Techniques in Neuroscience

Question 1

what does BOLD stand for?

Answer 1

Blood Oxygen Level Dependent contrast

Question 2

what does CBF stand for?

Answer 2

Cerebral blood flow

Question 3

define capillary

Answer 3

The smallest blood vessels in the body

Question 4

define cyclotron

Answer 4

A particle accelerator used to create radioactive isotopes for PET

Question 5

define EEG

Answer 5

Electroencephalography

Question 6

Define ERP

Answer 6

event related potentials

Question 7

define FMRI

Answer 7

functional magentic resonance imaging

Question 8

define metabolism

Answer 8

the set of biochemical reactions that serve to sustain life, growth and development, especially relating to the delivery of energy.

Question 9

define PET

Answer 9

Positron Emission Tomography

Question 10

define TMS

Answer 10

Transcranial magentic stimuluation

Question 11

define Tesla

Answer 11

Tesla

Question 12

what is electrophysioology

Answer 12

Single-unit recording studies the electrical activity of individual neurons

Multi-unit recording studies the composite electrical activity of groups of neurons (e.g., fiber pathway)

the branch of physiology that deals with the electrical phenomena associated with nervous and other bodily activity

EEG recording studies the low frequency, composite electrical activity of unspecified origin at select brain regions

We lose specificity- can’t pinpoint

Question 13

what is single unit recording

Answer 13

Single-unit recording is the use of an electrode to record the electrophysiological activity (action potentials) from a single neuron

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 Single- single to noise ratio too loud to pick up AP

Enable researchers to understand how individual neurons code information

No pain receptors in the cortex

Hasegawa et al., 2015

Question 14

what is a mirror neurone

Answer 14

Neurones activates both while observing and while performing:
Actions such as grasping
Emotions such as sadness
Watching someone receive painful events such as shocks

Thus, our capacity for empathy– the ability to share another’s emotions and feelings –is based in a simple ‘mirroring’ mechanism implemented by the human MNS that allows us to use the same neural resources to represent states of the self and others in an overlapping way”

Question 15

what is EEG

Answer 15

Electroencephalogram
EEG measures the activity of large numbers (populations) of neurons
EEG is non-invasive and painless
Electrodes measure voltage-differences at the scalp in the microvolt (μV) range
Voltages are recorded with millisecond resolution

Detecting changes in brain patterns
Can average several readings to obtain evoked potential
Often used for detecting epilepsy and other brain disorders (sleep disorders)

Question 16

evaluate EEG

Answer 16

Terrific temporal resolution: 1msec recording

Spatial resolution is poor L

Question 17

what are event related potentials?

Answer 17

Large background oscillations of the EEG trace make it impossible to detectthe evoked response from a single trial
By averaging from hundreds of trials, the background EEG is removed, leavingtheevent-relatedpotentials
Event Related Potentials (ERPs)
An event-related potential(ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event

Question 18

what does an ERP wave tell you?

Answer 18

info about the neural basis of processing is provided by the difference in activty

Question 19

how do brain imaging techniques work?

Answer 19

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

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

Question 20

why do we need changes in blood flow?

Answer 20

The brain consumes about 20% of energy of body
The brain receives about 20% of blood flow
Why do we need changes in blood flow?
Neural activity increases global blood flow marginally, but dramatically locally (up top 25% change!!!!)
basis of modern neuroimaging techniques
Cortex is densely packed with blood vessels
§ Distribution of blood vessels mirrors neuronal organisation
§ Evidence that blood flow is highly locally regulated, potentially at columnar level

Question 21

what does regional CBF mean?

Answer 21

regional cerebral blood flow

Question 22

what does PET measure?

Answer 22

Form of hemodynamically-basedfunctional brain imaging
POSITRON EMISSION TOMOGRAPHY (PET) Measures local blood flow (metabolic response)
§ 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!!

Question 23

what are the limitations of PET?

Answer 23

PET provides a relatively direct and easily interpretable measure of brain metabolism and it was the primary technique for functional imaging
BUT… it has many limitations:
Limited spatial resolution! 
Has no temporal resolution!
 Have to expose humans to radiation!
 Access to a cyclotron

Question 24

how does fMRI work?

Answer 24

§ Does not use radioactivity, but directly measures the concentration of deoxyhaemoglobinin the blood

§ This is called the BOLD response (Blood Oxygen Level Dependent contrast)

§ 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

Question 25

how does the magnetic field work?

Answer 25

Magnetic field strength is measured in Tesla (T) or Gauss (G)

§ 1 Tesla = 10,000 Gauss § Earth’s magnetic field: 0.5 Gauss § Refrigerator magnet: 200 Gauss § MR magnet strengths: 1.5 –9T (15,000 G –90,000 G or 30,000-180,000 times the Earth’s magnetic field)

§ Uses superconducting magnets

Uses superconducting magnets

The magnetic field

These are strong magnetic field!

Question 26

what does it mean that a brain area is active?

Answer 26

The brain has a constant supply of blood and oxygen; if it didn’t, it would die!
This means we cannot literally stick someone in a scanner and read their thoughts (because the whole brain would look active)
In order to infer functional specialization, one needs to compare RELATIVE differences in brain activity between two or more conditions
A region is “active” if it shows a greater response in one condition relative to another
If the experimenter chooses inappropriate conditions the regions of activity will be meaningless (junk in, junk out) –functional imaging isn’t straightforward!

Question 27

what are the limitations to fmri?

Answer 27

fMRI lacks fine spatial and temporal resolution

 Measures signals related to the amount of oxygen in brain regions 

It is NOT a direct measure of neural activity 

 It IS related to neural activity but the precise link between Cerebral Blood Flow and neural activity is not yet known 

 Caution should be taken in the interpretation of fMRI measurements with respect to brain activity 

Very powerful technique with great promise

Question 28

what techniques can be combined

Answer 28

fmri and EEG

Question 29

outline TMS

Answer 29

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

§ For example, if damage to a region disrupts reading, but not speaking or seeing, then one might conclude that the region is specialized for some aspect of reading

§ 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)

Transcranial Magnetic Stimulation (TMS) • Can impair or facilitate local processing (mechanism not well understood) • Temporary “virtual lesions” effects can last from msec to min brief effects are useful for studying timing of processes in different brain areas • thought to be safe for most subjects some exclusions, e.g., people with epilepsy

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Question 30

how does TMS work?

Answer 30

I MS: now does It work? Coil contains a wire carrying an electric current
• A rapid change in the current creates a magnetic field ROYAL HOLLOWAY UNIVERSITY
• 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 virtual lesion) the cornputer passes a current through a device called the coil two inner copper windings create a magnetic field when a current is applied the coil gives short 50Hz bursts 5 times per Second magnetic pulses stimulate electric current in the brain

 this causes cortical neurons under the •te of stimulation to depolarize and charge an action potential • Strong current sent through the coil magnetic field • Passes through scalp and skull creates electrical current in brain underneath coil which disrupts neurons Single Pulse TMS 
Repetitive TMS (rTMS) Longer-lasting effects. The mechanism is not clear but likely to reflect changes in synaptic efficacy

can only stimulate areas near the cortical surface spatial resolution difficult to determine, —10-20 mm ROYAL HOLLOWAY UNIVERSIT

Question 31

sumerise TMS

Answer 31

Enables the induction of temporary ‘lesions’ in healthy subjects
§ Single-pulse TMS has produced seizures in patients, but not in normal subjects
§ rTMS has caused seizures in patients and in normal subjects
§ Possible therapeutic applications