The data presented in this chapter, together with the observations reported in the previous chapters, can be summarized as follows. 1. Behaviourally spontaneous confabulation represents a confusion of reality, which induces currently inappropriate ideas (confabulations and disorientation) and acts (typically the enactment of previous habits). The patients’ reality is determined by elements of memories that do not relate to the present. 2. When behaviourally spontaneous confabulation results from focal brain damage, then damage involves anterior limbic structures (Figure 4.12). Damage may...
The data presented in this chapter, together with the observations reported in the previous chapters, can be summarized as follows. 1. Behaviourally spontaneous confabulation represents a confusion of reality, which induces currently inappropriate ideas (confabulations and disorientation) and acts (typically the enactment of previous habits). The patients’ reality is determined by elements of memories that do not relate to the present. 2. When behaviourally spontaneous confabulation results from focal brain damage, then damage involves anterior limbic structures (Figure 4.12). Damage may involve the posterior medial orbitofrontal cortex itself or structures having direct connections with it. According to lesion (Figure 4.12) and functional imaging data (Schnider et al. 2000b) (Figure 8.8), the functionally critical parts of the orbitofrontal cortex appear to be area 13 (Figure 4.2b) plus the ventromedial cortex. 3. Patients having the reality confusion typical of behaviourally spontaneous confabulation have a specific failure to distinguish between memories that pertain to ongoing reality and memories that do not (Schnider et al. 1996b). This failure is based on an inability to suppress the interference of memories that do not relate to ‘now’ (Schnider and Ptak 1999). 4. The failure to suppress (filter) the interference of currently irrelevant memories is also closely associated with disorientation (Schnider et al. 1996c) and appears to be a more important mechanism of disorientation in amnesic subjects than the difficulty to store enough information (Figure 8.3, see also Figure 5.3). 5. Recovery from behaviourally spontaneous confabulation, that is, the recovery of reality perception, is accompanied by the recovery of the ability to suppress the interference of memories that to not pertain to current reality (Schnider et al. 2000a). Most behaviourally spontaneous confabulators eventually regain the capacity to adapt behaviour and thought to ongoing reality; in some cases, this process may take many months. Most patients remain amnesic. 6. In the healthy brain, the need to exert such suppression (filtering) induces orbitofrontal activity centred on area 13 on both sides (Schnider et al. 2000b; Treyer et al. 2003) (Figure 8.8). 7. This filtration is a relatively early process occurring about 200–300 ms after stimulus presentation and precedes the stage of recognition and re-encoding (Schnider et al. 2002). That is, even before the content of a memory is recognized and re-encoded, the brain (orbitofrontal cortex) has already decided whether the forthcoming memory relates to ongoing reality or not. This sequence of events not only allows one to base behaviour on memories (thoughts) that pertain to ongoing reality, but also explains the capacity to distinguish between memories relating to previous real events and memories relating to thoughts. 8. Suppression of currently irrelevant memories (filtration) is cortically expressed by the absence of an electrocortical map configuration at 200–300 ms (Schnider et al. 2002). Source estimations suggest that suppression corresponds to the transient inhibition of neocortical synchronization, so that forthcoming memories having no relation with ongoing reality (fantasies) leave out a processing stage characterized by widespread neocortical synchronization (Schnider 2003). 9. An orbitofrontal–subcortical loop involving the ventral striatum, body of the striatum, substantia nigra and medial thalamus participates in the selection of currently relevant memories (Treyer et al. 2003) (Figure 8.11). Several of these structures are also part of the dopaminergic projection system. 10. Orbitofrontal area 13 is also activated in tasks involving other modalities (hearing) (Treyer et al. 2006b) and varying tasks performed in a constant environment, such as baseline tasks (Treyer et al. 2006a). The filtration of forthcoming memories appears to be a ubiquitous brain function. 11. The reality confusion underlying behaviourally spontaneous confabulation and disorientation probably results from the failure of this pre-conscious orbitofrontal memory filtering mechanism.
Chapter. 14549 words. Illustrated.
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