Lecture 4 -Research Methods Flashcards
Temporal Resolution
Difference in time between the measurement and brain activity
Spatial Resolution
The size of the brain region we are looking at (neuron, cortical column, entire brain, etc.)
High spatial resolution - we know where a change occurred
Low spatial resolution - we don’t know exactly where but we have a rough idea
Neural Stains
Selective
- Stains some tissue components but not others (nucleus, ribosomes and cell membrane)
Steps for Preparing Brain Tissue for a Neural Stain
1) Perfusion - remove blood with saline solution
2) Hardening - flash freezing or paraffin embedding
3) Slicing - microtome
4) Mounting - albumen
Golgi Stain
Silver chromate stains neurons black Not all neurons are stained Shape and size of neurons No intracellular details First look at the synapse - Cajal, Nobel Prize, Neuron Doctrine (neurons are single cells that are independent and separated by gaps)
Nissil Stain
Penetrates all cells Stains ribosomes Soma visible - Can better quantify (estimate) number of cells First view of structures within neuron Cresyl violet
Electron Microscopy
Greater magnification than light microscope
- Electrons are smaller particles of light
Slices coated with electron-absorbing substance (gold)
- Different parts of neurons absorb gold to different degrees
Electron beam passes through slice and image captured
Minute cellular details
- Difficult to assess overall or general structure
Scanning EM generates 3D images
Anterograde tracing
Where do axons go?
Autoradiography
- Amino acids with radioactive hydrogen isotopes are taken into cell bodies and incorporated into proteins
- Wait for a few days and identify radioactivity in axon terminals
Retrograde tracing
Where do axons come from?
HRP taken up by axon terminals
Wait a few days
Brain stained with HRP substrate to change it to black
- Black identifies originated cell bodies
Contrast X-rays
Effective only if internal structures differ from their surroundings - differences in x-ray absorption
Brain has too many overlapping structures absorbing x-rays to the same degree
To stand out - radioopaque material into structure of interest
- Discovered by Moniz
X-ray passed through brain onto photographic plate
Angiography
Contrast x-ray
Dye injected into carotid artery
Reveals enlarged or displaced blood vessels
Pneumoencelphalography
- Air injected into CSF (lumbar)
- Identify enlarged and displaced ventricles
(Very painful and has fallen out of use)
X-ray Computed Tomography
Early 1970s
Computer assisted x-ray
3D view of the brain
Brain CT composed of 8-9 horizontal sections
X-ray gun and detector rotate in opposition around the head
Not sharp image
- Low resolution axial image
Used to visualize structural abnormalities: tumors, stroke damage, concussion/brain injury
Low spatial resolution, no temporal resolution
Position Emission Tomography (PET)
Highlight metabolically active brain areas
Inject carotid artery with positron emitting radionuclide (2-deoxyglucose)
- 2DG structurally similar to glucose and active cells take up more glucose
- 2DG can’t be metabolized so it accumulates in active cells
Positrons interact with electrons, produce gamma rays (photons)
Scanner detects photons and how many gamma rays are coming from a particular region
Indicates areas of activity during task (reading, speaking, remembering, etc.)
Axial images
No structural information
- Poor spatial resolution
- Co-registered with MRI
Can also identify non-activity measures
- Neurotransmitters, receptors, transporters, ions
Some spatial resolution, some temporal resolution (delay of 40 minutes - not a snapshot)
Magnetic Resonance Imaging (MRI)
High spatial resolution
Horizontal, coronal, and sagittal planes
Expensive
No ferrous metal
Strong magnetic field passed through brain
- Aligns with hydrogen atoms
- Rf pulse causes hydrogen atoms to emit electromagnetic radiation
- Scanner detects emitted radiation
- Neural structures differ greatly in hydrogen atom density
High spatial resolution but no temporal resolution