Abstract
Any thought, whether it refers to the present moment or reflects an imagination, is again encoded as a new memory trace. Orbitofrontal reality filtering (ORFi) denotes an on-line mechanism which verifies whether upcoming thoughts relate to ongoing reality or not. Its failure induces reality confusion with confabulations and disorientation. If the result of this process were simultaneously encoded, it would easily explain later distinction between memories relating to a past reality and memories relating to imagination, a faculty called reality monitoring. How the brain makes this distinction is unknown but much research suggests that it depends on processes active when information is encoded. Here we explored the precise timing between ORFi and encoding as well as interactions between the involved brain structures. We used high-density evoked potentials and two runs of a continuous recognition task (CRT) combining the challenges of ORFi and encoding. ORFi was measured by the ability to realize that stimuli appearing in the second run had not appeared in this run yet. Encoding was measured with immediately repeated stimuli, which has been previously shown to induce a signal emanating from the medial temporal lobe (MTL), which has a protective effect on the memory trace. We found that encoding, as measured with this task, sets in at about 210 ms after stimulus presentation, 35 ms before ORFi. Both processes end at about 330 ms. Both were characterized by increased coherence in the theta band in the MTL during encoding and in the orbitofrontal cortex (OFC) during ORFi. The study suggests a complex interaction between OFC and MTL allowing for thoughts to be re-encoded while they undergo ORFi. The combined influence of these two processes at 200–300 ms may leave a memory trace that allows for later effortless reality monitoring in most everyday situations.
Highlights
Based on the observation of patients who suffer from confabulations and disorientation, we have described a mechanism which appears to filter upcoming thoughts and memories according to their relation with current, ongoing reality (Schnider, 2003, 2008)
Correct response to such stimuli evoked a frontal positivity at about 200–300 ms (Schnider et al, 2002; Wahlen et al, 2011; Bouzerda-Wahlen et al, 2015), which emanated from the posterior medial orbitofrontal cortex (OFC) (Schnider et al, 2000; Bouzerda-Wahlen et al, 2015)
This study indicates that as thoughts undergo Orbitofrontal Reality Filtering’’ (ORFi), they are simultaneously encoded about 200–300 ms after their evocation
Summary
Based on the observation of patients who suffer from confabulations and disorientation, we have described a mechanism which appears to filter upcoming thoughts and memories according to their relation with current, ongoing reality (Schnider, 2003, 2008) We call this mechanism ‘‘Orbitofrontal Reality Filtering’’ (ORFi; Schnider, 2013). Correct response to such stimuli evoked a frontal positivity at about 200–300 ms (Schnider et al, 2002; Wahlen et al, 2011; Bouzerda-Wahlen et al, 2015), which emanated from the posterior medial OFC (Schnider et al, 2000; Bouzerda-Wahlen et al, 2015) This frontal positivity seems to signal that an upcoming thought (memory) does not pertain to the ongoing reality. We used this frontal potential as a marker for ORFi
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