Chapter 2 Flashcards
How do group studies inform us about memory?
-Involve selecting patients whose damage is related to a specific cause
Name one disease that is least informative of memory functions & one that is most informative:
- TBI is not very informative of memory functions because attentional problems are also involved.
- Ranges from mild (a brief change in consciousness) to severe (extended unconsciousness or coma), the more severe the poorer the recovery chances.
Alcoholic Korsakoff syndrome is more informative
- Result of drinking too much & eating too little
- Attentional control is also disrupted aside from memory
- Amnesia is the most informative
- Case of HM demonstrates episodic LTM is separate from other capacities (dissociation)
What is double dissociation & what is a solution for it?
- When 2 patient groups show opposite patterns of deficit (e.g normal STM & Impaired LTM or vice versa)
- The solution is converging operations, which is carrying out a series of experiments with different methods & subject groups but focusing on one theoretical question
Describe Computerized Tomography (CT):
- Rotating X-Ray tube around the head
- Provide multiple viewpoints of brain
- Info fed into computer that creates 3D image of brain
- Replaced by MRI because of better resolution & no radiation
Describe Magnetic Resonance Imaging (MRI):
-Head placed in magnetic field
-Brain absorbs radio waves in a series of brief pulses with different frequencies which allows us to emphasize different aspects of brain structure
-Brain releases absorbed energy when the field is turned
off
-3D image is created that differentiates white matter from grey matter from cerebrospinal fluid
-Resolution depends on strength of magnet (1.5 Tesla magnet creates 1mm resolution)
What are the 3 aspects of the brain emphasized by MRI?
Grey matter–> neuronal cell bodies
White matter–>axons linking different brain areas
Cerebrospinal fluid–> cushioning for brain, fills ventricles, carries away waste)
What is Diffusion Tensor Imaging (DTI)?
- Important aspect of MRI
- Takes advantage of the fattiness of myelin sheaths surrounding white matter fibres tracts that allow water to flow along their tracts.
- DTI allows for tractography which is mapping these white matter bundles that transfer info to brain & coordinate brain functions
Describe memory studies involving the hippocampus:
- Can be done by implanting electrodes in the brain when they’re under surgery
- Brain does not have pain receptors so the person can report experiences when different areas are stimulated–> evokes deja-vu when confronted with a novel stimulus.
- Hippocampus volume is directly associated with the capacity to associate words to backgrounds against which they were learned
Describe Tanscranial Magnetic Stimulation (TMS):
- Less invasive, allows the experimenter to control the situation & compare performance with & without stimulation
- Set of coils held close to head where current passes through & causes a temporary lesion that demonstrates importance of specific brain area to cognitive activities
- Delivered as single pulse before stimulus presentation or repeatedly which causes disruption in brain area for few mins
- Limitation: Can affect large brain area & limited to the surface, causes discomfort or even seizures
Describe Electroencephalography (EEG):
- Much more applicable & noninvasive than TMS
- Picks up electrical brain activity through electrodes on scalp & records fluctuating voltages from 1-70 cycles per second
- Useful in detecting epileptic foci that cause seizures, studying sleep patterns & cognitive function by tracking patterns of activation
- Limitation: Shows complex activation pattern in whole-brain so hard to identify specific processes involved in performance
Describe Event-Related Potentials (ERP):
- More precise way of evaluating brain’s response to cognitive activities.
- Time-linking an event to specific EEG activation
- Obtained by averaging the brain’s responses to the same stimulus that is presented repeatedly
- ERPs are most sensitive to gyri activity–> peaks of the brain
- ERP signals are weaker than background EEG & location of response signals are not precise
Describe Magnetoencephalography (MEG):
- Neurons generate tiny magnetic fields that are detected using a range of detectors around the brain
- MEG is most sensitive to sulci activity–> valleys within brain folds
- MEG signals are less subject to distortion after going through skull & electrodes–> more precise localization of its origin in the brain.
- Limitation: more expensive than ERP
What is the difference between blood-flow based measures and ERPs & MEGs?
Blood-flow based measures allow us to assume that areas of the brains are more active when there is higher metabolism (higher oxygen being used).
ERPs & MEGs have good temporal resolution (track brain activity from milliseconds) but poor spatial resolution (unclear where activity originates from)
Describe Positron emission topography (PET):
- A radioactive tracer is injected in the bloodstream, areas of the brain that are more active demand more blood flow so they show higher radiation which is picked up by detectors around the head.
- PET has a poor temporal resolution but good spatial resolution.
- Limitation: very expensive, potentially dangerous for repeated testing since it uses radioactive reagents
Describe Functional Magnetic Resonance Imaging (fMRI)
- Measures flow of oxygen by tracking the changes in the magnetic resonance signal of hemoglobin that carries the oxygen, using detectors around the brain that can locate which area is receiving the oxygen
- Better spatial resolution than PET, but low temporal (response to stimulus starts at 1-2 sec after the presentation, peak at 5-6 sec, return to baseline at 10-20 sec)
- The pattern of brain areas activated resemble mountain ranges (large), and identifying these peaks involve:
a) using a subtraction method to obtain the difference in activation between trials that require memory & those that do not
b) Finding appropriate baseline condition to subtraction from, which leaves us with adjusted activation levels
c) Setting appropriate significance level for difference pattern, then interpreting results
d) Linking pattern to psychological theory
Limitation: Expensive & time-consuming
