Neuroimaging Flashcards
What 3 methods can be used for brain lesion studies?
- Physical
- Pharmalogical
- Reversible (cooling or transcranial magnetic stimulation )
What are the advantages of brain lesion studies?
- Can provide information on function
- Carry out otherwise unethical studies
What are the disadvantages of brain lesion studies?
- Difficult to say how precise/specific they are
- Is the effect due to solitary contribution or an imbalance effect
What is transcranial magnetic stimulation?
- The induction of an electric current in nearby neurons using a rapidly changing magnetic field
- Can activate (e.g muscle reponses) or inhibit b
What are the advantages of TMS?
- Ability to study healthy patients with a controlled stimulation
- Inexpensive
- Excellent temporal resolution
What are the disadvantages of TMS?
- Low spatial resolution
- Possible risk of inducing epilepsy, effects on mood, local headaches
- Long term effects are not well established
What is transcranial direct current stimulation (tDCS)?
Using + and - patches to induce an electron flow in the brain which can be
Cathodal - hyperpolarisation of neuronal membranes decreasing firing rate
Anodal - depolarisation of neuronal membranes increasing the firing rate
What are the advantages of tDCS?
- Inexpensive
- Allow for controlled neuromodulation
What are the disadvantages of tDCS?
- Low spatial resolution
- Cannot be used on patients with epilespy, implants or who are on medications
What are the two categories of neuroimaging techniques?
- Hemodynamic
- Electromagnetic
How does PET work?
- Ingestion of radioactively labelled material, emit positrons which are picked up
- Active brain accumulates oxygen and glucose
- Provides functional view with 45-60s integration period
What are the advantages of PET?
- Allow measurement of metabolism and blood flow
- Can use in conjunction with behaviour and pharmalogical studies
What are the disadvantages of PET?
- Expensive
- Invasive (eposure to radiation)
- Moderate spatial and poor temporal resolution
How does fMRI work?
- Uses huge magnet to induce nuclear magnetic resonance phenomenon where protons align in parallel or anti-parallel in response to strong magnetic field
- When RT is switched off measure time longitutional magnetization (T1) and transversal relaxation (T2) retun to normal
- High concentration of H has high sensitivity to NMR therefore there are differences between oxy-haemoglobin and deoxy-haemoglobin
What are the possible issues with fMRI?
- Indirect measure
- Inhibitory activity may increase or decrease energy consumption
- Susceptible to noise
- Arbitrary thresholds for significance
What are the two methods in fMRI?
Subtraction method - experimental minus control activated areas
Region of interest - look at patterns of activation across different experimental conditions
What is diffusion tensor imaging (DTI)?
- Used to determine anatomical connections
- Uses stats to examine interrelationships between brain areas
What are the advantages of fMRI?
- Safe and therefore repeatable
- High spatial resolution
- Moderate temporal resolution
What are the disadvantages of fMRI?
- Expensive (uses He)
- Movements are restricted
- Claustrophobia
- Large ammounts of acoustic noise (can’t carry out auditory experiments)
- Fields can generate body heat
What is spatial/temporal summation?
When action potentials summate either
temporally - close activity
spatial - summation of neurons in similar area firing at the same time
What is EEG?
Measure summation of post-synaptic potentials
What are the limitations of EEG?
- Must be measuring an open field which is synchronously active and arranged perpendicular and close to the skull
- Polarity sometimes not interpretable
How are EEGs recorded?
- Using reference electrode of minimal activity and measuring the difference
- Standardised system “International 10-20 system” with 4 reference points: inion (back), nasion (eyes), and left and right perpendicular points
What is the difference between EEG and ERP?
EEG - large voltage from large area of the brain
ERP - averaging across similar events timelocked to onset of the stimuli
