3 - Indirect Measures of Brain Activity Flashcards
What are the three famous brain damaged patients and what did symptoms did they exhibit?
Phineas Gage
- Rail road spike
- Frontal lobe damaged
- Aggressiveness and lack of inhibition
HM
- Brain surgery for epilepsy
- Hippocampus partially removed
- Inability to form long term memories
Victor Leborgne “Tan”
- Stroke
- Broca’s area damage; named after researcher
- Impaired speech but intact comprehension
How did researchers link function to anatomy?
Post-mortem studies of patients in which they had theorized about their anatomy
Explain CT Scans
- Developed in 1970s (Nobel Prize)
- Non-invasive, safe and high resolution
- X-ray used previously but looked “through” body
- Good as provided 3D (stacked 2D) images of anatomy.
- No longer needed dead patient to study functional anatomy
How does an MRI work?
- Protons line up in same direction from big magnet
- Perturb protons orientation through radio frequency pulse
- Measure how long it takes protons to re-align, releasing electromagnetic energy.
This varies across tissue type and therefore you can see different tissues in image. (Differing decay rates)
Explain MRI Scans
- Uses magnetic fields and pulses of radio wave energy to make pictures of organs and structures within body.
- Non-invasive, safe and provides high resolution images of varying body parts.
- Adaptable
How is cortical thickness measured and what does it demonstrate?
- Measured in MRIs. Algorithms on images separate white and grey matter, and you can measure amount of grey matter in varying areas of the brain.
- London Cab Drivers: thicker grey matter in navigation part of the brain.
- More neurons (more grey) if you use it.
- Cortical thinness part of aging.
Explain Diffusion Tensor Imaging (DTI)
- Measure movement of water molecules
- When path is constrained water moves in a specific path.
- Axon bundles act like ropes constraining movement of water.
- Allows us to measure connection between brain regions.
E.g.
- CSF and Grey Matter: water remains as circle as doesn’t favour any direction.
- White matter: horizontal on left because moving through two tracts
How can metabolic methods measure brain activity?
Brain is around 2% of body weight but uses 20% of bodies energy.
Metabolic methods use the brains consumption of energy to measure brain activity.
How do radioactive tracers measure brain activity?
- Used in animals mostly.
- Inject radioactive tracer (e.g. glucose) into animal and induce a functional response (e.g. visual stimulation).
- Measure where radioactive tracer goes, the brain is developed like a photograph
The image hits the visual cortex in a “flipped” manner
What is PET Imaging?
- Indirect imaging of brain using radioactive tracers that are safe for humans.
- Inject weak radioactive tracer (short delay) and induce functional response.
- Measure where it goes using PET.
Various areas of the brain will light up a “red” spot where the brain is consuming energy.
E.g. for walking in motor cortex and seeing - visual
Explain Optical Imaging
- Neuronal activity consumes oxygen (energy)
- Oxygenated blood is red and de-oxygenated is blue
- Measure the colour of blood to determine where resources are being consumed
E.g. Take photo of monkeys brain while doing a task, know a region is doing something if its getting more blue or red
- fNIR similar for humans
Explain fMRIs
- Combines metabolic consumption of oxygen and MRI.
- Blood oxygenation level dependent (BOLD) imaging is the standard technique
- De-oxygenated haemoglobin is paramagnetic and oxygenated is not.
- Initial dip in oxygen consumption as neural activity starts and then the brain massively overcompensates pumping fresh blood to the area.
- Metabolic process “rush in” new blood.
- Measures brains response to neural activity
What is BOLD?
Blood Oxygenation Level Dependent
Imaging used in fMRIs
Describe TMS
Stimulation and disruption of activity from regions in the brain.
Localised and non-invasive
Causal measure, disrupt particular area and see what it affects.
