The P600 is an event-related potential (ERP) component, or peak in electrical brain activity measured by electroencephalography (EEG).
It is a language-relevant ERP component and is thought to be elicited by hearing or reading grammatical errors and other syntactic anomalies.
[2][3][note 1] In other words, in the EEG waveform it is a large peak in the positive direction, which starts around 500 milliseconds after the subject sees or hears a stimulus.
It is typically thought of as appearing mostly on centro-parietal electrodes (i.e., over the posterior part of the center of the scalp), but frontal P600s have also been observed in several studies.
[4] In EEG, however, this distribution at the scalp does not mean the P600 is coming from that part of the brain; a 2007 study using magnetoencephalography (MEG) speculates that the generators of the P600 are in the posterior temporal lobe, behind Wernicke's area.
For example, Osterhout & Holcomb (1992) found P600s elicited by the word to in sentences such as The broker persuaded to sell the stock was tall.
[22] Another proposal is that the P600 does not necessarily reflect any linguistic processes per se, but is similar to the P300 in that it is triggered when a subject encounters "improbable" stimuli—since ungrammatical sentences are relatively rare in natural speech, a P600 may not be a linguistic response but simply an effect of the subject's "surprise" upon encountering an unexpected stimulus.