L13 Flashcards
what are the 2 stages of development in the brain
prenatal formation of the brain
postnatal plastisity
what happens to brain plasticity as we age
it decreases
what is prenatal development
Formation of the central nervous system occurs during prenatal development.
what are the 3 main stages in forming the structure (developing) of the brain
The structure of the brain develops in steps:
- Cell Division (i.e., cell proliferation)
- Cell Migration
- Cell Differentiation
what is the first step in wiring cerebral cortex
is generating neurons (cell division).
how does the brain generate neurons (prenatal)
Stem cells in the central nervous system divide into two cells.
stem cell -> another stem cell + daughter cell
after cell division in prenatal brain development what happens
After cell division, the newly divided cell migrates away to take up its position in the cortex and
the stem cell remains to undergo more divisions.
• Stem cells continue to divide until all the neurons of the cortex have been generated.
• Cell differentiation refers to the process by which, after migrating, new cells take on the
appearance and characteristics of a neuron or glial cell.
what is cell differentiation
• Cell differentiation refers to the process by which, after migrating, new cells take on the appearance and characteristics of a neuron or glial cell.
how does the new cell migrate in prenatal brain development
• The new cell migrates by slithering along thin fibres (process of a radial glial cell) that radiate toward the surface of the brain
describe how the brain forms/cell migrations effect on how the brain forms
the brain forms in layers therefore you can say that the brain is being formed from the inside out
how is the brain wired
Neurons extend their axons to the appropriate targets in order to form inter-neuronal connections
describe the relationship between postnatal development and plasticity
Brain development continues after birth, but the plasticity of the brain declines as we age.
- Although on a much smaller scale, plasticity of the brain continues after birth.
- The adult brain is comparatively rigid, but still undergoes plasticity (e.g., toy are still able to learn and remember new things as we age).
what is neural plasticity
neural plasticity (plasticity) refers to the ability of the nervous system to change.
describe the circuitry of the brain at birth
• At birth, the basic circuitry of the brain is largely in place.
Fine-tuning of the wiring of the brain is driven by what
neuronal activity.
what is an example of how neural activity causes fine tuning of the brains circitory
consider the level of overlap in the neural projections from the two eyes at birth versus after months of sensory experience.
• Recall that the LGN and V1 receive information about the opposite hemifield from both eyes (e.g., in the right hemisphere, the LGN and V1 receive information about the left visual hemifield from both the left and the right eye) and that if you were to loos sight fro one eye then you would loose some of the visual feild.
This is not the cause in babies as at birth the visuals feilds from both eyes overlap and it is through experience that the visual feilds of your eyes become separate
describe the formation of Ocular Dominance Columns in Primary Visual Cortex
At birth, the inputs from the LGN representing the two eyes are intermingled within striate cortex (V1).
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 sensory experience
what are Ocular Dominance Columns
what you can see with each individual eye
describe the anatomy of the auditory system
neurons in the inferior colliculus (IC) send their axons to the medial geniculate nucleus of the thalamus (MGN), which in turn send their axons to primary auditory cortex (A1).
That is, normally IC → MGN → A1
a single-cell recordings in primary auditory cortex (A1) was taken from newborn ferrets, within one hemisphere the axons of retinal ganglion cells
destined for the superior colliculus (SC) were redirected to the medial geniculate nucleus
(MGN), and the SC and inferior colliculus (IC) were removed. The other hemisphere was left
intact.
(info from left retina goes to MGN instead of superior colliculis. right hemisphere = normal)
what did they find
After the animals were raised to adulthood, the neurons in primary auditory cortex in the
rewired hemisphere behaved like visual neurons in response to visual stimuli (e.g., had retinotopic organization).
you would also have to cut the cortical pathway on the right side as well becuse that is 90% of out vission
what are the Effects of stimulating visual cortex in adults with impaired vision (with TMS)
participants had varying amounts of damage before V1
The results indicate that the effect of activating 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
the less residual vision they had the less likely they were to experience phosphenes
Do you think that completely blind participants that experienced phosphenes have congenital blindness (i.e., since birth) or that they have had previous visual experience?
if they were blind from birth then they would not experience phophenes
• One congenitally blind participant reproducibly reported the experience of a localized sensation
of warmth (‘like a heating-lamp’) in the contralateral half of his near-grasping space’ when his
occipital cortex was stimulated.
therefore their visual cortex has be used for sensory information in other areas of the body
Which brain structure is activated during mental imagery in sighted versus congenitally-blind
adults?
to test this a study recruited – 6 blind adults that were blind from birth
– 6 sighted adults that were blindfolded and asked them to produce mental images from animal names versus passive listening to abstract words
what kind of stimulis is this
endogenously (from within) as the stimulis is their imagination
Which brain structure is activated during mental imagery in sighted versus congenitally-blind
adults?
to test this a study recruited – 6 blind adults that were blind from birth
– 6 sighted adults that were blindfolded and asked them to produce mental images from animal names versus passive listening to abstract words
what kind of stimulis is this
endogenously (from within) as the stimulis is their imagination
Which brain structure is activated during mental imagery in sighted versus congenitally-blind
adults?
to test this a study recruited – 6 blind adults that were blind from birth
– 6 sighted adults that were blindfolded and asked them to produce mental images from animal names versus passive listening to abstract words
what did the fMRI data from this study show
Brain activity during passive listening to abstract words was subtracted from brain
activity during the mental imagery task.
• This subtraction procedure yields a more specific measure of brain activity associated with
mental imagery
Which brain structure is activated during mental imagery in sighted versus congenitally-blind
adults?
to test this a study recruited – 6 blind adults that were blind from birth
– 6 sighted adults that were blindfolded and asked them to produce mental images from animal names versus passive listening to abstract words
what were the results from this study
Results: In both congenitally blind and sighted participants, the production of mental images was associated with activation of visual cortex. (activation when they imagined something and no activation for abstract words)
therefore primary visual cortex is activated in congenitally blind people and that activation occurs in a mental imagery task that involves only verbal instructions.
primary visual cortex is activated in congenitally blind people in a mental imagery tasks that involve only verbal instructions.
if they have never seen these things how are they able to imagen them/what could be the cause of these results
they have never seen these animals therefore they might not be imagining what they look like but what they sound/feel like instead
Training monkeys to discriminate specific tone frequencies (training of A1) leads to what
an enlargement of the
cortical regions in which the trained frequencies are represented.
• This change provides a demonstration of functional plasticity within primary auditory cortex.
Training monkeys to discriminate specific tone frequencies leads to an enlargement of the
cortical regions in which the trained frequencies are represented.
what information does this provide us with
• This change provides a demonstration of functional plasticity within primary auditory cortex.
How can we test to see if the human adult motor system respond to training?
test plasticity of M1
Using your non-dominant hand, perform finger-to-thumb tapping in the specified sequence
(participants learned either A or B) and then trying to do it as fast and accurately as possible for 10-20
minutes per day.
Using your non-dominant hand, perform finger-to-thumb tapping in the specified sequence
(participants learned either A or B) and then trying to do it as fast and accurately as possible for 10-20
minutes per day.
what would the results of this be
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 contralateral 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.
Using your non-dominant hand, perform finger-to-thumb tapping in the specified sequence
(participants learned either A or B) and then trying to do it as fast and accurately as possible for 10-20
minutes per day.
what method would they need to mesure this
Using fMRI, the scientists measured activity-related changes in blood flow in primary
motor cortex for the practiced sequences and untrained sequences.
• Data comparison: Trained vs. Untrained motor sequence
• The fMRI activity elicited by performing untrained sequential movements (right) was subtracted
from the activity elicited by performing trained sequential movements (left).
• As we grow older, the brain becomes less plastic and begins to atrophy.
what is one conequence of this
• 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 (see above graphs).
• Engagement in aerobic exercise also improved the accuracy of spatial memory.
age related decline in memory function has been connected to what
age-related reductions in the size of the hippocampus.
what does engagement in aerobic exercise show
• Recent research in older adults indicates that engagement in aerobic exercise can increase the
size of the hippocampus (see above graphs).
• Engagement in aerobic exercise also improved the accuracy of spatial memory.
