t4 eeg and meg

Question 1

right hand rule

Answer 1

thumb is current

fingers are magnetic flux

Question 2

what does MEG measure

Answer 2

magnetic fields that are a consequence of electrical currents produced by the same dipoles that EEG measures, often arising from apical dendrites from neurons in sulci that are tangential/parallel to the closest part of the cortical surface.

Question 3

limitations MEG

Answer 3

• magnetic field very small: femtotesla )10^-15)
• ## magnetic shielding of the room, no metal objects

Question 4

MEG spatial and temporal res

Answer 4

spatial: mm
temporal: ms or better

Question 5

alpha waves 8 - 13

Answer 5

• occipital cortex
• eg when eyes closed, very relaxed, meditation, easily abolished by opening eyes, concentration/sudden alertness: alpha blockage
• inversely related to activity (in THAL due to sensory/cortical input), inhibited if more glucose (PET)
• medium freq, medium A

Question 6

what can ongoing EEG measure

Answer 6

• “normative” states: drowsiness, sleep arousal etc
  rhythms: produced by thalamocortical networks, between 10 and 100 microvolts
• alpha power assymmetry:(ln R - ln L) corr. emotionally reactive state, individual differences in that, risk for emotion disorders (right = NA)
• neurometrics: deviances
• coherence: synchronization of large brain networks, may be to bias input selection, create temporary assemblies, synaptic plasticity
• use in neurofeedback
• detect epilepsy

Question 7

delta waves 1 - 4 hz

Answer 7

• extremely big dudes
• deep dreamless sleep, inhibitory
• pathology: tumors, lesions, anesthesia
• inverse with glucose metabolism
• infants, it decreases with age into alha and beta

Question 8

theta waves 4 - 8 hz

Answer 8

• sleep
• big dudes
• awake: 1. drowsiness/impaired processing/drifting into sleep
  2. frontal midline: focused attention, mental effort, effective processing (focused by switching oth er things off?)

Question 9

beta waves 13 - 30 hz

Answer 9

• typically replaces alpha during activity
• wakefulness, normal bois
• symmetrical
• excitatory

Question 10

gamma waves 36 - 44 hz

Answer 10

• small, fast bois
• attention/arousal
• object recogntion/perceptual binding/topdown modulation/learning
• most clearly associated with metabolism and activity
• intermediate during REM, linearly decreases with anesthesia or SWS

Question 11

Nyquist theorem?

Answer 11

sampling rate should be at least 2x the highest freq of interest to ensure adequate sampling
if too short, aliasing happens: spurous slow waves
also think about this when selecting length of eeg segments

Question 12

Minimum current technique? minimum norm?

Answer 12

some MEG technique whereby the location is estimated without assumptions about whether they occur at same time, about the most probably distribution of currents.

Question 13

applications MEG

Answer 13

• tactile fields: ERFs in response to tactile stimuli on left hand are bigger in musicians than nonmusicians, correlated on age when starting playing
• cortex muscle coherence: mu rhythm produced in sensorimotor cortex when you move shows cortex muscle coherence, whereby muscle signal is always later than cortical signal
• action models in broca area: inhibited when you move/imagine/see someone else move that body aprt
• to detect what body part movement is encoded in a region you want to remove due to epilepsy