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.
Key Structures
- Distributed cortical generators depending on component (e.g., auditory cortex for N1, temporal cortex for N400, frontal-parietal for P300)
- Working Memory — A limited-capacity system for temporarily holding and manipulating information during complex cognitive tasks such as reasoning, comprehension, and learning.
Key Functions
Voltage fluctuations in the EEG time-locked to specific sensory, cognitive, or motor events, providing precise temporal markers of information processing stages including sensory registration (P1/N1), attention (N2/P300), and semantic integration (N400).
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.
Disorders
- Schizophrenia (reduced P300, MMN deficits) — Severe psychiatric disorder with hallucinations, delusions, and thought disorder; prominent cognitive deficits in memory, attention, and executive function.
- ADHD (attenuated P300) — Attention-Deficit/Hyperactivity Disorder — a neurodevelopmental condition characterized by persistent patterns of inattention, hyperactivity, and impulsivity affecting cognitive functioning.
- Dyslexia (abnormal N400) — A specific learning disability affecting reading accuracy, fluency, and comprehension, rooted in phonological processing deficits despite adequate intelligence and instruction.
- Alzheimer's disease (delayed P300) — A progressive neurodegenerative disease characterized by memory loss, cognitive decline, and personality changes — the most common cause of dementia in older adults.