Event-related potentials (ERPs) are small voltage changes in the EEG that are time-locked to the processing of specific events. Because the random background EEG noise cancels out with averaging, ERPs reveal the brain's systematic response to stimuli with millisecond precision. Major ERP components have become standard tools for studying the time course of attention, perception, language, memory, and cognitive control.
Major Components
The P1 and N1 (100-200 ms) reflect early sensory processing modulated by attention. The N170 (~170 ms) is enhanced for faces relative to other objects. The N2pc (~200-300 ms) tracks the deployment of spatial attention. The P300 (~300-600 ms) indexes attention allocation and working memory updating — its amplitude reflects the significance of the event, and its latency reflects classification speed. The N400 (~400 ms) indexes semantic processing difficulty. The P600 (~600 ms) indexes syntactic processing and reanalysis. The error-related negativity (ERN) appears within 100 ms of errors, reflecting rapid error monitoring.
ERPs are used clinically to assess cognitive function in patients who cannot perform behavioral tasks: the mismatch negativity (MMN) can assess auditory discrimination in comatose patients, the P300 can evaluate cognitive function in dementia, and auditory brainstem responses can assess hearing in infants. ERPs also serve as biomarkers for cognitive disorders and as outcome measures in clinical trials.