Neuroscientific Techniques & Cognition 1

Neuroscientific Techniques & Cognition 1: Structural & Functional Imaging

• This lecture covers background to neuroscientific techniques, MRI, DTI, fMRI, and fTCDS.
• Ciara Egan is the lecturer and director of MSc Clinical Neuroscience at the University of Galway.

Lecture 1: Structural & Functional Imaging

• Techniques discussed include: background to neuroscientific techniques, MRI, DTI, fMRI, fTCDS.
• fMRI is a type of MRI allowing to get functional activity.

Background – Why do we need so many gadgets?

• Techniques allow answering questions, not otherwise answerable.
• Behavioural testing limitations (e.g., implicit processing).
• Identification of brain regions without lesion studies/animal models.
• Evaluation of treatment efficacy at a mechanistic level.
• Potential biomarker identification.
• Each technique has its own pros and cons.
• Choice of technique is driven by the research question and practical constraints.

Background – What makes a good technique?

• Techniques are evaluated based on temporal resolution, portability, and spatial resolution.
• Different techniques have different strengths and weaknesses in terms of resolution and application. This is illustrated in a diagram, showing various techniques and their strengths in terms of spatial and temporal resolution.

Magnetic Resonance Imaging (MRI)

• MRI scanner components (radio frequency coil, gradient coils, magnet, scanner) are described and illustrated.
• When a material enters the MRI scanner, some protons in hydrogen molecules become oriented with the magnetic field.
• Radio waves (RF pulse) further shift the alignment of these protons.
• After turning off radio waves, protons return to their original orientations, releasing energy in the form of radio waves.
• The signals are captured, processed, and presented as images.
• Computer image creation is based on hydrogen density differences in grey matter, white matter, and cerebrospinal fluid.
• T1 and T2 weighted images in relation to the realignment of protons with the main magnetic field and the time it takes to return to equilibrium (showing different aspects of anatomy).

MRI Scanner Safety

• MRI machines are powerful magnets.
• Ferromagnetic objects (metal) are dangerous.
• Participants without metal in their bodies are necessary for safety.
• Participants must remove metal objects (jewelry, watches, piercings, coins, glasses).
• MRI is noisy, require earplugs for the participants.
• Claustrophobia and anxiety are potential concerns.

What is structural MRI good for?

• Patient studies identifying areas of damage relating to symptoms (e.g., Alzheimer's Disease).
• Volumetric changes in relation to behaviour (e.g., intervention studies).
• Relationship between structural changes and behaviour is not always clear-cut.

MRI – Pros and Cons

• Advantages: good spatial resolution, clinical/experimental utility, relatively non-invasive.
• Disadvantages: purely structural, not everyone can be scanned (metal implants/claustrophobia), participants need to remain still, and is very expensive.

Diffusion Tensor Imaging (DTI)

• Measures water molecule diffusion in the brain.
• Illustrates isotropic and anisotropic diffusion (equal in all directions vs different directions).
• Diffuse tensor imaging is a structural measure of white matter.
• Measured using an MRI machine.
• Mean diffusivity(MD), Fractional Anisotropy (FA) and color-coded orientation are used to measure white-matter integrity.
• Several microscopic and macroscopic factors contribute to anisotropy, such as axon diameter, axon packing density, myelin thickness, axonal alignment etc.

What is DTI good for?

• Patient studies examining white matter structural integrity in various disorders (e.g., schizophrenia).
• FA differences in specific brain structures (e.g., arcuate fasciculus).
• Studying changes in specific tracts relating to experience.

Research Spotlight: Van der Auwera et al (2021)

• Longitudinal study of the arcuate fasciculus (AF) in children with and without dyslexia.
• DTI used to measure AF FA at different stages of reading acquisition (pre-reading, early reading, advanced reading).
• Results indicate that FA differences in the AF exist before reading instruction in children with dyslexia, and suggest a predictive relationship between AF FA and reading skills throughout development.
• Supports the idea of an AF deficit core to poor reading ability.

DTI – Pros and Cons

• Advantages: good spatial resolution for white matter tracts, clinical/experimental utility, relatively non-invasive.
• Disadvantages: purely structural, not everyone is suitable (metal implants/claustrophobia), participants must remain still, very expensive.

Functional Magnetic Resonance Imaging (fMRI)

• A form of MRI used to study brain function.
• T2-weighted images are used to obtain functional information.
• Functional information is usually overlayed on a T1 scan taken in the same session.
• fMRI is based on the BOLD (Blood Oxygen Level Dependent) technique.
• Changes in oxygenated blood level in specific brain regions are used to infer activation.

What is fMRI good for?

• Relates structural information to brain function.
• Useful for studying the functional significance of brain areas.
• Useful for identifying regions involved in compensation mechanisms for functions compromised by injuries.

Research Spotlight: Cummine et al (2015)

• Investigated the relationship between rapid automatized naming (RAN) and reading ability using fMRI.
• Four tasks were used: RAN letters, RAN numbers, rapid word reading and rapid non-word reading.
• Results and conclusions suggest that RAN and reading activate common brain regions and there is a correlation between RAN ability and reading in motor brain regions, but differences occur in non-motor regions.

fMRI – Pros and Cons

• Advantages: good spatial resolution, functional measure.
• Disadvantages: poor temporal resolution, indirect measurement (blood flow), interpretation issues dependent on analysis.

Functional Transcranial Doppler Sonography (fTCDS)

• Ultrasound technique based on the Doppler effect.
• Measuring blood flow in the middle cerebral artery (MCA).
• Measures bilateral blood flow in the brain, using non-invasive ultrasound. This information is represented as an image, or graphic.

What is fTCDS good for?

• Measures cerebral dominance more accurately than behavioural tests.
• Assessing individual differences in cerebral asymmetries, and group-level differences (patients vs controls).
• Studying language, face processing, and object recognition functions.

fTCDS – Pros and Cons

• Advantages: validated measure of language dominance (WADA comparison), easy to administer, non-invasive, suitable for participants (cochlear implants/metal/claustrophobia), and movement resistant.
• Disadvantages: relatively poor spatial resolution, can only determine left or right sided dominance, poor temporal resolution, individual differences in MCA architecture.

Recap

• Today's topics include background to neuroscientific techniques, MRI, DTI, fMRI, and fTCDS.
• Lecture 2 will focus on electrophysiology and brain stimulation.

Any Questions?

• This is a general question.