ERP & Attention (1) Flashcards
What did Hans Berger do in 1924?
first to record EEG signals
How did people look at EEG signals in the beginning?
- looked at the wave pattern over time
- For example, seeing changes in the wave pattern when sleeping
What does EEG stand for?
electroencephalogram
Who conducted the first cognitive ERP study?
Gray Walter and the CNV 1964
What was the first cognitive ERP study?
It looked at ERPs for 4 conditions
- A: when you hear a click (spike in EEG signal right after click)
- B: light flashes (EEG activity in response to stimulus)
- C: click followed by flashes (EEG activity)
- D: click followed by flashes and pressing a button (in the time period between the click and the flashes there is an increase in EEG activity until the flash occurs
What is the Contingent Negative Variation (CNV)?
- the anticipation of a stimuli ramps up the activity of neurons
- on a graph negative is up!
What was found in the first cognitive ERP study?
- when the participant needed to press the button after the flash, the ERP waveform differed as they anticipated the flashes
- there was no difference in stimuli, just the mental state/process
What is an ERP?
looking at a specific point in time in response to a stimulus or event
When looking at an ERP, which way is up?
- Negative is up
- Contingent: dependent, negative: plotted up
What is the most important difference between EEG/ERP and TMS?
manipulation vs measurement
What is the instrument used for recording EEG?
- EEG cap with electrodes in specific places
- international 10-20 system
- place cap by measuring head and using bony bumps on head to mark certain places
What are strong signals caused by?
- eye blinks
- can also be from eye, neck or mouth movements
Where do ERPs come from?
- many orthogonal cortical pyramidal cells
- excitatory transmitter released on apical dendrites causes positive charges to flow into dendrites (net negative on outside)
- polarity reverses with inhibitory transmitter
What does the polarity at the scalp depend on?
orientation of the cortical surface and the position of the reference electrode
In what conditions are scalp-related potentials possible?
- only for open field or layered structures with consistent orientations
- primarily cerebral cortex
- if a closed field, the neurons are all facing in different directions and the consequent electromagnetic fields will cancel out instead of summing
How are voltages spread out?
- voltages are spread through the brain by “volume conduction”
- skull causes lateral spread
- measured as positive in direction of flow
- not much recorded where positive and negative meet
How do we get ERPs from EEG?
- stimulus is presented repeatedly and EEG averaged over all trials
- consistent peaks and troughs come through that are associated with stimulus
What are the ERPs “locked” to?
- stimulus locked: line up on stimulus and the average
- response locked: line up on responses and then average
What is the temporal resolution of ERPs?
about 1ms (because recording 250 to 1000 per second)
What are some typical ERPs?
- brainstem responses
- mid-latency responses
- long-latency responses
What is N170?
- voltage reflects face-related activity plus everything else that is active at 170ms
- difference reflects only brain activity that differentiates between faces and cars
What is the difference wave?
- difference wave shows what is changing in brain activity between two different types of trials
- can sometimes reveal the time course of the underlying component
What is the superposition problem?
- the voltage at an electrode at time ‘t’ is a weighted sum of all components that are active at time ‘t’
- this makes it difficult to determine underlying components from observed waveforms
- the recorded wave will look different depending on where we record it on the scalp
What is rule #1 about peaks and components?
- peaks and components are not the same thing
- there is nothing special about the point at which the observed waveform reaches a local maximum
- peaks are maximums and minimums in observed waveform
- components are possible waves that made up the waveform