College #1 - Electroencephalography and event related potentials

Question 1

Electroencephalography (EEG)

Answer 1

EEG measures the difference of electric potential. Measures voltage between two points on skull. These two points are always the mastoid and the sensor of interest. Most EEG peaks are muscle movements&raquo_space; volunteers need to relax their face&raquo_space; heart can’t be relaxed. Many seizures are visible on EEG; for example epilepsy.

EEG records mostly sources of interference:

• Eye movements and blinks
• Muscle movements
• Heart beats
• Any nearby electromagnetic activity

EEG also records brain activity

• Rhythmic activity (brain activity)
• Data analysis (ERPs)

Question 2

Mastoids

Answer 2

Neutral reference sensors (behind ear).

Question 3

Influence of eyes on EEG

Answer 3

Eyes are magnets

• Positively charged on outside
• Negatively charged on inside

Moving magnets give a difference in electoral potential, so we can cancel out eye noise.

Question 4

Rhythms in the brain

Answer 4

Delta = 4Hz&raquo_space; Alduts: slow wave sleep, Babies: Normal rhythm

Theta = > 4Hz < 8Hz&raquo_space; Very relaxed/meditation

Alpha = > 8 Hz < 14 Hz&raquo_space; Eyes closed and relaxed state

Beta = > 14Hz < 30 Hz&raquo_space; Movement and active thinking

Gamma = > 30&raquo_space; Coordination between neurons

Question 5

Frequency filters

Answer 5

Filters out noise on an EEG.

• Low pass filter < 2Hz; Only keeps waves lower than threshold = smoothing filter.
• High pass filter > 2 Hz; Only keeps waves higher than threshold.
• Band pass filter 2 - 10 Hz; Only keeps range.

Question 6

Epochs

Answer 6

Snippets of EEG.

Question 7

Event Related Potentials (ERPs)

Answer 7

A consistent brain response to an event.

• Is generated by the summation of the Post Synaptic Potentials of thousands od pyramidical neurons, organized in columns among the cortex.
• Noise inconsistent and averages out.

Question 8

P300/P3 component

Answer 8

Peak of interesting ‘card’.

P = Peak
N = Valley
300 = 300 ms after base
3 = third peak

Question 9

Pyramidal neurons

Answer 9

Neurons which are organized in columns close to the cortical surface. Due to grouped firing at the same time we can see a signal&raquo_space; happens to external events.

Question 10

Lexical processing

Answer 10

Same word written in different ways (differences in fontsize/capitals).

Question 11

EEG electrode positions

Answer 11

Name of electrode is based on underlying lobes.&raquo_space; Because of fold of brain this can be misleading.

Question 12

Written word recognition

Answer 12

Via experiments they found an timeline for word recognition.

• Manipulating font&raquo_space; gives a lower peak.
• Manipulating size&raquo_space; gives a lower peak.
• Changing word word position&raquo_space; Small second peak changes.

Timeline
Basic visual processing (N150)&raquo_space; Orthography (N250)&raquo_space; Lexical processing (P325)&raquo_space; Semantics (N400)

Question 13

Semantics

Answer 13

The study of the meaning of words/phrases/sentences.