L21 - Neural Plasticity Flashcards
What is a neural network?
Networks of neurons that are formed through synaptic pruning as we age.
What is the process called that allows for neural networks to be created?
Neural plasticity
What determines the state of a neuron?
The balance between inhibitory and excitatory signals.
What is neural plasticity?
The brain’s ability to reorganize itself by forming new neural connections.
When do we have the most neural plasticity?
When we are born and it slowly decays as we age.
What benefits does neural plasticity have for us?
It allows us to compensate for injury
It allows us to gain more proficient pathways as we gain our level of expertise.
We can adjust to new activities and new environments
What is synaptic pruning?
The process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions.
What are the three profiles of plasticity?
- Constrained (not highly modifiable)
- Highly modifiable dependent on experience (but only during critical/sensitive periods)
- Highly modifiable throughout life
What is meant by critical periods in neural development?
Learning or plasticity is confined to a short and sharply defined period
This learning is subsequently irreversible in the face of later experience.
What do these 3 graphs represent?
A and B represent critical periods of plasticity
C represents plasticity in adulthood (to a lesser extent over time)
What is meant by a sensitive period in neural development?
The effects of experience on the brain are unusually strong during a limited period in development.
What happens to the brain if you reduce input to that region of the cortex?
- Its size is shrunk and the surrounding regions of the cortex are increased
When happens when cortex is transplanted?
- It develops characteristics of its new location rather than its origin
- Inputs can be ‘rewired’ to a different region of the brain, the new recipient develops properties of the normal target tissue.
How did Hubel & Wiesel show the sensitive period in cats for vision?
Closed one or both of their eyes for the first three months of life. Those with closed eyes never were able to gain the neurons required to see out of them.
When is the sensitive period for language development in infant humans?
Exposure to language in the first year of life is predictive of language and reading skill
Critical periods for certain elements of language development in deaf children ends at around 7 years (also much harder to learn a second language)
How does the brain compensate with activation after a stroke?
It will shift it’s activation to other parts of the brain before normal function is restored.
- When does loss of brain weight accelerate in humans?
- Where are the neurons primarily lost?
- How does the brain cope with this?
- When people hit sixty
- Prefrontal cortex (executive function)
Corpus callosum
Cerebellum (balance)
Glial cells
- With alternate pathways and broader activation
What does EEG stand for?
Electroencephalography
What type of resolution is EEG good at?
Temporal resolution
(Time: Good at looking at things with millisecond accuracy)
What does EEG measure?
Measures the activity of large numbers (populations) of neurons
What are the research benefits of using an EEG?
Non-invasive,
painless,
do not interfere much with movement or perceive stimuli,
relatively low cost
recorded with millisecond resolution
How does EEG measure?
Measures voltage-differences at the scalp (where a cap is placed) in the microvolt range
It is done over numerous tests (min 20-30) where the average wave pattern is averaged out to get rid of interfering signals.
What is required of neurons in order to be detected?
Neurons must be in sync (this happens when they are working together).
This creates a bigger signal and is easier to detect
What is an event-related potential? (ERPs)
Small changes in the spontaneous electrical activity of the brain that are time-locked to certain sensory or cognitive events.
(This wavelength is an ERP in response to a stimulus)
ERP wavelengths that are under 300 milliseconds are typically considered to be ______ and are using _____ _____ process in regards to the engagement of attention
Subconscious,
bottom-up
What are the three components in ERP testing?
Latency (time after stimulus onset)
Polarity (negative or positive relative to a control)
Topography (which electrodes)
In ERP what does ‘amplitude’ refer to?
How high the peak is in the waveform.
(peak at N400)
What are the denotations used for negative and positive waveforms?
What does the number that comes after the denotation represent?
N = negative
P = positive
number = latency (time in milliseconds)
(e.g. N400 = negative 400ms)
What are the names of the 5 wavelengths from highest to lowest frequency?
Gamma
Beta
Alpha
Theta
Delta
What does higher frequencies in wavelengths represent in EEG’s?
Active processing, de-synchronised activity (alert wakefulness, “cognitive” frequency band or dream sleep)
What do lower frequencies in wavelength represent in EEG results?
Strongly synchronized activity (tend to look like they have a pattern)
(sleep stages, no dreaming sleep, coma)
What frequency are Gamma waves?
What does it represent?
20-60 Hz
‘Cognitive’ frequency band
What is the Beta frequency at?
What does it represent?
14-20 Hz
Activated cortex
What is the Alpha frequency at?
What does it represent?
8-13 Hz
Quiet waking
What frequency are Theta waves at?
What do they represent?
4-7 Hz
Sleep stages
What frequency are Delta waves at?
< 4 Hz
Sleep stages (deep sleep)
What did the Lutz et al (2004) EEG results show regarding buddhist monks and meditation?
That Buddhist monks have a much higher rate of gamma waves in a neutral state and could increase them in a meditative state when compared to normal participants who could not increase gamma with meditation.
High correlation between hours of time of meditation experience and gamma wavelengths
This spectral analysis was trying to determine when the best frequency for memory recall was and at what time did they have to be experiencing those wavelengths.
What do these results show?
That the best wavelength to have was ‘theta’ waves (4-7 Hz) about 150ms just prior to the stimulus in order to remember something.
What are the advantages of EEG?
Excellent temporal resolution (millisecond range)
Direct measure of neural activity
Multidimensional measure
What are the disadvantages of EEG?
Incomplete measure (only measures neural activity under certain circumstances)
Poor spatial resolution
What does fMRI stand for?
functional Magnetic Resonance Imaging
What type of resolution is fMRI good at determining?
Spatial Resolution
(Where the activity is occurring)
What is the signal that an fMRI measures?
BOLD signal (blood oxygenation level dependent)
What does fMRI detect?
Changes in blood oxygenation and flow that occur in response to neural activity.
(Enables researchers to identify brain regions that are activated during these tasks)
What is the output of an fMRI
A brain with coloured activation
How does the BOLD signal work for measuring brain activity?
It detects an increase in oxygenated blood to regions of the brain.
The bold contrast is based on the ratio of oxygenated and deoxygenated blood (oxyhemoglobin vs deoxyhemoglobin)
How does magnetic resonance work in an fMRI?
The MRI scanner applies a magnetic field that causes the protons in hydrogen (H) to align.
These give off energy as they return to the orientation of the magnetic field (MR signal).
What are voxels in fMRI imaging?
Voxels are a cube of space in the brain (a slice and then put a matrix over each slice) to create a 3d space.
This allows us to measure the level of oxygenated blood in the area
When using voxels to measure the difference in signal intensity between conditions, the resulting pictures reflect actual changes in brain activity.
True or False
False
They only reflect statistical probabilities
What are the advantages of using an fMRI?
Excellent spatial resolution (millimetre range)
Can bring together structure and function
What are the disadvantages of using an fMRI?
Indirect measure of neuronal activity
Poor temporal resolution (BOLD signal doesn’t reach its maximum until after approximately 4-6 seconds)
