Lecture 6 - Brain Imaging Flashcards
What does the term ‘brain imaging’ refer to?
Covers a variety of techniques that can be used to acquire images/signals reflecting the neuronal activity of the brain.
What is the idea that allows brain imaging to study behaviour?
Behaviour and neuronal activity should be related because they both originate in the brain
What are the two scales that brain imaging techniques can analyse activity on?
Spatial (from metres through to nanometres)
and
Time (from years to picoseconds/nanoseconds)
What is a static brain imagine technique?
It is a single, one-time scan of the brain, so typically examines structure and spatial organisation.
What are dynamic brain imaging techniques?
Completed over time, so analyze function and can involve comparisons of activity.
What are invasive imaging techniques?
Techniques which involve entering/penetrating the brain or head.
What are non-invasive imaging techniques?
Those that can be carried out from the outside of the brain and head..
Name two non-invasive, static imaging techniques.
MRI and DTI (magnetic resonance imaging and diffusion tensor imaging)
Name two non-invasive, dynamic imaging techniques.
fMRI and EEG/MEG (functional magnetic resonance imaging and electroencephalography/magnetoencephalography)
Name two invasive, dynamic imaging techniques.
SEEG and ECoG (stereotactic electroencephalography and electrocorticography)
Describe the principle/process of MRI.
- Before imaging starts, hydrogen protons in the body are aligned in random directions.
- a superconducting magnet creates a strong magnetic field which aligns all the protons in the same direction.
- radio waves are transmitted through the body, which spins protons off their axis so they are facing the same direction still.
- 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.
What does DTI stand for and what is it?
Diffusion tensor imaging - type of MRI that measures microscopic movement (diffusion) of water in the brain.
What information can MRI images transformed into white matter tracts reveal?
- number of fibres between brain regions
- fiber density within each region
What does fMRI do?
Collects images over time to investigate dynamic properties of brain activity
What is one of the most basic findings using fMRI by Fox and Raichle (2007)?
When the eyes open, BOLD signal is far greater than when the eyes are closed.
How long can it take for blood flow to change (for the BOLD signal to change)?
Up to 5 seconds after the stimulus
What is neurovascular coupling?
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.
Describe the 4 steps which comprise the BOLD response.
- neuronal activity in response to a stimulus/change in background activity
- neurovascular coupling (increase in CBF)
- haemodynamic response (blood flow, oxygenation level and volume increases)
- Increase in magnetic field strength can be detected.
How many cells are required to produce a signal detectable with EEG/MEG?
10,000-50,000
–> takes this amount of PSPs for several individual action potentials to be generated.
Compare resolution between EEG and MEG.
MEG is better than EEG for temporal resolution
EEG is better than MEG for spatial resolution
Where does ECoG pick up activity from?
Mainly from superficial cortical layers.
What is the largest contributor to electric flow?
Post synaptic potentials (PSPs)
How does SEEG work?
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.
