brain imaging & imagining final

Brain Imaging & Imagining

James M. DeCarli, MPH, MPA, CHES

[email protected]

mailto:[email protected]

Overview

• Background– Review brain imaging

techniques– Strengths & weaknesses of

each

• Neural Foundations of Imagery

• Key Imaging Study– Evidence that seeing and

imagining are the same to the brain

• Additional Supportive Imagery Studies

Background

• Brief Review of Imaging Techniques

– Structural Imaging• X-Ray• Computerized Tomography (CT) Scan• Magnetic Resonance Imaging (MRI ) Scan

– Functional Imaging• Positron Emission Tomography (PET)• Functional Magnetic Resonance Imaging (fMRI)• Single Photon Emission Computerized Tomography ( SPECT)

Positron Emission Tomography (PET)

• PET measures emissions from radioactively labeled chemicals that have been injected into the bloodstream

• Uses this data to produce two- or three-dimensional images of the distribution of the chemicals throughout the brain and body.

Positron Emission Tomography (PET)

Strengths

• Moderate accuracy of localization

• Provides image of brain activity

• Chemical specificity• Not subject to magnetic

artifacts• Quiet -- verbal responses

allowed, motion not as devastating to analysis

Weaknesses

• Expensive to use• Radioactive material used• Invasive• Low time resolution (>1-

minute)

Magnetic Resonance Imaging (MRI)

• MRI uses magnetic fields and radio waves to produce high-quality two- or three dimensional images of brain structures without injecting radioactive tracers

Magnetic Resonance Imaging (MRI)

Strengths

• No X-rays or radioactive material is used

• Provides detailed view of the brain in different dimensions

• Safe, painless, non-invasive• No special preparation is

required from the patient (except the removal of all metal objects)

• Patients can eat or drink anything before the procedure

Weaknesses

• Expensive to use• Cannot be used in patients

with metallic devices, like pacemakers

• Cannot be used with uncooperative patients because the patient must lie still

• Cannot be used with patients who are claustrophobic (afraid of small places). However, new MRI systems with a more open design are now available

Functional MRI (fMRI)

• Functional magnetic resonance imaging (fMRI) uses magnetic resonance imaging to measure the quick, tiny metabolic changes that take place in an active part of the brain

Functional MRI (fMRI)

Strengths• Cheaper, more accessible• Better spatial and

temporal resolution• Noninvasive• Does not require

injections of radioactive isotopes

• Imaging of oxygen

Weaknesses• Low time resolution

(around 8-seconds) • Poor anatomical definition• Movement sensitive

Neural Foundations of Imagery

• Stephen Kosslyn (Key researcher on Imagery)– Defines Imagery as a basic form of cognition– Plays a central role in numerous human activities

• Problem solving• Navigation to memory

– Imagery occurs when perceptual information is retrieved from long-term memory• Results in subjective impression of “seeing with the mind’s

eye” (Kosslyn, 2004)

Neural Foundations of Imagery

• Neuroimaging techniques (PET, MRI, fMRI, etc.) provide effective methods:

• Test theory of imagery on humans• Imaging studies suggest

– Mental imagery draw on the same neural functions as perception

– Engages similar mechanisms used in memory, motor control and emotion

Imagery Study

• Kosslyn, et al (2004)

• Assessed the degree of shared neural processing in visual mental imagery and visual perception

Imagery StudyMethodology

• Subjects:– 20 volunteers

• 8 male• 12 female• Mean age 21 years

– Normal or corrected-to-normal vision

– Right handed– No history of

neurological disease

• Scanning Procedures:– Standard fMRI

• Stimuli– 96 line drawings of

common objects– Two sets

• Imagery Scans• Perception Scans

Imagery StudyImagery Scan

• Subjects asked to close eyes

• Room lights off• Subjects presented by

auditory probe, with a name of a picture– Asked to generate the

corresponding visual mental image

Imagery StudyPerception Scan

• Subjects asked to keep eyes open

• Room lights on• Subjects presented

auditory probe with a line drawing of the named object shown on a screen after the auditory probe

Imagery StudyPerformance Results

• Subjects pressed one of two keys in response to the probe, then asked not to press the key if not understood

• No responses– 20.6% imagery missed– 5.2% perception missed

• Responses– 96.2 imagery– 97.3 perception

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No Response Response

Imagery

Perception

Imagery StudyfMRI Results

• Various brain regions activated– visual perception– visual imagery

• Pattern of activation in both imagery and perception were similar– However similarity was not uniform across brain regions

• Similarity– Greatest

• Frontal & parietal cortex– Smallest

• Occipital cortex

Imagery StudyImagery & Perceptual Activation Results

in Frontal Cortex

Reliable Activation (Positive Changes)

Negative Activation (Negative Changes)

Overlap

•Inferior frontal gyrus•Middle frontal gyrus•Superior frontal gyrus•Medial frontal gyrus•Insular cortex•Precentral gyrus•Anterior cingulate gyrus

•Medial frontal cortex•Superior frontal cortex•Anterior cingulate

•In all frontal areas

Sagital View: Illustrates position of each section

Grey area:(Z score)Significant overlap

Activation Map:

Coronal sections of the brain


in Parietal CortexReliable Activation (Positive Changes)


Overlap

•Left angular gyrus•Supramarginal gyrus

–Inferior parietal lobule

•Superior parietal lobule•Precuneus•Postcentral gyrus•Middle cingulate•Posterior cingulate

•Right supramarginal gyrus

• Precuneus•Left angular gyrus•Supramarginal gyrus•Inferior parietal lobule•Superior parietal lobule•Postcentral gyrus



Activation Map:

Pattern of similarity in parietal

& temporal regions


in Temporal CortexReliable Activation (Positive Changes)


Overlap

•Fusiform gyrus•Parahippocampal gyrus•Inferior temporal gyrus •Middle temporal gyrus•Superior temporal gyrus•Transverse temporal gyrus

•Right middle temporal gyrus•Right superior temporal gyrus

• Transverse temporal gyrus•Superior temporal gyrus•Left middle temporal gyrus


Activation Map:

Pattern of similarity in parietal & occipital regions


Kosslyn’s Conclusion

• Results suggest that visual images & visual perception draw on similar neural regions

• Overlap is not uniform:– “Visual imagery & visual perception appear to

engage frontal and parietal regions” more similarly than occipital and temporal regions• Indicates that “cognitive control processes function

similarly in both imagery and perception”

Additional Brain Imaging & Imagery Studies

• Preston, et al (2002)

• Investigated neural substrates of cognitive empathy by using emotional imagery paradigm

• Subjects: 11

• Procedure: PET

• Stimuli: Subjects imagined an emotional experience (fear of anger) from their past or a hypothetical situation form another subject

• Results: Similar brain activation between personal and hypothetical imagery


• O’Craven & Kanwisher (2000)

• Tested if specific regions of the extrastriate cortex activated during mental imagery depend on the content of the image

• Subjects: 8

• Procedure: fMRI

• Stimuli: Photographs of faces and familiar places via imagery & perception scans

• Results:– Imagery and perception share common processing neural

mechanisms– Specific brain regions activated during mental imagery depend on

the content of visual image


• Downs, et al (1999)

• Examined neural mechanisms involved in imagined self-rotation in a task that involved spatially updating the positions of objects

• Subjects: 10

• Procedure: fMRI

• Stimuli: – Before scanning: Memorize positions of 4-objects– During scan:

• 1) no visual input, • 2) test question-“rotate 90?, what’s on the right?” • 3) Control question-“rotate 0?, what’s on the right”

• Results: Imagined self-movement involves many of the same brain areas as physical-movement

Summary

• Function imaging techniques, such as PET and fMRI have made it possible to demonstrate that specific brain regions are activated similarly between:– Visual imagery & visual perception– Fear & hypothetical emotions– Imagined rotations of self & objects

• Application– While Stephen Kosslyn studies find that 90% of the brain

regions used for imagining visual images are the same ones used in actually seeing them:• Therapeutic application (due to many psychological

approaches integrating visualization as a way of healing):– Relearning from traumatic memories– Flooding to heal phobias

brain imaging & imagining final

Documents

positron emission

mental imagery

perceptual

visual imagery

neural foundations

sagital view

fmri stimuli

amp