L5 - Lecture 5: Experience Dependent Refinement of Neural...

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Unformatted text preview: Lecture 5: Experience Dependent Refinement of Neural Connections in CNS (outline) I. Critical periods. II. Visual deprivation and ocular dominance plasticity. III. Hebbs law and cellular mechanisms for activity- dependent plasticity. Required reading: Purves et al. Ch24 Supplemental reading: Bear et al. Ch23 (p709-716) Lecture 5: Experience Dependent Refinement of Neural Connections in CNS (outline) I. Critical periods. Critical Periods: -- temporal windows when environmental factors play critical role in influencing the development of the nervous system . Example 1: parental imprinting in birds. Konrad Lorenz and his geese. Goslings follow the first large, moving object they see and hear during their first day of life . Cues could be visual/auditory, as well as olfactory/gustatory. Critical Periods: -- temporal windows when environmental factors play critical role in influencing the development of the nervous system . Example 1: parental imprinting in birds. Example 2: bird song. -- Three stages of song learning: Sensory acquisition: juvenile birds listen to and memorized the song of its adult tutor. Vocal learning: juvenile birds matches its own song to memorized tutor model via auditory feed back. Song stabilization. -- Some species (eg. zebra finches): song learning is limited to a time period - critical period. Other species (eg. canaries) can develop new songs even as sexually mature adults. Critical Periods: -- temporal windows when environmental factors play critical role in influencing the development of the nervous system . Example 1: parental imprinting in birds. Example 2: bird song. Example 3: language development in human. Fluency in language decrease with age Critical Periods: -- Temporal windows when environmental factors play critical role in influencing the development of the nervous system . Example 1: parental imprinting in birds. Example 2: language development in human. Example 3: bird song sensory motor learning. -- Conclusion: Young brain is very dynamic and responsive to experience. As animals get older, the brain becomes increasingly refractory to the lessons of experience. -- Two possible mechanisms involved in experience dependent plasticity: 1) experience promote the growth of rudimentary circuitry; 2) unused circuits are weakened and eliminated. Lecture 5: Experience Dependent Refinement of Neural Connections in CNS (outline) I. Critical periods. II. Visual deprivation and ocular dominance plasticity. Plasticity and critical period in visual cortex Why visual system: amenable to experimental manipulations. David Hubel and Torsten Wiesel: Deprivation animals of normal visual experience during a restricted period ( critical period ) of early postnatal life irreversibly alters neuronal connections and functions (eg. ocular dominance) in the visual cortex. 1981 Nobel Prize Ocular dominance columns in visual cortex Visual pathways: Retina -> (some optic nerves cross at optic chiasm) -> LGN -> (optic radiation)...
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L5 - Lecture 5: Experience Dependent Refinement of Neural...

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