The shamanic state is a human constant, arising from the substrate of the brain. Hunter-gatherer shamanism is based on altered states of consciousness, induced  by a variety of means. This paper examines shamanism from a neuropsychiatric perspective, looking at hallucinations, epilepsy, schizophrenia and other psychoses, lycanthropy, and sleep disorders. While the majority of shamanic individuals do not have neuropsychiatric disorders, examination of these conditions can illustrate the underlying brain mechanisms.

The speciation of Homo sapiens led to lateralisation of the brain with significant expansion in the left temporo-occipital region that allowed the use of symbolism. Laterality changes - decreased left / increased right hemisphere dominance - link schizophrenia, schizotypy and increased creativity. From this it was a short step to the phenomena intrinsic to shamanism.