Methods of looking at the brain Flashcards
What method type is EEG/ ERP and is it invasive and what brain property is used?
It is a recording technique that is non-invasive. Is uses electrical brain properties
What method type is single cell and multi unit recording and is it invasive and what brain property is used?
It is a recording technique that is invasive and uses electrical brain properties
What method type is TMS and is it invasive and what brain property is used?
It is a stimulation technique that is non-invasive and uses electromagnetic brain properties
What method type is MEG and is it invasive and what brain property is used?
It is a recording technique that is non-invasive and uses electromagnetic brain properties
What method type is PET and is it invasive and what brain property is used?
It is a recording technique that is invasive and uses haemodynamic brain properties
What method type is fMRI and is it invasive and what brain property is used?
It is a recording technique that is non-invasive and uses haemodynamic brain properties
Is it possible to record from single neurons in the brain?
No, only in giant squid axons
How does single cell recording work?
A very small electrode is implanted into the axon (intracellular) or outside the axon membrane (extracellular) and records neural activity from population of neurons.
What is an Electroencephalography?
The measurement of the electrical activity of the brain by recording from electrodes placed on the scalp. The resulting traces are known as an eletrocephalogram and represent an electrical signal from a large number of neurons. EEG signals represent the change in the potential difference between two electrodes placed on the scalp in time. The EEG obtained on several trials can be averaged together, time locked to the stimulus to form an event related potential (ERP)
What are ERPs?
voltage fluctuations that are associated in time with a particular event (visual, auditory, olfactory stimuli)
How can ERPs be extracted from the ongoing EEG?
By filtering and signal averaging
How are electrodes labelled
p stands for parietal ect.
- even numbers on the right
- odd numbers on the left
How can we use an ERP to see how our brain responds to a particular stimulus?
Look at the EEG trave for the next 5 seconds after the stimulus is presented
What are ERPs useful for medically?
- Seeing if someone has Alzheimer’s disease (their P300 will be much lower)
- picking up mental health issues
What is magnetocephalography?
An imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices known as SQUIDS. They have excellent temporal and spatial resolution but are very expensive.
What is magnetic resonance imaging and when do we use it?
Uses different magnetic properties of types of tissue and of blood to produce images of the brain. We use it when we are interested in where things are happening in the brain.
What is the difference between structural and functional?
Structural: different types of tissue (skull, grey matter, white matter, CSF fluid) have different physical properties - used to create STATIC maps (CT and structural MRI)
- Functional: temporary changes in brain physiology associated with cognitive processing (PET and fMRI - often used in cognitive neuroscience)
What does PET do and how does it work?
- measure local blood flow (rCBF)
- radioactive tracer is injected into the blood stream
- the tracer takes up to 30 seconds to peak
- when the material undergoes radioactive decay a positron is emitted, which can be picked up by the detector
- areas of high radioactivity are associated with brain activity, based on blood volume
- the more red the image the more blood flow was there
- measures blood volume directly
What does fMRI do and how does it work?
- It directly measures the concentration of deoxyhaemoglobin in the blood (the BOLD response - blood oxygen level dependent contrast response)
- it measures deoxygenated blood after there has been a large amount of brain activity and oxygenated blood is used
- this change in BOLD response over time is called the haemodynamic response function
- oxygenated and deoxygenated blood have different magnetic properties which is why we can measure deoxygenated blood
- this haemodynamic response function peaks in 6-8 seconds which limits the temporal resolution of fMRI
- it measures activity in voxels (or volume pixels) which are the smallest distinguishable box shaped part in the 3D image
What are fMRIs used to study?
The correlation between brain activity and stimulus timing. They can produce activation maps showing which parts of the brainn are involved in a particular mental process
What does it mean to say a brain region is active?
It is active if it shows a greater response in one condition relative to another
What is cognitive subtraction and what is the problem with it?
Activity in a control task is subtracted from the activity in an experimental task
- problem: difficulty of the baseline control task
Can there ever be disagreement between imaging and lesion studies?
Yes
What is diffusion tensor imaging (DTI)?
An imaging method that uses a modified MRI scanner to reveal bundles of axons in the living brain. Measures white matter organisation based on limited diffusion of water molecules into axons. Used to visualise connections within the brain
What does functional near infrared spectroscopy (fNRIS) do? What are it’s advantages and disadvantages?
- measures the same BOLD response as fMRI but in a completely different way. ‘Light’ in infrared range passes through the skull and scalp but is scattered differently by oxy versus deoxyhaemoglobin. It is portable and more tolerant of head movement but can’t image deep structures
What is intracranial electro cephalography and why is it useful?
We record directly from the inside of the human brain when people are undergoing neurosurgery. It is the only method that gives us the high resolution in both place and time. It records straight from the cortical surface approximately from tens of thousands of neurons
