Exam 1 Flashcards
MR - Brain
Why are patient studies useful?
They are a major source of knowledge about the brain and mind
MR - Brain
Define agnosia
Loss of ability to recognize objects, people, sounds, shapes, or smells; that is, the inability to attach appropriate meaning to objective sense-data
MR - Brain
Define aphasia
A general term relating to loss of language ability
MR - Brain
Define apraxia
A general term for disorders of action
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Define amnesia
A lack of mnenomic abilities
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Define Ataxia
Poor coordination and unsteadiness due to failure to regulate the body’s posture, and strength and direction of limb movements
MR - Brain (not essential)
There are many subtypes of neurological disorders such as agnosia, give examples and definitions of three subtypes
Form agnosia - patients percieve only parts of details, not the whole object
Finger agnosia - The inability to distinguish the fingers on the hand. Present following lesions to occipital lobe.
Simultanagnosia - Patients can recognize objects or details in their visual field, but only one at a time
Associative agnosia - Patients can describe visual scenes and classes of objects but still fail to recognize them.
Apperceptive agnosia - Patients are unable to distinguish visual shapes and so have trouble recognizing, copying, or discriminating between different visual stimuli.
Prosopagnosia - also known as facial blindness
MR - Brain
What can the existence of selective deficits tell us?
They can tell us something about the way function is organised in the brain
MR - Brain
Define ‘dissociated’ in terms of cognitive functions
Seperated to a degree from each other through selective impairment
MR - Brain
Dissociation studies require what?
A minimum of two groups and two tasks. Comparison between patient/control groups shows deficit.
MR - Brain
What are the limitations of single dissociation?
In this study, its possible that the poor performance of patients was caused by another factor, such as a deficit in concentration, and that their test of declarative memory required more concentration than our test of nondeclarative.
MR - Brain
What is the benefits of testing for double dissociation?
- Provide strong evidence that there are cognitive processes critical for task X that are not critical for task Y, and vice versa, and that brain area A is critical for task X but not for task Y etc.
- Double dissociations provide evidence that the observed differences in performance reflect functional differences between the groups, rather than unequal sensitivity of the two tasks.
- Participants don’t have to be perfectly intact on either task, they just need to be significantly better at one task than the other
MR - Brain
What are the limitations of patient studies? (5)
- Assumption of modularity
- Lesions extensive and varied
- Lesion anatomy inaccurate, connections not considered
- Individual differences in functional anatomy
- Poor temporal resolution
MR - Brain
Limitations of patient studies: Explain ‘Assumption of modularity/modularity of function’
- Assumption that mental processes occur with a high degree of isolation from other mental processes and when one area is damaged other regions do not adapt their function
- Brain plasticity: In reality the brain reorganizes quickly. Intact regions change their behaviour so it is difficult to infer function of damaged region
- Processes/dynamics neglected: It is neurons, not black boxes, that perform the function - but how?
MR - Brain
Limitations of patient studies: Explain ‘lesions extensive and varied’
- 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
MR - Brain
Limitations of patient studies: Explain ‘Lesions anatomy inaccurate and connections not considered’
- Anatomical scans show regions that are destroyed, but intact regions may not be functioning
- Regions may be disconnected from other regions that provide input
MR - Brain
Limitations of patient studies: Explain ‘Individual differences in functional anatomy’
- We assume that an anatomical region of the brain does the same function in all individuals
- Clearly violated assumption - e.g. Wada test indicates left hemisphere predominates in language processing in most, but not all, individuals
- Variability of function across individuals reduces the power of group studies
MR - Brain
Limitations of patient studies: Explain ‘Poor temporal resolution and experimental control’
- Even if patient studies establish which regions are necessary for a task, and its inferred cognitive processes, it is not possible to infer the stages of processing
- A memory deficit may arise from a failure of encoding, retention or recall
- There is no experimental control over lesion location, but animal studies using experimental ablation can provide this
- Other methods overcome these limitations
MR - Brain
What are the benefits of patient studies?
- Show 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 (eg HM, no experimental design necessary, exploratory observations possible)
- Can be done right (overlay plots and control groups) to limit criticism
MR - Brain
Why can we not localise speech production in this (Broca’s) area?
- Damage is not limited by functional boundaries
- Lesion might be smaller than functional module
- Interindividual differences in brain organisation
- Result might reflect increased vulnerability of region to injury (eg because of vasculature)
- Area might just be interconnected with the actually relevant area (indirect disruption)
MR - Brain
What does fMRI stand for?
Functional Magnetic Resonance Imaging
MR - Brain
How do MRI machines work (the physics)?
- Uses a magnetic field (Bo) and radio energy to produce an image
- A large magnet (50,000 x Earth) aligns nuclei that have a net magnetic moment (from odd number of protons/neutrons)
- Nuclei absorb and re-emit radio frequency energy
MR - Brain
How is an image acquired in an MRI?
- 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 spins lose phase coherence. These changes are detected as the ‘MRI’ signal
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What can mapping changes over time look at?
- Grey matter volume
- Commisural myelination
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What does BOLD stand for? (in fMRI)
The Blood Oxygen Level Dependent (BOLD) response
MR - Brain
What is BOLD?
It is the basis of fMRI
The neural events are evident from a change in the blood level in the brain (haemodynamics) - Simple explanation
