Book: the imaged brain 2

What are the main problems with cognitive subtraction?

Regions of activity need to be compared to an appropriate baseline 1) Assumption of "pure insertion" i.e. adding a task/extra component does not affect the operation of earlier components, however this ignores interaction effects. 2) So a baseline task is

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Name 3 other methods in addition to cognitive subtraction

Cognitive conjunctions/factorial design, Parametric design, Functional integration

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What is the advantage of cognitive conjunction over cognitive subtraction?

Baseline task still needed, but risk of interaction effect is reduced

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How does cognitive conjunction design work?

CC requires set of tasks that have a particular component in common. Then look for regions of activation that are shared across several different subtractions, rather than relying on one single subtraction

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Give an example of cognitive conjunction/factorial design

Why can't we tickle ourselves (Blackmore et al 98). 2 factors: touch (felt/not) and self-mvt (moved/not)

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What is the parametric design?

Variable is continuous not categorical i.e. brain associations not differences

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what is the functional integration design?

how different regions communicate with each other e.g. task shows 'effective connectivity' cf specialisation

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which is the best design for one factor?

parametric or cognitive subtraction

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Pro and con of blocked design?

Pro: strong BOLD contrast, high signal to noise, simple design; Con: practice/fatigue effect

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Pro and con of event-related design?

Pro: No practive/fatigue effect; Con: weaker BOLD contrast, lower signal-to-noise, complex design

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what is meant by a 'session'?

A scanning session; all the data collected from the participant. Usually a structural scan and few functional scans

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What is meant by a 'run'?

A continuous period of scanning, consists of a specified number of volumes

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What is meant by a 'volume'? (image)

Set of slices taken in succession: a 3D spatial image with a temporal dimension. Expressed in TR

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What is meant by an 'epoch'?

a period when a certain condition is presented. Epochs can be grouped (blocked) or random (event-related)

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5 stages when analysing fMRI data

1) individual differences; averaging over many participants 2) correction for head movement 3) stereotactic normalisation 4) smoothing 5) statistical comparison

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What is stereotactic normalisation?

the mapping of individual differences in brain anatomy onto a standard template

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what is smoothing?

redistributing brain activity from neighbouring voxels on the assumption that cognition does not occur in single voxels. This enhances signal-to-noise ratio

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List the three issues implicated in interpretation

1) Inhibition v excitation 2) activation v deactivation 3) Necessity v sufficiency

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What is the issue of inhibition v excitation?

Activity can be inhibitory or excitatory i.e. an inhibited region could be mistaken as a region of activity

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What is the issue of activation v deactivation?

Merely refers to a difference between two conditions; doesn't suggest any direction

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what is the issue of necessity v sufficiency?

Are active regions critical to the task?

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Why should we be cautious with fMRI?

Can only show correlational not causal evidence of brain activity. Rare for single area to be implicated; when more than one task then hard to say which area is critical to task

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Book: the imaged brain 2

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