Introduction to Cognitive Neuroscience – fMRI results in context

Doug Schultz

3-2-2017

Overview

• In-depth look at some examples of fMRI results– Fusiform face area (Kanwisher et al., 1997)– Subsequent memory effect

• (Brewer et al., 1998)• (Wagner et al., 1998)

– Extinction learning (Phelps et al., 2004)

• How do we localize brain function using fMRI?

• Is there a cortical region specifically involved in face perception?

Hypothesis

• Where in the brain would you look for a region specific to perceiving faces?

Visual processing streams

Where?

What?

Background

• Face recognition may rely on different brain areas than object recognition– Single unit recordings in macques– Implanted electrodes in epilepsy patients– Damage in occipitotemporal regions impairs

face recognition

• fMRI studies show larger responses to faces than objects– Other possible explanations

Experimental design

• Part I - Identify regions that respond to faces

• Part II – Faces vs. scrambled faces, faces vs houses

• Part III – Different orientation faces vs hands, 1-back task with faces and hands

Part I

• 20 participants, 5 removed for excessive motion

• Six 30s blocks• Each block had 45 stimuli (each

presented for 670ms)• Between each block was 20s of

fixation• Two runs of the task, results

averaged

Part I results

Part I results cont.

Experimental design

• Part I - Identify regions that respond to faces

• Part II – Faces vs. scrambled faces, faces vs houses

• Part III – Different orientation faces vs hands, 1-back task with faces and hands

Part II Design

• Blocks of faces and scrambled faces– Scrambled faces control for some of

the lower level visual features (luminance)

• Blocks of faces and houses– Tests if “face areas” are simply

responding to differences between stimuli within a similar category

Part II Results

Experimental Design

• Part I - Identify regions that respond to faces

• Part II – Faces vs. scrambled faces, faces vs houses

• Part III – Different orientation faces vs hands, 1-back task with faces and hands

Part III Design

• Blocks of faces and hands– Controls for face orientation and for

animate vs. inanimate

• Blocks of faces and hands used in a 1-back task– Controls for potential attention differences

between faces and other objects

One-back task

Time

Part II Results

Conclusions

• There is a region in the fusiform gyrus “FFA” that responds to faces– This effect is not explained by low level visual

features (luminance)– Effect not driven by different examples of a

larger category (Faces v Houses)– Effect not explained by animate vs inanimate

or faces capturing more attention

Other explanations?

• Think of another possible explanation that would explain the data

• Expertise?• Involvement in emotion?

• How do we remember events?• Application of event-related designs

Memory encoding background

• Left PFC is involved in semantic processing during encoding

• When semantic processes are interrupted, activity in the PFC and memory are decreased

• ERP results show that remembered words evoke a different type of activity than non-remembered words

• Medial temporal lobe seems to be important based on lesion data, but not consistently detected with fMRI

Block vs Event Related Designs

• Block designs average across a number of consecutive trials• Event-related designs allow researchers to identify individual

events and average across some variable of interest

Experimental Design I

• Block design• Participants are exposed to word lists that

are either semantically encoded (abstract or concrete) or non-semantically encoded (uppercase or lowercase)

• Periods of fixation between word list blocks

Experimental Design I

• Mini-example below

If the word is concrete raise your right hand, if it is abstract raise your left

hand

TREElovebirdTRUSTIf the word is lowercase raise your right hand, if it is uppercase raise your

left hand

HONESTtrucktalentPENCIL

Results I

Block designWords vs fixation

Block designSemantic vs nonsemantic

Event-relatedWords vs fixation

Experimental Design II

• Words are intermixed with fixations and participants are performing semantic encoding

• Listen to this word list and answer if the word is concrete or abstract (don’t write anything)

Experiment Design II

• Number 1-24 on a piece of paper• Do you remember the word?• How confident are you (high/low)?• Now we would specifically look at the words

you recognized (high confidence) and compare brain activity on the encoding trials for those words and compare it to the encoding trials when you didn’t remember the word

Results II

Results II

Conclusions

• Increased activity in PFC and parahippocampal gyrus at encoding predicts better memory

• Extensive semantic processing in PFC may organize these details in WM and pass that information to parahippocampal gyrus

More subsequent memory

• Convergent results from another group using picture stimuli

• How can we use fMRI to answer questions about specific neural circuits?

• Are findings with human subjects consistent with those from non-human animal models?

Extinction learning

Neural circuit supporting extinction

Homberg, 2012

Experimental Design

Acquisition Extinction Training Extinction Test

Day 1 Day 2

Results

Results

Orange = CS+ > CS-Blue = CS+ < CS-

Results

A. Amygdala activity greater during acquisition than during extinctionB. Timecourse of CS+ response during acquisition (red) and extinction (yellow)C. During extinction the degree of amygdala activity is correlated to the magnitude of the fear response

Results

A. Subgenual ACC responses during the experimentB. During extinction test (Day 2) the activity of the subgenual ACC is correlated to the magnitude of the fear response

Conclusions

• fMRI can be used to test hypotheses about the neural circuitry supporting a particular phenomenon

• Subgenual ACC appears to be involved in the extinction of fear responses (consistent with non-human animal studies)

• Impact of instructions/expectations?• Interpretation of fMRI signal decreases

Take-home messages

• fMRI is a powerful tool– Non-intrusive method to examine many parts of

the brain– Good spatial resolution, not great temporal

resolution

• Results should be interpreted carefully• It is important to use appropriate

procedures for the question being asked• Contrasts and comparisons are critical