Near-death experiences (NDEs), including out-of-body experiences (OBEs), can be explained by neuro-functional models of altered brain states. By comparing reports from original NDEs with those from experimental settings—such as drug consumption, epilepsy, brain stimulation, ischemic stress, and fighter pilot tests under gravitational stress causing cephalic nervous system ischemia—a large overlap of themes emerged. These models offer scientifically appropriate causal explanations for NDEs. The generation of OBEs can be localized to the temporo-parietal junction, a multimodal association area. The literature suggests that NDEs may arise as hallucination-like phenomena from a brain in altered states of consciousness.
Neural markers of consciousness derived from human event-related potentials and gamma-wave activity can be applied to other species. In mammals and birds, these markers suggest that individuals in these groups can become subjectively aware of and conscious about perceived stimuli. For fish, cephalopods, and insects, the data remain inconclusive. Awareness and consciousness appear as evolved, attention-dependent options added to ongoing stimulus processing and action generation. Because gamma-wave generation for functional coupling of brain areas in conscious states is energetically costly, it remains to be shown which species gain reproductive fitness advantages from these options. The discussion begins with whether these brain activities are necessary for adaptive stimulus perception and response.