Using PET

We ’ ve seen how PET measures brain activity We ’ ve seen how PET measures brain activity How can we use it to measure the “ mind ” that works in the brain? How can we use it to measure the “ mind ” that works in the brain? Mapping mental functions in the brain Mapping mental functions in the brain

Measuring Mind Classically, mental functions have been measured behaviorally using the Donders (1850) method Classically, mental functions have been measured behaviorally using the Donders (1850) method Mental chronometry: mental processes can be measured by the time it takes to perform them Mental chronometry: mental processes can be measured by the time it takes to perform them

Measuring Mind Simple response time: “ press a key as quickly as possible in response to a light or sound ” Simple response time: “ press a key as quickly as possible in response to a light or sound ” Discrimination response time: “ press a key when you see light A but not light B ” Discrimination response time: “ press a key when you see light A but not light B ” Time it takes to discriminate between 2 lights = Task 2 – Task 1 Time it takes to discriminate between 2 lights = Task 2 – Task 1

Measuring Mind Subtractive method: Using tasks that are “ exactly the same ” but differ only in the particular function of interest Subtractive method: Using tasks that are “ exactly the same ” but differ only in the particular function of interest Adopted by PET (and fMRI) research Adopted by PET (and fMRI) research Activation of baseline is subtracted from task Activation of baseline is subtracted from task

Measuring Mind Difference map is calculated for each subject Difference map is calculated for each subject Supposed to reflect brain activity related to the function of interest Supposed to reflect brain activity related to the function of interest

Measuring Mind Great individual differences in brain anatomy Great individual differences in brain anatomy An average difference image is computed An average difference image is computed

Example: Visual System Retinotopic maps in visual cortex Retinotopic maps in visual cortex Upper vs Lower visual fields Upper vs Lower visual fields Eccentricity Eccentricity

Example: Visual System Fovea Periphery Upper visual fieldLower visual field

Example: Visual System Color vision Subjects watched black/white or color versions of same pictures Color vision Subjects watched black/white or color versions of same pictures Same visual processing apart from color Same visual processing apart from color TestBaseline

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

Example: Visual System Motion: Moving squares vs. static Motion: Moving squares vs. static

Example: Visual System Color and Motion Areas Color and Motion Areas

Illusory contours Does perceiving illusory contours require higher order cognitive processes? Does perceiving illusory contours require higher order cognitive processes? Or, is it processed at the earliest levels of vision only? Or, is it processed at the earliest levels of vision only? PET: If higher-order then activity at areas other than visual cortex. PET: If higher-order then activity at areas other than visual cortex.

Illusory contours Subjects viewed either A & C, or B & C Subjects viewed either A & C, or B & C 6 scans for every condition 6 scans for every condition In every scan one picture for 95 sec In every scan one picture for 95 sec Difference between test and control was calculated for each subject Difference between test and control was calculated for each subject

Illusory contours Only V2 (V3) was activated more in illusory contours than in control No significant difference between real and illusory triangles

Example: Illusory Motion

Enigma. Motion illusion Enigma. Motion illusion PET shows activity in an area contiguous and overlapping V5 PET shows activity in an area contiguous and overlapping V5

Words in the brain Visual & auditory processing, speech production, meaning

Words in the brain

Passively viewing words Listening to words

Words 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 intelligence? In intelligence tests, people who score highly in one area (logic, verbal, math, spatial, etc.) usually have high scores in the other areas. In intelligence tests, people who score highly in one area (logic, verbal, math, spatial, etc.) usually have high scores in the other areas. General (G) factor General (G) factor Is the G factor related to a special function or does it just reflect the system ’ s efficiency? Is the G factor related to a special function or does it just reflect the system ’ s efficiency? Is there a brain site for intelligence, or is it a characteristic of the whole system? Is there a brain site for intelligence, or is it a characteristic of the whole system?

A PET image of intelligence? Duncan et al, Science (2000) Duncan et al, Science (2000) Spatial & verbal tests Spatial & verbal tests High and low correlation to G High and low correlation to G Test similar in their visual and motor demands to separate the activity related to G from the rest Test similar in their visual and motor demands to separate the activity related to G from the rest

Lateral prefrontal cortex was activated in both high G tests and not the low G Researchers concluded: G factor relates to a specific neural system A PET image of intelligence?

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