fmri - what is it? then: example of fmri in face processing psychology 355: cognitive psychology...
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fMRI - What Is It?
Then: Example of fMRI in Face Processing
Psychology 355: Cognitive Psychology
Instructor: John Miyamoto
04/06/2015: Lecture 02-1
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Outline
• Brief review of single cell recordings & ERP
• fMRI - What is it?
• Application of fMRI to face perception.
Psych 355, Miyamoto, Spr '15 2Reminder - What Are Single Cell Recordings?
Single Cell Recordings
• The firing rate of individual neurons is measured by means of single cell recordings.
Psych 355, Miyamoto, Spr '15 3Strengths and Weaknesses of Single Cell Recordings
Strengths and Weaknesses of Single Cell Recording Methods
Strengths
• Excellent spatial resolution – the scientist has a very good idea where the recording is located in the brain.
• Excellent temporal resolution – the scientist knows when the neuron fires to a high level of precision.
Drawbacks
• Practically difficult to record from more than a small number of cells at a given time, e.g., 15 to 20 cells simultaneously.
• The method is very invasive.
Psych 355, Miyamoto, Spr '15 4Strengths & Weaknesses of Event-Related Potentials (ERP’s)
Event-Related Potentials (ERP’s)
• Strengths and weaknesses of ERP’s as research tool. ♦ Poor spatial resolution. ♦ Excellent temporal resolution. ♦ Relatively non-invasive. ♦ Sketchy understanding of the brain processes
that are producing the EEG signal.
Psych 355, Miyamoto, Spr '15 5Functional Magnetic Resonance Imaging (fMRI)
Psych 355, Miyamoto, Spr '15 6
fMRI Uses a Big Magnet
This images is used with permission of the author, J. J. B. Allen at the University of Arizona.
Graphic Showing BOLD Contrast
Psych 355, Miyamoto, Spr '15 7
ControlCondition
TestCondition
Measuring Activation – A Subtraction Measure
Brain Activity = Oxygen Concentration in Test Condition
MINUS
Oxygen Concentration in Control Condition
Details of fMRI Measurement
OxygenatedBlood
DeoxygenatedBlood
How Does fMRI Measure Brain Activity
Local neuronal activity
Increased local metabolic rate
Increased blood flow
Increased oxygenated hemoglobin
Uptake of O2 less than supply
Decreased concentrations of deoxyhemoglobin
Increased local fMRI T2* signal (electromagnetic signal)
• BOLD response – Blood Oxygenated Level-Dependent response
(the response is dependent on the level of oxygenated blood)
• A.k.a. hemodynamic response (response observed in the blood over time)
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ControlCondition
TestCondition
Define "Voxel" - The Voxels are Arranged along a "Slice" of the Brain
Different Slices of the Brain
• fMRI creates an image of brain activity within a slice of the brain.
• See images at <http://faculty.washington.edu/chudler/slice.html>.
• "Voxel" - a rectangular volume within a slice of the brain.
• fMRI detects changes in the BOLD response within each voxelalong a slice of the brain.
Psych 355, Miyamoto, Spr '15 9Strengths and Weaknesses of fMRI
Strengths and Weaknesses of fMRI Measures of Brain Activity
• Excellent spatial resolution ♦ Magnetic changes can be measured
at a resolution of 1 - 3mm³.
• Temporal resolution is poor.♦ In the 1990’s the temporal resolution
was about 4 seconds.♦ Today the temporal resolution is about 2 seconds.
• MRI machines impose physical limitations on the subjects.
Psych 355, Miyamoto, Spr '15 10Example of fMRI Study of Face & Place Processing
Next: fMRI Evidence for Brain Areas for Processing Faces and Places
O'Craven, K., & Kanwisher, N. (2000). Mental imagery of faces and places activates corresponding stimulus-specific brain regions. Journal of Cognitive Neuroscience, 12, 1013-1023.
FFA: Fusiform face area. Specialized for faces.(“ventral occipito-temporal cortex”)
PPA: Parahippocampal place area. Specialized for representing location info.(“ventromedial cortical region”)
Psych 355, Miyamoto, Spr '15 11Graphic Showing Location of FFA & PPA
Psych 355, Miyamoto, Spr '15 12
Location of the fusiform face area and parahippocampal gyrus
• Graphic from the article: Haynes, J-D., & Rees, G. (2006). Decoding mental states from brain activity in humans. Nature Reviews Neuroscience, 7, 523-534.
Parahippocampal place area (PPA)
Fusiform face area (FFA)
Diagram of BrainHead Facing Left
fMRI Results for Face & Place Recognition
Graphic from http://labnic.unige.ch/nic/htms/fmri.html
O’Craven & Kanwisher – Research Hypotheses
• Research Goal: To test the claim that the fusiform face area is specialized for face perception.
• Prediction: FFA will be activated by face stimuli but not by location stimuli. PPA will be activated by location stimuli but not by face stimuli.
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Psych 355, Miyamoto, Spr '15 14
Subjects views a face or a place .
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
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Look at Just the Upper Half of this Graph
fMRI Study of Face and Place Perception
Psych 355, Miyamoto, Spr '15 15
Subjects views a face or a place .
Face stimulus activates FFA; place stimulus does not.
fMRI Study of Face and Place Perception
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
% S
igna
l Cha
nge
% S
igna
l Cha
nge
Look at Just the Lower Half of this Graph
Psych 355, Miyamoto, Spr '15 16
Subjects views a face or a place .
Place stimulus activates PPA; face stimulus does not.
fMRI Study of Face and Place Perception
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
% S
igna
l Cha
nge
% S
igna
l Cha
nge
Point Out that There Is a Double Dissociation
Psych 355, Miyamoto, Spr '15 17
Face and place stimuli have opposite effects on FFA and PPA.
Double dissociation! Supports claim that FFA serves face perception and PPA serves spatial perception
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info. Perception
% S
igna
l Cha
nge
% S
igna
l Cha
nge
Define Double Dissociation; Discuss Double Dissociation
fMRI Study of Face and Place Perception
Psych 355, Miyamoto, Spr '15 18
Double Dissociation in Neuropsychology
Suppose you are studying the function of two brain areas,
A and B. Physiological results exhibit a double dissociation
with respect to areas A and B if ...
(i) one class of stimuli activates area A and
fails to activate area B;
(ii) a different class of stimuli activates area B and
fails to activate area A.
Example: • Viewing faces activates FFA but not PPA;• Viewing places activates PPA but not FFA.
• Double dissociations are important because they provide evidence
for specialization of function. Return to Slide with fMRI Results that Display a Double Dissociation
Psych 355, Miyamoto, Spr '15 19
Face and place stimuli have opposite effects on FFA and PPA.
Double dissociation! Supports claim that FFA serves face perception and PPA serves spatial perception
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info. Perception
% S
igna
l Cha
nge
% S
igna
l Cha
nge
Mention Concept of Localization of Function
fMRI Study of Face and Place Perception
Localization of Function
• Specific functions are served by specific areas of the brain
• Cognitive functioning breaks down in specific ways when areas of the brain are damaged
• Brain imaging can identify areas of the brain that serve specific functions.
Psych 355, Miyamoto, Spr '15 20Summary & END
Summary
• Physiological methods in cognitive neuropsychology♦ Single cell recordings♦ Event-related potentials (ERP’s)♦ Functional magnetic resonance imaging (fMRI)
• Localization of function – identifying parts of the brain that are involved in processing specific types of stimuli or performing specific tasks.
• Double dissociation – demonstrating that the neural response is specific to particular types of stimuli or specific tasks.
Psych 355, Miyamoto, Spr '15 21END