Neuropsychology: The Electrophysiological Brain Flashcards
Where can signals come from?
-Space: picked up by machines
-Smallest particles: picked up by machines
-Inside your head: picked up by machines
What kind of representations are there in the head?
-Mental representation
-Neural representation
-Not straightforward to link these 2, but cool if we can!
What is mental representation?
Way in which properties of outside world (ex: colors, objects) are copied/stimulated by cognition
What is neural representation?
Way in which properties of outside world (or inner events) manifest themselves in neural signal (ex: different spiking rates for different stimuli (spike: action potential))
Which 2 main electrophysiological techniques are there?
-Single-cell recordings
-Electroencephalography (EEG)
What are single-cell recordings?
-Invasive electrophysiological technique to observe changes in voltage or current in neuron
-Measures amount of action potentials per second from individual neurons
-Electrode(s) placed in or near neuron
-Action potentials of single neurons: basis of neural communication
What is an electroencephalography (EEG)?
-Non-invasive electrophysiological technique to record electrical activity of brain
-Measures summed electrical potentials from millions of neurons together (sensitive to dendritic currents)
-Electrode(s) placed on skull
What are neural codes?
-Codes by which stimuli are represented
-Single-cell recordings can tell us something about that
-Rolls & Deo (2002) summarize 3 codes for stimuli
What did Rolls & Deo (2002) find about codes for stimuli?
3 codes for stimuli
-Local representation
-Fully distributed representation
-Sparse distributed representation
What is local representation, according to Rolls & Deo (2002)?
Grandmother cells: hypothetically responds to only 1 stimulus
-Stimuli represented by individual neurons that only code for that stimuli
-Gradual transition in hierarchical information processing system
What is fully distributed representation, according to Rolls & Deo (2002)?
-Stimuli relevant for certain brain region represented by all neurons in that region
-Neurons equally relevant for representation
What is sparse distributed representation, according to Rolls & Deo (2002)?
-Stimuli represented by subset of neurons
-Between local and fully distributed representation
-Evidence with faces consistent with this representation
What kinds of examples are there for research about representation in context of face perception?
-Research in monkeys
-Research in human epileptic patients
What did research in monkeys about representation in context of face perception tell us?
-4 individual neurons have been recorded in brain
–>Face selective neurons: respond strongly to at least 1 face and not to other objects
-Results: different neurons respond to different faces (at least 1)
-Mix between local and more distributed: some neurons only respond to one face, other neurons to more faces in different amounts
-Evidence for sparse distributed representation
What did research in human epileptic patients about representation in context of face perception tell us?
-Faces from celebrities presented
–>Invariance of responses investigated
–>Data of 1 neuron given
-Results
–>Neuron responds to all images that represent something about Halle Berry (face, name, etc.)
–>Action potentials between time when stimulus comes on screen (first dotted line) and goes off screen (second dotted line)
-Evidence for more local representation in medial temporal lobe in humans
What other distinction for codes can be made?
-Rate coding
-Temporal coding
What is rate coding?
-Greater rate of response used to code information
-More action potentials as indication that neuron is representing stimulus
What is temporal coding?
Greater synchrony in response between neurons used to code information
-Ex: binding different parts of line together
What is an EEG and how does it work?
-Electroencephalography
-Used in few main research contexts in cognitive neuroscience
-Electrodes can be named by different systems
-EEG measures signal
-Different examples
-10-20 system of electrodes
In which main research contexts in cognitive neuroscience is EEG used?
-In analyzing rates of oscillation (wave) and linking it to cognitive functions
-In event-related potentials (ERPs)
-In representational dynamics
How can electrodes be named by different systems in EEG?
-Systems share certain features in terms of naming electrodes
-10-20 system: least number of electrodes
–>First named by position of lobes
–>Then named by side of brain: odd or even numbers
What kind of signal does an EEG measure?
-Measuring activity of neurons requires many neurons to fire together
-Possible to see if many neurons fire together or when they do not fire together
-Not possible to measure individual action potentials
-If millions of neurons fire together: wave-like structure observed at scalp
What are examples of measurements with an EEG?
-3 neurons all fire at similar rate, but two neurons fire also at same time
–>Creates 6 action potentials
–>Can influence each other’s excitability and communicate
-If million of neurons fire together, wave-like structure observed
–>Wave-like activity can be measured in signal
–>Signal will go up and down in same frequency as oscillation in image
What are advantages of EEG?
Excellent temporal resolution
-Temporal resolution: how precise difference can be measured in terms of time
-EEG signal directly related to neural activity and this electrical activity conducted instantaneously to scalp
-Can be measured at high sampling rate
What are disadvantages of EEG?
Poor spatial resolution
-Spatial resolution: number of pixels utilized in construction of digital image
-Inverse problem: EEG signal derived from different sources in brain and impossible to infer exactly where sources are from scalp
What can we see in oscillation-based analyses from an EEG signal?
-Neurons tend to fire in synchrony with each other, but at different frequencies (slow => fast), which explains wave-like neural activity
-Different oscillation frequencies have different meanings and relate to different factors
What different meanings can different oscillation frequencies have?
-Can characterize different phases of sleep-wake cycle
-Can characterize certain cognitive functions
How can different oscillation frequencies characterize different phases of sleep-wake cycle?
-With EEG recordings, knowing in which sleep phase person is
-Each stage has different properties
–>Stage 1: certain oscillation happing, Theta waves (4-7Hz)
–>Stage 2: sleep spindles and K-complexes
–>Stage 3 and 4: slower Delta waves (<4Hz)
–>REM sleep: looks lot like awake phase
How can different oscillation frequencies characterize certain cognitive functions?
-Increased alpha (7-14Hz) linked to visual attention
-Increased gamma (+30Hz) linked to perceptual grouping
What is an event-related potential (ERP)?
-Based on EEG (electroencephalography) recordings
-EEG signal averaged over many events (to reduce effects of random neural firing) and aligned to some aspect of event (ex: onset stimulus, pressing button)
-Electrodes record series of positive and negative peaks
-Timing and amplitude of peaks related to different aspects of stimulus and task
What is mental chronometry?
-Measuring timing of cognition: can be used for different things
-Classic method: RT
-Examples of research
-ERP signal continuous over time and some advantages over RT method
For what can mental chronometry be used?
-To infer structure of cognition
-To relate cognitive functions to timepoints
What is the classic method of mental chronometry?
-Response time (RT) to task/stimuli as variable
-Measuring changes in RT across conditions
-Attempts to decompose single measure (Sternberg)
What examples are there of research with mental chronometry?
-Experiment with working memory task 1
-Experiment with working memory task 2
What did the experiment with working memory task 1 teach us with mental chronometry?
-Procedure
–>Remembering series of numbers
–>Then another number represented and participant has to say (as fast as possible, RT), if it was in list or not
-Result: RT shorter if array smaller and linear increase in RT if array larger
-Mental chronometry
-Result: RT longer and additive effect (two main effects)
-Evidence for Sternberg: different mental components are independent (size of array independent of perceptual challenge added)
What did the experiment with working memory task 2 teach us with mental chronometry?
-Procedure
–>Remembering series of numbers
–>Responding by saying numbers
-Result: RT shorter if array smaller and linear increase in RT if array larger
-Mental chronometry
-Result: RT longer and interactive effect
-Not able to talk about independent stages of processing
How can ERP also decompose a single measure?
-Signal continuous over time (instead of using RT)
–>Signal changing over time
–>Gives much more information
-Advantages over RT method
How is mental chronometry related to ERP?
-In ERP: different peaks may approximately reflect functioning of different cognitive stages
–>Able to see when exactly it occurs in time
–>Able to see how it changes by manipulating certain aspects of presented stimuli
-But not simple relationship between ERP-peak and cognition
–>Because each peak is sum of different electrical activities
What was found when using ERP to study face recognition?
Different ERP-peaks associated with different aspects of face processing
-First: perceptual coding of face
–>N170 involved, affected by perceptual changes in stimuli
-Second: face recognition
–>N250 involved, affected by things related to identity of stimulus
-Third: person recognition
–>P400-600 involved, affected by faces and names
What is an N170?
Negative value that occurs 170msecs after stimulus onset
-In chart: seen as negative peak
-Component seen when presenting face, human or animal
-Component not seen when presenting object
-Often seen in electrodes around occipital-temporal cortex
