Neuroimaging Flashcards
Define “invasive” and “non-invasive” neuroimaging
Invasive: insert something into the body
Non invasive: Don’t insert anything into body
Name an example of invasive and non invasive neuroimaging methods
Invasive: PET scan (injection of radioactive substance
Non-invasive: EEG
Define spatial and temporal resolution
Spatial: How blurry or sharp. How easily you can tell two structures apart.
Temporal: how accurately you can tell when activity happens. How well you can tell events apart.
Place in order of low to high spatial resolution: fMRI, EEG, single cell recording
EEG (localised to several centimetres, low S.R.)
Place in order of low to high temporal resolution: EEG, fMRI, single cell recording
fMRI-seconds-low TR
EEG-within milliseconds-high TR
Single cell-microsecond-super high TR
What are the causal ways to study the nervous system?
lesioning, acquired brain injury, stimulating and disrupting activity
What are the correlational ways to study the nervous system?
Magnetoencephalography, electroencephalography, positron emission tomography, MRI, fMRI
What are some ways of stimulating and disrupting activity?
Transcranial direct current stimulation, drug blocks, cryogenic blocks, transcranial magnetic stimulation.
What is transcranial direct current stimulation? (tDCS)
Use anode to depolarise neurons and cathode to hyperpolarise and observe changes in behaviour
Anodal activity improves
Cathodal activity hinders
What is a drug block?
Injection of local anesthetic to disrupt activity and observe behaviour
What is a cryogenic block?
Insert cryoprobe that cools neurons to stop firing - virtual lesion, and observe behaviour
What is transcranial magnetic stimulation (TMS)?
-Single pulse at specific location on scalp during or before activity. —Magnetic activity causes neurons to fire
What is magnetoencephalography (MEG)?
Currents generate a magnetic field which is measured at scalp
What is electroencephalography?
Electrical activity generates electric field, measured at scalp, sum of electric events
What is positron emission tomography (PET)?
A technique that involves radioactive tracing of brain areas that are active during a task.
What is magnetic resonance imaging (MRI)? High or low spatial and temporal resolution?
A large magnet that detects magnetic fields of water molecules in the brain to capture images of structures. High spatial resolution, low temporal resolution.
What is functional magnetic resonance imaging (fMRI)? High or low spatial and temporal resolution?
A large magnet that detects magnetic fields. It detects oxygenated haemoglobin. Detects BOLD-Blood oxygen level dependent contrast. Low temporal resolution whilst measuring temporal activity, high spatial resolution…
What are some advantages of fMRI?
- Non invasive
- High spatial resolution
- No known health risks
- Structure and function in same image
- 3D images of activity over whole brain
What are some disadvantages of fMRI?
- Low temporal resolution
- Individual measure of activity
- 2-3 seconds to create image
- Not causal
What are the ways to measure behavioural responses in neuroscience?
Reaction times
Detection thresholds
Stimulus discrimination
Psychophysics
What are the ways to measure physiological responses in neuroscience?
Startle response Electrodermal activity Startle response Pupilometry Heart rate Muscle tension Polygraph
- What do we use amplitude of startle response to measure? 2. What happens to the amplitude of the startle response when fear conditioning is applied?
- Fear and conditioning 2. Amplitude increases when presented with a cue that has been paired with an aversive stimulus.
- What do we use electrodermal activity to measure? 2. What happens to the skin when electrical activity in nerves increases?
- Fight or flight response, index of autonomic activity (measure of emotional arousal) 2. Skin momentarily becomes better conductor
How did Broca identify causation in Patient Tan’s symptoms in which he could only say “tan”.
Acquired brain injury in the posterior inferior frontal gyrus (Broca’s area) allowed causation since “if not, x then not y”
Lesion in what area causes loss of the ability to produce language but comprehension of language remains intact?
Broca’s area
What are the types of lesion studies?
Removing/disability parts of the brain and observing behaviour
Aspiration lesion
Radio frequency lesion
Knife cuts
What are the problems associated with lesion studies?
Some neighbouring tissue is lesioned - functions lost as a result are inadvertently attributed to the target area
Sometimes a portion remains - as well as some function
What is the function of TMS?
Magnetic activity of TMS causes neurons to fire (focal stimulation) in order to observe behavioural consequences
How can TMS be used to test neural correlates of behaviour?
Can be used in two ways: by stimulating or disrupting neural activity; preventing or facilitating a behaviour
How does TMS disrupt activity?
Creates synchronised pattern of discharge that interferes with normal brain activity
How is TMS used clinically?
Repetitive TMS used to “fix” too high or too low neural activity e.g. clinical depression and neuropathic pain
What is an advantage of TMS?
Permits causal inference about the necessity of a specific brain region for performing a given task
What is an advantage of MEG?
Very high temporal resolution
Relatively direct measure of activity
What is a disadvantage of MEG?
No good for subcortical, hard to model sources, expensive
What is measured using EEG?
Gross electrical activity on scalp
What does the gross electrical activity recorded using EEG represent?
Sum of electrical events - action potentials, postsynaptic potentials, muscle activity etc
Measured electrical activity correlates with underlying neural activity
What are some default states observed in EEG?
Relaxed - alpha (8-12Hz)
Deep sleep - delta (less than 4 Hz)
Focused - beta (16-21 Hz)
What is an event related potential?
Waveforms that accompany an event temporally
How to extract signal from noise to gain event related potential?
Average lots of trials to extract signal
Is EEG good for spatial or temporal resolution, or both?
Temporal, but can be used to model certain areas based on relative activity location
What are the advantages of EEG?
High temporal resolution,
Non invasive
Relatively cheap
What are the disadvantages of EEG?
Low spatial resolution
Poor for activity below superficial layers
Low signal to noise - signal easily contaminated, thus need lots of trials which is time consuming
Does research use human brains to perform lesioning?
No, since it is unethical. Therefore, we only use animal brains.
Do researchers always use only one of the methods?
No, build a body of evidence using multiple methods
