electrophysiology Flashcards
EEG
measures electrical activity from the scalp
pick up electrical impulse from heart rate
needs to be subtracted using recording of heart rate
how does an EEG work?
electrodes far from electrical signal
fire in all directions but only detect those projecting in direction of electrode
multiple layers of skin, bone and tissue before detection
so only detect a tiny fraction of actual brain activity
subtract all noise from environment
frequency bands
higher in frequency when more active
gamma - concentration
beta - busy
alpha - restful
theta - drowsy
delta - asleep
what is sensory-motor rhythm?
between alpha and beta waves
different for everyone
one frequency band exclusively used by sensory and primary motor cortex
allows clear communication without interference from rest of brain
electromyography (EMG)
measures muscle response
senses muscular activity where no movement is produced
reveals nerve or muscle dysfunction
issues with nerve-to-muscle signal transmission
how does an EMG work?
detects invisible neuromuscular activity
can be used to detect emotions in experiments
even when face not moving, smiling and growing muscles still receive impulses when emotions experienced
electrodermal activity
variation of the electrical conductance of the skin
in response to sweat secretion
essentially detects stress levels by sweating
- stress, arousal, emotion, cognitive load
event related potentials (ERP)
event = stimulus
stimulus onset = event to which we relate the electric potentials that we are measuring
look at waveforms, maps and specific sources of impulses
how are ERPs categorised?
polarity (positive or negative)
latency (how long after onset)
amplitude (in microvolts)
topographic distribution (maps)
descriptive labelling of ERPs
labelled with a P or an N
positive or negative
number is the latency
(how long after onset)
eg N400
negative and 400 milliseconds after hearing meaningful word/stimulus
mismatch negativity
negative potential produced when experience something brain doesn’t expect
error related negativity
when mistake made
bereitschaftspotential
muscle activity when no muscle movement
N400
wave pattern happens every time word with meaning heard
N400 effect
changes in amplitude of wave
depends on how well word fits with context
ERP effect
a modulation of a particular ERP component
or just the difference between 2 conditions in ERP waveform
multidimensional nature of the signal
we can measure electrical signals from the scale while people engage with stimuli over time
and look at behaviour
continuous nature of signal
task does not need interruptions that interfere with natural behaviour
brain activity can be measured while people lives everyday life
strengths of ERPs
high temporal resolution
direct measure of neural activity
weaknesses of ERPs
measure only a part of the neural activity
poor spatial resolution
open brain EEG (ECoG)
recording EEG signals directly from the surgically exposed cerebral cortex
often used simultaneously with cognitive testing
measure which areas of the brain can be removed or cut into to preserve function
implants can be left in and used wirelessly
firing patterns used to do actions eg type in those who can’t
magneto-encephalography (MEG)
function neuroimaging technique for mapping brain activity
by recording magnetic fields
doesn’t record waves but magnetic fields
still only picks up open fields
better source localisation than EEG and fMRI
