using pet. we ’ ve seen how pet measures brain activity we ’ ve seen how pet measures brain...
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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
Measuring MindMeasuring Mind
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
Measuring MindMeasuring Mind
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
Measuring MindMeasuring Mind
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
Example: Visual Example: Visual SystemSystem
Fovea
Periphery
Upper visual field
Lower visual field
Example: Visual Example: Visual SystemSystem
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
Example: Visual Example: Visual SystemSystem
a) w/o subtraction, b) color – gray, c) p values, d) most significant
Example: Visual Example: Visual SystemSystem
Motion: Moving squares vs. staticMotion: Moving squares vs. static
Example: Visual Example: Visual SystemSystem
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
Words in the brainWords in the brain
Words in the brainWords in the brain
Passively viewing words
Listening to words
Words in the brainWords in the brain
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