Psychophysiological methods Flashcards
How is magnetic resonance (MRI) conducted?
Measurement of a magnetic resonance signal occurs when this magnetic field is applied to hydrogen atoms - must ensure that hydrogen atoms are aligned to obtain the signal
Explain how hydrogen atoms affect MRI scans
If the hydrogen concentration is different in different tissues, you can see the differences between these tissues in images
How is the magnetic field for MRI formed?
coil creates an enormous magnetic field using electricity
Spatial revolution and MRI
Smaller the pixels, the better the spatial resolution to compare brain structures in individuals
What is functional MRI?
More widely used than MRI and measures activation in the brain
How did fMRI originally work?
Originally, if an artificial contrast agent is injected into the blood stream, this reduces the signal when the task is run, with the darkest areas signalling the most active.
How does fMRI work now?
Later found out the blood naturally contains its own contrast agent (haemoglobin). Deoxyhaemoglobin reduces this signal due to the presence of iron that influence the signal when oxygen is removed. An increase in blood flow to the active are so there is more BOLD signal in the active tissues. Measures active neurons + oxygen is found near the capillaries.
What does BOLD stand for in relation to fMRI?
Blood Oxygen Level Dependent (BOLD) effect
What is a weakness of fMRI?
As you have to compare the data so quickly, spatial resolution can be lost - low precision
What are PET scans?
Positron Emission Tomography - older functioning technique than fMRI.
How do PET scans work?
Radioactivity introduced into the body measuring indirect metabolic correlates of neural activity (this can be pinpointed). 10x cheaper than fMRI and higher spatial resolution.
What is a disadvantage of PET?
Cannot image the same person multiple times as cannot expose a lot to radioactivity.
What is electrophalography (EEG)
Measuring the change in voltage recorded from sensors on the scalp. Sensors are put on the head and compare activity in the sensors where there’s more brain activity to where there’s less to generate this signal
How to oscillations relate to EEG?
Can have both slow and fast oscillations - reflect the state of the brain - can measure sleep well as brain wave oscillations change throughout the night
What are event-related potentials (ERPs)?
Present stimuli to patients and tell the computer when these stimuli were presented (e.g., a lexical decision task - whether you’re looking at a real word). Then cut out portions that correspond to different stimulus type and average these segments separately to compare.
What is transcranial magnetic stimulation (TMS)?
Large current briefly discharged into a coil of wire - generates rapidly that changes the magnetic field around the coil of the wire, passing this current into the brain
What does TMS do?
Increases the excitability of cells and sometimes inhibits - a ‘virtual lesion’ and increases ‘neural noise’
What is eye tracking?
Infrared radiation projected into the eye + measure reflection in the eye + track pupil position to see where the participant is looking
What parts of the eye does eye tracking measure?
Fovea (part of the retina) - nearly all cones in the retina to see colour.
Receptive cells in visual cortex field connected to the fovea - when light presented to fovea, performance drops dramatically.
Primary measures include fixation, saccades + pupil diameter
What is reverse inference?
Have preconceived ideas about where in the brain activation occurs + can make psychophysiological interpretations if the activation is shown in relation to the brain + must show consistency
Limitations of fMRI
Slow - blood changes don’t always correlate with brain activity time - max change of blood flow 8s after stimulus presented
Ps may feel claustrophobic - stress + discomfort
Can’t scan people with metal implants
Strengths/weaknesses of EEG
S - high temporal resolution
S - cheap and accessible compared to fMRI
W - poor spatial resolution - can’t localise activity in the brain without precision or confidence
W - inverse problem: inferring cortical generators from known scalp potentials so only making informed guesses
Strengths/weaknesses of TMS
W - switch cost e.g., asked to switch between a colour and shape task - can be reduced with opportunity for preparation
W - stimulation effects other areas so can’t assume you’re only stimulating the area where the coil is present
S - high temporal resolution so. can tell when specific processes take place
Strengths/weaknesses of eye tracking
W - Can’t assume eye-movements correlate with attention as attention moves to stimulus before eyes
S - Direct and precise - high spatial and temporal resolution
