Lecture 6 - Brain Imaging

Question 1

What does the term ‘brain imaging’ refer to?

Answer 1

Covers a variety of techniques that can be used to acquire images/signals reflecting the neuronal activity of the brain.

Question 2

What is the idea that allows brain imaging to study behaviour?

Answer 2

Behaviour and neuronal activity should be related because they both originate in the brain

Question 3

What are the two scales that brain imaging techniques can analyse activity on?

Answer 3

Spatial (from metres through to nanometres)

and

Time (from years to picoseconds/nanoseconds)

Question 4

What is a static brain imagine technique?

Answer 4

It is a single, one-time scan of the brain, so typically examines structure and spatial organisation.

Question 5

What are dynamic brain imaging techniques?

Answer 5

Completed over time, so analyze function and can involve comparisons of activity.

Question 6

What are invasive imaging techniques?

Answer 6

Techniques which involve entering/penetrating the brain or head.

Question 7

What are non-invasive imaging techniques?

Answer 7

Those that can be carried out from the outside of the brain and head..

Question 8

Name two non-invasive, static imaging techniques.

Answer 8

MRI and DTI (magnetic resonance imaging and diffusion tensor imaging)

Question 9

Name two non-invasive, dynamic imaging techniques.

Answer 9

fMRI and EEG/MEG (functional magnetic resonance imaging and electroencephalography/magnetoencephalography)

Question 10

Name two invasive, dynamic imaging techniques.

Answer 10

SEEG and ECoG (stereotactic electroencephalography and electrocorticography)

Question 11

Describe the principle/process of MRI.

Answer 11

1. Before imaging starts, hydrogen protons in the body are aligned in random directions.
2. a superconducting magnet creates a strong magnetic field which aligns all the protons in the same direction.
3. radio waves are transmitted through the body, which spins protons off their axis so they are facing the same direction still.
4. radio waves are turned off, and the protons return to the previous alignment. Different tissues take varying amounts of time to do this. The scanner measures the time taken by each proton to return to this alignment, allowing it to create a detailed image.

Question 12

What does DTI stand for and what is it?

Answer 12

Diffusion tensor imaging - type of MRI that measures microscopic movement (diffusion) of water in the brain.

Question 13

What information can MRI images transformed into white matter tracts reveal?

Answer 13

• number of fibres between brain regions

- fiber density within each region

Question 14

What does fMRI do?

Answer 14

Collects images over time to investigate dynamic properties of brain activity

Question 15

What is one of the most basic findings using fMRI by Fox and Raichle (2007)?

Answer 15

When the eyes open, BOLD signal is far greater than when the eyes are closed.

Question 16

How long can it take for blood flow to change (for the BOLD signal to change)?

Answer 16

Up to 5 seconds after the stimulus

Question 17

What is neurovascular coupling?

Answer 17

The relationship between local neural activity and subsequent changes in cerebral blood flow (CBF).

I presume, this is the cause of the 5 second delay seen between recognising a stimulus and seeing the resulting BOLD signal. Time taken for increased blood flow to the relevant area.

Question 18

Describe the 4 steps which comprise the BOLD response.

Answer 18

1. neuronal activity in response to a stimulus/change in background activity
2. neurovascular coupling (increase in CBF)
3. haemodynamic response (blood flow, oxygenation level and volume increases)
4. Increase in magnetic field strength can be detected.

Question 19

How many cells are required to produce a signal detectable with EEG/MEG?

Answer 19

10,000-50,000

–> takes this amount of PSPs for several individual action potentials to be generated.

Question 20

Compare resolution between EEG and MEG.

Answer 20

MEG is better than EEG for temporal resolution

EEG is better than MEG for spatial resolution

Question 21

Where does ECoG pick up activity from?

Answer 21

Mainly from superficial cortical layers.

Question 22

What is the largest contributor to electric flow?

Answer 22

Post synaptic potentials (PSPs)

Question 23

How does SEEG work?

Answer 23

Very thin, wire-like electrodes are inserted into small openings in the skull. These can precisely detect patterns of electrical activity deep inside the brain.

A whole helmet with electrodes all over (subdural grid) is used to get a more wholesome idea of activity. Typically used for determining the location/source of seizures.