Methods of Cognitive Neuroscience Flashcards
What is the utility of brain imaging over lesion studies?
- Brain damage is rarely selective
- Selective brain damage to subcortical structures does not occur
- The brain can reorganise itself following damage
- Baseline/pre-injury data is often unavailable
What does it mean that brain damage is rarely selective? And doesnt damage subcortical structures?
Head injury/impact - injury is twofold = coup injury (adjacent to injury site) + contracoup injury (opposite side of brain)
Stationary object hits head = coup injury
Moving head + stationary object = coup + contracoup injuries
The nature of both types of injury means damage is widespread and rarely restricted to deep structures
What does it mean that the brain can reorganise following damage?
Neural plasticity is immense and other areas of cortex can accommodate for lost areas of function in some instances
Phantom limb is an example - following loss of the limb, the motor and sensory homunculi can redistribute the roles of the cells
Conversely, following a stroke that initially may prevent speech, after training and slow neural regrowth, other brain centres can replace areas of lost function
What does it mean that we lack baseline data?
We have nothing to compare the current abilities with - original cognitive functioning could have been poor so the change isnt drastic following injury
Can be avoided (slightly) by comparing to similar people (ie IQ, EF, SES matched) and demonstrating no deficits
Why else is neuroimaging data important?
Some questions are unanswerable by neuropsychology (ie lesions)
Even those that are require converging evidence for support
What are the necessary assumptions for brain imaging?
- There is consistent correspondence between brain activity and mental activity
- When our thoughts or emotions (etc) change, as does our brain activity, and that this change is consistent
- Thoughts, emotions, actions (etc) arise from changes in brain activity = a materialist/physicalist view
How can neural activity be measured?
Ideally = electricochemical activity at the direct site of action = animal or human electrode implantation
ERP = electrical activity but at a distance
Imaging = PET/fMRI = monitor regional cerebral blood flow (rCBF) as a proxy of neural activity
What is ERP and how is it used?
Brain tissue/skull/skin = conductive to electrical activity of neurons
Scalp electrodes conduct brains activity = EEG
ERP = a discrete segment of EEG that is ‘time-locked’ to a particular stimulus ie object presented - Xms later = ERP
What are all the waves detectable on an EEG and what are their significance?
Alpha - 8-15Hz, relaxed/reflecting, eyes closed, inhibition control
Beta - 16-31, active thinking, focus, alert, anxious
Theta - 4-7Hz, inhibition of elicited responses, drowsiness/idling
Delta - <4Hz, slow wave sleep
Gamma - >32Hz, active perception combining two senses, STM matching of the same
How is ERP data analysed?
Single trials contain lots of noise - repetition of trials with the same stimulus allows for the signal-averaging = INCREASED signal:noise ratio
Multiple electrode sites allows detection of electrical electrical activity change with time and electrode location
How are ERP components named?
(C1 - visual processing)
P1, N1, P2, N2, P3 = one naming convention, giving ordinal values to the peaks; P+ve Vs N-ve
N100, P200 etc = second convention, gives m/s values to the peaks
How are ERPs used to measure cognitive processes?
Cognitive processes are time-dependent and ERP affords a high temporal resolution eg recognition memory task:
Presentation of probe/stimulus - 0ms
Recognition of probe (familiarity) - c.300-500ms - FN400 (frontal negative)
Retrieving the information related to the probe/context (recollection) - C.500-800MS - left parietal old/new effect (different site to FN400 and can differentiate between old/new stimuli)
What are some limitations of ERP?
Forward solution: we know how many sources of activity, their magnitude and where they are = we can model predicted electrical potentials some distance from sources
HOWEVER
Inverse problem:
although we know what data we can get from the skull, we dont know/cant infer the properties of the source - the regions below the electrodes might not be responsible for the activation
What is magnetoencephalography?
Similar to ERP as are reliant on inherent electromagnetic fields generated by neurons action potentials = event-related fields
All principles applying to ERP also apply to ERF
How do haemodynamic measures of neural activity work?
Reliant on neurovascular coupling - neural activity increases blood flow to areas of neurons that are expending more energy (greater need for oxygen + energy replacements and waste removal)
Neural activity increases - blood volume increases (c.5s)
Known as BOLD measures = blood oxygen level dependent