Developmental ProcessesNeurogenesisSynaptogenesisSynaptic PruningPlasticityConception – ChildhoodNeurogenesis: the proliferation of neurons through cell divisionBegins 3-4 week post conception250,000 cells/minuteEnds 18 weeks post conception (or may never end)Synaptogenesis: the exuberant generation of neuronal connectionsBegins prenatally; continues after birthDifferent rates (completes much earlier in the visual cortex than in the prefrontal cortex)40% of synapses created in the first wave of synaptogenesis are lost (more connections than needed)Synaptic Pruning: elimination of synapsesHighly influenced by experience – synapses frequently activated are selectively preserved (“Neural Darwinism”)Cognitive complexity related to synapse loss (promotes a more intricate organization of existing synapses)Fragile X syndrome – caused by a persistent failure of normal synaptic pruningResults in a form of mental retardation (dendrites become too long or too dense)We rely on normal synaptic pruning for cognitive development and experience determines which synapses will be prunedEvolutionary EconomyLess information needs to be encoded into the genes to complete the final wiring of the brainPlasticity: the capacity of the brain to be affected by experienceThere are two kinds of plasticityExperience-expectant plasticity: certain functions of the brain require basic experiences in order to developExperience-dependent plasticity: some brain functions depend on particular, idiosyncratic experiences Experience-expectant plasticityExperiences that must happen for normal brain maturation to occur; occurs primarily in young brainsEx. People who love them, objects to manipulate, voices to hear, freedom to move (brains need and expect these experiences)Ex. Visual and auditory stimulation by 4 monthsVulnerability“Sensitive periods” = time period when human brain is especially sensitive to particular stimuliEx. Genie and language acquisitionEx. Romanian orphanages resulting in intellectual and mental health deficits if adopted after 6 months, but not beforeResilienceReorganizationEx. Congenitally deaf children who learn ASL respond stronger to peripheral visual stimulation than non-deaf children (Neville, 1990)Suggesting that the brain systems that would normally be involved in hearing and spoken language processing become reorganized to process visual systems instead Experience-dependent plasticityExperiences that might happen and because of them, one brain differs from another; occurs throughout lifespanHumans: string musicians have increased cortical representation of the fingers of the left hand (Elbert et al., 1995)Animals: cognitive benefits of enriched environments (Greenough, 1982; Hebb, 1949)Those in an enriched environment had more neurons and more developed neuronsThey were also able to get through a maze quickerAdolescenceMore effective information processingCorpus callosum thickensIncreased risky behaviorCan brain development help explain this?Adolescent Risky BehaviorCross-sectional research suggested gradual maturation of the brainLinear decrease in grey matter and increase in white matter Giedd at al. (1999)Longitudinal research suggests a different patternMethodN=65, 4-21 y/o with 2-5 MRI scans, two years apartResultsGrey matter increased at preadolescence in the frontal lobe (dorso-lateral prefrontal cortex)Prefrontal cortex does not reach adult maturity until 20-25 y/oConclusionPrefrontal cortex regulates attention, impulse control, anticipating consequences, and setting priorities (responsible for executive functions)Because the prefrontal cortex is not fully developed, teenagers may engage in impulsive and risky behaviorImplications of Adolescent Brain DevelopmentSecond wave of synaptogenensis any synaptic pruningSensitive periodBinge drinking in adolescence is associated with:Reduced synaptogenesisIncreased synaptic pruning to damaging levelsNeurobiological Model of Adolescent Risk BehaviorImbalance ModelLimbic and striatal systems develop before the prefrontal cortexGoverned by feelings and reward-seeking without controlDopamine system is developingLower base level of dopamine and greater release; positive feedback loopContextEnvironmental risk factors:Risky peersDescriptive norms: perceptions of others behaviorParental supplyReligionMediaFactors that mitigate risk and enhance resilience:Older siblingsRefusal assertiveness and techniquesParental monitoringParents high in parental monitoring are engagedAdvantages of imbalanceAdolescents may be more open to new experiencesEnabling developing independenceBrain Development 09/16/2014Developmental Processes-Neurogenesis-Synaptogenesis-Synaptic Pruning-PlasticityConception – Childhood-Neurogenesis: the proliferation of neurons through cell divisionoBegins 3-4 week post conception o250,000 cells/minuteoEnds 18 weeks post conception (or may never end)-Synaptogenesis: the exuberant generation of neuronal connections oBegins prenatally; continues after birthoDifferent rates (completes much earlier in the visual cortex than in the prefrontal cortex)o40% of synapses created in the first wave of synaptogenesis are lost (more connections than needed)-Synaptic Pruning: elimination of synapses oHighly influenced by experience – synapses frequently activated are selectively preserved (“Neural Darwinism”)oCognitive complexity related to synapse loss (promotes a more intricate organization of existing synapses)Fragile X syndrome – caused by a persistent failure of normal synaptic pruning Results in a form of mental retardation (dendrites become too long or too dense)oWe rely on normal synaptic pruning for cognitive developmentand experience determines which synapses will be pruned oEvolutionary EconomyLess information needs to be encoded into the genes to complete the final wiring of the brain -Plasticity: the capacity of the brain to be affected by experience oThere are two kinds of plasticity Experience-expectant plasticity: certain functions ofthe brain require basic experiences in order to developExperience-dependent plasticity: some brain functions depend on particular, idiosyncratic experiences o Experience-expectant plasticity Experiences that must happen for normal brain maturation to occur; occurs primarily in young brains Ex. People who love them, objects to manipulate, voices to hear, freedom to move (brains need and expect these experiences)Ex. Visual