The P600 and P3 ERP components are linked to the task-evoked pupillary response as a correlate of norepinephrine activity

During language comprehension, anomalies and ambiguities in the input typically elicit the P600 event-related potential component. Although traditionally interpreted as a specific signal of combinatorial operations in sentence processing, the component has alternatively been proposed to be a variant of the oddball-sensitive, domain-general P3 component. In particular, both components might reflect phasic norepinephrine release from the locus coeruleus (LC/NE) to motivationally significant stimuli. In this preregistered study, we tested this hypothesis by relating both components to the task-evoked pupillary response, a putative biomarker of LC/NE activity. 36 participants completed a sentence comprehension task (containing 25% morphosyntactic violations) and a non-linguistic oddball task (containing 20% oddballs), while the EEG and pupil size were co-registered. Our results showed that the task-evoked pupillary response and the ERP amplitudes of both components were similarly affected by both experimental tasks. Crucially, the size of the pupillary response - both pupil size and its temporal derivative - predicted the amplitude of both ERP components on a trial- by-trial basis. This pattern of results supports the idea that both, the P3 and the P600, might rely on a shared neural generator and, more specifically, that they may both be linked to phasic NE release. Generally, our findings further stimulate the debate on whether language- related ERPs are indeed specific to linguistic processes or shared across cognitive domains. In the case of the P600, the present results indicate that anomalies during language comprehension might rather initiate transient NE activity in response to rare and motivationally significant stimuli more generally.