© Cengage Learning 2016 Genetics and Development of the Human Brain Chapter Five

© Cengage Learning 2016 The interaction between genetics (“nature”) and the environment (“nurture”) can influence physical and behavioral traits Genetics and Behavior

© Cengage Learning 2016 The contribution of genetics to the variation of a trait observed in a population –Heritability always refers to a population, not to individuals Heritability cannot be assessed without taking the environment into account Twin and adoption studies –Minnesota Study of Twins Reared Apart Heritability

© Cengage Learning 2016 Reversible genetic change –Not a DNA sequence change –Influenced by environmental factors Determines gene expression patterns –Histone modifications –DNA methylation Presence of methyl groups associated with gene silencing Abnormal DNA methylation associated with disease Epigenetics

© Cengage Learning 2016 DNA Methylation and Histone Modification

© Cengage Learning 2016 DNA Methylation and Child Maltreatment

© Cengage Learning 2016 Zygote forms from fusion of egg and sperm Early differentiation –Cell germ layers – ectoderm, mesoderm, and endoderm –Neural plate, neural groove, neural tube –Formation of prosencephalon, mesencephalon, and rhombencephalon Building a Brain: Prenatal Development

© Cengage Learning 2016 Division of the Neural Tube

© Cengage Learning 2016 Neurogenesis –Formation of neurons and glia –Originate from cells in the ventricular zone –Progenitor cells divide by mitosis Cell migration –Guided by radial glia –Cells in cerebral cortex arrive in an inside-out fashion Nervous System Development: Neurogenesis and Migration

© Cengage Learning 2016 Neurogenesis

© Cengage Learning 2016 Radial Glia Guide the Migration of New Cells

© Cengage Learning 2016 Differentiation of neural tube along the dorsal and ventral halves and along the rostral-caudal axis –Influenced by differentiation-inducing factors (DIFs) –Organization of cerebral cortex affected by intrinsic and extrinsic factors Nervous System Development: Differentiation

© Cengage Learning 2016 Axons and dendrites arise from neurites Developing axons and dendrites end in growth cones Filapodia and lamellipodia Nervous System Development: Axon and Dendrite Growth

© Cengage Learning 2016 Growth Cones Guide Axons to Their Targets

© Cengage Learning 2016 Growth Cones Respond to a Variety of Cues

© Cengage Learning 2016 Synaptic specificity – neurite identification of the correct target cell Movement of receptors to the synaptic site is guided by presynaptic and postsynaptic structures Interaction with target cells influences the type of neurotransmitter released by the presynaptic cell Nervous System Development: Formation of Synapses

© Cengage Learning 2016 Apoptosis = programmed cell death Access to neurotrophins influence the survival of a neuron Nervous System Development: Cell Death

© Cengage Learning 2016 Steps in the Formation of a Synapse at the Neuromuscular Junction

© Cengage Learning 2016 Reduces the number of functional synapses Influenced by neutrophins and functionality of the synapse Nervous System Development: Synaptic Pruning

© Cengage Learning 2016 Occurs in rostral direction starting with the spinal cord, then hindbrain, midbrain, and forebrain Begins at 24 weeks postconception, with a burst around the time of birth Prefrontal cortex not completely myelinated until early adulthood Nervous System Development: Myelination

© Cengage Learning 2016 Synaptic Rearrangement over the Lifespan

© Cengage Learning 2016 Plasticity –The ability to rearrange synaptic connections Experience and the visual system –Early in development, cells of LGN and primary visual cortex receive input from both eyes –Experience with sensory information influences segregation of ocular dominance Effects of Experience on Development

© Cengage Learning 2016 Input Influences the Development of the Optic Tectum

© Cengage Learning 2016 Input from Both Eyes Competes for the Control of Target Cells in the LGN

© Cengage Learning 2016 Early Experience Affects the Organization of Ocular Dominance Columns

© Cengage Learning 2016 Experience and social behavior –Imprinting in several species of birds –Romanian children and social deprivation Ending a critical period –Conclusion of growth spurt in myelin coincides with reduced abilities to learn additional languages –Presence or absence of neurotrophins may influence timing of critical periods –Epigenetics may play a role Effects of Experience on Development (cont’d.)

© Cengage Learning 2016 Effects of Enriched Environments

© Cengage Learning 2016 Neural tube defects –Anencephaly –Spinal bifida Genetic disorders –Down syndrome –Fragile-X syndrome –Phenylketonuria (PKU) Environmental toxins –Fetal alcohol syndrome Disorders of Nervous Development

© Cengage Learning 2016 Fragile X Syndrome

© Cengage Learning 2016 Fetal Alcohol Syndrome Produces Physical and Intellectual Abnormalities

© Cengage Learning 2016 Puberty –Surge of gray matter development and pruning –Thickening of cortex; frontal lobe –Amygdala matures first Explains teen risky behavior The Brain in Adolescence and Adulthood

© Cengage Learning 2016 White Matter Disruption and Binge Drinking

© Cengage Learning 2016 Brain is fully mature at age 25; weight of brain starts to decrease at age 45 Neurogenesis –Adult learning and memory –Decline of neurogenesis associated with cognitive decline –Multiple reserves help resist loss of function Important to distinguish between healthy aging and disease conditions The Adult Brain

© Cengage Learning 2016 Adult Neurogenesis