Neuroimaging techniques Flashcards
What is brain imaging?
Any technique used to obtain and integrate single or multiple measures of brain structure or function into a picture - or series of pictures - of the brain
Why is neuroscience research under the spotlight?
- Neuroscience is a young discipline - imaging techniques have tripled in the last 15 years
- Emergence of awake human imaging - first used in the 70s - now how the tools to answer questions
- We have the technology - human research, animal research - first picture = diffusion tensor imaging
Name some of the inventions in neuroscience which have changed the field
Golgi - Golgi staining - 1890s
Hubel and Wiesal - visual receptive fields 60s
Damadian - inventor of MRI early 70s
Ogawa - inventor of fMRI 1990s
Is there downsides to having such a fast changing field?
- Constant pressure to publish
- Increasingly sophisticated techniques needed
- Researchers need to understand the physical and statistical basis of the techniques they use
- Can lead to bad science
- Old interpretations of data is not always reliable today
What is an example of bad science?
Bennet salmon imaging
- Dead salmon placed in an fMRI scanner and asked to determine the emotion of the individual in the picture
- It appeared that there was activity in the salmon’s brain and they concluded that there must have been some processing in the salmon in response to the question
- In reality, it was random noise in the EPI time series that caused the activation as the salmon was dead
- Crucial to understand the stats behind the imaging to ensure the correct conclusions are made
Why study brain structure?
- Comparisons of clinical/sub-clinical populations
– size/shape or regions/whole brain
– expression of specific neurons - Localise site of neural insult
– assess impact on behaviour - Imaging white matter tracts/projections
- Vasculature
– understanding the link between blood flow and neural activity
What can we use MRI for?
Grey matter density and cortical thickness
White matter tract density and location
The sizes, location, and course of blood vessels
The flow of cerebrospinal fluid
Measures related to neural activity (bold fMRI)
Why is fMRI dominant but flawed?
DOMINANT
Whole brain awake imaging
Non-invasive
FLAWED
Relatively low spatial resolution (can only accurately measure within a centimetre of the brain)
Moderate temporal resolution (haemodynamic responses are often delayed)
Surrogate measure of neural
Hugely expensive
Fears about replicability
Why are mice a good animal model in neuroimaging research?
The mouse genome is entirely mapped - know what every gene does
Allows the insertion or deletion of various genes - assess behaviour
What are the different functional modalities of neuroimaging techniques?
Voltage based (visualises a direct indicator of activity by measuring changes in voltage - similar to electrophysiology)
Haemodynamic signalling
Chemical flux
What frequencies are used to obtain electrophysiological data?
Low frequency (<300Hz) sampled to obtain the local field potential (LFPs) - detectable at surface and deep brain
High frequency (>300Hz) samples to obtain multiple-unit activity (MUA) - detectable using deep brain recording
What techniques are used to measure electrophysiology?
EEG = non-invasive in humans
Electrophysiology in animals = invasive - electrode inserted into the brain
What are some examples of techniques using haemodynamic measures?
Laser Doppler flowmetry
Laser speckle imaging
Near infra-red spectroscopy
Optical imaging spectroscopy
BOLD fMRI
What is a major limitation of haemodynamic measures?
They are not a direct measure of neural activity - it is an indirect measure of blood oxygenation which represents neural activity
Need to measure neural activity simultaneously to compare haemodynamics to neural
Blood based changes are delayed and extended
Ceiling effect - limited by the vessels and how much blood can flow at a certain time
What are the different blood-based measures?
Flow and velocity
Vasodilation/vasoconstriction
Blood oxygenation
