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

Abstract

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.

Rapid consolidation and the human hippocampus: Intracranial recordings confirm surface EEG

“…Studies using surface EEG had shown late-amplitude differences over temporal or parietal scalp electrodes (Friedman, 1990;Schnider et al, 2002;Kayser et al, 2003). According to spatiotemporal analyses, however, these amplitude differences appeared in the context of similar electrocortical patterns and hence reflected amplitude modulation of similar cortical networks rather than different generators (Schnider et al, 2002;James et al, 2009). The present findings obtained with depth electrodes confirm the latter interpretation.…”

Children’s sense of reality: The development of orbitofrontal reality filtering

“…The mechanism underlying orbitofrontal reality filtering appears to be similar to extinction capacity, the ability to abandon anticipations that are no longer valid (Nahum, Ptak, Leemann, & Schnider, 2009). Recent studies have shown that this process is rapid (200-300 ms after stimulus presentation; Schnider, Valenza, Morand, & Michel, 2002), and that it dissociates from other memory control processes like context source memory (BouzerdaWahlen, Nahum, Liverani, Guggisberg, & Schnider, 2014;Johnson, Kounios, & Nolde, 1997;Mitchell & Johnson, 2009), strategic retrieval monitoring (BouzerdaWahlen, Nahum, Ptak, & Schnider, 2013;Gilboa et al, 2006;Wahlen, Nahum, Gabriel, & Schnider, 2011) and temporal order memory (Liverani et al, 2015). These processes are laborious and have different signatures in evoked potential studies (Bouzerda-Wahlen et al, 2014;Liverani et al, 2015;Wahlen et al, 2011).…”

Behaviorally spontaneous confabulation in limbic encephalitis: The roles of reality filtering and strategic monitoring

“…Finally, the extinction task used in this and our previous study (Nahum et al, 2009 ) requires explicit, conscious decisions. It is, therefore, unlikely to be a perfect measure of the pre-conscious process that reality fi ltering seems to be (Schnider et al, 2002 ). Nonetheless, the construction of tasks attempting to test theories of confabulation is crucial for future progress.…”

“…Positron emission tomography studies with healthy subjects performing adapted versions of the same task demonstrated activation of the posterior orbitofrontal cortex (area 13) (Schnider, Treyer, & Buck, 2000 ) and subcortical loops (Treyer, Buck, & Schnider, 2003 ). An evoked potential study indicated that the correct judgment of items as not-pertaining-to-now (the avoidance of false positive responses) occurs at an early stage of processing, at approximately 200-300 ms, before processes of (conscious) recognition and re-encoding set in (Schnider, Valenza, Morand, & Michel, 2002 ). Based on these fi ndings, the reality fi lter hypothesis holds that the reality confusion characterizing behaviorally spontaneous confabulation emanates from the failure of a preconscious orbitofrontal mechanisms that suppresses the interference of memories that do not pertain to ongoing reality (Schnider, 2008 ).…”

“…This distinction (fi ltering) process has an electrocortical correlate -absence of a specifi c electrocortical map confi guration-at an early stage in the re-activation of memories, at 200-300 ms, that is, even before the content of an upcoming memory is consciously recognized and again encoded (Schnider, 2003 ;Schnider et al, 2002 ).…”