Biology and Behavior - Genes, Genetics, and Development PDF

Model of Interaction Three key elements  Genotype: The genetic material an individual inherits  Phenotype: The observable expression of the genotype, including body characteristics and behavior  Environment: Includes every aspect of the...

Model of Interaction Three key elements  Genotype: The genetic material an individual inherits  Phenotype: The observable expression of the genotype, including body characteristics and behavior  Environment: Includes every aspect of the individual, and his or her surroundings, other than genes Traditional view: Genes to physical characteristics  ** Epigenetics**  Norm of Reaction Refers to all the phenotypes that could theoretically result from a given genotype, in relation to all the environments in which it could survive and develop “The phenotype is the unique consequence of a particular genotype developing in a particular environment” (Lewontin, 1982) What do genes do?  produce protein  start/stop protein production of other genes- regulatory genes Genetic Origins of Human Diseases and Disorders  Over 5,000 human diseases and disorders are presently known to have genetic origins  Recessive gene: PKU, sickle-cell anemia, cystic fibrosis  Single dominant gene: Huntington’s disease  Sex-linked inheritance: Fragile-X syndrome, hemophilia  Other neurodivergent phenotypes have a genetic basis, but the specific genetic mechanism has not been established (e.g., ADHD, Bipolar disorder, Tourette’s Syndrome, Autism)  http://www.sciencedaily.com/releases/2010/02/100201171404.ht m Are genes/proteins really that big a deal?  YES!  But to understand what genes and proteins contribute to behavioral development, we have to specify how genes are linked to behavior…  Genes to proteins…  Proteins to ?? Genes to behavior?  We have one good example of how genes are linked to behavioral development across different “levels”… GENE PROTEIN ORGAN BEHAVIOR build up of underproduction of CF-gene mucus in sick protein lungs   examples that attempt to link genes and behavior… GENE PROTEIN ORGAN BEHAVIOR Thrill- Over- Novelty- Build-up of seeking or excitation of seeking gene dopamine receptors “approach” cortical areas behaviors Failure to inhibit brain Aggressive Aggression Failure to produce areas behaviors gene nitric oxide involved in (in rats) disrupted (neurotransmitter) aggression Often polygenic and…where is the ‘development’ in these stories?? Are genes/proteins really that big of a deal in development?  YES!  clearly tied to some diseases  clearly part of the basic machinery of life  The challenges ahead as we try to link genes and behavior…  Need to understand much more about the “levels” between genes and behavior and their interaction  Need to explain how gene-protein-organ-behavior links play out over developmental time… Behavior Genetics  how variation in behavior and development results from GxE interaction  most traits of interest are multifactorial Behavior Genetics: Family Studies  Trait measured in people who vary in genetic relatedness  Question: higher correlations in measures of the trait for individuals who are:  genetically more similar  share the same environment Types of Family Studies  Twin-Study Designs:  Adoption Studies: Correlations on a trait of are adopted children more interest in like their biological or their  monozygotic vs. dizygotic adopted relatives twins Biol-genetic influence Adopted-environ influence Heritability  A statistical estimate of the proportion of the measured variance on a given trait among individuals in a given population that is attributable to genetic differences among those individuals Shared vs. Nonshared Factors  Shared environment: growing up together in the same family  Nonshared environment: experiences unique to the individual Nervous system, brain and behavior Stages of nervous system development Developmental Processes The Importance of Experience Brain Damage and Recovery The nervous system  Produces all behavior: talking, movement, thinking  How does the nervous system develop?  Main stages  Brain basics  Whatis the relationship between neural and behavioral development?  Brain development shaped by experience! Six stages of nervous system development 1. Cell production (proliferation) neurogenesis 2. Cell migration 3. Cell differentiation 4. Synapse formation synaptogenesis 5. Cell death 6. Synapse rearrangement synaptic pruning Cell migration: 3 methods 1. Spatial Layering  New cells push old cells out (old on top of new)  Or new cells migrate to the outside (new on top of old) 2. Chemical signals from: Rosenzweig, Leiman, &Breedlove (1999) Biological Psychology, 2nd edition 3. Ride the “glial rail” Cell differentiation Depends on:  Parent cells  Location  Chemical signals Kandel, Schwartz, & Jessell (2000) Principles of Neural Science, 4th edition Synapse formation (synaptogenesis)  Cells elongate at their axons to form connections (synapses) with other cells from: Rosenzweig, Leiman, &Breedlove (1999) Biological Psychology, 2nd edition Synapse formation (synaptogenesis)  Cells elongate at their axons to form connections (synapses) with other cells  Each cell forms multiple synapses Synapse formation (synaptogenesis)  Cells elongate at their axons to form connections (synapses) with other cells  Each cell forms multiple synapses from: Rosenzweig, Leiman, &Breedlove (1999) Biological Psychology, 2nd edition Cell death…Why? Perhaps a result of cell overproduction  Not all cells receive nutrients – those that don’t may die  Not all cells are active – cells that are not may die Synapse rearrangement 2 main types: 1. After cell death, remaining cells make new synapses 2. Synapses that aren’t active are “pruned” (lost) The BIG question:  how does the pattern of neural development relate to changes in behavior?  To answer this, we need to know a few basics about the brain and how it works… Brain Basics Cortices/lobes: different lobes serve different functions (though massive interconnections!) The BIG question: how does the pattern of neural development relate to changes in behavior?  One proposal: the changes that occur across the 6 stages of neural development provide global constraints on how experience can shape the brain Examine changes in grey matter = the “working” tissue in cortex… Brain Development Developmental changes in gray matter…  Early over production followed by pruning (pruning = more mature connections)  BUT: this doesn’t happen uniformly across the brain…  Perceptual and motor areas first to be pruned  Then areas involved in spatial orientation and language  Last are areas involved in higher cognition and “executive function”  Pattern of brain maturity is consistent with trends in behavioral development  Experience and the Brain Although global constraints are important, brain shows amazing plasticity or flexibility  Experience-expectant plasticity  Experience-dependent plasticity This is a really good thing! Don’t need to “program” behaviors ahead of time! Brain/child can learn stuff on the fly… Experience-Expectant Plasticity  The process through which the normal wiring of the brain occurs in part as a result of the general experiences  Is accompanied by vulnerability  If the expected experience is not available, development will be impaired  e.g.,both eyes typically have similar input during development-if occlude one, do not get typical development Sensitive Periods A key element in experience-expectant plasticity is timing  Period when species-typical experience is optimal to achieve species-typical functioning  Timing of occlusion will have differing effects Somatosensory Cortex: Experience-dependent plasticity Merzenich & Jenkins  Owl monkeys  Identified which neurons fired when fingers stimulated  2 fingers received extra stimulation (1½ hrs/day for 109 days) Results Results suggest:  Experience-dependent competition and selection  neurons are very flexible  Left hemisphere for language, right will be very active and take over if left damaged in childhood  experience matters!  Experience and the Brain Another reason plasticity is good: Potential for recovery after brain damage  Recovery depends on  Extent of the damage  Aspect of the brain developing at time of damage  Experience and the Brain Neurogenesis/migration Pruning Pruning  Experience and the Brain Another reason plasticity is good: Potential for recovery after brain damage  Recovery depends on  Extent of the damage  Aspect of the brain developing at time of damage  Timing of damage critical  “Worst time” is during prenatal development (neurogenesis and neural migration)  “Best time” is during infancy and early childhood (synapse generation and pruning)