2 - Direct Measures of Brain Activity

Question 1

What is optogenetics?

Answer 1

Infusing genes with algae to control animal.

Question 2

What are behavioural approaches to measuring brain activity?

Answer 2

Very productive measures

• Questionnaires
• Qualitative methods; interviewing patients
• Psychophysics: measuring mental quantities by reaction times and behaviours
• Adaptation; show something for extend period and a weakened response is noted by brain

Question 3

How has brain recording methods changed over time?

Answer 3

Prior to 1900s; methods were scarce. “Accidental experiments”
- Philosophy, psychology and medicine

From 1900-1990; slow progress as all human methods (EEG, TMS) all in infancy
- Addition of biology and other medical branches

From 1990-present; lots of progress

• Refinement of existing methods.
• New methods developed (fMRI, optigenetics) with sophisticated analysis to complement.
• Added neuroscience departments, physics, health,computer science, education, etc.

Question 4

What is the trade off with each tool to measure brain activity?

Answer 4

Space
Time
Invasiveness

Often no best method at all

Question 5

What are the levels of study for the brain sciences on a spatial scale?

Answer 5

Component parts of a neuron
Neurons
Neuronal networks
Brain Areas
Brain Networks

Question 6

What is a direct measure of brain activity and list some examples.

Answer 6

Record neural activity explicitly.

• MEG/EEG
• Local field potentials
• Intra- and extracellular recordings
• 2-photon imaging
• Intracranial recordings

Question 7

Explain single unit recordings and their pros and cons (Extracellular)

Answer 7

Pro:

• Do not penetrate the cell membrane
• Allows cell to be recorded for hours or days.
• High Spatial and Temporal Resolution

Con

• Cannot observe sub-threshold activity (only APs)
• Not good for measuring network activity

Only done on animals

Question 8

What are the steps in quantifying neural activity using single unit recordings?

Answer 8

1. Record activity for a stimulus
2. Identify spikes
3. Measure spiking activity over time
4. Repeat for multiple trials

Final metric; spikes/second

Question 9

What are the similarities between EEGs and MEGs?

Answer 9

• Direct measures of neural activity
• Excellent temporal resolution (milliseconds)
• Issues with source localization (i.e. where in the brain).

Question 10

What is the EEG/MEG Inverse Problem?

Answer 10

Recordings are done at the scalp (2D surface)

Signals come from the brain (3D object)

Brain faces same problem with vision (hand and shadow against wall).

Question 11

What’s different between the EEG and MEG?

Answer 11

• MEG less sensitive to radial sources (gyrus)
• EEG signal is smeared by skull and scalp.
• Magnetic fields are transparent to skull and scalp; thus MEG is better for localisation.
• MEG is much more expensive.
• Magnetic fields drop as a function of distance, thus less suitable for measuring deep structures.

Question 12

What is an EEG?

Answer 12

Records electrical activity of the brain through electrodes placed on the scalp.

Measures voltage fluctuations resulting from ionic currents within neurons of the brain.

Question 13

What is an MEG?

Answer 13

Direct measure of neural activity through recording magnetic fields produced by electrical currents naturally occurring in the brain.

Question 14

What is electrocorticography (ECoG)?

Answer 14

Electrodes placed directly on exposed surface of the brain.

Question 15

What is Local Field Potentials way of measuring brain activity?

Answer 15

• Summed electric current flowing from multiple nearby neurons within a small volume of neuronal tissue.
• Voltage is measured in extracellular space by action potentials and graded potentials in neurons in the area.
• Measures the input into the observed area (as opposed to spike data, which represents the output).
• Linked to the BOLD signal in the fMRI.