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What is an ERP?

An event-related potential is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus when the EEG signal is time-locked to stimulus. 


Why is EEG a good technique?

Can record activity in milliseconds, and safely/passively.


What is a weakness of EEG?

Poor spatial resolution.


How are EEG results plotted?

By plotting time (milliseconds) on the x-axis and electrode potential (microvolts) on the y-axis, in positive and negative peaks with an asymptote at 0 µV.


What is dipole?

A pair of positive and negative electrical charges separated by a small distance, which give rise to the peaks whose timing form event related potentials.


What is normally required of a participants in an ERP experiment?

To perform a task in which an overt behavioural response is required (such as a button press).


What are the different peaks and troughs of an ERP signal referred to as?

ERP components


What is the P300 ERP?

The P300 wave is an ERP elicited in the process of decision making. It is considered an endogenous potential, as its occurrence links not to the physical attributes of a stimulus, but to a person's reaction to it. 

More specifically, the P300 is thought to reflect processes involved in stimulus evaluation or categorization. It is usually elicited using the oddball paradigm, in which low-probability target items are mixed with high-probability non-target (or "standard") items.

In EEG it surfaces as a positive deflection in voltage with a latency (delay between stimulus and response) of roughly 250 to 500 ms.


What does the amplitude of the P300 ERP component reflect?

The amplitude of the P300 reflects the allocation of attentional resources, while the latency is considered to reflect stimulus evaluation and classification time.


What subcomponents does the P300 ERP have?

P3a, which associated with engagement of attention and processing of novelty and has peak latency rage of 250 to 280ms, and P3b (the original P300 component), which peaks around 300ms and is typically elicited using the oddball paradigm, i.e. improbable events.


Why can the P300 be used as a measure for the efficacy of various treatments on cognitive function?

Because cognitive impairment is often correlated with modifications in the P300.


When was the P300 component first investigated?

In the 1960's, 'late evoked potentials' were discovered. The clearest paper was by Sutton et al., (1965), describing a late positive component in the evoked potential to visual and auditory stimulus. Vaughan and Ritter first described its parietocentral scalp distribution (1970) and Smith et al named (also 1970).


What major problems can one encounter when recording the P300 wave?

Electrical components generated by eye movements and blinks.


Where is the P300 wave maximally recorded?

The midline centroparietal regions.


What is the amplitude of the P300 inversely proportional to?

The improbability of the stimulus.