Early onset of neural synchronization in the contextual associations network.

Objects are more easily recognized in their typical context. However, is contextual information activated early enough to facilitate the perception of individual objects, or is contextual facilitation caused by postperceptual mechanisms? To elucidate this issue, we first need to study the temporal dynamics and neural interactions associated with contextual processing. Studies have shown that the contextual network consists of the parahippocampal, retrosplenial, and medial prefrontal cortices. We used functional MRI, magnetoencephalography, and phase synchrony analyses to compare the neural response to stimuli with strong or weak contextual associations. The context network was activated in functional MRI and preferentially synchronized in magnetoencephalography (MEG) for stimuli with strong contextual associations. Phase synchrony increased early (150-250 ms) only when it involved the parahippocampal cortex, whereas retrosplenial-medial prefrontal cortices synchrony was enhanced later (300-400 ms). These results describe the neural dynamics of context processing and suggest that context is activated early during object perception.