Brain - Dr Matt Roser Flashcards
Define agnosia
Loss of ability to recognise objects, people, sounds, shapes, or smells; that is, the inability to attach appropriate meaning to objective sense data
Define aphasia
A general term relating to loss of language ability
Define apraxia
A general term for disorders of action
Define amnesia
Lack of mnemonic abilities
Define ataxia
Poor coordination and unsteadiness due to failure to regulate the body’s posture, and strength and direction of limb movements
Visual agnosia is associated with lesions of which two parts of the brain?
Left occipital and temporal lobes
What can the existence of selective deficits tell us?
They can tell us something about the way function is organised in the brain.
What is the goal of behavioural testing?
The goals are to relate brain anatomy to behaviour and to investigate mental processes.
In behavioural testing, what can the tasks tell us about the patients deficits? (2)
- What functions are compromised?
- What functions are spared?
What does dissociated mean in the following phrase; “cognitive functions can be dissociated from each other through selective impairment”?
Separated to a certain degree
Dissociation studies require what?
A minimum of two groups and two tasks
What are the limitations of patient studies?
- Assumption of modularity
- Lesions extensive and varied
- Lesion anatomy inaccurate, connections not considered
- Individual differences in functional anatomy
- Poor temporal resolution
Define modularity of function (a limit of patient studies)
Assumption that mental processes can occur with a high degree of isolation from other mental processes and when one area is damaged other regions do not adapt their function
Define ‘brain plasticity’
Intact regions change their behaviour so it is difficult to infer function of damaged region.
Why is ‘lesions extensive and varied’ a limitation of patient studies? (4)
- Most work done with patients who have large lesions
- Lesions often damage several function centres, so there are few patients with ‘pure’ deficits
- Lesion size and location variable, hard to find a group of similar patients. Inferences from single patients are weak.
- Individual differences in recuperative history.
Why is ‘lesion anatomy inaccurate and connections not considered’ a limitation of patient studies? (2)
- Anatomical scans show reginos that are destroyed, but intact regions may not be functioning
- Regions may be disconnected from other regions that provide input
A memory deficit may arise from a failure of what? (3)
Encoding, retention or recall.
There is no experimental control over lesion location, but animal studies using what can provide this?
Animal studies using experimental ablation
What are the benefits of patient studies? (4)
- Shows which areas are necessary for a particular cognitive function (double dissociation)
- Show cognitive, emotional, social consequences of a deficit
- Cost and time effective, single case studies are possible
- Can be done right to limit critism
Importance of a control group; looking at patients with Visual field deficits (vfd’s), all patients have lesions in the temporo-parietal junction (tpj). Why do we need a control group to study these patients?
We need a control group with right hemisphere brain damage but without VFD’s. This way we can control for the effect of right hemisphere damage and contrast only across the factor of VFD presence.
What does fMRI stand for?
Functional Magnetic Resonance Imaging
What does an MRI use to produce an image? (2)
A magnetic field (Bo) and radio energy
What is the physics behind MRIs?
- A large magnet aligns nuclei that have a net magnetic moment.
- Nuclei absorb and re-emit radio frequency energy
How is an image acquired (fMRI)?
Nuclei spin around the main magnetic field.
RF pulse (oscillating magnetic field) tips M out of alignment with Bo and synchronises the phase of spins.
M gradually returns to alignment and spin loses phase coherence. These changes are detected as the ‘MRI’ signal.
How can we map brain changes over time? (2)
- Grey matter volume
- Commisural myelination
What does BOLD stand for?
The Blood Oxygen Level Dependent Response (the basis of fMRI)
Explain briefly the blood oxygen level dependent response (the basis of fMRI) (4)
1- De/oxyhaemoglobin have different magnetic properties
2- Local field strength is affected by relative levels
3- This affects the local signal in the image
4- Increased signal is obtained from ‘active’ regions
What originated with reaction time experiments?
Cognitive subtraction
Define assumption of pure insertion
Can insert a component process into a task without disrupting the other components BUT tast difficulty (a confound) may differ between conditions, resulting in changed attention.
Modelling the data: A change in the signal is due to what? Therefore, what?
A change in the signal is due to regional hemodynamics.
Activations are distantly related to the underlying neurological events.
What has functional brain imaging told us? (4)
1- Identified functional areas
2- Corroborated findings from other methods
3- Allowed the localisation of function from undamaged brains
4- Meta-analyses bring some order to the flood of data, but are these maps from multiple different studies any more useful than the 1957 electrophysiology map?
What does functional connectivity analyses do?
Calculates correlations between activations in different areas.
What does dynamic causal modelling do?
Explicit models of distributed networks are tested to see which best fits the observed data.
What two techniques investigate distributed processing and overcome some of the limitations of lesion studies and earlier fMRI studies?
Functional connectivity analyses.
Dynamic causal modelling.
