The theory of the bicameral mind proposed by psychologist Julian Jaynes has fallen from fashion since the 1970s, as investigators of philosophy and medical science find more harmony between the two hemispheres of the human brain, interwoven for the purpose of speech.

Jaynes posited that our experience of consciousness emerged only 3,000 years ago in modern human history, before which the two hemispheres of the brain worked independently for the most part, creating an effect similar to the schizophrenic's auditory auditory hallucination as a “command from God” obeyed with little to no self-awareness. Now scientists continue to plumb the depths of human consciousness, while others study speech and language so connected to our consciousness. The observation contradicts a longstanding theory the brain lateralizes speech and language to the left hemisphere of the brain.

The discovery may lead to better speech therapies for stroke and other brain injury, too.

“Our findings upend what has been universally accepted in the scientific community — that we use only one side of our brains for speech,” said Bijan Pesaran, an associate professor at New York University’s (NYU) center for neural science who helped with the study. “In addition, now that we have a firmer understanding of how speech is generated, our work toward finding remedies for speech afflictions is much better informed.”

Scientists had based previous conclusions about speech lateralization in the brain on studies relying on indirect measurement of neurological activity, whereas the NYU team made direct observations of study participants implanted with specialized electrodes placed on the surface and within brain tissue. Thomas Thesen, director of the NYU ECoG Center, described observations of the brain functioning of patients with epilepsy. “Recordings directly from the human brain are a rare opportunity,” he said in a statement. “As such, they offer unparalleled spatial and temporal resolution over other imaging technologies to help us achieve a better understanding of complex and uniquely human brain functions, such as language.”

Previous models of speech and language proposed that both perceptual processing of speech and motor production processes — the call and response of conversation — occurred in the left side of the brain, within the left posterior superior temporal gyrus and the left inferior frontal gyrus, respectively. Now the NYU team has observed “robust sensory/motor neural responses” in the perception and response of the experiment’s speech task.

In the study, the investigators prompted participants with a couple of made-up words — “kig” and “pob” — to isolate speech from language in their observations. When engaged in speech, participants used both sides of the brain, as opposed to the more lateralized activity associated with other functions, Pesaran explained.

“Now that we have greater insights into the connection between the brain and speech, we can begin to develop new ways to aid those trying to regain the ability to speak after a stroke or injuries resulting in brain damage,” he said. “With this greater understanding of the speech process, we can retool rehabilitation methods in ways that isolate speech recovery and that don’t involve language.”

Source: Cogan GB, Thesen T, Carlson C, Werner D, Devinsky O, Pesaran B. Nature. 2014.