🧠Intro to Brain and Behavior Unit 6 – Neurodevelopment

Key Concepts

• Neurodevelopment encompasses the formation, maturation, and organization of the nervous system from conception through adulthood
• Involves complex interplay between genetic, environmental, and experiential factors that shape brain structure and function
• Neurogenesis, the process of generating new neurons, occurs primarily during prenatal development but continues in specific brain regions throughout life
• Neuronal migration, the movement of neurons from their site of origin to their final destination, establishes the basic architecture of the brain
• Synaptogenesis, the formation of synapses between neurons, enables communication and information processing within neural circuits
• Myelination, the insulation of axons with myelin sheaths, enhances the speed and efficiency of neural transmission
• Apoptosis, programmed cell death, eliminates excess or abnormal cells to refine neural networks
• Critical periods, specific time windows during development when the brain is particularly sensitive to environmental input, shape the acquisition of skills and behaviors

Stages of Neurodevelopment

• Embryonic stage (weeks 1-8) involves the formation of the neural tube, the precursor to the central nervous system
  • Neurulation, the process of neural tube formation, occurs during the first month of gestation
  • Neural tube differentiates into the forebrain, midbrain, and hindbrain regions
• Fetal stage (weeks 9-40) is characterized by rapid brain growth, neuronal proliferation, and the emergence of basic brain structures
  • Cortical development begins with the migration of neurons to form the six-layered cerebral cortex
  • Synaptogenesis accelerates during the second and third trimesters, establishing neural connections
• Neonatal period (birth to 1 month) marks the transition from intrauterine to extrauterine environment
  • Sensory experiences shape the refinement of neural circuits and the development of perceptual abilities
• Infancy and toddlerhood (1 month to 3 years) involve significant cognitive, motor, and language development
  • Synaptic pruning eliminates unused or inefficient connections, streamlining neural networks
• Childhood and adolescence (3 years to early 20s) are characterized by continued brain maturation and the acquisition of complex skills
  • Myelination of the prefrontal cortex supports the development of executive functions and impulse control

Cellular and Molecular Processes

• Neurogenesis is driven by the proliferation and differentiation of neural stem cells and progenitor cells
  • Asymmetric cell division gives rise to both self-renewing stem cells and differentiated neurons or glia
• Neuronal migration is guided by chemical cues, cell adhesion molecules, and extracellular matrix components
  • Radial glia serve as scaffolds for the migration of cortical neurons from the ventricular zone to the cortical plate
• Axon guidance molecules (netrins, semaphorins, ephrins) direct the growth and pathfinding of axons to their target regions
• Synapse formation involves the coordinated assembly of pre- and postsynaptic components, including neurotransmitter receptors and signaling molecules
  • Activity-dependent mechanisms, such as long-term potentiation (LTP) and long-term depression (LTD), modify synaptic strength and connectivity
• Neurotrophic factors (nerve growth factor, brain-derived neurotrophic factor) support neuronal survival, differentiation, and synaptic plasticity
• Epigenetic modifications, such as DNA methylation and histone acetylation, regulate gene expression and contribute to the fine-tuning of neural development

Brain Structure Formation

• Neural tube gives rise to the major subdivisions of the central nervous system: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
• Prosencephalon differentiates into the telencephalon (cerebral hemispheres) and diencephalon (thalamus, hypothalamus)
  • Cortical development involves the formation of the ventricular zone, subventricular zone, intermediate zone, and cortical plate
• Mesencephalon develops into the midbrain, including the tectum and tegmentum
• Rhombencephalon gives rise to the metencephalon (pons, cerebellum) and myelencephalon (medulla oblongata)
• Neural crest cells, derived from the dorsal neural tube, migrate to form the peripheral nervous system, including sensory and autonomic ganglia
• Ventricles, fluid-filled cavities within the brain, are lined by the choroid plexus and contain cerebrospinal fluid (CSF)
• Commissures, such as the corpus callosum and anterior commissure, connect the two cerebral hemispheres and enable interhemispheric communication

Neural Plasticity

• Synaptic plasticity refers to the ability of synapses to strengthen or weaken in response to activity or experience
  • Hebbian plasticity ("neurons that fire together, wire together") underlies associative learning and memory formation
• Structural plasticity involves changes in neuronal morphology, such as dendritic branching and spine density, in response to environmental stimuli
• Critical periods represent heightened windows of plasticity during which specific neural circuits are highly responsive to experience
  • Sensory deprivation (monocular deprivation) during the critical period for visual development can lead to permanent deficits in visual acuity (amblyopia)
• Adult neurogenesis, the generation of new neurons in the adult brain, occurs in the subgranular zone of the hippocampus and the subventricular zone of the lateral ventricles
  • Enriched environments and physical exercise promote adult neurogenesis and cognitive function
• Neuroplasticity underlies the brain's ability to adapt, learn, and recover from injury throughout life
  • Constraint-induced movement therapy exploits neuroplasticity to promote functional recovery after stroke or brain injury

Environmental Influences

• Maternal nutrition, particularly folate and omega-3 fatty acids, plays a crucial role in fetal brain development
  • Folic acid supplementation reduces the risk of neural tube defects (spina bifida, anencephaly)
• Maternal stress and exposure to toxins (alcohol, drugs, heavy metals) can disrupt normal brain development and increase the risk of neurodevelopmental disorders
  • Fetal alcohol spectrum disorders (FASD) result from prenatal alcohol exposure and are characterized by cognitive, behavioral, and physical abnormalities
• Sensory experiences, such as visual input, auditory stimulation, and tactile contact, shape the refinement of neural circuits during critical periods
  • Enriched environments, with complex sensory stimuli and social interaction, promote cognitive development and neural plasticity
• Social interactions and attachment relationships influence the development of emotional regulation and social cognition
  • Neglect or abuse during early childhood can lead to alterations in brain structure and function, increasing the risk of psychiatric disorders
• Learning and education support the acquisition of knowledge, skills, and cognitive abilities throughout development
  • Bilingualism and musical training are associated with enhanced cognitive flexibility and executive function

Developmental Disorders

• Autism spectrum disorder (ASD) is characterized by deficits in social communication and interaction, as well as restricted and repetitive behaviors
  • Genetic and environmental factors contribute to the etiology of ASD, with a strong heritability component
• Attention deficit hyperactivity disorder (ADHD) involves persistent inattention, hyperactivity, and impulsivity that interfere with daily functioning
  • Alterations in dopaminergic and noradrenergic neurotransmission are implicated in the pathophysiology of ADHD
• Specific learning disorders, such as dyslexia and dyscalculia, affect the acquisition of academic skills (reading, writing, mathematics)
  • Neuroimaging studies reveal differences in brain activation patterns during reading or mathematical tasks in individuals with learning disorders
• Intellectual disability is characterized by significant limitations in intellectual functioning and adaptive behavior
  • Genetic syndromes (Down syndrome, Fragile X syndrome) and environmental factors (prenatal infections, perinatal complications) can cause intellectual disability
• Schizophrenia, a severe mental disorder involving delusions, hallucinations, and disorganized thinking, typically emerges during late adolescence or early adulthood
  • Abnormalities in neurotransmitter systems (dopamine, glutamate) and brain connectivity are associated with the development of schizophrenia

Research Methods and Techniques

• Animal models, such as rodents and non-human primates, provide insights into the cellular and molecular mechanisms of neurodevelopment
  • Transgenic and knockout mouse models allow the study of specific genes and their roles in brain development and function
• Neuroimaging techniques, including magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI), enable the non-invasive study of brain structure and connectivity
  • Functional MRI (fMRI) measures changes in blood oxygenation as a proxy for neural activity during cognitive tasks or sensory stimulation
• Electroencephalography (EEG) and magnetoencephalography (MEG) record the electrical and magnetic activity of the brain, respectively, with high temporal resolution
  • Event-related potentials (ERPs) are time-locked EEG responses to specific stimuli or cognitive events, providing insights into the timing and sequence of neural processing
• Genetic and epigenetic studies investigate the role of specific genes and their regulation in neurodevelopmental processes and disorders
  • Genome-wide association studies (GWAS) identify genetic variants associated with neurodevelopmental disorders or traits
• Postmortem brain studies allow the examination of brain tissue at the cellular and molecular level, providing insights into the neuropathology of developmental disorders
  • Immunohistochemistry and in situ hybridization techniques enable the visualization of specific proteins or gene expression patterns in brain tissue samples
• Longitudinal studies follow individuals over time to track developmental trajectories and identify risk and protective factors for neurodevelopmental outcomes
  • Birth cohort studies, such as the Avon Longitudinal Study of Parents and Children (ALSPAC), collect data on a large sample of individuals from birth through adulthood