Associations, Study Types, and Noninvasive Lesioning

Single Dissociation Definition

when an impaired patient can perform task A but not task B

What are the two types of single dissociations?

1. classical single dissociation

2. strong single dissociation

What is a Classical Single Dissociation?

when someone with brain damage can perform task A completely normally, but cannot perform taks B

What is a Strong Single Dissociation?

when someone with brain damage is impaired on both task A and B, but they have significantly more trouble with one task, indicating that the damaged region may be affecting that process more

What are two different explanations for Strong Single Dissociations?

1. task resource artifacts

2. task demand artifacts

Tast Resource Artifacts Definition

if two tasks share the same neural/cognitive resource but one task uses this resource more, then damage to this resource/region will affect one task more than the other; can relate to the difficulty of the task

Task Demand Artifacts Definition

when a patient happens to perform one of the tasks poorly due to misunderstanding what they were supposed to do

What is Dysgraphia?

this is when someone has trouble with spelling and writing

Dysgraphia may be an example of what?

of an association; there probably isn’t one brain region specifically for spelling AND writing, but they may be located close to one another, meaning damage to one is likely paired with damage to the other

Syndrome Definition

a cluster of different symptoms that are believed to be related in a meaningful way

What brain regions famously have a double dissociation?

Wenicke and Broca’s areas

Diaschisis Definition

when damage results in a disconnection between regions that are necessary for a function

• function A and C are connected via B; B is damaged, so not A cannot get info from C, which has lead to an impairment

Classical Neuropsychology Approach

• attempts to infer the function of a given brain regions by taking patients with lesions to that region and examining their patterns of impaired and intact abilities

• focuseson what specific brain areas do

Classical Neuropsychology favours what type of study?

group studies in which data from different patients is combined to yield a group average

Cognitive Neuropsychology Approach

• uses intact and impaired abilities to infer the building blocks of cognition

• focuses on how cognition works

Cognitive Psychology favours what type of studies?

single-case studies

What three assumptions did Caramazza suppose?

1. the fractionation assumption

2. the transparency assumption

3. the universality assumption

Caramazza argued for why type of studies?

single-case studies

What is the Fractionation Assumption?

assumes that damage to the brain can produce selective cognitive lesions, meaning that damage to particular brain regions will affect particular cognitive functions

What is the Transparency Assumption?

that lesions affect one or more component within the preexisting cognitive system, but do not result in a completely new cognitive system being created

What is the Universality Assumption?

that all cognitive systems are basically identical

Argument agains the fractionation assumption

this assumption is challenged by the idea of cognitive networks; if a brain region is damaged but the rest of a network can still carry out a related task, then cognitive impairments may not be noticed

The transparency assumption makes the most sense for which type of population?

for adults

Argument against the transparency assumption

recovery after brain damage may lead to different brain regions taking on new roles/organization which means a new cognitive system has been built

What does it mean to group patients by syndrome?

this is when you assign people to an experimental group based on possessing a cluster of symptoms

What is syndrome grouping good for?

• examining neural correlates of a disease pathology (ex: schizophrenia) – but not good for detailed analyses on if damage creates certain symptoms, as not all syndrome symptoms are likely to be from one cause

What does it mean to group people by symptom

grouping participants based on a single cognitive symptom (Ex: experiencing hallucinations

What does symptom grouping allow us to do?

• allows us to identify if multiple brain regions are implicated in a single cognitive experience

• allows us to compare voxel data between subjects to see if there is a common brain region associated with the symptom

• provides a detailed level of analysis

What does it mean to group patients by anatomical lesion?

grouping people based on having a lesion to a particular area in the brain

Grouping by anatomical lesion helps us identify what?

helps us identify behavioural symptoms that are possibly a result of the lesioning/damage

What can complicate strucutral imaging techniques’ abilities to locate lesions?

certain forms of tumors or swelling, such as gliomas that do not have clear boundaries

What is the danger of neophrenology

lesion-deficit associations should not be made out to be 100% fact for everyone, as this can lead to preconcieved judgements against people with certain brain structures, which is essentially phrenology

what are three advantages of TMS?

1. the effects are brief and reversible

2. within-subject designs are possible (asking a patient to engage in a task with and without TMS)

3. the location of the stimulated site can be removed or changed whenever you want

Functional Integration Definition

understanding how one region influences another or how one cognitive function influences another

Walsh et al. Functional Integration Study

• was interested in examining if processing motion makes it harder to process colour

• presented participants with an array of different shapes of different colours, either static or moving

• TMS was delivered to V5

Walsh et al. Functional Integration Study Findings

• when searching for shapes that were in motion, V5 disruptions led to impairments in the visual search

• when searching for shapes based on colour, V5 disruptions were associated with more efficient reaction times, indicating that V5 processing was interfereing with colour-processing

Three practical considerations for TMS

1. when to deliver the pulses

2. where to deliver the pulses

3. selecting the appropriate control conditions

Inion Definition

the bony protrustion at the back of the skull that can be used to locate where to initiate TMS

Anion Definition

bony ridge between the eyebrows that can be used to locate where to initiate TMS

Vertex Definition

the midpoint between the inion and anion

Three types of transcranial electrical stimulations

1. direct current

2. alternating current

3. random noise

Direct Current Stimulation

when the electrical current flows in one direction

Alternating Current Stimulations

when the electrical current alternates in directions

Random Noise Stimulation

when the electrical current can randomly change direction

what happens if the anode (positive electropad) is over the area of interest?

this will increase the firing rate of the neurons

what happens if the cathode (negative electropad) is over the area of interest?

this will cause a decrease in the firing rate of neurons

alternating currents and random noise stimulation creates what type of brain activity?

stimulates brain wave oscillations