The early postnatal years are marked by a rapid maturation of cognitive, social, and behavioral abilities as infants progress from helplessness to autonomy, and children and adolescents develop more sophisticated ways of thinking. The information and abilities acquired by infants, children, and adolescents are staggering. The impact that these early years have on personality development and behavior is profound, longlasting, and at times, refractory to treatment interventions. The consequences of physical or emotional childhood trauma are seen in every psychiatric practice. For such dramatic cognitive, behavioral, and emotional changes, there must be an underlying neurobiological substrate. Neuroscience is exploring the structural and functional foundations of normal postnatal maturation and how it is impacted by the environment.
[...] These findings offer evidence for substantial remodeling of cognitive neural networks in response to early environmental manipulations. Additionally, the observation that a specific set of neural connections involved in memory processing normally regresses after infancy has potentially fascinating implications for understanding phenomena such as infantile amnesia. Critical Periods for Cognition and Emotion The importance of critical periods does not apply solely to visual and language cortices. It has stunning implications for how early childhood experiences can leave brain traces that affect brain function and behavior throughout adult life. [...]
[...] Although these animals are born with a normal CNS, the abnormal visual input and neural activity induced by strabismus causes structural CNS changes. The morphology of retinogeniculate axons is altered, with smaller arbors and fewer boutons compared to normal. The lateral geniculate nucleus contains smaller neuronal cell bodies. The anatomical organization of the visual cortex is also altered with a reduction in the proportion of cells that respond to binocular input and a loss of the normal orientation selectivity. Early environmental manipulations may also impact higher cognitive functioning. [...]
[...] It may continue to serve a role in the development of postnatal prefrontal cortico- cortical projections. Many neuronal types alter their shape postnatally, corresponding to altered synaptic connections. In several cortical layers in the prefrontal cortex and other association cortices, pyramidal neurons continue dendritic outgrowth and spine formation throughout the first 2 postnatal years. Pyramidal neurons in layers III and V of the prefrontal cortex may not develop adultlike dendritic fields until adolescence. The pyramidal neurons of layer III are a major source of cortico-cortical connections, and they show intensive spine growth during early childhood, possibly as targets of thalamocortical and cortico-cortical fibers. [...]
[...] However, during early adulthood they manifest dramatically abnormal behavioral responses to environmental and pharmacological stresses. Antipsychotic medications ameliorate some of these abnormal responses. The abnormalities appear to be modiated by rewiring of the connections involved in the regulation of mesolimbic dopaminergic function. Rats with this developmental lesion have been studied as a potential animal model of a number of phenomena associated with schizophrenia. Behavioral studies in monkeys have shown that early childhood experience can have a profound impact on adult adaptation, especially in the context of social stress. [...]
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