Lecture 5 - imaging the brain part 2

Question 1

EEG
Electrical potential
event-related potentials
components

Answer 1

-electrical potential = scalp recorded summation of PSP’s
quanitfied in 2 domains: time & frequency

-ERP = time locked activity. ( know whekn event happens, can detect what happens in EEG) NT binding.

• exogenous: related to things happening outside the body = sensory ERP. physical characteristics of stimulator
• endogenous = related to mental event.

Question 2

Electrode Placement in EEG

Answer 2

10-20 system - standarized placement. 10/20% of midline distance from nasion (nose dip) to inion( back of head dip)
z= 0
odd = left
even = right

Question 3

beta wave 
alpha wave
delta wave
deep sleep
coma

Answer 3

• excited, alert, aroused
• relaxed, slow oscillation
• sleep, but there are theta bursts involved too.
• complex pattern in slow roll
  1 Hz, brainstem activity

Question 4

EEG - seizure.
onset
clipping
origin?

Answer 4

• can see where onset is, vs where it travelled based on time until dramatic EEG recording.
• clipping = flat tops on recording. means strength of voltage is stronger than range in eeg.
• info can tell you where seizure may originate

Question 5

ERP
-amplified?
- averaged
Nd ?

Answer 5

• wave of brain activity during stimulus. signals amplified to be visualized. do task multiple times and average divided by stimuli to get solid wave.
  Nd = difference wave

Question 6

contingent negative variation (CNV)

- walter, 1964.

Answer 6

warning followed by interval followed by imperative stimulus
- EEG change in response to paradigm. - warning that you might get task, brain prepared. CNV = difference btw prepare and do.

Question 7

P300

- sutton 1965

Answer 7

oddball paradigm - low probability stimuli embedded in train of high probability stimuli.
- every time you hit the lower probability stimuli, p300 shows up. ~300 mV.

Question 8

N1 attention affect - dichotic listening paradigm (DLP)

- hillyard 1973

Answer 8

• covert attention = change attention without moving eyes. sound on same side as attention, N1 -ERP is larger.
  endogenous process of shifting attention withou overt sign.

Question 9

evoked potential
brainstem evoked potentials
visual evoked potentials
ERP defined by:?

Answer 9

-EP:ERP
-non-cortical PSP
VEP = ERP in response to visual stimulus
- peak size, time to peak post-stimulus, , topography, paradigm (stimulus unique to paradigm), slope of onset.

Question 10

signal averaging

Answer 10

superimpose all signals. divide by number of superimposed signals. common is kept, deflections cancelled out.

Question 11

filtering response

Answer 11

more repeats of trials = stabilize the response (average), filter out the endogenous actors and keep whats common to the task/stimuli.

Question 12

within subject
btw subject
signal averagin

Answer 12

within = after many sessions = more similarities
btw = each person has different ERP.
- average ERP usually doesnt look like anyone’s, but is average of all.

Question 13

caveats to ERP reliability

- grand averages

Answer 13

• large btw subject variability: diggerent brain., good within-subject reliability across sections
• latency jitter:: amplitudes misleading: average is related to everyones but not same as anyone’s
• less between session variability- sleep, drugs, hangover, diet.

Question 14

ERP comparison to behaviour.

Answer 14

ERP elucidate specific cognitive processes underlying overt behaviour
- Stroop + P300. change in p300 = perceptual thing happens. if not, then no motor prep.

Question 15

online measure in absence of overt behaviour

Answer 15

cover attention change, look at what brain is going. note correct vs error in responses.

Question 16

small amplitude = ERP =? # of trials compared to RT experiments

Answer 16

greater number of trials than RT experiments

Question 17

advantages of ERP

Answer 17

non-invasive
temporal resolution is decently good
cost - low.

Question 18

major ERP components

-visual sensory responses

Answer 18

-VSR: see difference when attending to same side, different when attending to opposite side.

Question 19

VSR
C1 - retinotopy & polarity
P1

Answer 19

C1: (80-130 ms)basic retinotopy = lower visual fiel maps to upper bank of calcarine fissure (V1 folded into this fissue. vice versa for upper visual field.

• polarity can vary. stimuli in LVF give +C1,, -C1 in UVF
• P1 100-130 mslateralized. early P1 - v2, later P1 = v4.
  sensitive to direction of spatial attention

Question 20

Auditory sensory responses
- BER
N1
Mismatch negativity (MMN)

Answer 20

brainstem evoked responses.
N1 = 70-150 msauditory cortex arousal - related to A1 processing. , vertex potential attention (at point Cz. related to attention), lateral potential -

MMN: 100-200msautomatic - novel stimuli elicit this. mapping enviro with auridoty info. orienting response always working. partt of endogenous activity.

Question 21

schizophrenics - MMN and Gray Matter Reduction.

Answer 21

look at schizophrenics. - increase (less negative) MMN over time = should be stable.
shrinkage in brain area in A1 - correlated with increase in MMN. = decreased symptoms.

Question 22

P300

Answer 22

• solicited by oddball paradigm.
  Parietal P3b - sshows task is relevant. frontal P3a = novel processing
  “context updating” updating awareness - is it here? no. now? no.
  target probablity - lower prob = higher p300 peak
  resource allocation - split attention = less resource to task = smaller p300
  time latency - mask stimulus = longer for p300 to peak

Question 23

dipole modeling and inverse problem

caveat?

Answer 23

try to find part of brain that is sending outthe signal.
- map image of brain, pick area and dipole within that. then create the wave that would come from that. = see how it matches to real EEG. If different fin a new area.
combine with fMRI for best results.

Image= spherical model of brain. not exactly what patient loos like.
conductivity thru different tissue is different too.

Question 24

MEG

right hand rule

Answer 24

electric current = magnetic field.

use electrodes to detect magnetic field.
drawback: expensive
sensitive to other fields - interruption
dipole orientation - too deep in sulci, cant reach electrode

Question 25

TMS

Answer 25

magnetic field perpendicular to flow of electricity. targets brain to stimulate or virtually lesion

Question 26

fNIRS

Answer 26

measure oxygenated:deoxygenated.
different tissue absorb in different ways. electrode sends out signal which is picked up by other electrode. = cant go deep - limited spatial resolution.

Question 27

neuronal code

Answer 27

firing patterns of neurons

Question 28

well-learned behaviour + cortical activity

Answer 28

sparse cortical activity.

Question 29

coherence theory

Answer 29

relate brains single cell activity and eEG activity.
high coherence = both correlated. large, slow waves = brain is idling
low coherence = poorly correlated = processing information

Question 30

DBS

Answer 30

implanted electrodes.