Brain Development PDF

Development BRAIN DEVELOPMENT - Brain development starts before birth (around 3 months) • Gyri and sulci especially (cortex) - Most neurons are already in place at the time of birth • Period of development from birth-3mo is very important • Exposure to toxins and trauma can have devastating impact...

Development BRAIN DEVELOPMENT - Brain development starts before birth (around 3 months) • Gyri and sulci especially (cortex) - Most neurons are already in place at the time of birth • Period of development from birth-3mo is very important • Exposure to toxins and trauma can have devastating impact on developing brain - From birth to one year synapses increase 10x • Connections between neurons (explosive growth) - After this initial growth period, synapses are pruned, or disappear • Di erent periods of growth and pruning for di erent regions • Explosion of synapses and pruning is relatively short • A1, V1, S1, M1 is done early - At the same time the axons that remain and form connections between regions become more myelinated • Start in rst year and lasts until adolescence IMPLICATIONS - Early changes in regions necessary for primary functions • Primary cortices are the regions that are growing more rapidly and earliest • Biggest growth occurs in PFC that lasts until 25yo - Executive controls, emotion regulation - Extended period of development allows maximum adaptation to the environment - Interconnected regions can in uence each other – interactive specialization • Likely relevant for the development of complex skills (language, reasoning) • Regions connected to each other have an in uence on one another - They can assist each other’s growth - But, extended development means greater opportunity for maladaptive changes • Goal of development: adapt to our environment - But if environment is hostile, we adapt as well - Challenges occurring early in childhood can have long term impact - 1mo: mostly great matter: myelination has not yet occurred - By 9 mo: brain is relatively similar to what an adult brain looks like - Initial myelination takes place in infancy - Volume and thickness of grey matter decreases with age - Volume of white matter increases • As we have more white matter, there’s less gray matter measured by MRI (voxel) • In a single voxel, white matter grows into gray matter and hides it - Not really losing gray matter - Connections are what is changing ff fl fl fi fi fi ff - GM changes occur rst in primary regions (motor regions and parietal regions) • Later in frontal regions (and temporal lobe) - White matter changes occur rst for connections between basic sensory and motor systems • Later for connections between higher level regions - Functional connectivity (correlated activity across regions) also continues to change with age • Activity between regions changes over time DEVELOPMENT AND BEHAVIOUR - Greater increases in WM from 5 to 8 in left arcuate fasciculus (connects language and visual regions) were related to better reading skills - Even when controlling for: • Family history of dyslexia • Socioeconomic status • Pre-literacy skills • Global cognitive function - Individual di erences in connectivity are important for reading skills • These connections are important for our ability to read regardless • Probably are other factors contributing to this ADOLESCENT DEVELOPMENT - Emotional response to negative images decreases with age • Emotion regulation changes over time • Study shows negative image and neutral image and rate how negative you felt - Negative images: as age increases, negative feelings decreases - Neutral at - Amygdala response decreases in parallel - Response in ACC increases and OFC decreases • OFC: connected to amygdala (evaluative system) - As we age, our ability to evaluate negative images increases • ACC: inhibition/regulation of amygdala response - As we age, ACC has more inhibition and regulation - Changes in emotional evaluation result from changes in regions related to valuation and inhibitory control ENVIRONMENTAL INFLUENCES: PLASTICITY EXPERIENCE EXPECTANT - The system is “waiting for” input, system waits for stimulation - Binocular vision • Without experience, normal vision and cortical function does not develop • Droopism: deci ct in binocular vision convergence - Narrowing of perception for native language sounds • i.e. /b/ and /v/ sounds in Spanish are similar - Basic functions, less exible, usually develops earlier • Harder to learn language later in life EXPERIENCE DEPENDENT - Systems are changed by individual experiences • Family and social environment • Stress • Education, language, music, sports - More complex functions, exible, develop later INTERACTIVE DEVELOPMENT fi ff fl fl fi ff fl - Changes in one system a ect the rest - Early bilingualism may bene t executive function • Having to control which language to use may help in control in over thing ENVIRONMENTAL INFLUENCES: ENRICHMENT - Animals raised in enriched environments • Better perceptual skills • Better maze solving • Abilities may be transferred from mums to pups COUPLED CORTICAL AND CEREBELLAR CHANGES WITH TRAINING - changes in the cortex - Changes in the cerebellum - Changes related to each other INTERACTION OF ENVIRONMENT AND DEVELOPMENT - Critical period (experience expectant): narrow window of development where speci c experience is required for normal development • Mice exposed to white noise - Auditory cortex frequency tuning disturbed by exposure to white noise - 11-14 days post-natal – not before or after (critical period) • It messes up the organization of how sounds are represented in the brain - Sensitive period (experience dependent): developmental window where speci c experience has long-term e ects on behaviour and the brain - musical exposure - Bilingual experience - Sport experience Study done on deaf children given auditory implant - By age 5, deaf children given a cochlear implant before 24 mths performed as well as hearing children on a test of word comprehension - Children implanted later did not catch up study done on bilingualism - Immersion learners do better, but if learned at 12yo, they do not perform aas well • Including accent - Adult language skill is greater for those who begin earlier Study on absolute pitch - 78% of musicians with absolute pitch began training before age 6 - Especially true for instruments where individuals have to regulate it themselves (i.e. violin, cello, etc.) SENSITIVE PERIODS FOR MUSIC TRAINING? - Anecdotal evidence (and your child’s music teacher) suggest that early training is linked to fi fi ff later expertise • YoYo Ma began training at 4 • Oscar Peterson at 5 • Dave Brubeck at 4 - But, Jimi Hendrix, Aaron Copeland, Leonard Cohen, etc. did not Early vs late-trained musicians - less error made in early-trained, then late-trained, and non-musicians White matter di erences - early-trained: had changes in corpus callosum - Region that connects motor and premotor cortex - Greater white matter concentration - Correlated with age of onset WHY THIS REGION OF THE CORPUS CALLOSUM ? - connects motor regions from both hemisphere and integration of movements from both hemispheres - Unique environmental contribution • More susceptible to impacts/contributions of environment - Signi cant change between 6 and 8 • Because of sensitive period e ects, with rapid changes in this region of CC - Size is related to bimanual skill DEVELOPMENTAL DISORDERS: INTELLECTUAL DISABILITIES GENETIC CAUSES - Down’s syndrome • Pronounced intellectual disability in both verbal and non-verbal domains • Slowed cognitive development in childhood • Accelerated cognitive aging in adulthoo - Fragile X syndrome • More variable intellectual disability that is more pronounced in non-verbal domains INFECTIONS AND TOXINS - Viral infections: Rubella (German measles), herpes, chickenpox, etc • Until the development of a vaccine, Rubella infection prenatally was an important cause of intellectual disability • Prenatal exposure to viruses can impact • Rubella infection in infancy can also result deafness - Fetal alcohol syndrome • Excessive alcohol consumption, especially in the rst trimester • Range of intellectual impairment • Also, ADHD, impulsivity, higher risk of substance abuse DEVELOPMENTAL DISORDERS - Learning disabilities: dyslexia • No general cognitive disability – speci c di culties with written language • A ects 5-10% of people (M>F) • Primary de cit: phonological processing - Relationship between phonemes and connectivity between auditory and frontal regions fi ffi fi ff ff fi fi ff (Broca’s area) - “Chart” = “ch” + “ar” + “t” or worse yet “comb” = “co” “m” • May be related to processing of rapidly changing sounds like consonants • Or to higher level disruption - Dyslexia is relatively, heritable, runs in families - Cell migration irregularities in the region of the Sylvian ssure (ie, Wernicke’s area and inferior parietal cortex) - Irregularities disrupts connections between visual word-form (temporal lobe) area and inferior fi frontal (Broca) that is important for decoding the sounds of words