Neuroplasticity Flashcards
Neuroplasticity
Ability of the brain to exhibit changes in neurons and synaptic connections as a result of
environmental interactions.
Which sensory system is the most plastic
Visual system
Visual adaptation
short-term change in sensitivity or perception caused by
the aftereffects of exposure to a visual pattern.
Visual perceptual learning
A long-term improvement in performance on a visual task.
What is a deviant stimuli
A deviation from the frequently occurring standard stimulus. deviant stimuli cause large spike in activity
Where in visual cortex does deviant stimuli spikes occur
In layer 2/3
Impact of exercise on perceptual learning (Virethrone et al., 2021)
our findings suggest that exercise alone can influence visual processing, but we did not find evidence that combining exercise with patching enhances visual plasticity beyond patching alone.
Vernier acuity task
Tests visual perceptual learning. Measures the ability to discern a disalignment among two line segments.
Visual perceptual learning-VPL
defined as performance enhancement on a visual task as a result of visual experience and has been regarded as a manifestation of brain plasticity.
Studies of VPL mechanisms should distinguish the process that leads to learning from the changes resulting from learning.
You are able to improve visual perceptual learning.
What’s interesting is even if you are not conscious of it, it is not necessary for you to be able to improve visual perceptual learning, this is demonstrated in rapid serial visual presentation tasks
Homeostatic visual plasticity
Process of temporarily covering one eye can cause a shift in visual dominance toward the covered eye
What happens when visual system is unbalanced
Visual hallucinations, occurs in neuropsychiatric disorders like schizophrenia- disorder is associated with visual processing impairments like contrast sensitivity and percetual orgnaisation.
What is the clinical evidence for plasticity in the visual system
Amblyopia treatment
Stroke/ Injury recovery
Charles bonnet syndrome
Charles bonnet syndrome- visual plasticity
causes visual hallucinations to those who have lost a lot of sight, e.g. in age-related macular degenration or cataracts. This phenomenon is similar to the way people feel phantom limbs. Confabulation of visual information causes these hallucinations. The hallucinations can be still or move. The hallucination can be both formed or unformed. Being in the dark can make hallucinations more likely
Ganzfeld technique.
Perceptual deprivation artificially induces ganzfeld visual hallucination. Blindford yourself with white material tape a half over each eye, then listen to white noise with a red light over you (uniform light).
“Underactivity in the sensory cortices that triggers the brain to start filling in the gaps- confabualation of vision”
Difference between Ganz Flicker and Ganzfeld
Ganzflicker was more effective than Ganzfeld at eliciting simple hallucinations, while complex hallucinations remained equivalent across the two conditions. Complex hallucination more likely from Ganzfeld.
What is Amblyopia
Abnormal visual development
most common cause of visual impairment among children, affecting approximately 2 to 3 out of every 100 children.
Affects central vision- peripheral remains normal
When can Amblyopia be fixed?
before the critical period is finished, before age 7.
age 7-17 do respond to treatment.
The critical period can also be termed….
Ocular dominance plasticity.
Treating amblyopia in Adults Versus children
Children: atropine to relax muslce for eye or patching over good eye for months.
Adults: visual lost if crticail period is over- need to identify ways to enhance plasticity
Ocular dominance
Prefrence for one eye. (disocered by hunel and wisel in cats- how?)
Balance in OD is crucial for binocular vision.
ODI and its range
Ocular dominance index.
ODI ranges from +1 to −1, positive value indicates contralateral bias
negative value an ipsilateral bias.
What mimics Amblyopia
Monocular deprivation
What visual aspect is impacted in amblyopia?
Binocular vision and stereopsis also impacted parlty due to decreased visual acuity
Visual acuity def
the clarity or sharpness of vision
Stereopsis def
Visual fucntion.
Stereopsis refers to the perception of depth that occurs due to the slight positional differences in the images received by each eye. This binocular disparity is used by the brain to estimate the depth of objects relative to the observer’s point of focus.
What do both Adult and juvenile plasticity depend upon
NMDA receptors
Effect on V1 after monocular deprevation
If the contralateral eye was shut then the number of cells would deplete there and increase in the ipsilateral side of the V1. This process is driven by synaptic plasticity- Hebbian plasticity
Critical Period def
Time window in early life that the organization of neural circuits is extremely susceptible to external environments because the brain is very plastic.
Human: first year most important, but extends to 5-10 years
Critcial period for stereopsis
extends through late infancy and early childhood and continues to at least 4.6 years of age.
critical period in layers of v1
Cells at higher levels of the system have a critical period that lasts for a longer time. For example, the ocular dominance of cells in layers II, III, V, and VI of the primary visual cortex can be changed by monocular deprivation after the ocular dominance of cells in layer IV has been established
What does MD do to cells in OD
Shifts it from OD eye to other eyesm so cells decrease in OD eye and spread more toward an equal or other eye spread
What are the strucutral changes following MD and in which V1 layer does this happen?
In layer 4 and in dLGN
Spines retract and density lower.
Size of neurons lower
They saw rapid OD plasticity - just one day of MD causes rapid shift in OD
Experience-dependent structural plasticity at pre- and postsynaptic sites of layer 2/3 cells in developing visual cortex- Sun et al 2019 study
Fluorescent labelling spines with PSD95 or SYP-GFP (presynaptic marker)
and GFP for layer 2/3 neurons
2p imaging to track over days
Results:
MD induces rapid changes in synaptic structure & spine numbers corresponding to population response.
Ocular dominance in individual neurons tightly correlate with its spine remodeling
Spines serve as an anatomical basis for rapid ocular dominance plasticity in L2/3
After reopening the deprived eye within the critical period, recovery of responses to normal levels occurs within 2 days
DIfference in contralateral and ipsilateral eye following MD?
Disadvantage of Sun et al 2019 study
cannot distinguish if synapse is listening to input from the contralateral or ipsilateral eye
Sun, 2019 Post synaptic changes
Rapid remodeling of postsynaptic spines in response to MD:
1.Significant increase in spine elimination after 3 days of MD (15.6% vs 7.9% in controls)
2.Decrease in spine formation (5.4% vs 8.5% in controls)
3.Bimodal changes in spine density: some neurons lost many spines while others gained spines. This correlated with the neurons’ ocular dominance preference
**(look at papers for this) VEP for MD recordings of contra & ipsi eye
VEPs (measure electrical signal of visual cortex in response to stimuli) used to measure cortical plasticity
Name the therapies to increase adult plasticity
- Pharma-Serotonin signalling enhance plastic changes (fluoxetine- the depression drug)
Activation of Rho GTPase- increases plasticity too
2.Transplantation of Paravlb and Sst interneruons. The age of transplanted interneuron defines
the new critical period. Transplanted interneurons form
numerous, weak synaptic connections
- Running (disputed in recent studies) -Running Promotes Recovery From Amblyopia in Adult Rodent models
Strabismus def
abnormal alignment of the eyes; the condition of having a squint.
Amblyopia is most likely to occur as a result of
Monocular deprivation during childhood
Do strcutral changes occur in thalamus following MD?
Yes- changes to the dLGN which links to L4
What is required for MD to occur
High plasticity so OD can shift
