Spatiotemporal brain maps of delayed word repetition and recognition

Whole-head magnetoencephalography (MEG) was used to spatiotemporally map the brain response underlying episodic retrieval of words studied a single time following a long delay (approximately 40 min). Recognition following a long delay occurs as a strong, sustained, differential response, within bilateral, ventral, and lateral prefrontal cortex, anterior temporal and medial parietal regions from approximately 500 ms onward, as well as ventral occipitotemporal regions from approximately 700 ms onward. In comparison with previous tasks using multiple repetitions at short delays, these effects were centered within the same areas (anteroventral temporal and ventral prefrontal) but were shifted to longer latencies (approximately 500 ms vs. approximately 200 ms), were less left-lateralized, and appear more in anterolateral prefrontal regions and less in lateral temporal cortex. Furthermore, comparison of correctly classified words with misclassified, novel and repeated words, suggests that these frontotemporal-parietocingulate responses are sensitive to actual as well as perceived repetition. The results also suggest that lateral prefrontal regions may participate more in controlled effortful retrieval, while left ventral frontal and anterior temporal responses may support sustained lexicosemantic processing. Additionally, left ventromedial temporal sites may be relatively more involved in episodic retrieval, while lateral temporal sites may participate more in automatic priming.