The paper "Event-related potentials in clinical research: Guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400" by Duncan et al. (2009) provides comprehensive guidelines for the use of event-related potentials (ERPs) in clinical research. The authors focus on three major cognitive components—mismatch negativity (MMN), P300, and N400—and review their applications in various psychiatric and neurological disorders. The guidelines aim to standardize methodology and facilitate data comparability across laboratories. **MMN** is a small, fronto-central negativity elicited by discriminable changes in auditory stimulation. It reflects an automatic process detecting differences between incoming stimuli and sensory memory traces. The paper outlines the optimal recording conditions, including stimulus attributes, electrode placement, and data acquisition parameters. MMN has been used to monitor coma recovery, predict awakening, and assess cognitive decline in conditions like multiple sclerosis and Alzheimer's disease. **P300** is a large, broad, positive component that peaks 300 ms after onset of a rare, task-relevant stimulus. It is sensitive to stimulus probability, expectancy, and attentional resources. The paper discusses the neural generators of P300 and its clinical applications, such as assessing cognitive function in dementia, predicting cognitive impairment in neuropsychiatric disorders, and monitoring cognitive function in communication-impaired individuals. **N400** is a component that reflects semantic processing and is often used to study language and cognitive disorders. The paper does not provide detailed guidelines for N400 but highlights its importance in clinical research. The authors emphasize the need for standardized procedures to ensure reliable and comparable ERP data, particularly in clinical settings. They also discuss the clinical applications of these components, including their use in diagnosing and monitoring various neurological and psychiatric conditions.The paper "Event-related potentials in clinical research: Guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400" by Duncan et al. (2009) provides comprehensive guidelines for the use of event-related potentials (ERPs) in clinical research. The authors focus on three major cognitive components—mismatch negativity (MMN), P300, and N400—and review their applications in various psychiatric and neurological disorders. The guidelines aim to standardize methodology and facilitate data comparability across laboratories. **MMN** is a small, fronto-central negativity elicited by discriminable changes in auditory stimulation. It reflects an automatic process detecting differences between incoming stimuli and sensory memory traces. The paper outlines the optimal recording conditions, including stimulus attributes, electrode placement, and data acquisition parameters. MMN has been used to monitor coma recovery, predict awakening, and assess cognitive decline in conditions like multiple sclerosis and Alzheimer's disease. **P300** is a large, broad, positive component that peaks 300 ms after onset of a rare, task-relevant stimulus. It is sensitive to stimulus probability, expectancy, and attentional resources. The paper discusses the neural generators of P300 and its clinical applications, such as assessing cognitive function in dementia, predicting cognitive impairment in neuropsychiatric disorders, and monitoring cognitive function in communication-impaired individuals. **N400** is a component that reflects semantic processing and is often used to study language and cognitive disorders. The paper does not provide detailed guidelines for N400 but highlights its importance in clinical research. The authors emphasize the need for standardized procedures to ensure reliable and comparable ERP data, particularly in clinical settings. They also discuss the clinical applications of these components, including their use in diagnosing and monitoring various neurological and psychiatric conditions.