Human research methods Flashcards
How is the brain studied?
- if want to know what an area of the brain is good for, find someone with brain damage in that area
What is computerised tomography (CT) scan?
- cheap and fast
- resolution is not great
- computer assisted X-ray procedure
- take a “photograph” of the brain
How does the CT scan work?
- X-ray beam (high energy light) is projected through the head to an X-ray detector
- beam delivered from all angles
- computer translates the information received from the X-ray detector into a series of pictures of the skull and brain
What are the ways to photograph a living human brain?
- CT scan
- MRI
- DTI
- fMRI
- PET
What is magnetic resonance imaging (MRI)?
- strong magnetic field and radio waves
- relative density of hydrogen atoms throughout the body
- high spatial resolution
How does an MRI work?
- strong magnetic field is applied to the body
- the proton of every hydrogen atom in the body to orient in a particular direction
- radio waves (low energy light) are administered to the body
- energy is absorbed by protons, changing the direction they are facing
- each proton immediately flips back to the position determined by the magnet
- protons emit their own radio waves, which are detected by the scanner
- scanner provides an estimate of the relative density of hydrogen atoms throughout the body
What is diffusion tensor imaging (DTI)?
- MRI can be optimized to better detect the hydrogen atoms in water molecules
- variation of the MRI technique
- measures the direction and speed of the diffusion of water molecules
- used to identify axon tracts
What is functional magnetic resonance imaging (fMRI)?
- rapid series of MRI scans
- provides both structural and functional information
- decent spatial resolution (1 to 5 mm) and temporal resolution (several seconds)
How does fMRI work?
- amount of oxygen in blood distorts the local magnetic field
- detect changes in blood oxygenation
- reflects blood flow and correlates with neural activity
- when brain area is active, blood flow to that region quickly increases
Why are researchers trying to modify the fMRI technique?
- measure fluctuations in neurotransmitter signaling
- uses “enzyme-activated magnetic resonance contrast agents”
- molecules that distort the magnetic field differently when they bind to neurotransmitter
- create a molecule that distorts the magnetic field when bound to a neurotransmitter
What is positron emission tomography (PET)?
- recording neural activity in human brain
- measure changes in the expression levels of neurotransmitter receptors across weeks (use radioactive drugs - agonists or antagonists)
How does PET work?
- injecting a person with a radioactive compound
- radioactive sugar molecules (2-DG) used to detect changes in energy use in the brain
- scanner identifies where radioactive 2-DG molecules are located over time
- radioactive molecules are designed to decay rapidly (over hours), have to be made on site
What is 2-DG?
- radioactive sugar molecules (injected in person during PET)
- similar to glucose
- taken up by active cells in the body
- not broken down as easily as sugar is, so it stays around for hours
How does PET use L-Dopa?
- radioactive L-Dopa picked up by dopamine neurons
- converted into dopamine
- released as normal
What are macroelectrodes?
- metal discs
- EEG uses macroelectrodes attached to scalp
- records the summed population-level activity of millions of neurons
- used as a diagnostic tool
- specific patterns of EEG activity are associated with different states of consciousness, stages of sleep, and types of cerebral atrophy
What is the short description of CT?
- Utilizes X-rays to image brain structure
What is the purpose of CT?
- structure
What are the pros of CT?
- cheap
- fast
- non invasive
What are the cons of CT?
- poor spatial and temporal resolution
What is the short description of MRI?
- Utilizes radio waves emitted from magnetically aligned water molecules
- Different density of different substances create image
What is the purpose of MRI?
- structure
What are the pros of MRI?
- high spatial resolution
- non invasive
What are the cons of MRI?
- expensive
What is the short description of fMRI?
- Same as MRI, but utilizing the difference in magnetic fields around oxygenated vs nonoxygenated blood to measure activity
What is the purpose of fMRI?
- correlation
What are the pros of fMRI?
- pretty good temporal and spatial resolution
- non invasive
What are the cons of fMRI?
- expensive
What is the short description of DTI?
- Same as MRI, but changes indirection speed of radio wave emittance from water molecules resolves axon tracts
What is the purpose of DTI?
- structure
What are the pros of DTI?
- High spatial resolution for microstructure of axon tracts
What are the cons of DTI?
- expensive
What is the short description of PET?
- Radioactive molecule is injected, can record use of that molecule via energy emission
What is the purpose of PET?
- correlation
What are the pros of PET?
- Can make any isotope radioactive – image whatever you want
What are the cons of PET?
- expensive
- isotopes must be synthesized within hours of imaging
What is the short description of macroelectrode EEG?
- Conductive discs placed on scalp record electrical changes in the brain
What is the purpose of macroelectrode EEG?
- correlation
What are pros of macroelectrode EEG?
- cheap
- non invasive
- high temporal resolution
What are cons of macroelectrode EEG?
- Meaning of waves is difficult to interpret
- low spatial resolution
