brain imaging techniques Flashcards
what does EEG stand for?
electroencephalogram
what does an EEG do?
records electrical activity on the surface of the scalp through electrodes
what does the 10-20 system refer to?
the universal system for placing electrodes on the scalp in eeg
what is the EEG recording?
the difference in potential between different electrodes
what are oscillations?
postsynaptic potentials - they change in frequency and amplitude (waves)
what does hertz mean?
cycles per second
what is monopolar montage?
potential difference between a referent site and all other brain sites
what is REM sleep?
- rapid eye movement
- most accociated with dreaming
- oscillations look very similar to those when the body is awake
- the source of information is internal
what is paradoxical sleep?
the brain appears to be awake from the EEG but the musculater is flacid and unresponsive.
what does ERP stand for?
event related potentials
what are erps?
averages EEG recordings that measure brain responses to repeated presentations of a stimulus
what is good about ERPs?
they cancel out any noise from an EEG
- responses to discrete stimuli can only be seen by averaging
what is mismatch negativity? (MMN)
indicates that the person has detected a stimulus that deviates from the preceding stimuli.
the more complex the stimulus, the later the MMN.
this only appears if the stimulus is task relevant and the individual is attending to the stimulus
N2
what does the P3 reflect?
the conscious resolution of the task eg detecting the target.
- the top of the wave - highest point
- can be used to measure the depth of processing as larger p3s indicate deeply processed words.
what does Computerised Tomography (CT) do?
uses x rays to measure tissue density
what is tomography
taking multiple pictures
what is the main issue with xray?
its a 2D image
- does not provide adequate info about the brain
how is a CT scan conducted?
- xray source is moved in steps in an arc around the head
- at each point, detectors measure the amount of xray radiation passing through - the value is proportional to the density of the tissue
- a computer deconstructs the results into an anatomical map of the brain
what downside is there to CT?
its a medium resolution image
- difficult to distinguish brain structures.
what is Magnetic Resonance Imaging? (MRI)
uses magnetic energy to generate images and provide information about tissue composition
how are MRIs conducted?
- patients head is placed in the center of a v powerful circular magnet. electrical fields in the brain line up parallel
- removing the magnetic field makes the atoms go back to where they were before - RELAXATION
- each atom has a different rate of relaxation meaning that you can distinguish which types of atoms are which depending on the rate of relaxation
- this info is computerized into a sectional map of the brain.
what is important about the relaxation rate of hydrogen?
different brain areas contain different levels of hydrogen.
MRI therefore lets us see the differenet brain structures
what positives are there to tomography?
- 3D info at different levels
- provides more info on the extent of brain lesions and brain structure in mental illness
what is interesting about the ventricles in schizophrenic brains?
they are larger.
what is Positron Emission Tomography? (PET)
requires the injection of a radioactive substance
measures brain metabolism
what substances are injected during PET scans?
glucose - direct measure
water - measures blood flow
limitations of PET?
- invasive
- constrained as can only be used 2/3 times
- expensive
explain the process of a PET scan
- when a positron is emittedm it travels a certain distance. when is has expended all of its kinetic energy, it meets with a free electron
- they mutually annihilate one another and give off 2 gamma ray photons.
- the gamma rays are detected and information is used to reconstruct an image of the collision sites
gamma ray photons are emitted at what angle
180 from one another
what is the key point to be made about PET?
they detect the collision between a positron and an electron, NOT the source of the electrical activity.
what is useful about the mean difference image from PET scans?
can compare brain activity from contrasting stimulus and create a difference image which reflects the areas of the brain that were the most active during the experiment.
what is fMRI measuring?
the change in blood flow.
- difference in oxegenated and deoxygenated blood - changes.
what is haemoglobin?
iron and oxygen.
what is blood level dependency imaging? (BOLD)
- blood is brought ot tissue through the artery and contains lots of haemoglobin
- the arterty breask up into capillaries which allows substance to go from the blood into tissue. oxygen leaves.
- as oxygen leaves the blood the capillaries become deoxgenated.
- this then leaves deoxygenated haemoglobin
what is the basis of thought for fMRI?
active neurons attract more arterial blood flow and more oxygenated haemoglobin.
- areas that are more active will generate more action potentials and therefore more use of the Na/K pump
what is the main difference between PET and fMRI?
fMRI can be repeated many times unlike PET
what is good about event related fMRI?
responses can be averaged
what is good about tomographic fMRI?
can compute different slices of the brain to see activity at different sites
done without injection of a radioactive substance.
what imaging techniques measure brain structure?
CT and MRI
what imaging techniques measure brain metabolism?
PET and fMRI.
