Lectures Flashcards
Where are the external electrodes placed during an EEG and why?
(1+2): The brain electrode comparisons are made with the electrodes on the mastoid because it serves as a relatively neutral reference point.
(3+4): eyes are magnets; positively charged in the front and negatively towards the back. Therefore this sensor records eye movement and no brain activity, so then the eye activity (noise) can be subtracted from the brain activity. This is necessary because EEG recordings also pick up EMG (electromuscular) signals (incl. heart palpitations)
What is an EEG?
Electroencephalograms measure the difference in electrical potential (V) of pyramidal neurons between two points
What are alpha waves?
10 Hz signal that is produced under a state of awakeness and relaxation
what are beta waves indicative of?
movement and active thinking
what are gamma waves indicative of?
coordination between neurons
what are delta waves indicative of?
deep sleep
what are theta waves indicative of?
relaxed or meditative state
What do frequency filters do?
bypass noise in EEG and get cleaner signals
name the 3 types of frequency filters and what each filters out
Low-pass filter: keeps waves that are below a defined threshold
High-pass filter: keeps waves that are above a defined threshold
Bandpass filter: keeps waves that are within a defined range
What is an ERP?
the average of waves from different locations
Why do we perform baseline corrections when examining ERPs?
because there is neural activity between stimulus presentations that set signals above or below 0. These corrections are done to make more accurate comparisons between ERPs
What is the P300?
an ERP elicited during decision making, thought to reflect processes involved in stimulus evaluation or categorisation
what is the N400?
an ERP indicating semantic processing → relatedness correlates to the strength of the N400 potential
What is the N150?
indicates basic visual processing → fires maximally when the letters, font, and letter size are the same
What is the N250?
indicates orthographic processing, i.e., how (dis)similar words are based on their letters. This applies to entirely different letters, but not to differences between the same uppercase and lowercase letter
What is the P325?
indicates lexical processing, i.e., whether a word actually exists and is identifiable by the reader or not. Other factors such as font or letter size don’t influence this potential
What is MEG? How does it differ from EEG?
Records tiny magnetic fields that are generated within the brain, instead of the differences in electrical potential. These magnetic fields are much less distorted by brain tissue compared to EEG recordings
What is depicted here?
the ventral processing stream