FMRI - What Is It? Then: Example of fMRI in Face Processing Psychology 355: Cognitive Psychology Instructor: John Miyamoto 04/06 /2015: Lecture 02-1 This

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


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)


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


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

http://www.nature.com/nrn/journal/v7/n7/full/nrn1931.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.



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



Face stimulus activates FFA; place stimulus does not.







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Perception

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Look at Just the Lower Half of this Graph



Place stimulus activates PPA; face stimulus does not.







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Perception

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Point Out that There Is a Double Dissociation


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






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Define Double Dissociation; Discuss Double Dissociation



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


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






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Mention Concept of Localization of Function


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

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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 This