Direct Measures

Question 1

Thomas Carlson (surprisingly) states that the single, most informative measure for the brain is….

Answer 1

behaviour - questionnaires, qualitative, and psychophysics

Question 2

Spatial precision describes…

Answer 2

The 3D level of focus, from synapse/soma/axon to neuron, to cortical area.

Question 3

Temporal resolution describes…

Answer 3

time focus - msec to days or lifeline (with injury)

Question 4

Besides temporal and spatial resolution, it is important to consider the ________ of the technique to determine ______ for humans

Answer 4

invasiveness, safety

Question 5

Direct measures record the actual activity of neurons. Name the ones discussed in the lecture

Answer 5

– MEG/EEG
– Local field potentials
– Intra and extracellular recordings
– 2-photo imaging
– Intracranial recordings

Question 6

It is best to study the neuron to study the brain (considered the basic unit) as it _____ information about the world

Answer 6

encodes

Question 7

Single unit recordings can be _______ or ________. The latter places an electrode ______ neurons and measures ______ _____. Basically, it measures ______ activity over time. So output measure is spikes/sec.

Answer 7

intracellular or extracellular
between
action potentials
spiking

Question 8

What are some advantages/disadvantages of extracellular recordings?

Answer 8

Adv

• measures at the level of the neuron - high spatial resolution
• measures spiking activity - high temporal resolution
• can record from hours to days

Disadv

• cannot observe sub-threshold activity (ion channels)
• cannot tell us about network activity

Question 9

Intracellular recordings go directly into the cell, however…

Answer 9

they are very invasive and may damage cells

Question 10

Electroencephalography (EEG) measures ______ _____ of _______ cells, by placing _______ on the scalp.

Answer 10

electrical potential
pyramidal
electrodes/sensors

Question 11

EEG has _____ temporal resolution and _____ spatial resolution.

Answer 11

High

Low

Question 12

Magnetoencephalography (MEG) measures ______ fields as opposed to ______ fields. This is because the _____ fields produced by pyramidal cells also produce ______ fields

Answer 12

magnetic, electric

electric magnetic

Question 13

Name similarities and differences of EEG and MEG

Answer 13

Similarities

• both direct measures of neuronal activity
• both have high temporal resolution
• both have issues with source localisation (low spatial resolution). We don’t know exactly where the activity is coming from.

Differences

• MEG better for sulci and EEG better for gyri
• Electrical signals are smeared by scalp and skull, whereas magnetic fields are not (they are transparent with the skull), hence MEG better for localisation.
• EEG better at measuring deep brain regions, MEG difficult to measure deep sources as magnetic field drops over distance.
• MEG is much more expensive $750

Question 14

What is the inverse problem?

Answer 14

The issue of recording neurons on 2D surface and making inferences about 3D brain (similar to flat sheet on retina of 2D image to perceptions of 3D world)

Question 15

Does it seem single unit, MEG and EEG measure the same thing?

Answer 15

YES - the activity of neurons. single unit has higher spatial resolution.

Question 16

Local field potentials measure the ______ in the _____ space (aka the summed _____ of multiple nearby neurons). This is about the ______ to various neurons, not the _____ (which would be the spikes). It is usefule to measure neurons and ____ ______.

Answer 16

activity 
extracellular
potential
input
output
neural networks

BOLD fMRI is more closely related to local field potentials (input to particular cortical area as opposed to output)

Question 17

2 -photon imaging measures _______ in ________ concentration. It is useful to look at many _______ simultaneously.

Answer 17

changes
calcium
neurons

Question 18

Electrocorticography (ECoG), or intracranial electroencephalography (iEEG) is often done when a patient has to go in for surgery. A ______ of electrodes is placed ______ on the brain. Hence, much better _____ resolution than EEG. it is great to measure _____ ______ or ______ ______

Answer 18

sheet
directly
spatial
brain areas or brain networks

Question 19

Describe Adv and Disadv of EEG

Answer 19

Adv

• very accessible and cheap
• non-invasive
• great temporal resolution

Disadv

• lots of set up - cap - electrode gel
• source localisation
• correlational
• signals are global brain activity - don’t tell us about specific region
• 2D vs 3D inferences - inverse problem

Question 20

Describe Adv and Disadv of single unit recordings

Answer 20

Adv
- fine temporal resolution

Disadv

• high spatial resolution –> single neuron…but that’s not going to tell you much - you need context
• invasive
• often too specific - limited questions you can ask