Lecture 6 - Methods of studying the brain Flashcards
How do CT scans work?
CT scans use X-rays passed through the brain at different angles
–> CT measures the amount of radiation not absorbed by the brain as X-rays are passed through
How does a CT scan image appear?
Bone absorbs the most and so appears white
Cerebrospinal fluid appears black
The brain appears grey
Advantages of CT scans
- Can be used in healthy and clinical samples
- Non-invasive
- indicates areas of structural brain abnormality
Disadvantages of CT scans
- Poor spatial resolution
- provides only measure of structure, not activity
- involves radiation
- expensive
How do MRI scans work?
Create high-resolution images of the brain based on changed in the magnetic properties of hydrogen atoms.
Radio waves tased though head whilst a strong magnetic field is used to align protons of the hydrogen nuclei
Reverberations of wobbling protons detected and recorded
Advantages of MRI scans
- Non-invasive and non-toxic
- allows structural imaging in vivo
- high spatial resolution
- no known biological risk
Disadvantages of MRI scans
- Claustrophobic
- noisy
- images near to large cavities difficult to obtain
- expensive
How do PET scans work?
Uses a radioactive tracer injected into the bloodstream to track blood flow
The greater the blood flow = greater signal emitted by tracer
Map produced superimposed onto brain scan image
Advantages of PET scans
- Can be used to measure brain activity during a task
- Suitable for most clinical and healthy subjects
Disadvantages of PET scans
- Invasive
- Poor spatial and temporal resolution
- unsuitable for certain subjects
- expensive
- indirect measure of neural activity
How do fMRI scans work?
Uses standard MRI equipment to produce images of brain activity
produces images representing oxygen flow in the blood to active areas of the brain
What is the name of the signal recorded by fMRI?
Blood-Oxygen-Level-Dependent (BOLD signal)
Advantages of fMRI
- Non-invasive and non-toxic
- Allows functional imaging
- No known risks
- Widely available and cheaper than PET
Disadvantages of fMRI
- Claustrophobic
- Noisy
- Poor temporal resolution (better than PET)
- Susceptible to movement artefacts
Advantages of Neuropsychology
- Utilises naturally occurring lesions
- May highlight role/function of damaged region
- can provide insight
Disadvantages of Neuropsychology
- Locus of damage can be variable and not always described accurately
- Other damaged brain regions could be having an effect
- May be other confounding factors
Describe the process of Transcranial Magnetic Stimulation (TMS)
Uses a highly focused magnetic field to disrupt the function of neurons
Magnetic stimulation temporarily turns off part of the brain
Advantages of TMS
- non-invasive
- lesion is focal
- temporary
- can study human brain directly
- can determine causation
Disadvantages of TMS
- questions regarding safety
- Deep structures cannot be reached
- effects often smaller/less noticeable
Advantages of animal lesion methods
- Each animals behaviour can be compared before and after the lesion
- highly selective lesions
- not possible in humans
Disadvantages of animal lesion methods
- Ethics
- Hard to determine functions due to structures being interconnected
What happens during single-cell recording?
Action potential directly measured
Single-cell recordings obtained by implanting a very small electrode into the axon or outside the membrane
Penfield and Jasper (1954) Electrical stimulation
Simulating certain parts of the brain of patients undergoing surgery for epilepsy produced reports of sensations
How does an EEG work?
Electrical activity of the brain is recorded by electrodes placed on the scalp
Advantages of EEG’s
- Non-invasive
- high temporal resolution
- cheap and easy
- applicable to healthy and clinical populations
- brain activity recorded in real time
Disadvantages of EEG’s
- Poor spatial resolution
- Activity reflects millions of neurons
- brain activity may be unpredictable and chaotic
- susceptible to movement artefacts
What does the Wada Technique involve?
Sodium amytal is injected into the carotid artery in order to temporarily anaesthetise the ipsilateral hemisphere
Advantage of the Wada technique
Provides means of examining functions of an entire hemisphere
Disadvantages of Wada technique
- Invasive
- cannot be used on healthy subjects
