Cog Neuro - Txb C3: Combination of Function and Structure Neuroimaging and Connectivity Maps (3.6-3.7)

what are PET scans?

position emission tomography: a neuroimaging method that measures metabolic activity or blood flow changes in the brain by monitoring the distribution of radioactive tracer. The PET scanner measures the photons produced during the decay of a tracer. (more active neural areas have higher metabolic demand and thus receive more tracer)

what is fMRI

functional magnetic resonance imaging: a neuroimaging method that uses MRI to track blood flow changes in the brain that can correlate with local changes in neural activity.

what is the limitation of PET and fMRI scans

they do not directly measure neural events. have spatial but not temporal resolution

hemodynamic response

a change in blood flow to neural tissues. Hemodynamic responses can be detected by PET and fMRI

regional cerebral blood flow (rCBF)

The distribution of the brain’s blood supply, which can be measured by various imaging techniques. In PET scanning, rCBF is used as a measure of metabolic changes following increased neural activity in restricted regions of the brain.

whats the main difference between MRI and fMRI

MRI follow the proton resonance whereas fMRI look specifically at the magnetic properties of deoxyhemoglobin (BOLD effect)

why is there an increase in the ratio of oxygenated to deoxygenated hemoglobin surrounding brain tissue

as a region of the brain becomes more active, the amount of blood directed to that area increases. the neural tissue is unable to abosrb all of the excess oxygen.

why are fMRIs so much better than PET

• better spatial resolution

• less invasive

• can be repeated 

• cheaper

• less hazardous

what is block design

an experimental design used in PET (less common in fMRI). block consists of multiple trials of the same type. The activity of the block is averaged and compared to activity in another block at a different type of trial

what is event related design

used in fMRI in which different types of trials occur randomly. The BOLD response to particular stimuli or responses can be extracted from signal data

what is the benefit of event-related design for fMRI

helps ensure that participants are in similar attention state during both control and treatment trials increasing the likelihood that the observed differences reflect the hypothesized processing demands rather than just mere arousal.

benefit of block design

better detects small effects

magnetic resonance spectoscopy (MRS)

A technique to analyze data from MRI that uses signals from hydrogen protons in localized regions of the brain to determine the relative concentrations of different biochemicals

what is a consequence of imbalance in the excitatory and inhibitory neurotransmitters

autism resulting from disruption in GABA pathways

binocular rivalry

Binocular rivalry is when each eye is shown a different image and, instead of merging them, your perception alternates back and forth between the two. creating competition between excitatory and inhibitory process in the visual cortex

what causes the low temporal resolution of PET scans and fMRI scans?

PET: constrained by the decay rate of the radioactive agent

fMRI: dependent on the hemodynamic changes that underlie the BOLD response (on the order of seconds)

connectivity maps (connectomes)

a visualization of structural or functional connections within the brain

what are the 4 steps of brain network construction?

1. define network nodes

• use structural imaging methods to map nodes

2. define the network edges

• use DTI or BOLD

3. generate an association matrix by compiling all such relations

• weigh strength and relation of all elements

4. visualize the relations in a connectivity map

map it out

what is a solution for having low temporal resolution in fMRIs and PET scans and low spatial resolution in DTI and BOLD response

connectomes that compare the both and map it

what is rs-fMRI and what is it used for?

resting-state data produce highly reliable connectivity maps

can rs-fMRI can predict some behavioural differences

yes

what is another way connective maps have proven effective

in describing how that changeability can be altered in people with mental health

dynamic network analysis

understand learning, effects of training, creativity, stroke recovery, altered states of consciousness, basic biological variablity

what does the data suggest about network flexibility

intermediate phenotype related to the genetic liability for schizophrenia that manifests during cognitive states demanding working memory