Neuroimaging Intro/Techniques

Question 1

Define Neuroimaging

Answer 1

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

Question 2

Overview the history of neuroimaging

Answer 2

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

Question 3

what are the trade offs of different imaging techniques?

Answer 3

spatial resolution/ temporal resolution/ scope (whole brain to single cell)/ invasiveness/ limitations of imaging/statistical hardware

Question 4

why study brain structure?

Answer 4

• 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

Question 5

describe the versatility of MRI

Answer 5

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

Question 6

what are the pros of fmri/why is it so dominant in cognitive neuroscience?

Answer 6

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

Question 7

what are the cons of fMRI?

Answer 7

low spatial resolution
moderate temporal resolution
neurovascular coupling not fully understood- can’t always apply blood flow to neural activity
expensive
issues in replication

Question 8

which animal model is used most in neuroscience research?

Answer 8

mice

Question 9

what are the 3 broad categories of functional imaging modalities?

Answer 9

voltage-based (e.g. electrophysiology)
haemodynamic signaling (e.g. fMRI BOLD signals)
chemical flux (e.g. calcium imaging)

Question 10

overview the relationship between voltage-based imaging and frequency

Answer 10

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

Question 11

flow chart overview of how sensory event effects haemodynamics

Answer 11

sensory event-> neural activity-> vasodilation (or constriction) -> increased (or decreased) blood flow velocity-> change in deoxyhaemoglobin (fast)-> change in oxyhaemoglibin (slow)

Question 12

which elements of haemodynamics are measured?

Answer 12

blood flow velocity, vasodilation/constriction, blood oxygenation

Question 13

name 5 haemodynamic measurement techniques

Answer 13

laser doppler flowmetry (measures blood flow velocity)
laser speckle imaging
near infrared spectroscopy
optical imaging spectroscopy (OIS)
BOLD fMRI

Question 14

what has greater flexibility- haemodynamic-based or voltage-based imaging?

Answer 14

haemodynamic based

Question 15

what is the key issue with haemodynamic-based imaging?

Answer 15

it is not a direct measurement of neural activity and we still have many unknowns regarding our understanding of neurovascular coupling

Question 16

why can we not compare different brain regions/structures using fMRI BOLD signals?

Answer 16

different regions have different nv coupling and different metabolic needs

Question 17

compare voltage-based imaging against blood-based imaging

Answer 17

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.

Question 18

what are the 2 main measures using chemical flux techiques?

Answer 18

measuring neurotransmitter levels using microdialysis
measuring calcium signalling

Question 19

which processes is calcium signalling involved in?

Answer 19

exocitosis of synaptic vesicles containing NTs
backpropogation of APs
gene transcription
synaptic plasticity
vasodilation

Question 20

how is calcium signalling imaged?

Answer 20

inserting calcium imagers (genetically encoded indicators) into the animal with a molecule which gives off light when bound to calcium

Question 21

what are 2 key genetically encoded calcium indicators?

Answer 21

FRET-based and GCaMP

Question 22

how does FRET-based calcium imaging work?

Answer 22

when bound to Calcium, there’s a shift in fluorescence from blue to yellow wavelengths

Question 23

how does GCaMP calcium imaging work?

Answer 23

when bound to calcium is increases photon emission- increased intensity of fluorescence seen

Question 24

does calcium imaging tend to have a high or low temporal resolution?

Answer 24

high because changes in calcium are transcient and measured as they happen in real time

Question 25

what are the cons of calcium imaging?

Answer 25

• it’s an indirect measure- you are measuring light fluorescence, rather than ca2+ directly hence relying on statical models and estimation
• imaging depth is limited by laser power- can only penetrate to shallow layers currently
• expensive

Question 26

what is the advantage of using multimodal imaging techniques?

Answer 26

it reduces the weaknesses in single technique and increases the certainty in the results