Neuroimaging Flashcards
Franz Josef Gall
Phrenology
Phrenology
Different parts of the brain have different function
brain areas can be overdeveloped, leading to skull bumps, indicating the faculties of an individual
Paul Broca
Found impairment with speech production
Broca’s area = left frontal lobe area
Karl Lashley
Law of mass action
Equipotentiality, all other regions of cortex take over function following damage
Too strong but related to modern underestanding of neuroplsaticity
Wilder Penfield
Treated epilepsy by stimulting cortex of and then showing what happens
Sensory: people feeling tingling, numbness, shocks
Motor: flexion of the wrist, could not hepl closing eyes, vocalizations
Penfield’s homunculi
in somatosensory cortex, people feel in different areas when you stimulate different areas of the cortex
2 Modern Methods of localizing function
TMS (trancranial magnetic stimulation)
Single neuron recording
TMS
Stimulating motor cortex using magnetic fields
can either suppress or amplify activity
Single neuron recording
hippocampus-entorhinal cortex circuit
implanted electrode which can see what makes neurons fire
neurons will fire differently based on stimulation, but is very invasive
3 methods of structural brain imaging
Angiography
Computed tomography (CT scan)
Magnetic resonance imaging (MRI)
Angiography
Contrast X-ray
radio-opaque dye into cerebral artery
locates vascular damage, large tumours, arteriosclerosis, aneurysms
CT scan
Rotates x-ray source and detector to reconstruct image based on density of tissue
uses algorithms to combine its images together, but is only as good as these algorithms
used for skull fractures, intracranial bleeds, tumours
cons: radiation exposure
MRI
- Aligning hydrogen with large magnetic fields
- momentarily pertrub alignment with second magnetic field
- measure radio frequency signal produced during realignment with large magnetic field
particular tissues will different signals because of more/less water content
good for: small/subtle lesions
3 methods of functional brain imaging
EEG (electroencephalography)
PET (positron emission tomography)
FMRI (functional MRI)
EEG
Looks at electrical activity in cerebral cortex with the net of electrodes on head
Electrical signals separated into different frequncies
used for epilepsy, delirium, encephalitis
not good for measuring deep brain structures
PET scan
Radioactive substance is injected
areas of brain that consume glucose will also consume tracer, which can then be tracked
useful for looking at specific systems or proteins, and for looking lifespan/condition and changes
expensive and has poor spatial imaging
fMRI
Most dominant
Checks BOLD response
Takes image and subtracts from another image to give us an isolated brain region
BOLD response
Blood Oxygen Level Dependent response
- neural activity triggers increase in bloodflow to brain region. binding to glutamate to astrocytes, triggering more blood to go to area
- more new blood temporarily changes the high-oxygen blood/low-oxygen blood ratio in this region, causing a change in magnetic property
- changes in magnetic properties of the brain region is visible in fMRI image
Challenges in interpreting fMRI
- Spatial averaging - epiphenomena
- temporal resolution - bloodchanges slower than electrical activity
- doesn’t tell us about causality - may mismatch lesion studies
- focuses on increases in activity and not on tonic activity
- testing environment - does not work for people who cannot stay still for extended periods
- replicability - need to make pipeline choices for different anatomy, filtering noise, multiple comparisons, etc.
Default mode network
Some regions are more active at “rest” than during goal oriented tests
maybe for inwardly focused attentional processes; construction of the sense of self
