the cognitive neuroscientist’s toolkitcs182/sp07/notes/rissman_cogneuromethods_final.pdfe = mc2...
TRANSCRIPT
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fMRILESION EEG/MEG
QuickTim
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ncompressed) decom
pressorare needed to see this picture.
PET TMS
The Cognitive Neuroscientist’s Toolkit
Jesse Rissman CS 182 Guest Lecture, 2/1/07
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Ventricular theory of brain function
* Anterior ventricle controls perception * Middle ventricle controls cognition * Posterior ventricle controls memory
Galen (129-200 AD)
A little history…
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Could he have been right?
Don’t believe everything you read in Glamour Magazine!
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Franz Joseph Gall(1758-1828)
Phrenology: the start of localizationism
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Mr. Burns: Who could forget such a monstrous visage? She has the sloping brow and cranial bumpage of the career criminal.”
Smithers: "Uh, Sir? Phrenology was dismissed as quackery 160 years ago.”
Mr. Burns: (measuring Smithers' head) "Of course you'd say that... you have the brainpan of a stagecoach tilter!"
Some people still believe in phrenology to this day.
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Lesions as tool to gain insight into brain function
Broca’sArea
The brain of patient “tan”
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Another landmark case
Carl Wernicke(1848-1904)
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Cytoarchitectonic Areas (Brodmann, early 1900s)
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Electrocortical Stimulation Mapping
the motor homunculus
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E = mc2
???
The First “Brain Imaging” Experiment
“[In Mosso’s experiments] the subject to be observed lay on a delicately balanced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in consequence of the redistribution of blood in his system.”
-- William James, Principles of Psychology (1890)
Angelo MossoItalian physiologist
(1846-1910)
… and probably the cheapest one too!
Source: Jody Culham’s fMRI for Dummies web site
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Positron Emission Tomography (PET)
• Subjects injected with radioactive isotope, which emits positrons• Positrons collide with electrons, emitting two photons (gamma rays) in
opposite directions• Detectors surrounding brain register simultaneous photons and compute
likely source• Neural activity ==> increased metabolic demand ==> local increase in
blood flow the active region
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PET• Compares regional cerebral blood
flow (rCBF) between cognitive states (experimental conditions)
• Integrates signal over 45-60 sec• Need to wait a number of half-lives
before next injection
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Listening to wordsPassively viewing words
Speaking words Generating verbs
Petersen et al. (1988). Positron emission tomographic studies of the cortical anatomy of single-word processing. Nature.
The first cognitive PET study
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PET: Pros and Cons
• PROs– Decent spatial
resolution (5-10mm3)– Can also measure
neurotransmitter metabolism.
– Can be used as a tool to aid in early diagnosis of disorders such as Alzheimer’s disease
• CONs– Invasive
(radioactive injection)
– Very expensive– Poor temporal
resolution– Cannot detect the
neural response to discrete cognitive events.
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MRI studies brain anatomy.Functional MRI (fMRI) studies brain function.
MRI vs. fMRI
Source: Jody Culham’s fMRI for Dummies web site
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Berkeley’s 4 Tesla Magnet1 Tesla (T) = 10,000 Gauss
Earth’s magnetic field = 0.5 Gauss
4 Tesla = 4 x 10,000 ÷ 0.5 = 80,000 X Earth’s magnetic field
B0
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Magnets attract metal objects
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Necessary Equipment
Magnet• very strong magnetic field
Gradient Coil• enables spatial encoding
Radio Frequency Coil• receives and transmits radio frequencies
Source for Photos: Joe Gati
RF Coil
giant magnet
gradient coil(inside)
fMRI for Dummies
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Very Basic MRI Physics
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MRI vs. fMRI
↑ neural activity ↑ blood oxygen ↑ fMRI signal
MRI fMRI
one image
many images (e.g., every 2 sec for 20-60 mins)
high resolution(1 mm)
low resolution(~3 mm but can be better)
fMRI Blood Oxygenation Level Dependent (BOLD) signal
indirect measure of neural activity
…
Source: Jody Culham’s fMRI for Dummies web site
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As the ratio of oxygenated to deoxygenated hemoglobin increased, BOLD fMRI signal increases
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Hemodynamic Response Function (HRF)
brief stimulus
peak BOLD response (4-6 sec post-stimulus)
signal decay
undershoot
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fMRI Setup
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A basic fMRI experimental design
• Subject is given sensory stimulation or task, interleaved with control or rest condition
• Acquire BOLD-sensitive MRI images during stimulation
• Analyze image timeseries to determine where signal changed in response to stimulation
PredictedBOLD signal
time
Stimuluspattern
on
off
on
off
on
off
on
offoff
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The first fMRI Experiment
Time
BrainActivity
Source: Kwong et al., 1992
Flickering CheckerboardOFF (60 s) - ON (60 s) -OFF (60 s) - ON (60 s) - OFF (60 s)
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W. W. Norton
BOLD signal change during presentation of static and moving visual stimuli
QuickTimeª and aTIFF (LZW) decompressor
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Blocked vs. Event-Related Designs
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Advantages of event-related designs
Wagner et al., 1998, Science
Characterize individual trials after-the-fact, based on the subject’s behavioral response
Blumenfeld et al., 2006 J Neuroscience
Correct trials vs. Incorrect trials
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Modularity vs. Networks
Functional Segregation
Functional Integration
Localization of category-specific visual processing regions
Statistical modeling of functional interactions between brain regions
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Diffusion Tensor Imaging (DTI)
• Water diffusion restricted along white matter pathways
• Tractography: tracing white matter pathways between gray matter regions
Tract-based connectivity
Color-coded directions
xy
z
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Can fMRI read your mind?
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The Era of Neuromarketing Has Begun
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A more reasonable example
O’Craven & Kanwisher, 2001FFAFFA- Fusiform Face Area- Fusiform Face AreaPPAPPA- Parahippocampal Place Area- Parahippocampal Place Area
FFAPPA
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But we still have a long way to go
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Spatial and Temporal Resolution
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Single-unit recording:Identifying neuronal receptive fields
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Memory Cells in the Prefrontal Cortex
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A Face Area in the Monkey Brain
An area of the monkey’s brain that responds to faces
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A Halle Berry neuron?
Quiroga et al., 2005, Nature
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Electroencephalography (EEG)
• fMRI does not provide precise info about the timing of neural activity.
• Single-unit recordings can only measure activity in one brain region at a time.
• EEG can record electrical potentials of large populations of simultaneously active neurons at the scalp with millisecond resolution.
• Plus, EEG is a direct measure of neural activity.
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W. W. Norton
Arousal states of the brain: characteristic waveform patterns
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What about electrical activity for specific cognitive events?
Event-Related Potentials (ERPs)
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ERP example:The face-sensitive N170
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Magnetoencephalography (MEG)
SQUID Array:64 to 275 Sensing Locations
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Cortical surface rendering of MEG activity
Gonsalves et al. (2005) Neuron
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Electrocorticography (ECoG):Direct recordings from the cortical surface
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Transcranial Magnetic Stimulation (TMS)
• Brief powerful (several thousand amperes) electrical charge is created in coil
• Creates a 1.5-2.0 Tesla magnetic field capable of inducing eddy currents in tissue 1-2 cm deep
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Transcranial Magnetic Stimulation (TMS)
– Disrupts normal neural function by adding noise
– In essence, TMS creates a temporary “virtual patient”
– Unlike fMRI and PET, TMS can assess the causal influence of a region on behavior.
– Unlike naturally-occurring lesions, TMS gives the researcher more control, better temporal resolution, and the ability to create multiple virtual patients in the same individual.
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Safety Issues
• Generally thought to be free from harmful effects
• Examination of brain tissue submitted to thousands of TMS pulses has shown no detectable structural changes
• It is possible in unusual circumstances to trigger a seizure in healthy subjects, but using the proper guidelines eliminates this risk
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A simple TMS experiment
• Coil placed over target brain region• Cognitive failures recorded
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Real lesion
Blue = sighted; Red = early blind
Cohen et al., 1997. Occipital TMS disrupts braille reading in early blind, but not control subjects
Hamilton et al., 2000. Reported case of blind woman who lost ability to read braille following bilateral occipital lesions
Establishing causal links between brain activity and behavior
TMS “lesion”
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fMRI-guided TMS stimulation
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Converging Methodolgies: fMRI guided-TMS/ERP
FFA
PFC)))TM
SEEG
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