Neuroimaging Techniques

• Structural and functional neuroimaging techniques are useful in neuroscience and cognition studies.

Lecture 1: Techniques Covered

• Magnetic Resonance Imaging (MRI) is covered.
• Diffusion Tensor Imaging (DTI) is covered.
• Functional Magnetic Resonance Imaging (fMRI) is covered.
• Functional Transcranial Doppler Sonography (fTCDS) is covered.

Lecture 2: Additional Topics

• Electroencephalography (EEG) and Event-Related Potentials (ERPs) are touched on in the second lecture.
• Transcranial Magnetic Stimulation (TMS) is also included in the second lecture.

Why Use Neuroscientific Techniques?

• These techniques help answer questions that behavioral testing alone cannot.
• They overcome limitations in behavioral testing, like examining implicit processing.
• Key brain regions are identified without animal models or lesion studies.
• These techniques help to evaluate treatment efficacy at a mechanistic level.
• They help with the potential identification of biomarkers.
• Each technique has pros and cons.

How to Choose a Technique

• The specific research question drives the selection of the neuroscientific technique.
• Practical constraints influence the choice of technique.

Magnetic Resonance Imaging (MRI)

• Protons in hydrogen molecules align with the magnetic field when a person is inside the MRI scanner.
• Applying a radio wave shifts the alignment of the protons.
• After radio waves are turned off, protons emit energy as radio waves.
• A coil of wire around the head detects radio waves, which are then are sent to a computer.
• Variations in hydrogen atom density in grey matter, white matter, and cerebrospinal fluid result in different signals.
• T1 measures the speed at which protons realign with the magnetic field.
• T2 measures proton energy release as they return to equilibrium.

MRI Safety

• MRI machines have powerful magnets that can make ferromagnetic objects dangerous.
• Participants cannot have metal in the body, including pacemakers, aneurysm clips or metal/cochlear implants
• Participants cannot have certain IUDs, dental work, or tattoos.
• Participants must remove jewelry, watches, piercings, coins, wallets, and glasses.
• The MRI is very loud and participants should use earplugs because the MRI is very loud.
• Claustrophobia and anxiety are a concern.

Structural MRI Applications

• Identifying brain damage areas and relating it to symptoms.
• Observing volumetric changes related to behavior or intervention.
• Understanding that the relationship isn't always clear-cut.

MRI: Pros and Cons

• MRI provides good spatial resolution.
• MRI is clinically and experimentally useful.
• MRI is relatively non-invasive.
• MRI is purely structural.
• Not everyone can be scanned due to metal implants or claustrophobia.
• Participants must remain very still and it is expensive.

Diffusion Tensor Imaging (DTI)

• DTI measures water molecule diffusion (freedom of movement from high to low concentration.
• DTI is a structural measure of white matter.
• DTI is also measured using an MRI machine.
• Mean Diffusivity (MD) measures a voxel's overall water diffusion.
• MD is insensitive to fiber orientation.
• MD is often used clinically.
• High MD often denotes poor white matter connections.
• Fractional Anisotropy notes red = left-right, green = anterior-posterior, blue = superior-inferior
• Maps display orientation, not direction.
• Microscopic and macroscopic factors can cause anisotropy.

DTI Applications

• Investigates white matter structural integrity in cases such as schizophrenia.
• Examines fractional anisotropy (FA) differences in specific structures, such as the arcuate fasciculus in dyslexia.
• Focuses on tracking changes in fractional anisotropy (FA) of specific tracts as they relate to particular experiences.

Van der Auwera et al. (2021) Research

• A three-time longitudinal investigation of the arcuate fasciculus with kids developing dyslexia.
• DTI was used to assess FA in arcuate fasciculus (AF).
• The study looked at typically developing children and those with dyslexia across different age ranges.
• Differences in fractional anisotropy were present between children with and without dyslexia before reading instruction began.
• There is a predictive link between AF FA and reading skills.
• Supports the idea that an AF deficit is core to poor reading ability.

DTI: Pros and Cons

• Good spatial resolution for white matter tracts.
• Has strong clinical and experimental utility.
• Relatively non-invasive.
• Purely structural.
• Some contraindications exist (eg. metal implants, claustrophobia).
• Participants have to remain completely still.
• Very expensive.

Functional Magnetic Resonance Imaging (fMRI)

• Is a form of MRI.
• It is T2 weighted to get the functional component (EPI: echo-planer imaging).
• It's is usually overlaid on a T1 scan taken in the same session.
• BOLD (Blood Oxygen Level Dependent) technique measures brain activity by changes in oxygenated blood levels.

fMRI Applicaitons

• Relates structural and functional information.
• Useful for studying functional significance of brain areas.
• Reveals where compensation happens for functions after an injury.

Cummine et al Research (2015)

• Investigated the rapid automatized naming and reading relationship.
• Tasks included RAN letters, RAN numbers, rapid word reading, and rapid nonword reading.
• RAN and reading activate common brain regions.
• Correlation exists between RAN and reading in motor brain regions.
• Differences exist between RAN and reading in non-motor regions.

FMRI: Pros and Cons

• Has good spatial resolution.
• Measures where specific activity is occurring.
• Identifies key areas involved in different processes.
• Poor temporal resolution.
• The BOLD response takes approx. 4 seconds.
• It is an indirect measure of activity via blood flow.
• Issues arise in interpretation from statistical thresholds and the dead salmon paper.

Functional Transcranial Doppler Sonography (fTCDS)

• Uses ultrasound to measure blood flow based on the Doppler effect.
• The frequency of ultrasound waves corresponds to blood flow toward or away from the probe.
• Measures bilateral blood flow in the middle cerebral artery (MCA) territory.

fTCDS Applications

• Measures hemispheric cerebral dominance.
• fTCDS is better than behavioural tests.
• Examines group/individual differences in cerebral asymmetries among patients.
• This is done in patients vs. controls.
• Lateralised functions include language, face processing, and object recognition.

COLA Consortium Research

• Studied the relationship between language lateralisation using fTCDs.
• Inconsistent language lateralization was tested using a behavioural test with lateralised cerebral blood flow.
• Parker et al., (2022) tested the dissociable language laterality hypothesis using behavior and lateralized cerebral blood flow.
• Language laterality is not a unitary trait.

fTCDS: Pros and Cons

• Validated measures of language dominance.
• Easy to administer and non-invasive.
• Participants can have cochlear implants, metal, or claustrophobia.
• Resistant to movement
• Poor spatial resolution.
• Only determines if activity is more left or right, but not where.
• Poor temporal resolution.
• Individual differences in MCA architecture or skull density mean a clean signal may not be possible.