07 Flashcards
what did Richard canon find out? and when?
Electrical phenomena in
animal’s brains (1875)
what did Adolf beck find out? and when?
Recordings of oscillatory
electrical brain activity in
response to different types of stimulation (visual, auditory) (1890)
who discovered Electrical phenomena in animal’s brains?
Richard canon
who discovered Recordings of oscillatory electrical brain activity in response to different types of stimulation (visual, auditory)
Adolf beck
who recorded the first human electroencephalogram? and when?
Hans berger 1929
who reported the first alpha waves? and what else did they report?
Hans berger
First report of alpha waves (~8 12 Hz) and their
suppression when the subject opens the eyes
electric
changes in membrane potential
chemical
synaptic transmission
intracranial measurements
- intraparenchimal recordings
- electrocorticography (EcoG)
extra cranial measurements
- magnetoencephalography (MEG)
- electroencephalography (EEG)
how is the temporal resolution of EEG?
excellent
on what time scale can EEG measure?
Measuring electrical (or magnetic) potential on a sub
millisecond scale
how is spatial resolution in EEG? and why?
low
-> because of volume conduction
-> difficulty recording activity from deep sources
->inverse problem
what is volume conduction?
The spreading of electrical
current from the source to the receiver while crossing
different media
is volume conduction an issue with MEG?
no
what is difficult to record with EEG and why?
Difficult to record activity
from deep sources
> Electrical field spreads as a
function of distance
> The activity from neural
populations with different
orientations cancels out
what is the inverse problem?
Estimate the location of brain activity given the pattern of activity measured on the scalp
> ill-posed problem: impossible to solve perfectly
what are the advantages of EEG? (4)
- High temporal resolution
(milliseconds) - Directly measures electrical activity of the brain
- (relatively) mobile and non
invasive - (relatively) cheap
what are disadvantages of EEG? (3)
- Poor spatial resolution
- Very weak signal (small
signal to noise ratio) - Difficult to measure deep
structures
where is electric potential measured from?
Electric potential is measured from an array of electrodes placed
on the scalp with respect to a reference point (different possible locations, but mostly also on the scalp)
how is the position of the electrodes on the scalp?
standardized
what is the system for the electrode placement?
> 10- 20 system
what is the most common number of electrodes? and why?
64 -> good trade off
how many electrodes can be used?
max 256
what are pro/cons of more electrodes?
- more spatial accuracy
- more time to prepare
where are additional electrodes placed and why?
Additional electrodes placed on the face to record EYE
MOVEMENTS
how are the additional electrodes placed?
> Horizontal electrooculogram
HEOG ): to the corner of the eyes
Vertical electrooculogram
VEOG ): above and below the eye
what is the equipment? (9)
- cap
- electrodes bundles
- gel
- flat electrodes
- amplifier
- battery pack
- trigger box
- computer to record EEG data + software
- computer to administer the task (if needed)
what is the EEG procedure? (3 steps?
- step 1: place cap on the participant’s head
- step 2: add gel in each hole of the cap
- step 3: insert electrodes
what is the goal of data cleaning?
Remove all the noise and keep only the signal coming from the brain
what are you filtering out?
- Low frequencies (drifts)
- High frequencies (muscle contraction)
- Line noise (50 Hz)
what are parts of preprocessing?
- filtering
- referencing
- interpolarting bad channels
what is referencing?
Change in voltage with respect to this reference (external electrodes, average of all channels, one specific channel)
what is interpolating bad channels?
Correcting data from one electrode based on the average of its surroundings
what is epoching?
epoching is a procedure in which specific time-windows are cut from the continuous EEG signal
