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
acute recordings
made over a relatively short period (often after surgery)
electrical stimulation
involves passing an electrical current through a wire inserted into the brain
high-frequency electrical stimulation patterns ___
tend to produce the same behavioural effects as lesioning the brain area
chemical stimulation
Drugs are administered through a guide cannula (hollow tube) implanted in a particular brain region
optogenetics
The use of light to control neurons which have been made sensitive to light through the instruction of foreign DNA
opsins
light-sensitive ion channels
excitatory opsins
you can either pulse light or leave it on to drive action potential activity
inhibitory opsins
continuous light pulses can be used to inhibit action potential activity
excitatory opsin example
ChR2
inhibitory opsin example
halorhodopsin
virus
A small infectious agent that replicates inside the cells of other organisms
The DNA of a virus encodes instructions on how to make more virus
virus-mediated gene delivery
adding foreign DNA to the virus that encodes things like optogenetic proteins. when a modified virus is injected into an animal’s brain, it infects the cells it comes into contact with. Once the virus gets its DNA into the infected cell’s nucleus, that cell will start to transcribe it and make the foreign protein
we can target opsin expression to specific neurons according to
- where their soma is located
- where their axons are located
- the proteins they express
- whether they recently had more action potentials than normal
fluorescent calcium imagining
records neural activity from specific genetically-defined neurons. Green fluorescent protein (GFP) is modified into GCaMP, allowing it to bind to calcium and fluoresce much brighter when it does.
Since a calcium influx occurs during action potentials, monitoring GCaMP fluorescence is a good way to measure neural activity
retrograde labelling
tracing afferent axons
anterograde labelling
tracing efferent axons
retrograde tracers example
flurogold
anterograde tracers example
PHA-L
stereotaxic surgery
uses a stereotaxic apparatus to inject and permanently implant things into the brain
bregma
the junction where pieces of the skull fuse together. often used as a reference point for stereotaxic surgery
reasons for sterotaxic surgery
- lesion a brain area
- lesion a specific type of cell
- change gene expression
- implant guide cannula
- implant microelectrodes
- implant fibre optic cables
guide cannula
hollow tube
microdialysis
the use of a semipermeable membrane to either deliver molecules or measure the number of molecules in some solution or brain area
microdialysis probe
small metal tube that holds dialysis tubing. these can be placed in the animal’s head
fastest sampling rate for molecules to equilibrate across a dialysis membrane
once per minute
typical sampling rate for molecules to equilibrate across a dialysis membrane
once per 10 mins
only serotonin neurons express ___
serotonin reuptake proteins
only glutamate neurons express ___
vesicular gluatamate transporter proteins
immunohistochemistry
a histological method that is used to label proteins and peptides of biological tissue. when fluorescent antibodies that selectively bind to different types of proteins are washed over a brain slice, the brain slice of interest becomes fluorescently labelled
t or f: it is easy to make an antibody that selectively binds to a small molecule such as a classic neurotransmitter
false; it is impossible
t or f: it is easy to make an antibody that binds to a specific protein
true
antibodies
proteins made by the immune system of mammals.
advantages of fMRIs
they are not invasive & provide structural and functional information with decent spatial & temporal resolution
do recpetor agonists & antagonists affect axons passing through the area
no
what do anesthetics do to neural activity?
shut it down
how do researchers identify cells that make and release classical neurotransmitters?
using antibodies against the enzymes that make these neurotransmitters
the downside of excitotoxic lesions
animals can’t serve as their own controls; sham lesions are needed
advantage of chemical stimulation
animals can serve as their own controls
neuronal projection
Function: map axonal projections in the brain
Method: inject fluorescent molecules
2 types of neuronal projection
retrograde & anterograde labelling
immunohistochemistry disadvantage
can’t localize small molecules like classical neurotransmitters
