(5) Techniques in Neuroscience Flashcards
What is electrophysiology?
The branch of physiology that deals with the electrical phenomena associated with nervous and other bodily activity
What is Single-unit recording in terms of electrophysiology?
studies the electrical activity of individual neuron, the use of an electrode to record the electrophysiological activity (action potentials) from a single neuron
What is Multi-unit recording in terms of electrophysiology?
studies the composite electrical activity of groups of neurons (e.g., fibre pathway)
What is an EEG recording in terms of electrophysiology?
studies the low frequency, composite electrical activity of unspecified origin at select brain regions, EEG measures the activity of large numbers (populations) of neurons
How does single-unit recording work?
- An electrode is introduced into the brain of a living animal
- It detects electrical activity generated by the neuron adjacent to the electrode tip
- The animal is usually immobilized, but awake
- Enable researchers to understand how individual neurons code information
- No pain receptors in the cortex
What did Rizzolatti et al find out about neurons and performance? (single-unit recording)
- Neurones activates both while observing and while performing:
- Actions such as grasping
- Emotions such as sadness
- Watching someone receive painful events such as shocks
How does EEG work?
- EEG is non-invasive and painless
- Electrodes measure voltage-differences at the scalp in the microvolt (μV) range
- Voltages are recorded with millisecond resolution
Why is EEG used?
- Detecting changes in brain patterns
- Can average several readings to obtain evoked potential
- Often used for detecting epilepsy and other brain disorders (sleep disorders)
What is An event-related potential (ERP)?
An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event
How are ERPs created?
- Large background oscillations of the EEG trace make it impossible to detect the evoked response from a single trial
- By averaging from hundreds of trials, the background EEG is removed, leaving the event-related potentials
What does neural activity consume and generate?
Neural activity consumes oxygen as well as generating electrical signals
-In order to compensate for increased oxygen consumption, more blood is pumped into the active region
What is a PET?
PET measures the blood flow in a region, whereas fMRI measures the blood oxygenation
- The time taken for this response is slow (several seconds) and so functional imaging has a poor temporal resolution, but a good spatial resolution
- This is the complementary profile to EEG
How much energy does the brain consume?
The brain consumes about 20% of energy of body
How much blood flow does the brain receive?
The brain receives about 20% of blood flow
How does blood flow in neural activity change?
Neural activity increases global blood flow marginally, but dramatically locally (up to 25% change!!!!)
What is the cortex packed with?
Cortex is densely packed with blood vessels
What level is blood flow regulated?
Evidence that blood flow is highly locally regulated, potentially at columnar level
How does PET work?
- Form of hemodynamically-based functional brain imaging
- Subject is given a radioactively tagged substance(e.g., sugar)
- Compute the locations of decaying radioisotopes that emit gamma rays
- Infer higher regional cerebral blood flow in areas that emit many positrons
- Tracer takes up to 30 seconds to peak
What are the limitations to PET?
- Limited spatial resolution!
- Has no temporal resolution!
- Have to expose humans to radiation!
- Access to a cyclotron
What does FUNCTIONAL MAGNETIC RESONANCE IMAGING (Fmri) do?
Measures local blood flow
-Does not use radioactivity, but directly measures the concentration of deoxyhaemoglobin in the blood
What is the BOLD response in FMri
This is called the BOLD response (Blood Oxygen Level Dependent contrast)
What happens to the BOLD response over time?
The change in BOLD response over time is called the haemodynamic response function and it has a number of distinct phases
-The Haemodynamic Response Function peaks in 6–8 seconds and so this is the temporal resolution of fMRI
How do you know if a region is active in an fMRI?
A region is “active” if it shows a greater response in one condition relative to another
What are the limitations of fMRI?
- fMRI lacks fine spatial and temporal resolution
- It is NOT a direct measure of neural activity
- Caution should be taken in the interpretation of fMRI measurements with respect to brain activity
What are the positive to fMRI?
- Measures signals related to the amount of oxygen in brain regions
- It IS related to neural activity but the precise link between Cerebral Blood Flow and neural activity is not yet known
- Very powerful technique with great promise
What is Transcranial Magnetic Stimulation (TMS)?
- Uses electro-magnetic induction via coils to temporarily disrupt cortical function
- Infer the function of a region (or cognitive mechanism) by removing it and measuring the effect on the rest of the system
What effects disruption of brain function?
Disruption of brain function comes about through natural damage (strokes, etc.), elicited damage (e.g. animal models), or harmless temporary changes induced electro-magnetically (TMS)
How long can virtual lesions last for? (TMS)
-Temporary “virtual lesions” effects can last from msec to min brief effects are useful for studying timing of processes in different brain areas
How does TMS work?
- Coil contains a wire carrying an electric current
- A rapid change in the current creates a magnetic field
- The magnetic field induces a current in the nearby neurons (causing them to “fire”, i.e. generate action potentials)
- This disrupts the cognitive function that they may be doing at that point in time (a virtual lesion)
- Strong current sent through the coil à magnetic field
- Passes through scalp and skull à creates electrical current in brain underneath coil which disrupts
