The Neuropsychology of Hallucinations

D.M. Pavlovic and A.M. Pavlovic, Archives of Biological Sciences, 2011, 63, 1, 43-48.

Excerpt: An interesting hypothesis is posed by Julian Jaynes (1976) on the “bicameral brain” where one hemisphere (right) gives orders and the other (left) listens and executes orders. This Latin term means “consisting of two chambers” and is used in contemporary language for two legislative or parliamentary chambers. According to the bicameral theory, up to around 1000 BC, humans used the right hemisphere to process the supernatural voices of “gods” and “demons” (actually hallucinations), and the left one to produce speech. People of that era were not self-conscious and could not, for example, distinguish between the living and the dead, hence the cult of ancestors, embalming and the like. The collapse of bicameralism occurred during the second millennium BC, due to the great migrations and growing social complexity that required changes in the human mind towards a greater flexibility, introspection and abstraction. Societies that did not evolve in this direction disappeared (the ancient Maya, the Middle Kingdom of ancient Egypt and others). In schizophrenia, the brain processes are again bicameral. These patients experience auditory hallucinations as commands in the same way the ancient people, according to the theory of bicameralism, received “God’s” commandments.Studies have shown that patients with schizophrenia indeed have reduced cerebral lateralization. Results are still controversial. The latest studies have shown bilateral activation of Broca’s area instead of only left side activation that brings new life to the theory of mind bicameralism (Weiss et al., 2006). The reduction of lateralization even correlated with the intensity of hallucinations. Another assumption is that in patients lacking adequate ACC-left upper temporal lobe connection there is an erroneous impression that inner speech has an external source.