8 - HOW TO MEASURE BRAIN ACTIVITY Flashcards
basic logic behind measuring metabolic activity
- more active neurons = more oxygen and glucose needed
- oxygen and glucose levels = index of how much activity is going on
- localise oxygen and glucose measurements precisely = know where higher or lower activity is going on
measuring metabolic activity
fMRI - Functional Magnetic Resonance Imaging
- measures oxygen levels through the different magnetic properties of oxygen rich vs oxygen poor blood
- poor = already delivered the oxygen
- more oxygen taken up = higher activity
measuring metabolic activity
PET - positron emission tomography
- measures distribution of radioactive substance (typically glucose)
- radioactive marked form of glucose
- take an image to se where more glucose is taken
= more activity
basic logic behind measuring electrical activity
3 things required of combined signals
- active neurons = exchange electrical signals
- a single neurons signal is too small to measure at a distance (only measure it if we stick an electrode into/next to neuron
- need combined signals if many neurons
~ group must consist of sufficiently many neurons
~ aligned in parallel (so their electrical currents all move in the same direction) (different directions would cancel each other out)
~ activity is synchronised (all fire at the same time)
measuring electrical activity
EEG - electroencephalogram
- electrodes on the scalp (some distance from the neurons)
- EEG measures synchronous firing of groups of neurons (see previous card)
- can provide millisecond by millisecond record (as fast as neuronal activity itself)
- amplitude of EEG increases with amount of neurons contributing
information:
brain is like a sponge drenched in saltwater = electrically conducive
- so all electrical signals will eventually make it to the surface
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what areas are easier to measure with an EEG?
- cortical areas are easier to measure than subcortical areas
- subcortical areas get entangled in noise due to further distance from electrodes on scalp
- easier to measure gyri
- harder to measure sulci due to same season as subcortical
what does an EEG trace look like
a bunch of dots
- represents patches of cortical neurons
Beta EEG activity
- small, rapidly changing groups
- desynchronised EEG activity
- highly active brain
- small amplitude and high frequency
- quick
- WAKEFUL
- only small groups synchronised
- electrode outside of the brain only measures buzzing activity - not in detail
Theta activity EEG
- large, persistent groups
- synchronised EEG activity
- less active brain
- large amplitude and low frequency wave forms
- slow
- SLEEPING BRAIN
- not exchanging info between them - all signalling the same thing
SLEEPING BRAIN IS LESS ACTIVE THAN WAKEFUL BRAIN
information:
PET SCAN- reduced metabolic activity during sleep / higher levels in REM sleep (similar pattern as when awake)
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information:
electrical activity during REM sleep resembles activity during wakefulness (alert)
- beta waves
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alpha waves when relaxed or bored
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theta waves when asleep
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delta waves when asleep (slow wave sleep)
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