Orbitofrontal reality filtering

Abstract

Decades of research have deepened our understanding of how the brain forms memories and uses them to build our mental past and future. But how does it determine whether an evoked memory refers to the present and can be acted upon? The study of patients who confuse reality, as evident from confabulation and disorientation, has opened ways to explore this vital capacity. Results indicate that the brain recurs to a phylogenetically old faculty of the orbitofrontal cortex - extinction - and structures of the reward system to keep thought and behavior in phase with reality.

Keywords: confabulations; continuous recognition; orbitofrontal cortex; reality monitoring; reward system.

Figure 1

Anatomy of reality filtering. (A) Typical orbitofrontal lesion causing reality confusion. In this case, the right gyrus rectus is destroyed (arrowheads) following rupture of an aneurysm of the anterior communicating artery. (B,C) Superimposition of the lesions of 14 patients who confused reality for weeks to months. (B) Sagittal cut; (C) axial cut. As indicated by the shades of gray, maximal lesion overlap was in the posterior medial orbitofrontal area. The white crosses indicate the area of peak activity in healthy subjects who performed a similar task as the one on which the reality-confusing patients failed. (B,C) Reproduced from Schnider (2008), with permission.

Figure 2

Task to measure the sense of present reality. Subjects make two runs (or more) of a continuous recognition task, each run composed of the same set of pictures. Subjects have to indicate, in both runs, only repetitions within the ongoing run (original version: Schnider et al., 1996a). (A) The first run demands learning and recognition and can be solved on the basis of familiarity alone. (B) In the second run, all items are already familiar. The task now demands the ability to distinguish between memories that pertain to the ongoing run (repetitions within the run, T2) and memories that do not (d2; not previously presented within the run, albeit familiar from the first run). Confabulating patients had a steep increase of false positives in response to d2 stimuli. “d” denotes “distracters,” i.e., pictures’ first appearance within a run; “T” denotes targets, i.e., repeated pictures within the run. “d1” and “T1” are stimuli presented in the first run, “d2” and “T2” are stimuli of the second run. “Yes” and “no” indicate correct responses. Illustration reproduced from Schnider (2008), with permission.

Figure 3

Functional model of the orbitofrontal reality filter. (A) Normal function: 200–300 ms after activation of a memory (thought), reality filtering sets in, inhibiting extended neocortical activation when the upcoming memory does not relate to ongoing reality. At 400–600 ms, the activated memory (thought) is recognized and again encoded (Schnider et al., ; Wahlen et al., 2011). (B) Hypothetical dysfunction of reality filtering in reality-confusing patients: memories (thoughts) are normally activated, but are not checked regarding their relation with reality; all memories are activated, and later recognized and re-encoded, as if they related to ongoing reality. Adapted from Schnider (2008), with permission.