Neuropsychology: The Electrophysiological Brain Flashcards by Exploding Bluppie

Where can signals come from?

-Space: picked up by machines
-Smallest particles: picked up by machines
-Inside your head: picked up by machines

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What kind of representations are there in the head?

-Mental representation
-Neural representation
-Not straightforward to link these 2, but cool if we can!

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What is mental representation?

Way in which properties of outside world (ex: colors, objects) are copied/stimulated by cognition

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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))

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Which 2 main electrophysiological techniques are there?

-Single-cell recordings
-Electroencephalography (EEG)

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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

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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

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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

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What did Rolls & Deo (2002) find about codes for stimuli?

3 codes for stimuli
-Local representation
-Fully distributed representation
-Sparse distributed representation

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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

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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

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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

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What kinds of examples are there for research about representation in context of face perception?

-Research in monkeys
-Research in human epileptic patients

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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

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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

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What other distinction for codes can be made?

-Rate coding
-Temporal coding

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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