deprivations

Defining neuroplasticity

Neuroplasticity, i.e., the modifiability of the brain, is different in development and adulthood. The first includes changes in: (i) neurogenesis and control of neuron number; (ii) neuronal migration; (iii) differentiation of the somato-dendritic and axonal phenotypes; (iv) formation of connections; (v) cytoarchitectonic differentiation. These changes are often interrelated and can lead to: (vi) system-wide modifications of brain structure as well as to (vii) acquisition of specific functions such as ocular dominance or language. Myelination appears to be plastic both in development and adulthood, at least, in rodents. Adult neuroplasticity is limited, and is mainly expressed as changes in the strength of excitatory and inhibitory synapses while the attempts to regenerate connections have met with limited success. The outcomes of neuroplasticity are not necessarily adaptive, but can also be the cause of neurological and psychiatric pathologies.

An Infant's Question on COVID-19 and Music: Should I Attend My Online Classes?

In the last few months, we all have faced a profound challenge to balance our lives amidst fighting the COVID-19 pandemic. The reactions to this coronavirus pandemic have no doubt affected all aspects of our everyday normalcy as they have called for an extended set of measures that have greatly impacted our social interactions and well-being. During this unprecedented global situation, the pandemic has also taken its toll on education, as schools, universities, and other educational institutions have suspended their programs or moved online to retain educational momentum. Among the programs that tried to adapt to this online model was the early years music education. This mini-review article aims to discuss the framework of online existence for the early years music programs amid the COVID-19 crisis, while considering their benefits and character under these extraordinary circumstances.

Structural brain plasticity induced by early blindness

It is well established that early blindness results in behavioural adaptations. While the functional effects of visual deprivation have been well researched, anatomical studies are scarce. The aim of this study was to investigate whole brain structural plasticity in a mouse model of congenital blindness. Volumetric analyses were conducted on high-resolution MRI images and histological sections from the same brains. These morphometric measurements were compared between anophthalmic and sighted ZRDBA mice obtained by breeding ZRDCT and DBA mice. Results from MRI analyses using the Multiple Automatically Generated Templates (MAGeT) method showed smaller volume for the primary visual cortex and superior colliculi in anophthalmic compared with sighted mice. Deformation-based morphometry revealed smaller volumes within the dorsal lateral geniculate nuclei and the lateral secondary visual cortex and larger volumes within olfactory areas, piriform cortex, orbital areas and the amygdala, in anophthalmic compared with sighted mice. Histological analyses revealed a larger volume for the amygdala and smaller volume for the superior colliculi, primary visual cortex and medial secondary visual cortex, in anophthalmic compared with sighted mice. The absence of superficial visual layers of the superior colliculus and the thinner cortical layer IV of the primary and secondary visual cortices may explain the smaller volume of these areas, although this was observed in a limited sample. The present study shows large-scale brain plasticity in a mouse model of congenital blindness. In addition, the congruence of MRI and histological findings support the use of MRI to investigate structural brain plasticity in the mouse.

The Target of Exuberant Projections in Development

In addition to neuronal death and elimination of synapses, the production of transient, exuberant axons, and axonal branches is a general phenomenon in development across species and systems. To understand what drives the decision of which axons are maintained and which are eliminated, it is important to monitor the interaction of juvenile axons at their target. As old and more recent work show, unlike what is claimed by Ribeiro Gomez et al. (2019), in the cerebral cortex, both classes of axons branch in the white matter near the target; axons destined to be maintained massively invade the gray matter where they develop terminal arbors and synapses. Axons destined to elimination remain in the white matter although a few transient, exploratory branches can enter the cortex. Axonal behavior and fate seem dictated by positional information probably conveyed by thalamic afferents and activity. Unlike what is suggested by Ribeiro Gomez et al. (2019), axonal selection should not be confused with synaptic reduction, which is a later event with minor or no impact on the topography of the connection.

Behavioral consequences of mild traumatic brain injury in preschoolers

BACKGROUND

Pediatric traumatic brain injury (TBI) is a leading cause of long-term disability in children and adolescents worldwide. Amongst the wide array of consequences known to occur after pediatric TBI, behavioral impairments are among the most widespread and may particularly affect children who sustain injury early in the course of development. The aim of this study was to investigate the presence of internalizing and externalizing behavioral problems 6 months after preschool (i.e. 18-60 months old) mild TBI.

METHODS

This work is part of a prospective, longitudinal cohort study of preschool TBI. Participants (N = 229) were recruited to one of three groups: children with mild TBI, typically developing children and orthopedic injured (OI) children. Mothers of children in all three groups completed the Child Behavior Checklist as a measure of behavioral outcomes 6-month post-injury. Demographics, injury-related characteristics, level of parental distress, and estimates of pre-injury behavioral problems were also documented.

RESULTS

The three groups did not differ on baseline characteristics (e.g. demographics and pre-injury behavioral problems for the mild TBI and OI groups) and level of parental distress. Mothers' ratings of internalizing and externalizing behaviors were higher in the mild TBI group compared with the two control groups. Pre-injury behavioral problems and maternal distress were found to be significant predictors of outcome.

CONCLUSION

Our results show that even in its mildest form, preschool TBI may cause disruption to the immature brain serious enough to result in behavioral changes, which persist for several months post-injury.

Relationship Between Cortical Thickness and Functional Activation in the Early Blind

Early blindness results in both structural and functional changes of the brain. However, these changes have rarely been studied in relation to each other. We measured alterations in cortical thickness (CT) caused by early visual deprivation and their relationship with cortical activity. Structural and functional magnetic resonance imaging was performed in 12 early blind (EB) humans and 12 sighted controls (SC). Experimental conditions included one-back tasks for auditory localization and pitch identification, and a simple sound-detection task. Structural and functional data were analyzed in a whole-brain approach and within anatomically defined regions of interest in sensory areas of the spared (auditory) and deprived (visual) modalities. Functional activation during sound-localization or pitch-identification tasks correlated negatively with CT in occipital areas of EB (calcarine sulcus, lingual gyrus, superior and middle occipital gyri, and cuneus) and in nonprimary auditory areas of SC. These results suggest a link between CT and activation and demonstrate that the relationship between cortical structure and function may depend on early sensory experience, probably via selective pruning of exuberant connections. Activity-dependent effects of early sensory deprivation and long-term practice are superimposed on normal maturation and aging. Together these processes shape the relationship between brain structure and function over the lifespan.

Contextual and social influences on valuation and choice

To survive in our complex environment, we have to adapt to changing contexts. Prior research that investigated how contextual changes are processed in the human brain has demonstrated important modulatory influences on multiple cognitive processes underlying decision-making, including perceptual judgments, working memory, as well as cognitive and attentional control. However, in everyday life, the importance of context is even more obvious during economic and social interactions, which often have implicit rule sets that need to be recognized by a decision-maker. Here, we review recent evidence from an increasing number of studies in the fields of Neuroeconomics and Social Neuroscience that investigate the neurobiological basis of contextual effects on valuation and social choice. Contrary to the assumptions of rational choice theory, multiple contextual factors, such as the availability of alternative choice options, shifts in reference point, and social context, have been shown to modulate behavior, as well as signals in task-relevant neural networks. A consistent picture that emerges from neurobiological results is that valuation-related activity in striatum and ventromedial prefrontal cortex is highly context dependent during both social and nonsocial choice. Alternative approaches to model and explain choice behavior, such as comparison-based choice models, as well as implications for future research are discussed.

Frontolimbic neural circuitry at 6 months predicts individual differences in joint attention at 9 months

Elucidating the neural basis of joint attention in infancy promises to yield important insights into the development of language and social cognition, and directly informs developmental models of autism. We describe a new method for evaluating responding to joint attention performance in infancy that highlights the 9- to 10-month period as a time interval of maximal individual differences. We then demonstrate that fractional anisotropy in the right uncinate fasciculus, a white matter fiber bundle connecting the amygdala to the ventral-medial prefrontal cortex and anterior temporal pole, measured in 6-month-olds predicts individual differences in responding to joint attention at 9 months of age. The white matter microstructure of the right uncinate was not related to receptive language ability at 9 months. These findings suggest that the development of core nonverbal social communication skills in infancy is largely supported by preceding developments within right lateralized frontotemporal brain systems.

Sodium valproate exposure during the brain growth spurt transiently impairs spatial learning in prepubertal rats

The brain is extremely vulnerable to teratogenic insults during the brain growth spurt, a period that starts during the third trimester of human gestation and is characterized by synaptogenesis establishment of neuronal circuits. While the treatment of epilepsy during pregnancy increases the risk of neurodevelopmental disorders in offspring, the consequences of exposure to anticonvulsants during the brain growth spurt remain poorly known. Here we investigate whether exposure to sodium valproate (VPA) during a similar period in rats impairs spatial learning of juvenile rats. Long-Evans rats were exposed to VPA (200mg/kg) or saline solution (SAL) every other day between postnatal day (PN) 4 and PN10. At PN23 and PN30, Morris water maze performance was evaluated during 6 consecutive days. In the group of animals which started their tests at PN23, the VPA exposure impaired both, swimming speed and learning/memory performance. Interestingly, no differences were observed between VPA and control animals tested from PN30 to PN35. Our data suggests that the neurobehavioral deficits caused by VPA exposure during the brain growth spurt are transitory.

The association between financial hardship and amygdala and hippocampal volumes: results from the PATH through life project

This study examined whether middle-aged adults exposed to poverty in childhood or current financial hardship have detectable brain differences from those who have not experienced such adversity. Structural magnetic resonance imaging (MRI) was conducted as one aspect of the Personality and Total Health (PATH) through life study: a large longitudinal community survey measuring the health and well-being of three cohorts from south-eastern Australia. This analysis considers data from 431 middle-aged adults in the aged 44-48 years at the time of the interview. Volumetric segmentation was performed with the Freesurfer image analysis suite. Data on socio-demographic circumstances, mental health and cognitive performance were collected through the survey interview. Results showed that, after controlling for well-established risk factors for atrophy, adults who reported financial hardship had smaller left and right hippocampal and amygdalar volumes than those who did not report hardship. In contrast, there was no reliable association between hardship and intra-cranial volume or between childhood poverty and any of the volumetric measures. Financial hardship may be considered a potent stressor and the observed results are consistent with the view that hardship influences hippocampal and amygdalar volumes through hypothalamic-pituitary-adrenal axis function and other stress-related pathways.

The impact of perinatal stress on the functional maturation of prefronto-cortical synaptic circuits: implications for the pathophysiology of ADHD?

Enriched as well as impoverished or adverse perinatal environment plays an essential role in the development and refinement of neuronal pathways, which are the neural substrate of intellectual capacity and socioemotional competence. Perinatal experience and learning events continuously interact with the adaptive shaping of excitatory, inhibitory, and neuromodulatory synaptic as well as the endocrine stress systems, including the neuronal corticotropin-releasing factor (CRF) pathways. Adverse environments, such as stress and emotional deprivation can not only delay experience-dependent maturation of these pathways, but also induce permanent changes in prefronto-cortical wiring patterns. We assume that such dysfunctional connections are the neuronal basis for the development of psychosocially induced mental disorders during later life. The aim of this review is to focus on the impact of perinatal stress on the neuronal and synaptic reorganization during brain development and possible implications for the etiology and therapy of mental disorders such as ADHD.

Cortical maps and white matter tracts following long period of visual deprivation and retinal image restoration

Abnormal visual input during development has dramatic effects on the visual system. How does the adult visual system respond when input is corrected? MM lost his left eye and became blind in the right due to corneal damage at the age of 3. At age 46, MM regained his retinal image, but his visual abilities, even seven years following the surgery, remain severely limited, and he does not rely on vision for daily life. Neuroimaging measurements reveal several differences among MM, sighted controls, sighted monocular, and early blind subjects. We speculate that these differences stem from damage during the critical period in development of retinal neurons with small, foveal receptive fields. In this case, restoration of functional vision requires more than improving retinal image contrast. In general, visual restoration will require accounting for the developmental trajectory of the individual and the consequences of the early deprivation on cortical circuitry.

A microinjection technique for targeting regions of embryonic and neonatal mouse brain in vivo

A simple pressure injection technique was developed to deliver substances into specific regions of the embryonic and neonatal mouse brain in vivo. The retrograde tracers Fluorogold and cholera toxin B subunit were used to test the validity of the technique. Injected animals survived the duration of transport (24-48 h) and then were sacrificed and perfused with fixative. Small injections (<or=50 nL) were contained within targeted structures of the perinatal brain and labeled distant cells of origin in several model neural pathways. Traced neural pathways in the perinatal mouse were further examined with immunohistochemical methods to test the feasibility of double labeling experiments during development. Several experimental situations in which this technique would be useful are discussed, for example, to label projection neurons in slice or culture preparations of mouse embryos and neonates. The administration of pharmacological or genetic vectors directly into specific neural targets during development should also be feasible. An examination of the form of neural pathways during early stages of life may lead to insights regarding the functional changes that occur during critical periods of development and provide an anatomic basis for some neurodevelopmental disorders.

Selectionistic neurocostructivism in evolution and development

Neurocostructivism aims to illustrate and explain cognitive development in relation to the underlying neural structures, with the help of computational models. This enterprise should be grounded both in the evolutionary and in the developmental perspectives. In both, selection plays a fundamental role in the construction of neural and cognitive structures.