Often represented in cartoons as the little devils or angels that sit upon our shoulders, our internal monologues aren't just our conscience speaking to us. Also known as our inner voice or internal speech, this stream of verbal consciousness can take almost any form: from running through a list of things you need to do today, to playing out past conversations, or imagining new ones.

According to Peter Mosely, a psychologist with Durham University in the UK, understanding where inner monologues come from and how they work in healthy people could help us treat those who hear imaginary voices in harmful ways – such as people with schizophrenia or other serious mental disorders.

Mosely is involved with Hearing the Voice, a project that aims to better understand why some people hear voices in the absence of any external stimuli – also known as auditory verbal hallucinations.

Psychologists have a long history when it comes to studying the inner voice. Russian psychologist Lev Vygotsky suggested back in the 1930s that our internal monologue was tied to our ability to speak aloud. And the technique of electromyography, which measures muscle movement, shows that our larynx is actually active during inner speech.

But it's more recent research that's getting us closer to understanding where the internal monologue really comes from, says Mosely. Neuroimaging testing performed in the 1990s demonstrated that parts of Broca's area - the region of the brain responsible for speech - are also active when our inner voice is speaking to us.

According to Mosely, auditory verbal hallucinations "might simply be a form of inner speech that has not been recognised as self-produced". Evidence to support this view is that the same regions of the brain that are active during inner speech, such as Broca's area, are also active during auditory hallucinations.

Interestingly, a 2012 study by researchers in Finland found that brain activity was different when people heard auditory hallucinations from when they tried to imagine the same voices. The researchers discovered that during auditory hallucinations, less activity occurred in the supplementary motor area of the brain, which is tied to self-awareness. They hypothesised that this lower level of neural activity in the supplementary motor area could prevent "the sense of ownership of one's own verbal imagery".

Not that the search for where our inner voice originates should come at the expense of all other psychological research and treatments for people who experience auditory hallucinations, Moseley points out. "We also need to understand what the experience is like, how we can help people who are distressed by it, and when there's a need for psychiatric care," he says. "But to do any of this, we first need to know what typical inner speech is like, and the underlying neuroscience is part of that understanding."