Our brain considers talking to ourselves in our minds very similar to talking to other people, according to new research, and that could help us get a better understanding of mental conditions like schizophrenia.
In other words, if you're keeping up a silent dialogue with yourself, as far as certain parts of your brain activity are concerned, it's not that much different to chatting to someone else.
Based on electroencephalography (EEG) scans of 42 individuals, the team looked at the effects of the efference copy created by our brains – a copy of the instructions also being sent to our mouth, lips, and vocal cords.
By having this copy, the brain knows what we're about to say, and can use that information to distinguish other voices. You see the same internal process happening when people try and tickle themselves: it doesn't work, because they're expecting it.
The efference copy reduces the impact of the sound of our own voice in our minds, so we're better able to deal with unexpected voices and sounds. What the research found was that this reduction still happened, even when the words weren't spoken.
"The efference copy dampens the brain's response to self-generated vocalisations, giving less mental resources to these sounds, because they are so predictable," says lead researcher Thomas Whitford, from the University of New South Wales in Sydney, Australia.
If you want to test it out, try playing a recording of your voice rather than speaking some words out loud – your brain will have a stronger, more active response, because there's no efference copy.
That recording sounds louder to your brain than speaking out words at the same volume, and what this new research shows is that the brain applies the same sort of quietening in our minds for internal monologues.
In fact, that's exactly the test the researchers ran – playing voice recordings and asking the volunteers to either imagine something different, or imagine the same words in their heads.
As far as future research goes, knowing how this efference copy mechanism works could help us understand and treat mental problems like schizophrenia, where people imagine voices in their head.
The researchers suggest that perhaps what's happening is the dampening or quietening just isn't happening as it should, so to our brains these internal voices end up sounding like someone else.
And if you do spend a lot of time wittering away to yourself in your own head, don't worry too much about it: it's estimated that about a quarter of us do the same.
"By providing a way to directly and precisely measure the effect of inner speech on the brain, this research opens the door to understanding how inner speech might be different in people with psychotic illnesses such as schizophrenia," says Whitford.
The research has been published in eLife.