If you’ve ever had an imaginary argument in your head, you may have “heard” two voices at once. Your own inner voice and that of the other person in the dispute. You can even “hear” the other person’s accent or pitch of voice.
So what happens in the brain when is this interior monologue running? How is it that you can “hear” your thoughts?
It turns out the brain goes through similar processes when you think words and when you speak out loud.
Interior monologues are considered a simulation of open speech, said Hélène Loevenbruck, a senior neurolinguistics researcher and head of the linguistics team at the Psychology and Neurocognition Laboratory at CNRS, France’s national research institute. When we are children, we are virtual sponges, absorbing new information from all angles. Children playing alone will often talk aloud, such as between a toy truck and a stuffed animal. Towards 5 to 7 years old (opens in a new tab)that verbalization moves inward, Loevenbruck said.
Related: Does everyone have an interior monologue?
Previous studies (opens in a new tab) showed that the brain exhibits similar activity with internal speech and with verbalized speech. When study participants are asked to deliberately ‘talk’ in their heads while lying in a magnetic resonance imaging (MRI) machine, scientists can see parts of the brain that process auditory information activate as if the participant actually hears the words.
“The brain regions activated during inner speech are quite similar to those activated during open speech during actual speech,” Loevenbruck told Live Science. These regions include the frontal lobe and the parietal lobe of the left hemisphere, which help process external stimulation.
But when you think of something like a fictional argument with another person, the brain goes even further. During this internal argument, you play two roles: yourself and the person with whom you are arguing. When you play yourself, the auditory centers on the left side of your brain activate, Loevenbruck said. But when you switch roles internally to play the person you’re arguing with, “there’s kind of a shift in activation from the brain region to the right hemisphere,” in equivalent areas like the parietal lobe and the frontal lobe, she continued. Seeing the situation from a different perspective, even if it’s a perspective you’re working out in your head, changes which regions of the brain are engaged.
The researchers also observed this phenomenon when participants were asked to imagine the movement, Leovenbruck continued. Dancers, for example, use another part of their brain to imagine themselves dancing against someone else dancing, a study published in the August 2005 issue of the journal Cerebral cortex (opens in a new tab) found.
It’s one thing to see these brain regions activate when we tell a person to think something, but we understand much less about what’s going on in our brains when we let our minds wander, Leovenbruck said. Not all interior monologues are deliberate. Sometimes words or phrases pop into your head, unprovoked.
This phenomenon may have something to do with the brain’s “default mode network” (DMN), said Robert Chavez, a neuroscientist at the University of Oregon. The DMN is a network of brain areas that are active when not engaged in a specific task. The DMN is thought to be involved in aspects of internal thinking, such as retrieving memories, imagining the future, or interoception – a sense or “feeling” of what is going on in your body, like hunger or thirst.
“The default mode network seems to be most active when your mind wanders,” Chavez told Live Science. Since default mode networking involves planning for the future by leveraging memories, recent experiences, and mental associations, it is believed that this combination of activities give place (opens in a new tab) to an inner monologue as you focus inward.
Much more research is needed to understand how inner thoughts arise spontaneously, Leovenbruck said. When taken to extremes, inner thoughts can become dysfunctional, such as rumination after an uncomfortable or traumatic event, or in mental disorders, such as schizophrenia, in which people experience auditory hallucinations.
Originally posted on Live Science.