Neuroimaging Flashcards
What was the major contribution of FRANZ JOSEF GALL?
idea of PHRENOLOGY
- different parts of brain = different functions
- brain areas can be overdeveloped = skull bumps
- bumps indicate faculties (personality) of individual
What was the major contribution of KARL LASHLEY?
idea of LAW OF MASS ACTION (more cortex = better)
- trained rats on task -> cut cortex -> see task performance again
- large lesion = large impairment, regardless of location
- EQUIPOTENTIALITY: other regions of cortex take over functions following damage
What was the major contribution of PAUL BROCA?
localization in HUMAN!
- following stroke M. Leborgne only say 1 word
- had intact comprehension but impairment speech production
- discovered left frontal lobe LESION = broca’s area
What was the major contribution of WILDER PENFIELD?
developed method to treat epilepsy
- directly stimulating cortex of awake patients to make surgical decisions
- created penfield’s homunculi (electrical stimulation correlates to different physical & somatory sensations)
What are the 2 modern methods of localizing function that involve stimulating brain activity?
- Transcranial Magnetic Stimulation (TMS): can stimulate/suppress cortical activity
- Single-neuron Recording: patients implanted w/ electrode (prior to epilepsy surgery)
What are the 3 methods of STRUCTURAL brain imaging?
- Cerebral Angiography - blood vessels
- Computed Tomography (CT) - strokes, tumors, and traumatic injuries.
- Magnetic Resonance Imaging (MRI) - soft tissue abnormalities like tumors and neurodegenerative diseases
What is CEREBRAL ANGIOGRAPHY (structural brain imaging)?
contrast x-ray, use radio-opaque dye into cerebral artery
used to locate:
- vascular damage
- large tumours
- arteriosclerosis (narrowing of blood vessels)
- aneurisms
What is COMPUTED TOMOGRAPHY (CT) (structural brain imaging)?
version of x-ray, rotates x-ray source & detector to reconstruct image on density of tissue (fat vs tissue vs bone)
used for:
- skull fracture
- intracranial bleeds
- tumours
pros: quick, inexpensive
cons: radiation exposure
What is MAGNETIC RESONANCE IMAGING (MRI) (structural brain imaging)?
both vary in hydrogen & oxygen content
used for:
- small/subtle lesions
- conditions affecting white matter
How does an MRI machine work?
- align all protons w/ large magnetic field
- momentarily perturb (knock down) alignment w/ second magnetic field
- measure radiofrequency (RF) signal produced during realignment w/ large magnetic field
*changing properties of pulse sequence, further enhance differences b/w gray vs white matter, brain vs CSF
pro: spatial resolution
con: slow, expensive, exclude patients w/ pacemakers
What is the MRI: Diffusion Tensor Imaging (DTI)?
variant of MRI, relies on how water molecules move in brain
pros: good for network connectivity & white matter
cons: expensive; computationally complex
What are the 3 methods of FUNCTIONAL brain imaging?
- Electroencephalography (EEG)
- Position Emission Tomography (PET)
- Functional MRI (fMRI)
What is ELECTROENCEPHALOGRAPHY (EEG) (functional brain imaging)?
electrodes on scalp surface detect electrical activity in cerebral cortex
electrical signals can be statistically separated into different frequencies
used for:
- epilepsy
- delirium
- encephalitis
pros: quick, inexpensive, high temporal resolution
cons: hard to measure deep brain structures, low spatial resolution
What is POSITRON EMISSION TOMOGRAPHY (PET) (functional brain imaging)?
radioactively labelled substance is injected & imaged (ie. active brain areas consume more fuel)
less common w/ rise of fMRI
pros: useful for looking at specific systems/proteins, also lifespan/condition changes
cons: expensive, poor spatial resolution
What is fMRI (functional brain imaging)?
dominates cognitive neuroscience, BOLD response
paired image subtraction:
1. task of interest: remembering learned words
b/w 1-2 bilateral hippocampi, left posterior STG, left caudate LIGHT UP
- stuff we want to control out: motor components of speech, visually reading something on screen, hearing loud MRI sounds,etc
What is the BOLD response in fMRI?
BOLD = Blood Oxygen Level Dependent Response
- neural activity triggers increase in blood flow to brain region (functional hyperaemia)
- increased ratio of high-oxygen blood : low-oxygen blood (oxyhaemoglobin (new): deoxyhaemoglobin (old))
- changes in magnetic properites of brain region -> visible in fMRI image
What are challenges in collecting & interpreting fMRI data?
- spatial averaging (over trials & over subject)
- temporal resolution (blood changes slower than electrical activity, may miss brief but important events)
- doesn’t tell us about causality (sometimes mismatches lesion studies, sites can be activated by connections)
- focus on increases in activity (important but tonic activity subtracted out)
- testing environment (anxiety, children, movement, lying down)
- replicability & statistic flexibility (need make pipeline choices for different ppl)
What is the default mode network?
some regions more active AT REST than during goal-oriented tasks
may be for inwardly-focused attentional processes; construction of the “sense of self”
areas:
- medial prefrontal cortex, posterior cingulate cortex, angular gyrus/lateral parietal cortex
