Methods Flashcards
What is the method of converging operations?
The technique of examining whether all the answers obtained from a set of interrelated experiments lead to the same conclusion.
What is the lesion method?
If damage to a particular brain region results in an inability to perform a specific mental function, scientists usually assume that the function must have depended on that brain region.
Research participants can be animals, in which scientists carefully create lesions. In the case of human participants, investigators rely on cases of brain damage. The investigator has no control over location, extent, or cause of lesion.
What is localization of function?
Where a subsystem or module is learned to be located in a specific region of brain tissue, i.e. a portion of a processing system that is dedicated to a single function not performed elsewhere.
What is the main strength of the lesion method?
It allows a specific region of brain tissue to be directly linked to a specific aspect of mental processing. We can directly observe that when a particular region is damaged, a particular mental process is lost.
This provides invaluable information to physicians, other medical professionals, and neuropsychologists.
What does it mean if a researcher emphasises neural substrates in their lesion study?
This means that they are asking, “What functioning are supported by a particular piece of brain tissue?” They will recruit a population of individuals whom the site, cause, and extent of damage are as similar as possible. They will also recruit a group of patients with damage elsewhere in the brain. If the patients in Group B do not exhibit the symptoms that Group A collectively demonstrates, then conclusions can be made about how a particular brain region is critically important to a specific component of cognition.
What does it mean if a researcher emphasises cognitive function in their lesion study?
Researchers select a group of individuals who exhibit the same behavioural symptoms, with little regard for the location of the brain damage. They examine the nature of the cognitive impairment, for example, if it can be minimised or maximised with different stimuli.
This can be useful in designing effective methods of rehabilitation.
What is double dissociation?
A method that allows researchers to determine whether two cognitive functions are independent of one another. A double dissociation occurs when lesions have converse effects on two distinct cognitive functions: one brain lesion causes a disruption in Cognitive Function A but not Cognitive Function B, whereas a different lesion causes a disruption in Cognitive Function B but not Cognitive Function A. From such a pattern, we can infer that the functions can be independent, because the viability of one cognitive function does not depend on the viability of the other.
E.g. Broca’s and Wernicke’s aphasia.
What are the four assumptions of cognitive neuropsychology psychology?
- Functional Modularity: Functional architecture is a configuration of modules. 2 systems: Input modules = encoding and recognising perceptual inputs, and Central system = “higher order” cognitive processes.
- Anatomical Modularity: Functional modules are realised in some specific and relatively restricted region of the brain
- Uniformity of Functional Architecture across People: The same cognitive domains and systems are identical across different individuals
- Subtractivity: Brain damage can impair existing components in the system but cannot introduce new ones.
What are the disadvantages of the lesion method?
- Heterogenous patient group: e.g diverse age, socioeconomic status, educational background, and life experiences. Expiriences post injury vary too (e.g. rehab). The lesion sustained is also much less specific.
- Can lead to inaccurate conclusions: do not directly observe the function of the brain, but only how the rest of the brain performs without that area. Will therefore only identify functions critical to that area, or may observe the impairment because that region connects other brain regions, not because it is critical to that area.
- Disconnection syndrome: When axons that connect two or more brain regions critical for the function are damaged information carried by these fibres cannot be transmitted from one brain region to another.
- Underestimating role of specific brain region: patient may compensate using a different strategy, or the brain may reorganize tissue after damage.
What are the benefits of researching neurological intact individuals?
Understanding of brain structure and functions under normal conditions and normal development
Understanding of individual differences in brain function
Comparison group for brain-injured group
Matched on key variables, namely demographic
What is Computerised Axial Tomography (CAT or CT)
Density of brain structures determined using X-ray Cerebrospinal fluid (CSF) is less dense than brain tissue, which is less dense than blood, which is less dense than bone. Dense tissue such as bone appears white, whereas materials with less density such as CSF appears black. Damaged areas appear darker than surrounding tissue because they are filled with less dense CSF. Hemorahages are light areas because blood is denser than brain tissue. Horizontal slices of the brain.
What is an advantage of a CAT scan?
Relatively inexpensive
Available in most hospitals
No restrictions on who can receive a CAT scan
What is Magnetic Resonance Imaging?
Uses magnetic fields to distort the behaviour of protons. The information recorded about how long the protons take to recover from this distortion is then used to create an image of the anatomy of the brain
What are the advantages of an MRI?
MRIs do not require X-rays (like CAT) so they do not require high-energy ionizing radiation.
Great spatial resolution (clarity)
What are the disadvantages of an MRI?
Not everyone can use it (pacemakers or people with metal in their body)
What is Positron Emission Tomography (PET)?
Molecules altered to have a radioactive atom are introduced into the blood supply and carreid to the brain. The become stable/nonradioactive, and release positrons. When positrons collide with electrons two photons of light are produced that go in opposite directions. Brain areas of high metabolic activity emit many photons of light, whereas those that are less active emit fewer. Computer extrapolate backward to determine the point from which the phtons emanated, allowing the activity of various brain regiosn to be determined.
This measures body functions such as blood flow, oxygen use, and sugar (glucose) metabolism to evaluate organs and tissue functioning
What are the advantages of PET?
- It allows researchers to determine the amount of a specific compound of interest, such as a neurotransmitter, that is being used by specific brain regions.
- It provides information on absolute levels of brain metabolism.
What are the disadvantages of PET?
Uses high-energy ionizing radiation. Use is therefore limited to 2-5 scans a year.
Temporal (Time periods required to obtain a picture of the brain are quite long) and spatial resolution is poorer than fMRI.
What is a Functional MRI?
Measures brain activity by detecting associated changes in blood flow.This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.
The primary form of fMRI uses the Blood-oxygen-level dependent (BOLD) contrast. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells.
the magnetic properties of deoxygenated blood makes the static magnetic field inhomogenous, making it more diffcitul to detect signal change, whereas the magnetic properties of oxygenated blood does not have such an effect.When a particular area of the brain is active, the local increase in oxygen-rich blood is greater than the amount of oxygen that can be extracted from the brain tissue. A decrease in deoxygenated blood allows increased signal clarity
What are the advantages of fMRI?
Can compare two conditions: the condition of interest (Light on) to a baseline (light off).
Temporal resolution is faster than PET, but is slower than EEG.
It is widely available
It is non invasive (no high-energy radiation)
Multiple scans can be run on an individual
It provides a measure of brain activity over seconds rather than minutes as is the case for PET.
Precision of the scans enables us to examine brain-behaviour relationships.
What are the disadvantages of fMRI?
BOLD: It can only provide information about the relative concentration of oxygenated and deoxygenated blood. Absolute measurements are not available.
What is Transcranial magnetic stimulation (TMS)?
A pulsed magnetic field over the scalp induces an electrical field which interferes with the electrical firing of neurons in the underlying tissue. It can be used to identify those regions of the brain that are critical to performance of a task.
What are advantages of TMS?
It can be used to confirm findings of the lesion method.
It can provide insight into how the brain reorganizes
It can provide information about whether a behaviour is critically dependent on a particular brain region or whether it results from the interaction between brain regions.
It can also be used therapeutically.
What are the disadvantages of TMS?
Because it alters brain function, it must be used with caution. It could possibly induce seizures, headaches, nausea, or muscle twitches.
It can only stimulate the region of the brain closest to the surface, not deeper tissue.
It is not possible to precisely control what regions fo the brain are affected.
How is clinical assessment of behaviour done?
Either via a test battery that samples a large number of mental functions without going into a detailed examination of any one function, or a customized approach that assesses very specific cognitive functions in addition. In either case, a measure of general intelligence often also is obtained.
Why is neuropsychological assessment done?
Neuropsychological assessment is generally performed to determine the degree to which damage to the CNS may have compromised a person’s cognitive, behavioural, and emotional functioning.
