Flashcards in 2 - Direct Measures of Brain Activity Deck (15):
What is optogenetics?
Infusing genes with algae to control animal.
What are behavioural approaches to measuring brain activity?
Very productive measures
- 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
How has brain recording methods changed over time?
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.
What is the trade off with each tool to measure brain activity?
Often no best method at all
What are the levels of study for the brain sciences on a spatial scale?
Component parts of a neuron
What is a direct measure of brain activity and list some examples.
Record neural activity explicitly.
- Local field potentials
- Intra- and extracellular recordings
- 2-photon imaging
- Intracranial recordings
Explain single unit recordings and their pros and cons (Extracellular)
- Do not penetrate the cell membrane
- Allows cell to be recorded for hours or days.
- High Spatial and Temporal Resolution
- Cannot observe sub-threshold activity (only APs)
- Not good for measuring network activity
Only done on animals
What are the steps in quantifying neural activity using single unit recordings?
1. Record activity for a stimulus
2. Identify spikes
3. Measure spiking activity over time
4. Repeat for multiple trials
Final metric; spikes/second
What are the similarities between EEGs and MEGs?
- Direct measures of neural activity
- Excellent temporal resolution (milliseconds)
- Issues with source localization (i.e. where in the brain).
What is the EEG/MEG Inverse Problem?
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).
What's different between the EEG and MEG?
- 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.
What is an EEG?
Records electrical activity of the brain through electrodes placed on the scalp.
Measures voltage fluctuations resulting from ionic currents within neurons of the brain.
What is an MEG?
Direct measure of neural activity through recording magnetic fields produced by electrical currents naturally occurring in the brain.
What is electrocorticography (ECoG)?
Electrodes placed directly on exposed surface of the brain.