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==== HYPOTHESIS FOUR: THE NEUROLOGICAL MODEL FOR BICAMERAL MENTALITY ====

**Theoretical Claim**

Jaynes contended that the two-chambered mentality lateralized language so that what conscious people call volition took the form of hallucinatory “voices of the gods” (right hemisphere) who commanded the human “listener” (left hemisphere). So far a number of brain imaging studies have confirmed Jaynes’s arguments.

**Supporting Evidence**

//The Neurological Basics of Speech//

Natural selection often ensures protective redundancy in its design of organisms so that most functions are bilaterally represented. But if the most crucial functions are bilaterally represented within our brains, why are our speech regions (located in the left hemisphere, the supplementary motor cortex; Broca’s area; and Wernicke’s area), that subserve an indispensable human ability, laterally dominant in the left cerebral hemisphere (this is for right-handed people; about 5%—lefties—have mixed or right-side dominance)? This is even more mysterious when one considers that corresponding structures for language do exist in the right hemisphere. Jaynes argued that they once had an important function in humankind’s past While presently right-sided neurological structures play some role in language, they are not dominant for most of us. 

Jaynes proposed a "stronger" and a "weaker" version of Hypothesis Four. The stronger form, which for Jaynes is more convincing and easier to prove, postulates that the speech of the gods was produced by what corresponds to the Wernicke’s area on the right hemisphere. It was then “spoken” to the auditory areas of the left temporal lobe.

The weaker from states that the articulatory qualities of the hallucination were of left hemisphere origin like the speech of the person himself. However, its sense, direction, and different relation to the person arose due to right temporal lobe activity sending excitation over the anterior commissures as well as the splenium (back part of the corpus callosum) to the left hemisphere’s speech regions, and then “heard” from there (Jaynes, 1990, pp. 105‒106).

The central feature of both forms is that the “amalgamating of admonitory experience was a right hemisphere function and it was excitation in what corresponds to Wernicke's area on the right hemisphere that occasioned the voices of the gods” (Jaynes, 1976, p. 106).

//Evidence Supporting Bicameral Neurology//

First, note that both hemispheres can understand language, though normally only the left can speak. Jaynes relied on the groundbreaking experiments of the neuroscientist M. S. Gazzaniga (1939‒), neurophysiologist J. E. Bogen (1926‒2005), and neuropsychologist R. W. Sperry (1913‒1994) 
to make his arguments.

Second, if you stimulate what corresponds to the Wernicke’s area on the right, nondominant side people will hear voices. These voices possess a quality of otherness, as if coming from an entity opposed to the person’s normal self. There is, then, some vestigial functioning of the right hemisphere’s Wernicke's area that are similar to the voices of gods.

Third, under certain conditions the two hemispheres can act almost as if independent persons. Indeed, their interaction seems to correspond to that of the god‒human relationship of bicameral times.
Fourth, contemporary differences between the hemispheres in cognitive operations parallel similar variations of function between god and mortals as seen in the ancient texts of the bicameral period.

The right hemisphere focuses on the guiding and planning of behavior in novel circumstances. Its prerogative is organizational, cataloguing, categorizing, sorting out, and synthesizing, operations that would be expected from a supervising divine being concerned with building civilizations and stabilizing social relations. An examination of the speech of gods as recorded in ancient texts illustrates this.

Fourth, neuroplasticity. The brain is much more capable of being configured by the environment than we once understood. This means that the human neurological system could have undergone dramatic changes—from bicamerality to consciousness—mostly on the basis of learning and culture. The early developmental history of an individual can make a huge difference in how the brain is organized. Moreover, neuroplasticity gives an organism impressive adaptability in the face of relentlessly changing environmental challenges. 

Finally, evidence from brain imaging studies over the past 40 years. (MK to add).

//"Hardware" versus "Software"//

Jaynes never claimed that the brains of ancient peoples were in an anatomical sense substantially different from our own. In other words, the “hardware” is the same, but the “software” (sociolinguistic environment) is not, and this difference led to the cultural invention of an introspectable subjective space in which a self dwells.

See also: [[https://www.julianjaynes.org/blog/featured/neuroscience-confirms-julian-jaynes-neurological-model/|Neuroscience Confirms Julian Jaynes’s Neurological Model]]