Resting brain activity reveals two anticorrelated cortical systems linked to conscious awareness: an extrinsic system (lateral fronto-parietal areas) associated with external awareness and an intrinsic system (medial brain areas) associated with internal awareness. In 31 healthy volunteers, external and internal awareness were significantly anticorrelated, with a mean switching frequency of 0.05 Hz, similar to BOLD fMRI slow oscillations. In 22 volunteers, fMRI showed that precuneus/posterior cingulate, anterior cingulate/mesiofrontal cortices, and parahippocampal areas (intrinsic system) correlated with internal awareness, while lateral fronto-parietal cortices (extrinsic system) correlated with external awareness.
Near-Death Experiences (NDEs) are not well explained. Because NDEs are sometimes considered imagined, researchers compared the phenomenological characteristics of NDE memories with memories of real and imagined events. Coma survivors with NDEs (8), with coma memories but no NDE (6), and without coma memories (7), plus 18 healthy volunteers, completed the Memory Characteristics Questionnaire. NDE memories had more characteristics than memories of imagined or real events, and more self-referential and emotional information and better clarity than coma memories. These findings suggest NDE memories cannot be considered imagined events; they may be perceived as real despite not being lived in physical reality.