27 Development of the Brain Flashcards
What is prenatal formation of the brain? and development
Development before birth
formation of the central nervous system occurs during prenatal development
Development of the brain
- Cell Divisions (Cell proliferation)
- Cell migration
3 Cell Differentiation
the first step in wiring the cerebral cortex is generating neurons (cell division)
Stem cells in the central nervous system divide into two cells
after cell division, the newly divided cell migrates away to take up its position in the cortex and the stem remains to undergo more divisions
Stem cells continue to divide until all the neuorns of the cortex have been generated.
Cell differentiations refer to the process by which after migrating, new cells take on appearance and characteristics of a neruon of glial cell.
What is plasticity?
it refers to the ability of the nervous system to change
although, on a much smaller scale, the plasticity of the brain continues after birth.
The adult brain is comparatively rigid, but still undergoes plasticity e.g. learning
How are connections modified by sensory experience?
At birth, the basic circuitry of the brain is largely in place.
Fine-tuning of the wiring of the brain is driven by neuronal activity. For example, consider the level of overlap in the neural projections from the two eyes at birth versus after months of sensory experience.
Formation of Ocular Dominance columns in primary visual cortex?
Top: At birth, the inputs from the LGN representing the two eyes are intermingled with the striate cortex (V1)
Bottom: Over the course of early postnatal development the inputs from the two eyes segregate into ocular dominance columns
This fine-tuning of the wiring of the brain is driven, at least in part by the sensory experience.
Experiment: Rewiring the brain in Newborns: Evidence of functional Plasticity. Results?
In newborn ferrets within one hemisphere, the axons of retinal ganglion cells destined for SC were redirected to the medial geniculate nucleus (MGN), and the SC and inferior colliculus were removed. The other hemisphere was left intact.
Results: after animals were raised to adulthood, the neurons in primary auditory cortex in the rewired hemisphere behaved like visual neurons in response to visual sitmilu (retinotopic organisation)
Experiment: effects of stimulating visual cortex in adults with impaired vision. Results?
Participants all had visual impairment due to damage before the LGN
Group 1: 10 adults with some residual vision
Group 2: 15 adults with very poor residual vision
Group 3: 10 adults without any residual vision
Results indicate that the effect of activating the visual cortex via TMS is altered in people with severe visual impairment, as evidenced by a reduction in the ability to elicit phosphenes in people with a high degree of visual impairment, especially in those without previous visual experience.
Experiment: mental imagery in sighted and congenitally blind adults? Conclusion & Results??
What brain structure is activated during mental imagery in sighted versus congenitally-blind adults?
- 6 blind adults from birth
- 6 sighted adults that were blindfolded
Task: produce mental images from animal names versus passive listening to abstract words.
Results: In both congenitally blind and sighted participants, the production of mental images was associated with activation of the visual cortex.
Conclusion: primary visual cortex is activated in congenitally blind people and that activation occurs in a mental imagery task that involves only verbal instructions.
What is functional placisity
Training monkeys to discriminate specific tone frequencies leads to an enlargement of the cortical regions in which the trained frequences are represented
Experiment: Training and plasticity: M1. Results & Conclusion
Task: Using your non-dominant hand, perform finger-to-thumb tapping in the specified sequence
Results: greater changes in blood flow occurred in the contralateral primary motor cortex for trained than for untrained sequences after only three weeks of training.
8 weeks after the final session: Greater changes in blood flow in the controlateral motor cortex for trained (left) compared to untrained (right) sequences persisted, even without training in the interim.
Conclusion: In the human adult brain, training can induce relatively rapid changes in brain activity that reflect the plastic ability of the nervous system to acquire and retain new information and skills.
Explain the aging brain with regard to plasticity.
As we grow older the brain becomes less plastic and beings to atrophy.
One of the consequences of this is a decline in memory function, which has been connected to age-related reductions in the size of the hippocampus.
Recent research in older adults indicates that engagement in aerobic exercise can increase the size of the hippocampus.
Engagement in aerobic exercise also improved the accuracy of spatatial memory.
what part of the cell form last in cells.
surface layers
