Predictive brain activity shows congruent semantic specificity in language comprehension and production.

Sentence fragments strongly predicting a specific subsequent meaningful word elicit larger pre-word slow waves, Prediction Potentials (PP), than unpredictive contexts. To test current predictive processing models, 128-channel EEG data was collected from both sexes to examine whether (i) different semantic PPs are elicited in language comprehension and production, and (ii) whether these PPs originate from the same specific 'prediction area(s)' or rather from widely-distributed category-specific neuronal circuits reflecting the meaning of the predicted item. Larger slow waves after predictable than unpredictable contexts were present both before subjects heard the sentence-final word in the comprehension experiment and before they pronounced the sentence-final word in the production experiment. Crucially, cortical sources underlying the semantic PP were distributed across several cortical areas and differed between the semantic categories of the expected words. In both production and comprehension, anticipation of animal words was reflected by sources in posterior visual areas, whereas predictable tool words were preceded by sources in frontocentral sensorimotor cortex. For both modalities, PP size increased with higher cloze probability, thus further confirming that semantic predictions are reflected, and with shorter latencies with which participants completed sentence fragments. These results sit comfortably with theories viewing distributed semantic-category-specific circuits as the mechanistic basis of semantic prediction in the two modalities. Significant statement We report larger anticipatory negative-going Prediction Potentials (PPs) after sentence fragments with predictable than unpredictable endings both during language comprehension and production. In production and comprehension experiments, PP topographies resembled each other but, for each modality, PPs differed in the same way between semantic categories of the predictable words. Likewise, cortical source estimation revealed similar prediction-related cortical activations across modalities but consistent activation differences reflecting the meaning of predicted symbols. Furthermore, PP size was linked with behavioural measures of predictability (Cloze probability) and ease of processing (Reaction Times) and correlated PPs were seen in production and comprehension; these observations are consistent with similar prediction mechanisms across modalities but different ones for semantic types.