Basic Terms and Concepts Flashcards
Electroencephalography
measures synchronized synaptic activity in populations of cortical neurons
Event-related potential
extraction of response evoked by an external event from EEG data in order to examine the way that tasks modulate brain activity
Magnetencephalography
measures magnetic field changes produced by brain activity
Magnetic Resonance imaging
creates images of soft tissues in body through magnetic field reoreintation following radiofrequency pulse of protons
Computerised tomography
creates images of amount of x-ray absorbed by different tissue types
Positron Emission Topography
radiolabelled pharmacological agents are used to trace certain specific pathways of neural activity
Functional Near Infrared Spectroscopy
measures changes in electrochemical activity and blood levels through their effect on optical properties
Lesion studies
makes use of already-existing lesions to examine their effect on behaviour
Transcranial magnetic stimulation
non-invasive focal stimulation of the brain to create temporary lesions
Classic neuropsychology (lesion studies)
inference of function of brain regions by examining impairment of abilities of patients with lesions in that area
Cognitive neuropsychology (lesion studies)
examination of impairment of abilities to infer the building blocks of cognition
Donder’s subtraction method
- A, B, C type tasks
- based on isolation of specific cognitive processes –> subtraction of one from another to determine length of cognitive process
- assumes seriality and pure insertion
Additive factor method
- aimed at discovering the processing stages
- information is processed in successive stages : input –> transformation –> output
- theory: if experimental manipulation increases RT, the duration of 1+ processing stages is increased but output quality is not affected
Speed-accuracy tradeoff
- instructions: be fast and accurate
- no proof that RTs produced are actually as fast as pp can go with minimum errors
Outliers
- lapses of attention
- premature responses
- natural skew
- slower mean RT
- skew towards caution
- bad day
-> hard to discriminate naturally slow RTs from outliers
Diffusion model of decision making
- neutral point: no information
- information builds in either direction
- at a certain point, threshold is reached –> response is made
- more often correct than incorrect
- smaller boundaries: more focus on speed, but less accuracy
Signal detection theory
- stimulus vs. no stimulus
- stimulus close to perceptive threshold
- Hit: yes when tone is present
- miss: no response when tone is present
- false alarm: response when tone is not present
- correct rejection: no when tone is not present
–> depends on sensitivity (d’)
ROC curve
measures % of hits against % of false alarms
- higher d’ changes shape of curve
–> differences are caused by differences in response criteria
Sensitivity d’
likelihood of responding to a stimulus
- determined by comparing experimentally determined curves to standard ones
- high sensitivity = large distance between N and S+N curve -> steeper ROC curve
- d’ = 0: full overlap = guessing
- d’<0: large overlap = bad sensitivity
- d’>0: small overlap = good sensitivity
Dipole
- extracellular region of pos charge separated from region of neg. charge
- source: pos. charge
- sink: neg. charge
- radial: perpendicular
- tangential: parallel
Volume conduction
- pools of ions repel nearby ions of same charge -> creates wave-like effect that travels through extracellular space
- brain is not homogenous -> signal hits body tissue this may interpede flow or not
- dura layers: skull layers and scalp are very bad conductors
- electrode gel transmits signal
bigger dipole = stronger wave that travels further
Capacitator
- 2 pools of charges are separated by insulating layer
- charge difference builds up across insulating layers (anions push against one side, cations accumulate on other side)
- amount of charge building up depends on properties of layer, size of charge pool, and distance
- stacks of capacitors: volumes
Event-related potentials
- extraction of response evoked by external event from EEG data in order to examine how tasks modulate brain activity
Components
- exogenous sensory components: triggered by stimulus
- endogenous sensory components: task-dependent neural processes
- motor : accompany preparation and execution of motor responses
inverse problem
difficulty of identifying which brain currents are responsible for which signals (EEG and MEG)
Event-related fields
average of recorded MEG signals –> allows more accurate estimation of source localisation than ERPs because of minimal distortion
Spectral analysis
any oscillatory activity can be characterised as sum of different sinusoidal waves with distinct frequencies and amplitudes
- Fast Fourier Transformation: estimation of contribution of various frequencies on measured EEG signal
Structural imaging
- different types of tissue have different rates of absorption
- used to construct detailed maps of brain structure
Functional imaging
- based on assumption that neural activity produces local physiological changes in that region of the brain -> used to produce dynamic maps of moment-to-moment brain activity during cognitive tasks
Stereotactic normalisation
- each brain is mapped onto a standard reference brain to correct for differences in brain size and shape –> Talairach coordinates
Smoothing
- enhances signal-to-noise ratio
- facilitates detection of common activity across individuals
- spreads raw activation of voxel to its neighbours
- SNR: increases size of active regions –> voxels mutually reinforce each other: by turning signal into cluster activity and single voxels into noise
–> helps with averaging: greater area = greater chance of finding common regions of activity
Correction for head movement
- small movements in scanner produce spurious results which have ot be eliminated
Cognitive subtraction
- comparison of brain activity in a task which uses cognitive component X vs. baseline task without X
= inference which region is specialised - meaningful interpretation only occurs relative to baseline
- depends on assumption that 2 tasks can be found which differ only in small number of cognitive processes
Factorial design
- set of tasks with common component –> looking for shared region across different subtractions rather than in single subtraction
- baseline task is required
Parametric design
- variable of interest is treated as continuous instead of categorical
- measures association between brain activity and variable of interest
- no baseline needed
- allows separation of areas from other brain regions involved in maintenance / basis for cognitive processes
Functional integration
brain regions communicate with each other: models how activity in different regions is interdependent –> used to infer effective functional connectivity between regions while performing a certain task
Functional specialisation
- implication that given region responds to limited range of stimuli that distinguishes it from neighbouring regions
vs. localisation:
- doesn’t assume other regions don’t also respond to same stimulus
- doesn’t assume region is solely responsible for task performance
Brain computer interface
interface which connects brain to computer –> allows control over external devices without relying on motor input
Dissociation of function
performance on one task is impaired while performance on anohter isn’t –> functions and processes are dissociable and separable
- logic: separate neural resources may be indicated by difficulty in one demain rel. to absence of difficulty in another domain
Single dissociation
- non-reciprocal dissociation: impairment on one task but not the other
possible reasons:
- hierarchical relationship: one function is necessary for the other
- task-resource artifact: Task A and B use same resources but A requires it more than B –> Task A suffers more from damage
- Task-demand artifact: single dissociation occurs because patient performs suboptimally on one task due to instructions becoming unclear, e.g., due to impairment
Double dissociation
reciprocal dissociation of function: impairment on one task but not the other and vice versa
- relatively independent functions: each lesion gives insight into involvement in one function but not the other
