Brain Plasticity. Brain Plasticity. Recovery from Deprivation 1/2/11. Dogma. Modern neuroscience. Deprivation can lower IQ. Deprivation reversed

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1 Brain Plasticity Brain Plasticity Dogma Adult brain is stable, unchanging Lose neurons Do not grow/repair neurons Modern neuroscience Brain changes throughout life plasticity Extra capacity Face life s challenges Recovery from Deprivation Deprivation can lower IQ Poverty, life in an orphanage Deprivation reversed IQ increases Limits to reversibility Genie 1

2 Recovery from Surgery Left hemispherectomies Prior to age 5 Little speech disturbance Older children Speak with some language deficits Adults Serious speech deficits (aphasia) Brandi Binder Right hemispherectomy to control epilepsy Lost muscular control Left side of body Years of rehabilitation A student Excels at many right brained tasks Brain finds ways of compensating for damage Regaining Lost Function Nerve damage (not destroyed) Function returns over time Nerve destruction natural recovery Increased blood flow Axonal regrowth Sprouting Denervation supersensitivity Reorganization 2

3 Increased Blood Flow Brain injuries associated with decreased blood flow Stroke Blood flow critical to neuron function Recovery of function associated with increase in blood flow Axonal Regrowth Occurs in fish PNS and CNS Occurs in mammal PNS NOT in CNS Growth inhibiting chemicals produced by central myelin Discovering mechanism for regrowth Stimulate in CNS Collateral Sprouting/Sprouts Neuron damage Uninjured neurons sprout branches Fill vacated synapses Collateral sprouting Connecting axon is damaged Previously connected neurons secrete neurotrophins Induces undamaged axons form new branches Collateral sprouts 3

4 Denervation Supersensitivity Increased sensitivity of postsynaptic neuron to neurotransmitter Occurs during decreased exposure to transmitter Allows message transmission With fewer active neurons Adaptive function Reorganization of Mental Maps Michael Merzenich Changing brain input changes brain organization Occurs throughout life Does not involve surgery or drugs Implications for recovery from brain damage Plasticity: Strengthening Connections Create connections Enhance neural communication Can be driven by environmental changes 4

5 Plasticity: Remapping Merznich Amputated monkey finger Motor cortex started processing information from adjacent finger Remapping of millimeters Plasticity: Remapping Severed nerves in one arm of monkey Animal rights activist s lawsuit terminated research Years later, monkeys examined Brain areas originally devoted to arm now processing facial information Huge cortical reorganization Plasticity: Remapping Massive remapping possible in humans Lost limb Cortical area processes information from stump or face String musicians Cortex are serving fingering hand larger than area of non-fingering hand Braille readers Visual cortex becomes activated 5

6 Constraint Induced (CI) Movement Therapy Intense behavioral therapy Regain lost function Restrain movement of functional limb Perform intensive motor tasks Many hours each day for 2 weeks Causes cortical map reorganization Brain Plasticity Still do not know a lot about plasticity Limits of plasticity Plasticity of adult brain vs. child brain How plasticity operates How much lost function in remapped area Regaining Lost Function Nerve damage (not destroyed) Function returns over time Nerve destruction Replace neurotransmitters L-dopa in Parkinsons Temporary relief from symptoms Implant fetal brain tissue Modest success 6

7 Neurogenesis Producing new neurons From neural stem cells In adult CNS Stem cells differentiate Glial cells (mostly) Neurons Brain areas Ventricles Hippocampus Cells proliferate Neural stem cells Neural precursors Cells must migrate to differentiate Neurogenesis 50% successful migration Hippocampus Olfactory bulb Induce repair Control when and where development occurs Neurogenesis 7

8 Regaining lost function: Circumstances Age Recovery is greater if the damage occurs earlier in life True for language, motor and sensory cortex Destruction of a limited brain area In some circumstances, adults fare better Less likely to suffer low IQ or learning disabilities Less affected by damage due to infection, alcohol, drugs, poor nutrition, lack of oxygen Regaining lost function: Circumstances Nature of Trauma Slow, gradual lesions lead to better recovery than sudden dramatic lesions Possession of Behavior More likely to recover a behavior if organism has had prior experience with the behavior 8