* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 2605_lect9
Clinical neurochemistry wikipedia , lookup
Subventricular zone wikipedia , lookup
Cortical cooling wikipedia , lookup
Neuroeconomics wikipedia , lookup
Axon guidance wikipedia , lookup
Types of artificial neural networks wikipedia , lookup
Synaptic gating wikipedia , lookup
Recurrent neural network wikipedia , lookup
Optogenetics wikipedia , lookup
Neuroanatomy wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Metastability in the brain wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Nervous system network models wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Neural engineering wikipedia , lookup
Synaptogenesis wikipedia , lookup
BIOPSYCHOLOGY 8e John P.J. Pinel Copyright © Pearson Education 2011 Topics 9.1 Phases of Neurodevelopment 9.2 Postnatal Cerebral Development in Human Infants 9.3 Effects of Experience on the Early Development, Maintenance, and Reorganization of Neural Circuits 9.4 Neuroplasticity in Adults 9.5 Disorders of Neurodevelopment: Autism and Williams Syndrome Copyright © Pearson Education 2011 Neurodevelopment • Neural Development – an ongoing process; the nervous system is plastic • Experience plays a key role • Dire consequences when something goes wrong Copyright © Pearson Education 2011 The Case of Genie Illustrates the impact of severe deprivation on development • At age 13, Genie weighed 62 pounds and could not chew solid food • Beaten, starved, restrained, kept in a dark room, denied normal human interactions • Even with special care and training after her rescue, her behavior never became normal Phases of Development Ovum + sperm = zygote Developing neurons accomplish these things in five phases Induction of the neural plate Neural proliferation Migration and aggregation Axon growth and synapse formation Neuron death and synapse rearrangement Copyright © Pearson Education 2011 Induction of the Neural Plate • A patch of tissue on the dorsal surface of the embryo becomes the neural plate • Development induced by chemical signals from the mesoderm (the “organizer”) • Visible three weeks after conception • Three layers of embryonic cells: • Ectoderm (outermost) • Mesoderm (middle) • Endoderm (innermost) FIGURE 9.1: How the neural plate develops Copyright © Pearson Education 2011 Neural Proliferation • Neural plate folds to form the neural groove, which then fuses to form the neural tube • Inside will be the cerebral ventricles and neural tube • Neural tube cells proliferate in species-specific ways: three swellings at the anterior end in humans will become the forebrain, midbrain, and hindbrain • Proliferation is chemically guided by the organizer areas – the roof plate and the floor plate Copyright © Pearson Education 2011 igration • Once cells have been created through cell division in the ventricular zone of the neural tube, they migrate • Migrating cells are immature, lacking axons and dendrites Copyright © Pearson Education 2011 Migration Two types of neural tube migration Two methods of migration Radial migration (moving out) Tangential migration (moving up) Somal – an extension develops that leads migration, cell body follows Glial-mediated migration – cell moves along a radial glial network Most cells engage in both types of migration FIGURE 9.2: Radial Migration and Tangential Migration Copyright © Pearson Education 2011 Migration FIGURE 9.3: Somal Translocation and Glia-Mediated Migration Copyright © Pearson Education 2011 Neural Crest • A structure dorsal to the neural tube and formed from neural tube cells • Develops into the cells of the peripheral nervous system • Cells migrate long distances Copyright © Pearson Education 2011 Aggregation • After migration, cells align themselves with others cells and form structures • Cell-adhesion molecules (CAMs): – Aid both migration and aggregation – CAMs recognize and adhere to molecules • Gap junctions pass cytoplasm between cells – Prevalent in brain development – May play a role in aggregation and other processes Copyright © Pearson Education 2011 Axon Growth and Synapse Formation • Once migration is complete and structures have formed (aggregation), axons and dendrites begin to grow • Growth cone – at the growing tip of each extension, extends and retracts filopodia as if finding its way • Chemoaffinity hypothesis – postsynaptic targets release a chemical that guides axonal growth, but this does not explain the often circuitous routes often observed Copyright © Pearson Education 2011 Axon Growth and Synapse Formation • Mechanisms underlying axonal growth are the same across species • A series of chemical signals exist along the way – attracting and repelling • Such guidance molecules are often released by glia • Adjacent growing axons also provide signals FIGURE 9.5: Sperry’s classic study of eye rotation and regeneration. Copyright © Pearson Education 2011 Axon Growth and Synapse Formation • Pioneer growth cones – the first to travel a route, interact with guidance molecules • Fasciculation – the tendency of developing axons to grow along the paths established by preceding axons • Topographic gradient hypothesis – seeks to explain topographic maps FIGURE 9.7: The topographic gradient hyphothesis Copyright © Pearson Education 2011 Synapse Formation Formation of new synapses: • Depends on the presence of glial cells • High levels of cholesterol are needed—supplied by astrocytes • Chemical signal exchange between pre- and postsynapctic neurons is needed • A variety of signals act on developing neurons Copyright © Pearson Education 2011 Neuron Death and Synapse Rearrangement • ~50% more neurons than arebrain needed are The human produced – death is normal • Neurons die due to failure to compete for chemicals provided by targets: • The more targets, the fewer cell deaths • Destroying some cells increases survival rate of remaining cells • Increasing number of innervating axons decreases the proportion that survives Copyright © Pearson Education 2011 Life-Preserving Chemicals • Neurotrophins – promote growth and survival, guide axons, stimulate synaptogenesis • Nerve growth factor (NGF) • Both passive cell death (necrosis) and active cell death (apoptosis) • Apoptosis is safer than necrosis – does not promote inflammation Copyright © Pearson Education 2011 Life-Preserving Chemicals FIGURE 9.8: The effect of neuron death and synapse rearrangement on the selectivity of synaptic transmission • Neurons that fail to establish correct connections are particularly likely to die • Space left after apoptosis is filled by sprouting axon terminals of surviving neurons • Ultimately leads to increased selectivity of transmission Copyright © Pearson Education 2011 Postnatal Cerebral Development in Human Infants • Postnatal growth is a consequence of: – Synaptogenesis – Myelination – sensory areas and then motor areas. Myelination of prefrontal cortex continues into adolescence – Increased dendritic branches • Overproduction of synapses may underlie the greater plasticity of the young brain Copyright © Pearson Education 2011 Development of the Prefrontal Cortex • Believed to underlie age-related changes in cognitive function • No single theory explains the function of this area • Prefrontal cortex plays a role in working memory, planning and carrying out sequences of actions, and inhibiting inappropriate responses Effects of Experience on the Early Development, Maintenance, and Reorganization of Neural Circuits • Permissive experiences: those that are necessary for information in genetic programs to be manifested • Instructive experiences: those that contribute to the direction of development • Effects of experience on development are timedependent • Critical period • Sensitive period Copyright © Pearson Education 2011 Early Studies of Experience and Neurodevelopment • Early visual deprivation – Fewer synapses and dendritic spines in primary visual cortex – Deficits in depth and pattern vision • •Enriched environment – Thicker cortexes – Greater dendritic development – More synapses per neuron Copyright © Pearson Education 2011 Competitive Nature of Experience and Neurodevelopment Ocular Dominance Columns example: • Monocular deprivation changes the pattern of synaptic input into layer IV of V1 (but not binocular deprivation) • Altered exposure during a sensitive period leads to reorganization • Active motor neurons take precedence over inactive ones Copyright © Pearson Education 2011 Competitive Nature of Experience and Neurodevelopment FIGURE 9.10: The effect of a few days of early monocular deprivation on the structure of axons projecting from the lateral geniculate nucleus into layer IV of the primary visual cortex. Axons carrying information from the deprived eye displayed substantially less branching. (Adapted from Antonini & Stryker, 1993.) Copyright © Pearson Education 2011 Effects of Experience on Topographic Sensory Cortex Maps • Cross-modal rewiring experiments demonstrate the plasticity of sensory cortexes – with visual input, the auditory cortex can see • Change input, change cortical topography – shifted auditory map in prism-exposed owls • Early music training influences the organization of human auditory cortex – fMRI studies Copyright © Pearson Education 2011 Experience Fine-Tunes Neurodevelopment • Neural activity regulates the expression of genes that direct the synthesis of CAMs • Neural activity influences the release of neurotrophins • Some neural circuits are spontaneously active and this activity is needed for normal development Copyright © Pearson Education 2011 Neuroplasticity in Adults • The brain changes and adapts • Neurogenesis (growth of new neurons) seen in olfactory bulbs and hippocampuses of adult mammals'—adult neural stem cells created in the epedymal layer lining in ventricles and adjacent tissues • Enriched environments and exercise can promote neurogenesis Copyright © Pearson Education 2011 Effects of Experience on the Reorganization of the Adult Cortex • Tinnitus (ringing in the ears) – produces major reorganization of primary auditory cortex • Adult musicians who play instruments fingered by left hand have an enlarged representation of the hand in the right somatosensory cortex • Skill training leads to reorganization of motor cortex Copyright © Pearson Education 2011 Disorders of Neurodevelopment: Autism • Three core symptoms: – Reduced ability to interpret emotions – Reduced capacity for social interaction – Preoccupation with a single subject or activity • Intensive behavioral therapy may improve function • Heterogenous – level of brain damage and dysfunction varies • Often considered a spectrum disorder Copyright © Pearson Education 2011 Disorders of Neurodevelopment: Autism • Incidence: 6.6 per 1,000 births (or 1 in 166) • 80% males, 60% have mental retardation, 35% epileptic, 25% have little or no language ability • Most have some abilities preserved – rote memory, jigsaw puzzles, musical ability, artistic ability • Autistic Savants – intellectually handicapped individuals who display specific cognitive or artistic abilities – ~1/10 autistic individuals display savant abilities – Perhaps a consequence of compensatory functional improvement in one area following damage to another Copyright © Pearson Education 2011 Genetic Basis of Autism • Siblings of children with autism have a 5% chance of having autism • 60% concordance rate for monozygotic twins • Several genes interacting with the environment Source: Bouchard & McGue, 1981 Copyright © Pearson Education 2011 Neural Mechanisms of Autism Understanding of brain structures involved in autism is still limited, so far implicated: • Cerebellum • Amygdala • Frontal cortex Two lines of research on cortical involvement in autism: • Abnormal response to faces in autistic patients – Spend less time than non-autistic subjects looking at faces, especially eyes – Low fMRI activity in fusiform face area • Possibly deficient in mirror neuron function Copyright © Pearson Education 2011 Disorders of Neurodevelopment: Williams Syndrome • Incidence: 1 in every 7,500 births • Mental retardation and an uneven pattern of abilities and disabilities • Sociable, empathetic, and talkative– exhibit language skills, music skills, and an enhanced ability to recognize faces • Profound impairments in spatial cognition • Usually have heart disorders associated with a mutation in a gene on chromosome 7 – the gene (and others) is absent in 95% of those with Williams Copyright © Pearson Education 2011 Disorders of Neurodevelopment: Williams Syndrome • Evidence for a role of chromosome 7 (as in autism) • General thinning of cortex at juncture of occipital and parietal lobes, and at the orbitofrontal cortex • “Elfin” appearance – short, small upturned noses, oval ears, broad mouths FIGURE 9.13 Two areas of reduced cortical volume and one area of increased cortical volume observed in people with Williams syndrome. (See Meyer-Lindenberg et al., 2006; Toga & Thompson, 2005.) Copyright © Pearson Education 2011 Watch: The Central Nervous System Watch: Brain Building Note: To view the MyPsychLab assets, please make sure you are connected to the internet and have a browser opened and logged into www.mypsychlab.com. Copyright © Pearson Education 2011 Acknowledgments Slide Image Description Image Source template lightning ©istockphoto.com/Soubrette template background texture ©istockphoto.com/Hedda Gjerpen Chapter 09 image Grandmother and grandchild smelling flowers ©iStockphoto.com/hanhanpeggy 3, 16, 21 28, 30, 33 brain ©istockphoto.com/Stephen Kirklys 4 paper clip ©istockphoto.com/Jon Patton 4 folder ©istockphoto.com/kyoshino 4 tabletop ©istockphoto.com/Andrew Cribb 5 human egg ©istockphoto.com/ChristianAnthony 5 human sperm ©istockphoto.com/Alexander Kozachok 6 Figure 9.1 Pinel 8e, p. 221 7 person thinking ©istockphoto.com/akurtz 9 Figure 9.2 Pinel 8e, p. 222 10 Figure 9.3 Pinel 8e, p. 223 11 book ©istockphoto.com/Carmen Martínez Banús 12 two puzzle pieces ©istockphoto.com/Henrik Jonsson 13 woman observing & taking notes ©istockphoto.com/Claudio Arnese 14 Figure 9.5 Pinel 8e, p.224 15 Figure 9.7 Pinel 8e, p. 227 17 neuron ©istockphoto.com/ktsimage 18 toddler listening to adult speak ©istockphoto.com/Jani Bryson Studios, Inc. Copyright © Pearson Education 2011 Acknowledgments 19 Figure 9.8 Pinel 8e, p. 228 20 two babies ©istockphoto.com/schwester 22 head - woman ©istockphoto.com/Angel Herrero de Frutos 23 hand holding rat ©iStockphoto.com/sidsnapper 24 binoculars ©iStockphoto.com/Alex Staroseltsev 25 Figure 9.10 Pinel 8e, p. 231 26 wires ©istockphoto.com/Take A Pix Media 27 swinging ©istockphoto.com/HooRoo Graphics 28 person with thought bubble ©istockphoto.com/Digital Savant LLC 29 piano and violin ©iStockphoto.com/Yenwen Lu 32 twins ©istockphoto.com/Thomas Gordon 35 Figure 9.13 Pinel 8e, p. 237 36 laptop ©istockphoto.com/CostinT 36 table and wall ©istockphoto.com/David Clark Copyright © Pearson Education 2011