using pet. we ’ ve seen how pet measures brain activity we ’ ve seen how pet measures brain...

Using PETUsing PET

Using PETUsing PET

We’ve seen how PET measures We’ve seen how PET measures brain activitybrain activity

How can we use it to measure the How can we use it to measure the “mind” that works in the brain?“mind” that works in the brain?

Mapping mental functions in the Mapping mental functions in the brainbrain

Measuring MindMeasuring Mind

Classically, mental functions have Classically, mental functions have been measured behaviorally been measured behaviorally using the Donders (1850) methodusing the Donders (1850) method

Mental chronometry: mental Mental chronometry: mental processes can be measured by processes can be measured by the time it takes to perform themthe time it takes to perform them

Measuring MindMeasuring Mind Simple response time: “press a Simple response time: “press a

key as quickly as possible in key as quickly as possible in response to a light or sound”response to a light or sound”

Discrimination response time: Discrimination response time: “press a key when you see light A “press a key when you see light A but not light B”but not light B”

Time it takes to discriminate Time it takes to discriminate between 2 lights = Task 2 – Task between 2 lights = Task 2 – Task 11


Subtractive method:Subtractive method:Using tasks that are “exactly the Using tasks that are “exactly the same” but differ only in the same” but differ only in the particular function of interestparticular function of interest

Adopted by PET (and fMRI) Adopted by PET (and fMRI) researchresearch

Activation of baseline is Activation of baseline is subtracted from tasksubtracted from task


Difference map is calculated for Difference map is calculated for each subjecteach subject

Supposed to reflect brain activity Supposed to reflect brain activity related to the function of interestrelated to the function of interest


Great individual differences in brain anatomyGreat individual differences in brain anatomy An average difference image is computedAn average difference image is computed

Example: Visual Example: Visual SystemSystem

Retinotopic Retinotopic maps in visual maps in visual cortexcortex

Upper vs Lower Upper vs Lower visual fieldsvisual fields

EccentricityEccentricity


Fovea

Periphery

Upper visual field

Lower visual field


Color visionColor visionSubjects watched black/white or Subjects watched black/white or color versions of same picturescolor versions of same pictures

Same visual processing apart from Same visual processing apart from colorcolor

Test Baseline


a) w/o subtraction, b) color – gray, c) p values, d) most significant


Motion: Moving squares vs. staticMotion: Moving squares vs. static


Color and Motion AreasColor and Motion Areas

Illusory contoursIllusory contours

Does perceiving illusory contours Does perceiving illusory contours require higher order cognitive require higher order cognitive processes?processes?

Or, is it processed at the earliest Or, is it processed at the earliest levels of vision only? levels of vision only?

PET: If higher-order then activity PET: If higher-order then activity at areas other than visual cortex.at areas other than visual cortex.

Illusory contoursIllusory contours

Subjects viewed either A & C, or B & CSubjects viewed either A & C, or B & C 6 scans for every condition6 scans for every condition In every scan one picture for 95 secIn every scan one picture for 95 sec Difference between test and control Difference between test and control

was calculated for each subjectwas calculated for each subject

Illusory contoursIllusory contoursOnly V2 (V3) Only V2 (V3)

was activated was activated more in more in illusory illusory contours than contours than in controlin control

No significant No significant difference difference between real between real and illusory and illusory trianglestriangles

Example: Illusory Example: Illusory MotionMotion

Example: Illusory Example: Illusory MotionMotion Enigma. Motion illusionEnigma. Motion illusion

PET shows activity in an area PET shows activity in an area contiguous and overlapping V5contiguous and overlapping V5

Words in the brainWords in the brain

Visual & auditory processing, speech production, meaning


Passively viewing words

Listening to words


Speaking words aloud [motor cortex, SMA, cerebellum, insula, no Wernicke (!?)]

Generating verbs [left frontal, a. cing, p. tempor, r. cerebellum]

A PET image of A PET image of intelligenceintelligence??

In intelligence tests, people who score In intelligence tests, people who score highly in one area (logic, verbal, math, highly in one area (logic, verbal, math, spatial, etc.) usually have high scores spatial, etc.) usually have high scores in the other areas.in the other areas.

General (G) factorGeneral (G) factor Is the G factor related to a special Is the G factor related to a special

function or does it just reflect the function or does it just reflect the system’s efficiency?system’s efficiency?

Is there a brain site for intelligence, or Is there a brain site for intelligence, or is it a characteristic of the whole is it a characteristic of the whole system?system?

A PET image of A PET image of intelligenceintelligence?? Duncan et al, Duncan et al,

Science (2000)Science (2000) Spatial & verbal Spatial & verbal

teststests High and low High and low

correlation to Gcorrelation to G Test similar in Test similar in

their visual and their visual and motor demands to motor demands to separate the separate the activity related to activity related to G from the restG from the rest

Lateral Lateral prefrontal cortex prefrontal cortex was activated in was activated in both high G both high G tests and not tests and not the low Gthe low G

Researchers Researchers concluded:concluded:G factor relates G factor relates to a specific to a specific neural systemneural system

A PET image of A PET image of intelligenceintelligence??

R.R. Lanzenberger et al. BIOL PSYCHIATRY 2007;61:1081–1089

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