Experimental Designs

Why do we have to find a relative difference between baseline brain activity and activitty during a task?

because the brain is always active; if we dont know where we are starting, we cannot be sure that the activity during a task is truly from engaging with the task

Cognitive Subtractions Definition

a type of experimental design in functional imaging in which activity in a control task is subtracted from activity in an experimental task

Petersen et al. cognitive subtraction example study

utilized cognitive subtraction to examine if  there were brain regions specialized for the processing of written and spoken words

3 processes Petersen studied

• Recognizing written words

• Saying the words

• Retrieving the meaning of the word

How did petersen evaluate processing written words?

• Petersen et al. had the participant passively view the word "cake" and then passively view a cross (+)

• Passively viewing these two stimuli can cancel out/subtract areas of the brain involved with visual processing, and the remaining active brain regions are suspected to be used for understanding the word cake

How did petersen evaluate processing saying words?

• Petersen et al. had participants passively read the word "cake" and then say "cake" aloud

• Both trials involved reading the word cake, but only one involved saying it out loud, meaning the remaining brain activity would be for saying the word

How did petersen evaluate retrieving meaning?

• Petersen et al. had participants read "Cake" in both trials, but then say either "eat" (an associated word) or say "cake" out loud

• The remaining brain activity is assumed to represent semantic associations

Pure Insertion Definition

the assumption that adding a different component to a task does not change the operation of other components

How did pure insertion affect Petersen’s study?

It was assumed that the only difference between reading "cake" and viewing the cross was that one was a word, however different brain processes may be present when understanding a more complex stimuli (cake) than a simple one (a cross)

How do interaction effects affect cognitive subtraction studies?

Cognitive subtraction assumes that a cognitive component can be added on to a task without changing the other components in the task, however we know this is not true as interaction effects exist

Factorial Designs help reduce what?

they help decuce interaction effects by addressing the effects of multiple factors

What is a parametric design?

a correlational study

Price et al. Parametric Study example

• wanted to know which brain regions activated depending on rate of speech

• found that areas involved in auditory processing experienced more activity as rate of speech sped up

• wernicke’s area did not have more activity

• working memory regions sped up a bit, and then declined when speech got too fast to process

What is parametric modulation?

looking for variables that modeate one another; as ___ goes up, ___ also increases

Functional Specialization Definition

when a region responds to a limited range of stimuli/conditions and that this distinguishes it from the responsiveness of other neighbouring regions

Functional Integration Definition

the way in which different regions communicate with each other; used to infer functional connectivity

What is the Resting State Paradigm?

a technique for measuring functional connectivity in which correlations between several regions are assessed while the participant is not performing any tasks

The resting state paradigm led to the discovery of what functional network?

the default mode network

5 aspects of a good study design

• measures a specific cognitive function (decision-making)

• sets up an experimental condition (choice response)

• sets up a control condition (simple response)

• measures a baseline if necessary

• has a concrete way for participants to show that they are responding to the stimulus (pressing a button)

What are perceptual control problems?

• these occur when the presentation of stimuli is not consistent and creates control issues

  • the stimuli in the experimental and control groups are different sizes even when they shouldn’t be

What are conceptual control problems?

• do the different conditions measure the same aspect concept other than the variable of interest?

• do participants understand how to properly complete the task?

What are Strategy Effects?

effects that occur when a participant does not use the typical strategy for completing your experimental task

What is a common problem with functional imaging in regard to the patient’s unique head shape?

the size and shape of the brain is relatively the same, however it does vary from person to person, meaning specific steps must be taken to accurately locate specific brain regions

What are the steps to correct for individual brain differences in functional imaging?

1. correct for head movement

2. stereotactic normalization

3. smoothing

4. analyze data

Stereotactic Normalization Definition

mapping the imaged brain onto a standard reference brain

Smoothing Definition

enhancing the signal-to-noise ratio to better detect common active regions within a brain

How do we correct for head movement in functional imaging?

a graph will be made that documents the patient’s head movement along the Y place (up and down), X plane (left to right), and Z plane (forward and back), then this movement data is accounted for in the activation data

How do we initiate stereotactic normalization?

by aligning the voxels of the scanned brain onto a common reference brain; this may require stretching or squishing the brain to fit onto the model

Smoothing increases statistical power by transforming the data into:

3D bell curves called gaussian kernels

What does smoothing the brain image do?

in order to capture a more acurate image of the activity, voxels near each other will be compared based on relative activity; many active voxels near each other will have their activity spread out a bit over some outside voxels; single active voxels surrounded by many inactive voxels will have their activity dimmed down

Craters in a brain scan are due to ______ ____-___

signal drop-out

What is signal drop-out

these are blank spaces in brain scans due to specific areas of the brain being difficult to image, such as where the eyes are and where the spinal cord meets with the brain

Functional imaging captures changes in ____ signals, which can be caused by _______ or _______ activity

BOLD signals; excitatory; inhibitory

What does “activation” refer to in brain imaging?

an increase in physiological processing in one condition relative to another condition; does not necessarily denote if it was excitatory or inhibitory

What does “deactivation” refer to in brain imaging?

a decrease in physiological processing in one condition relative to some other condition; does not denote if it was excitatory or inhibitory

why might a brain region become active even if it is not related to the task?

some brain regions provide support in tasks that they are not neccessary for: a hard math problem will activate regions associated with deep concentration, even though those areas may not be related to mathematical reasoning

How do functional imaging and lesion data differ when looking at semantic dementia

in functional imaging data, it has been found that semantic memory is associated with atrophy in the left anterior temporal lobe

in lesion data semantic memory is associated with the left inferior frontal gyrus