Lecture 4 Flashcards
What are neuroanatomical techniques?
• The day-to–day of biopsychologists • “Seeing the forest for the trees” • General approaches vs specific approaches • Selecting level analysis – Molecular – Structural/anatomical – Functional • More detail not always beer – Neurons tightly packed • Differences in resolution • Total understanding can result only from convergence of studies at all levels
What are neural stains?
• Selective
– Stain some Mssue components
and not others
• Nucleus, ribosomes, cell membrane
• Preparing brain tissue – Perfusion
• Remove blood
– Hardening
• Freezing or paraffin embedding
– Slicing
• Microtome
– Mounting
• AlbumenWhat are golgi stains?
• Silver chromate stained neurons black • Not all neurons pick up stain • No intracellular details • Shapes and sized of neurons • First view of synapse – Cajal, Nobel Prize, Neuron Doctrine
What are missile stains?
• Penetrates all cells • Stains ribosomes • Soma visible – Can better quantify (esMmate) number of cells • First view of structures within neuron • Cresyl violet
What are 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
• Minutecellulardetails
– difficult to assess overall or general structure
• Scanning EM generates 3D images
What is tracing neural pathways?
• Identify pathways that connect structures
– Axon staining
• 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
What are contrast x-rays?
• Effective only if internal structures differ from their surroundings
– Differences in X-ray absorption
• Brain too many overlapping structures absorbing Xrays to same degree
– To stand out: radioopaque material into structure of interest
– Discovered by Moniz
• X-ray passed through brain onto photographic plate
• Angiography
– Dye injected into carotid artery
• Reveals enlarged or displaced blood
vessels
• Pneumoencephalography
– Air injected into CSF
• Identify enlarged and displaced ventricles
What are x-ray computed tomography (CT)?
• Early 1970s
• Computer assisted Xray
• 3-d view of brain
• Brain CT composed of 8-9 horizontal secMons
• Xray gun and detector rotate in apposiMon around head
• Not sharp image
– Low resoluMon axial image
• Used to visualize structural abnormalities: – Tumors
– Stroke damage
– Concussion/brain injury
What is a positron emission tomography (PET)?
• Highlight metabolically active brain areas
• Inject carotid artery with positron emiong radionuclide (eg. 2-deoxyglucose)
– 2-dg 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 photons (gamma rays)
• Scanner detects photons and how many gamma rays coming from particular region
• Indicates areas of acMvity during task (reading, speaking, remembering, etc.)
– No temporal resolution
• Axial images
• No structural informaMon
– Poor spatial resolution
– Coregistered with MRI
• Can also identify non activity measures
– Neurotransmitters
– Receptors
– Transporters
– Ions
What are magnetic resonance imaging (MRI)?
• High spatial resolution
• Horizontal, coronal and sagiRal planes
• Expensive $$$
• No ferrous metal
• Strong magneMc field passed through brain
– Aligns hydrogen atoms
– Rf pulse causes hydrogen atoms to
emit electromagnetic frequency
• Scanner detects emitted radiation
– Neural structures differ greatly in hydrogen atom density
What is an fMRI?
• Most influential tool in cog neuro
• Uses MRI methods
– Functional
– Structural
– Non invasive
• No injection
– 3D images of activity over brain
– High spatial resolution
– Poor temporal resolution; better than PET
• 2-6 sec delay
– AP msec
• BOLD response: Activity related-changes in blood flow
– Oxygenated blood accumulates in active areas
• Oxy and deoxy hemoglobin different magnetic moments
– Detect changes in blood oxygenation
• Hemodynamics
• Warning: pictures do not reflect changes in activity, they reflect changes in BOLD signal
What is diffusion tensor imaging (DTO)?
• Identify white matter tracts in brain
– Connections among structures
– Human “connectome” project
• Use MRI technology
• Water molecules move in same direction in white matter
– Outside of white matter water molecules diffuse randomly
• Example DTI findings:
– Alcohol degrades white matter
– Pre clinical AD deterioraMon of white matter
What is transcranial magnetic stimulation (TMS)?
• Disrupts neural activity by placing magnetic field under coil positioned over skull
– during cognitive and behavioural tasks
– Assess functions of different cortical areas
• Establish structure-function
• PET and fMRI correlate activity to task
• TDCS
– Apply current directly to scalp
• Noninvasive
• Intervention
– Mixed results
• Current quesMons: – Depth of effect
– Safety
– Exact mechanism of neural disruption
