Early Cortical Distinction between Memories that Pertain to Ongoing Reality and Memories that Don't

Patients with anterior limbic lesions, in particular of the posterior orbitofrontal cortex, often act on the basis of memories that do not relate to ongoing reality and justify their behavior with invented stories that can mostly be traced back to real events (spontaneous confabulation). Recent studies demonstrated that the patients fail to suppress activated memory traces that do not pertain to ongoing reality. In the present study, we used a similar paradigm and high-resolution event-related potentials to explore when this suppression happens. Healthy subjects made two runs of a continuous recognition task, composed of the same set of pictures, and were requested to indicate picture recurrences only within the ongoing run. Thus, performance in the first run depends on new learning, whereas the second run requires the ability to realize whether a picture is solely familiar from its occurrence in the previous run ('distracter') or whether it has already appeared in the ongoing second run ('target'). We find that correct rejection (suppression) of currently irrelevant pictures (distracters of run 2) is associated with absent negative deflection of a frontal potential and absence of a specific cortical potential map configuration after 220-300 ms. By contrast, learning and recognition of repeatedly presented information is associated with cortical amplitude modulation after 400-480 ms. These findings indicate that by the time the content of a mental association is recognized and consolidated, its cortical representation has already been adjusted according to whether it relates to ongoing reality or not. This sequence may also explain the ability to distinguish between the memory of a true event and the memory of a thought.