Selection of Currently Relevant Memories by the Human Posterior Medial Orbitofrontal Cortex

Abstract

We have demonstrated previously that patients producing spontaneous confabulations fail to suppress currently irrelevant memory traces, so that they act and think on the basis of a false, temporally displaced (past) reality. All spontaneous confabulators had anterior limbic damage, in particular of the orbitofrontal cortex and basal forebrain. These findings indicated that these structures are essential for distinguishing between mental representations of ongoing reality and currently irrelevant memories. In the present study, we used a similar experimental paradigm as in our clinical studies and H 2 15O positron emission tomography to explore the selection of currently relevant memories by the healthy human brain. Subjects were repeatedly presented with the same set of pictures, arranged in different order each time, and were requested to indicate picture recurrences within the runs. Thus, performance in the first run depended on new learning, whereas subsequent runs required the distinction between picture repetitions within the current run ("now") and previous picture presentations in earlier runs. Whereas initial learning activated medial temporal structures, subsequent runs provoked circumscribed posterior medial orbitofrontal activation. We suggest that this area is essential for sorting out mental associations that pertain to ongoing reality.

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

“…In adults, the mechanism depended on the orbitofrontal cortex: lesions always involved the posterior medial orbitofrontal cortex (area 13) or directly connected structures (Schnider, 2008;Schnider et al, 1996a;Schnider & Ptak, 1999). Functional imaging studies in healthy subjects showed activation in the orbitofrontal cortex area 13 in the second run of continuous recognition tasks, either when using pictures (Schnider, Treyer, & Buck, 2000;Treyer, Buck, & Schnider, 2003) or meaningful sounds (Treyer, Buck, & Schnider, 2006). 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reality filtering appears to be similar to extinction capacity, the ability to abandon anticipations that are no longer valid (Nahum, Ptak, Leemann, & Schnider, 2009).…”

Confabulation: Damage to a specific inferior medial prefrontal system

“…This function has also been specifically linked to the anterior limbic system, of which the orbitofrontal cortex is a central component (Schnider, Treyer and Buck, 2000;Treyer et al, 2003). Most recently, Gilboa, Moscovitch and colleagues (Gilboa, 2004;Gilboa and Moscovitch, 2002;Gilboa et al, 2006) have suggested that confabulation results from failure of a monitoring system which facilitates early, intuitive rejection of false memories o n t h e b a s i s o f " f e e l i n g o f r i g h t n e s s " .…”

Orbitofrontal reality filtering

“…When subjects do such a task for the first time, they can recognize picture repetitions on the sole basis of familiarity (Figure 2A). Healthy subjects performing such a first run activated the hippocampal area (Schnider et al, 2000b). As subjects repeat the task, always composed of the same picture series, familiarity alone is not sufficient anymore; all items look familiar.…”

“…When healthy subjects performed repeated runs of this task, they had activation of the posterior medial orbitofrontal cortex, area 13 ( Figures 1B,C) (Schnider et al, 2000b), which corresponds to the area of maximal damage in patients who confuse reality.…”