Talking to ourselves in our heads may be the same as speaking our thoughts out loud as far as our brain is concerned, according to new research from the University of New South Wales.The findings may have implications for better understanding why individuals with mental illnesses hear voices, such as observed in schizophrenia.
Professor Thomas Whitford says that is has been assumed these auditory verbal hallucinations arise from abnormalities in inner speech, the silent internal dialogue, and this study provides the tools for further investigation of this once untestable assumption.
Research conducted in the past suggests that when beginning to speak aloud the brain makes a copy of the instructions about to be sent to the vocal cords, mouth, and lips, called an efference copy. This is sent to the region of the brain that is responsible to process sound to predict what sounds it is about to hear, allowing the brain to distinguish between sounds we produce, and the sounds that are produced by others.
These copies dampen the response the brain has on sounds that are self generated, giving less mental resources to them because they are predictable. This is also why we can not tickle ourselves explains Whitford.
The study was conducted to determine whether the internal mental process, of inner speech elicits a similar efference copy as the one with the production of spoken words. The findings of this study were published in the journal eLife.
Researchers devised an objective method for calculating the mental actions involved in inner speech. The study involved 42 healthy participants that were assessed to that degree with imagined sounds interfering with brain activity generated with actual sounds using an EEG.
The research findings were that the act of imagining the sounds was the same as for actual vocalized speech, that imaging sounds reduced the brain activity that occurred when simultaneously hearing that sound. The imagined thoughts were enough to change the way the brain perceived the sounds. When people imagined sounds, they seemed quiter.
This study may provide a manner in which to possibly understand how inner speech might be different in people with psychotic illnesses says Whitford. Adding that we all have heard voices in our heads, the problem may be when the brain is unable to tell that we are making the sounds ourselves.
