Lecture 1 - CNS

Question 1

CNS

Answer 1

brain = spinal cord

Question 2

EEG invention

Answer 2

1924 by Hans Berger
took 5 years before publishing (age of slow science)
lot of backlash initially
already discovered things like alpha waves
committed suicide after his lab was shut down

Question 3

fMRI invention

Answer 3

1990s

Question 4

TMS invention

Answer 4

1985

Question 5

Galvani

Answer 5

first discovered electrical activity moving bodies
in frogs
18th century

Question 6

Eduard Hitzig

Answer 6

showed stimulation of cortex in dogs
1870
-> direct brain body connection

Question 7

Caton

Answer 7

spontaneous, ongoing electrical activity in rabbits

1875

Question 8

EEG measurement properties and origin

Answer 8

extremely high temporal resolution
combined activity of thousands of neurons
measures in distance from actual neurons

Question 9

voltage

Answer 9

potential of a current to flow
like water pressure
a relative measure
measured in EEG

Question 10

current

Answer 10

number of charged particles / electrodes / ions
in a given time
the actual flow

Question 11

cells measured in EEG

Answer 11

pyramidal cells

oriented vertically / perpendicular to surface of head

Question 12

potential measured in EEG

Answer 12

postsynaptic potential

at the ends of axons

Question 13

LFP

Answer 13

local field potential

larger difference between net negative and net positive charge

Question 14

what is measured with EEG

Answer 14

mostly LFP

sometimes also spikes = action potentials

Question 15

equipotential lines

Answer 15

points along circles where voltage is the same

measurable by EEG

Question 16

equivalent current dipole

Answer 16

sum of many neurons together
with the same direction
= unidirectional voltage field
= open field

Question 17

problem with brain folds

Answer 17

local cancellation

Question 18

closed field

Answer 18

no single orientation of neurons

Question 19

smearing

Answer 19

distortion and spread of voltages
due to the tissues between brain and device
and volume conduction

Question 20

what we cannot say about peaks

Answer 20

whether signal comes from excitation or inhibition
the direction of the neurons
orientation of the reference eletrode
where the PSPS comes from, soma or axon

Question 21

what EEG cannot detect

Answer 21

tangential dipoles

because they don’t have a voltage differencew

Question 22

topo(graphic) map

Answer 22

colourful map depicting the amplitude/the dipoles around the dhead
over time
plots every 2 to 5 ms

Question 23

source reconstruction

Answer 23

from topomap to underlying neural activity

Question 24

inverse problem

Answer 24

which activity leads to the dipoles we measure?
cannot be solved
is underdetermined / ill-posed
because there are too many possible solutions

Question 25

superposition problem

Answer 25

infers actual dipoles
C1, C2 etc = component one etc
is a generalization

Question 26

weight matrix

Answer 26

approximates which dipole contributes what to what is measured
problem: often many combinations possible

Question 27

forward problem

Answer 27

which dipoles will this neural activity create?

easily solvable with sufficient head model

Question 28

common solutions to the inverse problem

Answer 28

limit number of sources
or limit the position
use other techniques with higher spatial resolution
or data like single cell recordings

Question 29

ECoG

Answer 29

electrocorticography
directly from brain surface
only during surgery
e.g. when localising sources of epilepsy

Question 30

MEG

Answer 30

brother of EEG
measures magnetic equivalent of dipoles
with Squid sensors, very large coild
right hand grip rule: thumb is direction, fingers point in direction of magnetic field

Question 31

MEG advangtages

Answer 31

less blurring because no smearing
slightly better spatial resolution
can measure tangential dipoles
opposite of EEG! Combining both however is not very informative

Question 32

MEG disadvantages

Answer 32

very expensive, between EEG and fMRI
huge device, huge running costs
same temporal resolution as EEG

Question 33

signal summation

Answer 33

many sources contribute to the voltage measurement at each point
analogous to local field potential