Neuroimaging Intro/Techniques Flashcards
Define Neuroimaging
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
Overview the history of neuroimaging
late 19th/early 20th century- Cajal and Golgi- first silver staining of neurons/ angelo mossi- using the balance table to exhibit blood travelling to brain during cognitive tasks
1910-50s- early electrophysiology- giant axon of squid recordings
1960s- Hubel and Weisel- alive animal electrophysiological recordings in cats looking at primary visual cortex
1970s/80- CT scans - first time seeing inside brain of living human non-invasively/ dalmidian invention leading to MRI/ PET scans
1990s- fMRI- looking at functional changes caused by external stimuli- disruptive technology
2000s/2010s- multimodal imaging in cognitive neuroscience fmri plus another imaging technique e.g. PET
2020s- still multimodal/ AI/ optogenetics/ smaller chipboards allowing electrophysiology in alive awake animals/ calcium imaging/ CLARIFY
what are the trade offs of different imaging techniques?
spatial resolution/ temporal resolution/ scope (whole brain to single cell)/ invasiveness/ limitations of imaging/statistical hardware
why study brain structure?
- compare between healthy and disease groups to better understand disease
- localise lesion - can be combined with functional study
- image white matter tracts- brain systems
- look at vasculature to link it with neural activity
describe the versatility of MRI
it can image a number of components of the brain- grey matter density/ cortical thickness, white matter density/location, blood vessels, CSF
links to function in fMRI
what are the pros of fmri/why is it so dominant in cognitive neuroscience?
it can study the whole brain in an awake individual doing cognitive tasks in a non-invasive manner
there is a lot of pressure to use it as it has a publishing bias
what are the cons of fMRI?
low spatial resolution
moderate temporal resolution
neurovascular coupling not fully understood- can’t always apply blood flow to neural activity
expensive
issues in replication
which animal model is used most in neuroscience research?
mice
what are the 3 broad categories of functional imaging modalities?
voltage-based (e.g. electrophysiology)
haemodynamic signaling (e.g. fMRI BOLD signals)
chemical flux (e.g. calcium imaging)
overview the relationship between voltage-based imaging and frequency
neuronal events occur at a range of frequencies
low frequency events are <300 Hz and are measured as local field potentials (LFPs), which can be mostly measured at a surface level (with some deep brain)
high frequency events are >300Hz and are measured to obtain multiple unit activity (MUA)- measuring action potentials in deep brain
flow chart overview of how sensory event effects haemodynamics
sensory event-> neural activity-> vasodilation (or constriction) -> increased (or decreased) blood flow velocity-> change in deoxyhaemoglobin (fast)-> change in oxyhaemoglibin (slow)
which elements of haemodynamics are measured?
blood flow velocity, vasodilation/constriction, blood oxygenation
name 5 haemodynamic measurement techniques
laser doppler flowmetry (measures blood flow velocity)
laser speckle imaging
near infrared spectroscopy
optical imaging spectroscopy (OIS)
BOLD fMRI
what has greater flexibility- haemodynamic-based or voltage-based imaging?
haemodynamic based
what is the key issue with haemodynamic-based imaging?
it is not a direct measurement of neural activity and we still have many unknowns regarding our understanding of neurovascular coupling
why can we not compare different brain regions/structures using fMRI BOLD signals?
different regions have different nv coupling and different metabolic needs
compare voltage-based imaging against blood-based imaging
blood based have lower temporal resolution (seconds), whereas voltage based has higher (miliseconds)
BOLD is seen as a single peak response, whereas voltage-based tends to have more different responses
haemodynamics can have a cieling effect- where a vessel can only dilation so wide/blood can only flow so fast/ can reach a maximum oxygenated level.
what are the 2 main measures using chemical flux techiques?
measuring neurotransmitter levels using microdialysis
measuring calcium signalling
which processes is calcium signalling involved in?
exocitosis of synaptic vesicles containing NTs
backpropogation of APs
gene transcription
synaptic plasticity
vasodilation
how is calcium signalling imaged?
inserting calcium imagers (genetically encoded indicators) into the animal with a molecule which gives off light when bound to calcium
what are 2 key genetically encoded calcium indicators?
FRET-based and GCaMP
how does FRET-based calcium imaging work?
when bound to Calcium, there’s a shift in fluorescence from blue to yellow wavelengths
how does GCaMP calcium imaging work?
when bound to calcium is increases photon emission- increased intensity of fluorescence seen
does calcium imaging tend to have a high or low temporal resolution?
high because changes in calcium are transcient and measured as they happen in real time
