NPB 100 Lecture 17

NPB 100 Lecture 17 - Lecture 17-Critical periods and...

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Lecture 17 -Critical periods and requirement for binocular experience -Role of activity dependent development and coherent activity in the formation of normal cortical properties -How we extract information from sound -How the CNS synthesize a map of auditory space from information that is inherently not positional -receptive fields in the cortex show orientation preference and are binocularly driven -congenital cataracts: born with defective lenses; don’t have any form of vision -strabismus: one or another of the eye is either crossed or tilted out because the extra-ocular muscle is misplaced on the eye. Both eyes are normal in the optical sense and the neural sense but cannot focus on the same position in visual space; cannot bring fovea to bear on the same point. -if uncorrected, have permanent monocular vision; blinded in one eye -as an adult, can surgically correct the extra-ocular muscle so that the fovea can focus on the same point in visual space but cannot achieve true binocular vision; visual loss is not corrected -this leads to the idea that binocular experience during post-natal development, normal visual experience is needed for the development of full visual capability. -acquisition of true stereoscopic vision requires binocular vision -experiments in which kittens were deprived of normal visual experience by occluding one eye or putting on lens that would alter the light path coming into the eye -instead of finding the normal distribution of binocular receptive fields in a normal adult, they found animals with only right eye or left eye receptive fields -did an experiment where they record from a cell and see to what extent does it respond to light coming in from the left eye and then from the right eye in the appropriate place. If the responses were equal, they would give it a score of 4. If it is purely left eye dominant, it is less and if it is purely right it is 7. -in newborn animals, you see a flat histogram. Equal probability of finding cells that are left-eye driven, right eye driven, and all variations in between. That is what you see early in postnatal development. -in the adult animal, we see the same thing if the animal is normal
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-in animals that are monocularly deprived, see only neurons that are either left eye or right eye driven and nothing that is binocular. This says that during postnatal development, if an animal is deprived of true binocular experience, then it loses the true characteristic of the neurons in the visual cortex that are present at birth and instead, they become exclusively driven by one eye or the other. -during the development of the visual projection, you can map the anatomy of geniculate neurons projecting into the cortex using some interesting tricks -looking at axons of genicular neurons projecting into the cortex -here is the eye, axons will project into the geniculate and relay neurons will go up to the cortex. This tracing is done by injecting radioactive amino acids into the eye where they are incorporated
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This note was uploaded on 03/15/2010 for the course NPB NPB taught by Professor Bales during the Winter '09 term at UC Davis.

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NPB 100 Lecture 17 - Lecture 17-Critical periods and...

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