cortical plasticity Flashcards
where is most of the cerebral cortex found?
burried in the sulci, because the cortex is a thin film about 3mm thick
how big is the cortex if flatted out?
as wide as a kitchen table
brain functions are localized, but not entirely what?
static
what is Kennard Principle from Margaret Kennard?
brain damage early in life is easier to repair than later in life;
there is more cortical plasticity when we are younger
what’s the definition of cortical plasticity?
Changes that occur in the function and organization of the cerebral cortex as a consequence of experience
how does the brain adapt after damage?
it adjusts its “maps” to the available brain tissue
what is crossmodal plasticity? give example
plstic changes that occur between sense;
ex if someone looses vision, how does it affect his auditory cortex
what happens to layer 4 of V1 when someone becomes blind from one eye?
layer 4 becomes 95% dedicated to the input from the eye that is still open
what happens to layer 4 of V1 if you reopen the eye?
after a certain time the layer 4 goes back to normal (representing both eyes the same)
what is the critical period?
period during which you have plasticity; pass that, plasticity becomes harder
give an example of the sensitive period
The success of treatment for strabismus (lazy eye) early in life;
treating strabismus in adulthood can do more damage than good
why would it be hard for us to have plasticity all of our life?
simple things such as walking would not be hardwired anymore
give 2 examples of plasticity in the somatosensory system
- Changes in cortical maps caused by increasing or decreasing stimulation.
- Plasticity from amputation.
changes in cortical representation is a consequence of what?
activity
what happened after stimulating a monkey’s finger tip everyday for a while?
even just stimulation increased the representation of the finger in the monkey’s cortex
what happens if a monkey looses its 3rd finger?
the overall representation of the hand doesn’t change, but the finger details do:
- loose representation of 3rd finger
- increase representation and sensitivity in 2nd and 4th fingers
what happens if you give food rewards associated with 2nd and 3rd finger stimulation?
discrimination training of finger 2 and 3 increases their representation in the cortex and their sensitivity at the expense of other fingers
what happens when a monkey is trained on a task that required fine-digit manipulation such as grabbing small objects?
the cortical representation of digits expands at the expense of the representation of the wrist and forearm
what happened when they removed the inferior colliculi in immature ferets?
it induced new connections from the retina to the MGN, the brain area usually connected to the inferior colliculi.
This caused the auditory cortex to be visually responsive
what is pruning?
the process of removing neurons and processes that
are not needed
what is apoptosis
is a form of cell death that is normal in development and enables the cells to die without affecting adjacent neurons.
what happened to patient BK who had a visual cortex stroke?
he got scotoma (bad vision) in the upper-left field of both eyes, and after a while the stroke damaged area shrunk and he could see almost perfectly
are only young brain plastics?
no
when do you stop forming neurons?
never; at maturity you still make some, but you just stop making more than you are loosing
describe the 2 visual streams in the brain?
- dorsal stream to parietal cortex: spatial and motion processing, visual control of movement (where)
- ventral stream to temporal lobe: object and pattern recognition (what)
how did they test to look for what and where processing areas in the non-primary auditory cortex?
3 behavioral tasks:
1. acoustic spatial localization (testing for where)
2. auditory pattern discrimination (test for what)
3. acoustic detection task (control)
what areas did they specifically look at in cat for “what” and “where” auditory areas?
AAF anterior and PAF posterior auditory fields
name 3 types of permanent neural deactivation
physical ablation
chemical (neurotoxins)
electrolytic
name 2 types of reversible neural deactivation
chemical (lidocaine, muscimal, GABA)
thermal (thermoelectric-peltier, cryoloop)
what is the cryoloop technique?
cooling down of a brain area with cool methanol to reversible deactivate it
what does cryoloop impair?
it disrupts calcium uptake at the axon terminal which eliminates synaptic transmission, without impairing axonal transmission
at what temperature is synaptic transmission eliminated?
below 20 deg C
how long does reversible cooling deactivation take?
few minutes only
how did AAF and PAF deactivation affect cats in sound localization task?
AAF deactivation = not affected
PAF deactivation = can’t localize the sound at all
how did AAF and PAF deactivation affect cats pattern discrimination task?
AAF deactivation = can’t discern pattern
PAF deactivation = no effect
how did AAF and PAF deactivation affect cats sound detection task?
no effect (control experiment)
from these results, what would be the auditory pathway equivalent of the “where” and the “what” processing areas?
- where = sound localization = PAF
- what = acoustic pattern discrimination = AAF
this experiment shows that it is possible to double dissociate regions of ___-______ ____ involved in spatial and pattern processing
non-primary cortex
this is true for what kind of animals?
mammals with highly developed cerebral cortices. (only tested on that for now)
in what lobe are areas for specificity of increasingly complex visual and acoustic stimuli found?
temporal lobe
what is Area T important for?
the accurate discrimination of conspecific vocalizations (same specie)
unilateral deactivation of what side of Area T has effects? what are the effects?
left area T deactivation causes deficits during conspecific vocalization discriminations
does bilateral Area T deactivation affect conspecific vocalization discrimination too?
yes, more than only left deactivation
bilateral deactivations of what other areas close to area T cause what kind of deficits?
A1 = deficit in tones, noise, and vocalization discrimination
A2 = deficit in noise and vocalizations discrimination
why does the effect of A1 and A2 deactivation make sense?
because A1 projects to A2 which project to Area T
what animal has a similar auditory system to humans? who’s is better?
cats; their auditory system is better, they can hear ultrasonic sounds
what % of cat’s cerebrum is acoustic?
20%
difference between cat’s and humans brain in general?
cats just have a few sulci, humans have a lot
what are the main parts of a cochlear implant?
magnetized transmitter outside the head, processor around the ear, and a receiver under the skin surface
and stimulator that goes around the cochlea
why do you need to get a cochlear implant on both sides if you have a hearing deficit?
because non-symmetry is bad for the brain
why may it be important for other senses to take up the auditory cortex?
to maintain the auditory cortex’s survival
what is adaptive cross-modal plasticity?
following the impairment of a sensory system, enhance performance is observed in the remaining systems; one or more modalities compensate for the loss of another modality
do deaf people see better?
they are better at noticing changes in the visual world
what part of congenitally deaf cat’s brains are responsible for enhance visual abilities?
the auditory cortex
how does crossmodal reorganization in congenitally deaf cats affect the ROLE of the auditory cortex?
it switches sensory but not behavioral roles of the auditory cortex
what happens to congenitally deaf cats hair cells?
they die shortly after they are born
when do they start training and testing the deaf cats?
once they reach maturity (1 yr old)
what is ABR and what is it used for?
auditory brainstem response: test for brainstem activity following click stimulus
how do normal vs deaf cats respond to click stimulus (ABR?)
hearing cat: start seeing activity at 20 dB
deaf cat: tiny response to very loud sound from the sound MOTION
visual task: what is vernier acuity?
telling the difference between a straight line and bars with a slight difference
visual task: what is grating acuity?
telling the difference between grated pattern and a plain color
visual task: what is orientation discrimination?
telling when a line is slight orientation or completely straight
visual task: what is direction of motion?
telling the difference between dots moving straight or at an angle
visual task: what is velocity of motion?
telling the difference between dots moving fast vs slow
visual task: what is detection of movement?
telling the difference between static or moving dots
in what visual tasks were deaf cats statistically better than hearing cats?
- detection of movement! they can detect slower movement than normal cats
- visual detection in the peripheral field
the functions affected by deafness were all linked to what?
motion
since the functions affected by deafness were all linked to motion, what stream of the auditory cortex was tested?
dorsal stream (WHERE stream)
what brain areas consist the dorsal / where stream of auditory cortex? (4)
PAF, AAF, A1, DZ
what happened when they cooled down A1, AAF, PAF, and DZ in deaf cats?
- cats ability to detect visual stimulus across a visual field decreased a lot
- cat’s ability to detect movement decreased (less sensitive to movement)
what happened when they cooled down each area specifically?
- PAF cooling decreased the ability to detect visual stimulus across the visual field
- DZ cooling decreased the ability to detect movement
- A1 and AAF cooling didn’t have much effect
cooling down PAF in deaf cats had what effect compared to hearing cats?
it eliminated the advantage that the deaf cat had in performing detection across the visual field task
what did cooling of PAF on the left side of the cat’s brain cause?
eliminated its capacity to localize visual cues on its right side
what can we conclude about PAF? posterior auditory field
it is important for auditory (already known) localization in hearing cats but in visual localization in deaf cats
cooling down DZ in deaf cats had what effect compared to hearing cats?
it eliminated the advantage that the deaf cat had in performing detection of movement task
what can we conclude about DZ?
it is important for detection movement of visual stimulusin deaf cats
how did they test for dorsal zone DZ’s involvement in detection of the DIRECTION of motion of a sound?
swept broadband noise across speakers, train the cat only to move if the sound is moving in one direction
in hearing ats, what did deactivation of each brain area cause?
no change in visual tasks! serve has good control
we can conclude that what auditory areas become visual and for what tasks?
PAF becomes an area involved in visual localization in the peripheral field.
DZ becomes an area involved in the detection of movement.
