neuroplasticity Flashcards
Define neuroplasticity
what is sensory neuroplasticity
basically a subsection of neuroplasticity.
neuroplasticity in response to a change in sensory input.
plasticity that arises as a response to change to the peripheral sensors and sensory conduits to the brain e.g., damage to. the eye or the optic nerve, or losing a limb.
Having a stroke that affects visual paths in the brain is not considered sensory deprivation. This is because the damage is actually happening in the brain.
what things could produce a change in sensory input?
- sensory deprivation e.g., loss of smell/limb
- sensory augentation/substitution
what is sensory augmentation/substitution
Augmentation - something providing information to a sense that’s damages e.g., things like glasses, hearing aids cochlea implants
substitution - taking information from one sense e.g., vision, transform it and express it via another sense e.g., sound
within the topic of sensory plasticity, people have differentiated intra-modal vs cross-modal
describe these
intra-modal change: change in modality that is the same as the one in which the deprivation/augmentation occurs e.g., having a hearing loss and we measure a change in the auditory processing. it’s an intra-modal change
cross modal: changes in modularity that is different from the modality in which the deprivation/stimulation occurs e.g., having a hearing loss then we measure a change in visual processing
In human, how much of the cerebral cortex does the visual cortex occupy
20%
what lobes does the visual cortex intrude
occipital lobe and posterior parts of the parietal and temporal lobes
where is the primary visual cortex (V1) located?
calcarine sulcus
contains a map of the visual field
how is visual information transmitted to brain?
- Visual information is transmitted from the retina via the optic nerve.
- Retinal projections split/cross in the optic chiasm.
- A major part of retinal projections then travel on to the LGN (part of the Thalamus) and then on to primary visual cortex (V1, calcarine cortex).
what 2 streams transmit visual information
dorsal and ventral stream
how do we measure visual acuity properly?
Snellen scale
that thing where the numbers get smaller as you move down the page
results of the test are written as: 6/60
- first number = how many meters you were away from the chart
- second number = the number of lines you are able to read from that distance
- standard vision = 6/6
international classification of diseases 11 (2018)
how do they classify visual impairment?
2 groups:
- distance vision impairment
- Mild –visual acuity worse than 6/12 to 6/18
- Moderate –visual acuity worse than 6/18 to 6/60
- Severe –visual acuity worse than 6/60 to 3/60
- Blindness –visual acuity worse than 3/60
- near vision impairment
* Near visual acuity worse than N6 or M.08 at 40cm (fk knows what M.08 means)
* near vision impairment
how many people globally have near or distance vision impairment
in how many of these could have been prevented?
2.2 billion
1 billion of these could have been prevented
what are the leading causes of vision impairment and blindness?
- uncorrected refractive errors
- cataracts
what is azimuth angle
left to right
what is elevation angle?
head moving up or down
combining both azimuth and elevation angle
basically up-down and left-right angles of the face
psycho-acoustic cues:
what tells you if a sound is located to the left or right?
(timing)
- Timing - Interaural Time Difference (ITD) (azimuth)
psycho-acoustic cues:
what tells you if a sound is located to the left or right?
(level/intensity)
level/intensity - Interaural Level/ Intensity Difference (ILD/IID)
- Sound intensity is inversely proportional to distance from the sound source squared (inverse square law)
- double the distance, decrease intensity by factor of four
psycho-acoustic cues:
what tells you if a sound is located to the left or right?
(level/intensity)
Head-Shadow
Elevation
what tells you if a sound is up or down?
spectral pinna cues (?)
distance
what tells you if sound is close or far
(echos)
echos - or in a fancy way “direct to reverberant ratio”
- direct sound energy (d) goes straight from source to listener
- reverberant sound energy (R) - bounces on surfaces before reaching the listener
- the ratio of direct-to-reverberant sound decreases as source distance increases
distance
what tells you if sound is close or far
(level/intensity)
Monoaural Intensity (& familiarity)
- Sound intensity is inversely proportional to distance from the sound source squared
- double the distance, decrease intensity by factor of four.
Interaural Time Difference (ITD) and Interaural Level/ Intensity Difference (ILD/IID)
ILD as compared to ITD (laterally positioned sounds)
- Intensity drop-off as a function of distance is not linear. Thus, magnitude of ILD depends on absolute distance
- ITD independent of distance
- relative magnitudes in ILD and ITD can be used to infer distance
- Only applies for sounds where ILD and ITD exists (laterally positioned sounds)
distance
what tells you if sound is close or far
(spectral composition)
Air absorbs higher frequencies (& familiarity)
- the further away a sound, the more lower frequencies
- Only effective at distances > 15m
Different types of acoustic information (IID/ILD, ITD, spectrum) are transmitted through different sub-cortical pathways
name the pathways
On the cortical level (in humans), there are two separate, yet interacting, auditory streams
name them
which auditory stream carries information about spatial hearing
dorsal stream
the brain typiclaly supresses echos - what is this called?
‘Precedence Effect’ or
‘Echo Suppression’
Litovsky et al (1999) JASA; Wallach et al (1949) Am J Psych; Haas (1949) JAES
how can frequency communicate something about the distance of a sound?
what term do we use to say locate this sound to either the left-or-right
Binaral sound localisation (Azimuth)
who is better at locating sounds the their left or right
blind vs sighted people?
Blind people
Voss et al., (2014)
- dark room
- n hear sound, silence, and then a second sond
- they have to say whether the second sound was more left/right than the first
- blind people are better locating sonds to the left or right
whats are blind people who NEVER had any vision called
congenitally blind
who is better at locating sounds central to them
blind vs sighted people?
no difference
- Voss et al., (2004)
- asked blind and sighted people to locate a sound straight ahead
- no difference btw both groups in this skill
blind people are better locating sounds rrepresented in perohpheral space (left vs right)
true or fals?
true
what is the fancy way of saying:
the ability to localize a sound using one ear?
Monoaural sound localization
whoa are better at locating sounds in peripheral space(left/right) using one ear?
monoaural sound localization (Azimuth)
- Gougoux et al., (2005)
- sighted peopel bad at this! percieve sounds being more ot the right
- early blind n - some were equally bad as sighted n, some were suprior to sighted n
so SOME early lind n are better than sighted people
SOME blind n better at monoaural sound localization and ALL are better at binaral sound localization
what does this mean?
- That there are neuroplastic changes that follow sight loss. more likely due to better use of these spectrum cues available.*
- But something else seems to begoing on elsewhere (some individual differences play a role).*
using both ears
who are better at locating the distance of a sound blind or sighted n
Binaral sound localization - DISTANCE
Voss et al., (2004)
- n hear one sound, then the other - have to say whether the second sound was close/further than the first
- blind n much better than sighted
wha does “2 alternative forced choice” measure mean
when n forced to make one choice out of two
e.g., Voss et al., (2004) study where they hear 2 sounds and are forced to say whether the second sound was closer/farther than the first
elevation
Zwiers et al., (2001)
- n asked to point towards a sound
- altered the height of the sound and asked n to point to the height
- as a control asked n to point in terms of azimuth (left/right)
- varied levels of background noise during the task
see image - right side “dB” marks the signal-to-noice ratio. how much noise there was, 0 dB is 0 background noise.
results
- early blind n are worse than sighted when jusging elevation in the presence of a noise
n asked to locate the elevation of a sound, background noise slowly introduced.
blind people struggeld much more at the task when background noise was introduced
what does this mean
suggests that as we grow up we use the visual system to calibrate these sounds to elevation angle
maybe when vision is not available n are more suceptible to distuption (e.g., background noises)
in what way does visual sensory deprivation affect spatial hearing
what does it improve vs impair?
studies where blind people showed a deficit involved pointing, why might thie be a possible confound?
pointing is not something blind n do very often
- Group analyses shows that pointing specificity in blind n are quite variable. Possible confound to explain why some elevation studies did not find the improved spatial hearing in blind n.*
- pointing = sensory-motor confound*
study to measure localization performance w/o the pointing confound.
using the 2 alternative forced choice task
- used an array of speakers to present sounds
- while. indarkeness - so couldnt acc see
- given a center sound (blue spot in pic) then a second sound (red)
- n say if second sound was more to left or right
results
- used % correct
- and fit psychometric functions to the data - steeper curve means performance is better
- red curve = sighted n; blue curve = blind n
- blind n perform better than sighted n in both azimus and elevation tasks
so previous studies finding deficits in elevation reflected an artefact of the response method (pointing)
are blind people better or wose locating sounds in azimuth and elevation dimensions?
Better! yes… some studies found deficits in elevation locating abilities but this was because they measured poiniting (confounded results)
what is the spatial bisection task
Gori et al., (2014)
- n hear 3 sounds
- 1st and 3rd sound on the ends, they have to say whether 2nd sound was cloesr tot he left or right
what is the minimum audible angle task
Gori et al., (2014)
- n hear a sound, then hear a second sound
- have to say whether the second sound was more left or right of the first sound
what is the difference between the spatial bisection and minimum audible ngle task?
The spatial bisection task requires us to make relative spatial judgments (allocentric). Judging something (sound) relative to another thing (another sound) and NOT relative to the observer (egocentric).
In contrast minimal audible task – entirely dependent on your perspective. Judging things with respect to own body position (more to my right).
Do blind n differ in their abiltiy to locate noice using an allocentric vs egocentric frame?
Gori et al., (2014)
Yes. scholars presented both the spatial bisection and minimum audible angle task to blind (congenitally and late blind n) and sighted controls
spatial bisection task (allocentric-dependent)
- blind n were bad at this
- struggled to judge where sunds were with relation to one another
minimum audible angle task (egocentric-dependent)
- blind n were fine at this
- fine judging where sounds were with relation to themselves
what do we learn from Gori et al., (2014) study showing blind n were bad at spatial bisection task but sound on the minimum audible angle task?
Spatial deficit is probably more cognitive than perceptual.
- They can localise an individual sound fine (otherwise would have struggled with MAA task).
- The difficulty was when they had to locate sounds relative to other sounds – cognitive deficit.
Association between early blindness and difficulty making allocentric spatial judgments.
so basically blind people hear better?
NO!!!! you fool
yes visual sensory deprivation is associated with improvments in spatial hearing but this does NOT just mean oh if your blind your hear better
we know this becuase if you measure things like frequency tuning blind and sighted people actually perform similarly. also when juding location of a sound straight ahead = also perform similarly.
improvments are in
- azmiuth localization in periphery
- azimuth monoural localization
- distance perception
blind people - spatial hearing
What are they better at, and what are they worse at?
improvments are in
- azmiuth localization in periphery
- azimuth monoural localization
- distance perception
- elevation
impairments are in
- spatial bisection
what did the little weisel and hubel study
Weisel and Hubel (1963)
- Cats
- Measured how fast information travelling to the two eyes are processed (V1)
- in normally developed brain we have ocular dominance columns
- neurons responding to input from both eyes but slight preference for the contralateral eye
then they excluded input from one eye
weisel and Hubel (1963) the ocular dominance columns of cat reared with normal visual experience.
how does this change when they stop information reaching one eye from birth?
the disrtribution of information processed across the columns changes
when one eye doesnt provide input, after 2 and a half months the brain doesnt respond to input from that eye anymore. like it doesnt exist even though it functions perfectly fine.
Why do scholars think with visual deprivation the brain stops recieving input from the faulty eye? (weisel and hubel 1963)
What seems to happen is the visual system comes into existence with all connections there, but when input isn’t received (information from one eye) – those connections from that eye to the brain are pruned. Its lost.
Weisel and Hubel (1963)
If visual deprivation is induced later (not from birth) how does this affect the brain activity?
- with some initial experience
- effect of deprivation is less drastic
- we see still some responsiveness to the eye (even if the deprivation goes on for a little longer)
seems ther is a critical period where the visual system is very sensitive to input. If proper input isnt recieved here then the visual system doesnt develop normaly
Weisel and Hubel (1963)
what happens when they applied visual deprivation to an adult cat that had grown with normal visual experience?
fuck all
Very little effects on the ocular dominance distributions
how did hte findings from the Weisel and Hubel (1963) cat study lead to treatments for amblyopia?
- realisation that deprivation in early years = very problematic
- led to theory that the nervous system is most suceptible to change within certain time windows
- if child has faulty eye they are given glasses from early, or have one eye (good one) patched to encourage processing form impaired eye. Brain forced to use it.*
- This is still a problem though because one eye patched prevents you learning to use both eyes together.*
what are critical and sensitive periods?
window of increased plasticity of typically young organisms.
when do critical and sensitivt periods occur?
during early post-natal periods
whats the basic gist of critical/sensitive period theory?
if appropriate experience is not recieved during specific time windows then development goes astray, sensory areas will not develop.
How did he et al (2006) measure ocular dominance differeently to Hubel and Weisal (1963)
measured occular cdominance but instead of recording cells responding to visual input they recorded viusally evoked pootentialt (VEP)
both measure ocular dominance just in different ways
Describe the intramodal effects of visla deprivation on an organism
He et al., (2006)
experiment 1
- mice
- normally reared - then applied monocular deprivation for 3 days
- measured the effects - not much happened - not surprising given the critical period had passed
experiment 2
- normal reared mice now adults
- then put them in the dark for 10 days
- then applied the 3 day monocular deprivation
- found large change in ocular dominance responses - what we would expect if we deprived organism pduring postnatal period
the 10 days of visual deprivation sort of reignighted the plasticity of the brain
when he et al., (2006) followed up the effects of the 10 day visudal deprivation in reignighting the plasticity of hte brain. inearly years
what did they find?
found not just the response of neurons that change, but other properties characteristic of juvenile plasticity – changed as well.
what things increase plasticity in the brain?
- visual deprivation (he et al., (2006)
- physical exercise
Describe the cross-modal effects of visual deprivation on an organism
Petrus et al., (2014)
- induced short term visual dperivation (6-8 days of darkness)
- then measured how the neurons responded to sound in A1, and light in V1
A1
- in animals exposed to darkness -
- spontaneous rate: more neurons in A1 respond to a sound
- first spike latency (how quickly a neuron responds to a sound) animals respond quicker to a sound
so brief dark exposure increases the resonsivness of neurons in A1 - cross modal effect.
v1
- visual deprivation actually had no effect on the responsivness of neurons in V1
Petrus et al., (2014) found 6-8 days of darkness had no effect on the responsivness of neurons. inV1. but he et al., (2006) found 10 days of disual deprivation increased the sensitivity of neurons in V1.
how can we explain these contradicting results?
He et al., didnt just stop at the visual deprivation, they induced monocular deprivation after this.
P just had dark exposure then measured responsivness to a simple light.
word of caution when interpreting the effects of sensory deprivation
- differences in findings from petrus et al., (2014) and He et al., (2006) point out the important of not comparing everythign so directly together*
- Suggests when we look at plasticity, look at different processes within a sensory system as having their own time scales. And different modalities, also with different time scales.*
- So when we find a results like these, doesn’t simply apply to everything in the same way.*
wat is a big argument against the notion of a critical and sensory period?
The findings that visual deprivation can reignight juvinile plasticity in adult organisms
what has taught us a lot abuot the relationship between age and neuroplasticity
what is echolocation useful for in blind n
- Identify landmarks (main reason)
- Also to identify obstacles
- Larger scale orientation and you aim to position yourself
- supports blind in in their mobility (Thaler, 2013)
- normal n when gettting from A-B they know where they are by visually noting certain posts, okay theres mcdonalds, and now im oging bpst the station etc.* Echolocation fulfils the same function!
- Landarks located via sound (clicks). If you have to locate something further, the clicks become louder and the echo is softer.*
could echolocation be considered a special form of spatial hearing
yes
special bc its more active form of hearing (you have to makre the click noises)
what could we use echolocation to investigate
neuroplasticity
- Skill only some n use
- can compare n who use it against those who dont
- then control for age / sensory experience / whether they’re blind or not
could use echolocation to investigate the cocktail of things that give rise to the skill (or don’t) revealing a lot about the nature of neuroplasticity
Do blind people show retinotopic-like mapping in V1 for sounds?
- Normal and Thaler (2019)*
- Research question: is there evidence for retinotopic-like mapping in V1 following sound?*
study design
- 5 blind echo locator experts, 5 echo locators non-expert, 5 sighted non experts
- measured brain activity in V1 in response to echo sound or source sound
- correlated the pattern of echo-acoustic brian activity (source, echo) with the pattern expected based on visual stimulation in sighted people (probabalistic brain map)
results
- confusing some blind echolocators showed this retinotopic like mapping while other dont.
- when they correlated how good they were at echolocation with retinotopic-like mapping of echo sounds in V1
- almost a perfect correlation between those two
This was not seen for blind non-echolocators. Thus the retinotopic like map of sound in blind n is driven by expertise in echolocation as opposed to blindness
how do the findings from Norman and Thaler (2019) challenge critical peiod theory
as if the Critical period theory posits you need relevant sensory experience to develop proper organisation of a retinotopic map for example in V1 and all the people in their study had never had functinal vision. They shouldnt show this kind of mapping but some do
What changes do we see in brain activity in response to blindness
- size of tonotopic areas (a1) - MEG
what happens to the representation of sound on a cortical level in blind n?
Elbert et al., (2002) - MEG
- Blind n – size of this tonotpic area was larger than sighted n
- Sample were quite heterogeneous in their onset of blindness but findings were farly consistent
However Huber et al., (2019)
- failed to find a larger tonopic area in blind n
- In this study they did however find a difference in tuning bandwidth
So blindness does indeed lead to changes in A1 but there’s some disagreement in terms of how we quantify it. Follows quite nicely the petruis paper that found visual deprivation induced changes in A1 in an animal model.
what was the first paper evidencing a correlation between neural functioning and behaviour in central and peripheral space.
EEG studies looking at auditory spatial tuning in blind n
Roeder et al., (1999)
- ERP
- N asked to identify whether a tone was present or not
- Asked to do this with respect to reference speaker
- Reference could be central (speaker 1) or periphery (speaker 8)
- Measured amplitude of N1 (indicative of attention devoted to stimuli)
results
- when n attend to speakers in center - no difference across the different locations (1-4)
- peripheral - reveals a more systematic shift in n1 amplitude as a function of speaker position
some early blind were superior at monoaural loalization
whaere in the brain was active for them when doing this?
Gouux et al., (2005)
- the occipital cortex
- absent in early blind n poor at the skill, and sighted people who were equally poor at this task
neuroimaging study looking at binaural localisation?
Collignon et al., 2011
- fMRI
- n performed binaural localisation task in scanner and 2nd part they had to discriminate the pitch of a sound in a scanner
- Looked at brain activity – what regions engaged when more engaged in spatial judgment vs pitch judgment and which part of the brain was more active in blind vs sighted (conjunction contrast)
- Found right middle occipital gyrus – handles auditory localization in blind n
interestingly the MOG in sighted people isnt interested i n auditory spatial processing, for these guys it does visual spatial processing
When blind people do auditory spatial processing they additionally call the middle occipital gyus to help them out.
other modelities do spatial processing
is sound the only modality the middle occipital gyrus helps blind n process spatial information?
Renier et al., 2010
- nope
- found with a tactile spatial task the MOG active in blind n
Seems to be something about MOG involved in spatial processing regardless of modality
any difference in brain activity in blind vs sighted n when processing auditory stimuli in motion.
Poirier et al., 2006
- n listen. toa sound that is either moving or stationary
- Blind n – showed increased activity in V1 with motion processing
- No activity in what we would expect in the visual motion areas (MT/MST)
shocking ! now auditory infomration thinks its hot stuff coming over to visual system turf! not on our watch >:0
cross modal effect
So we have behaviour on one hand and brain activation on the other. how can we determine one CAUSES the other.
(neurocimaging studies are only correlational)
- disrupt activity and see the effect on behaviour during spatial auditory processing (TMS; Collignon et al., 2009)
- Model functional connectivity
- first you get activity measurements of specific tasks
- Explore different connectivity models
- Then can compare models
- Gives you idea of which connectivity pattern/which direction of flow of information will fit best
- Patient work
how did Gougoux et al., (2005) study link behaviour with brain activation
Correlational/predictive analysis
Monoaural auditory localisation task again
- A (occipital lobe) - see strong correlation between brain activity and localisation performance
- B – middle occipital gyrus, also show this correlation with performance in monaural localisation
