Lecture 8: Research Methods Flashcards
how does a CT Scan work?
High-energy electromagnetic radiation is delivered to the head from all angles. A computer translates the information received from the X-ray detector into a series of pictures of the skull of the brain
advantages & disadvantages of a CT scan
advantages: cheap and fast
disadvantages: the resolution is not great for soft tissue like the brain
how do MRIs work?
- A strong magnetic field is applied to the body,
- the spin of every hydrogen atom (proton) assumes a particular direction in line with the magnetic field
- Radiofrequency waves are administered to the body
- The energy is absorbed by protons, changing the direction of their spin
- Protons then emit their radio waves when their spin flips back to that determined magnet
the MRI can estimate ____
the relative density of protons in each area of the body
there are more protons in
fat and water
MRIS can be optimized to detect
the hydrogen atoms in water molecules
how does diffusion tensor imaging (DTI) work?
measures the direction and speed of the diffusion of water molecules by taking several pictures in rapid succession
DTI is used to identify ___
axon tracts
how does Functional Magnetic Resonance Imaging (fMRI) work?
infers the movement of oxygenated blood around the brain by collecting a rapid series of MRI scans and measuring the movement of these magnetic field distortions over time. goal = measure brain activity during behaviour
how does Positron Emissions Tomography (PET) work?
injects a person with a radioactive compound (ex. 2-DG) to detect changes in energy use in the brain. identifies where radioactive molecules are located over time & measures the changes in expression levels of neurotransmitter receptors.
disadvantage of PET scans
operating costs (2-DG has to be made on-site the morning fo the experiment because it decays so quickly)
what are macroelectrodes?
metal discs attached to the scalp to record the summed population-level activity of millions of neurons on cortical surfaces
diagnosis & EEGs
macroelectrodes and EEGs can be used as diagnostic tools since specific patterns of EEG activity are associated with different states of consciousness, sleep, and type of cerebral atrophy
experimental ablation
Involves the removal or destruction of a portion of the brain
radiofrequency lesions
destruction of a brain region. burning a part of the brain with low-energy radiation.
Small lesions made by passing a radiofrequency current through a metal wire that is insulated everywhere but the tip.This electric current produces heat that burns cells around the tip of the wire
how are the size and shape of radiofrequency lesions determined?
the duration and intensity of the current
the downside of radiofrequency lesions
axons & cell bodies just passing through will also be burned
excitotoxic lesions
destruction of a brain region. lesions produced by intracerebral injection of a glutamate receptor agonist, such as kainic acid. causes cause so much calcium influx that the affected neurons undergo apoptosis
advantage of excitotoxic lesions
axons passing through are usually spared
sham lesion
Placebo procedure that duplicates all steps of producing brain lesions except for one that causes extensive brain damage
reversible lesions
Temporary brain lesions achieved by injecting drugs that block or reduce neural activity in a given region
common drugs for reversible lesions include
voltage-gated sodium channel blockers and GABA receptor agonists
voltage-gated sodium channel blockers
stop all action potentials
GABA receptor agonists
hyperpolarize cell bodies
microelectrodes
Thin metal wires with a fine tip that can record the electrical activity of individual neurons (called a single-unit recording)
new microelectrodes can
record the activity of hundreds of neurons simultaneously
chronic electrical recordings
electrical recordings made over an extended period of time