Hallucinations linked to differences in brain structure

 People with schizophrenia who are prone to hallucinations are likely to have structural differences in a key region of the brain compared to healthy individuals, a new study has found.

The study shows that reductions in the length of the paracingulate sulcus (PCS), a fold towards the front of the brain, were associated with increased risk of hallucinations in people diagnosed with schizophrenia.

In a previous study, a team of researchers led by Jon Simons from the University of Cambridge in UK, found that variation in the length of the PCS in healthy individuals was linked to the ability to distinguish real from imagined information, a process known as 'reality monitoring'.

In this study, Simons and his colleagues analysed 153 structural MRI scans of people diagnosed with schizophrenia and matched control participants, measuring the length of the PCS in each participant's brain.

As difficulty distinguishing self-generated information from that perceived in the outside world may be responsible for many kinds of hallucinations, the researchers wanted to assess whether there was a link between length of the PCS and propensity to hallucinate.

The researchers found that in people diagnosed with schizophrenia, a 1cm reduction in the fold's length increased the likelihood of hallucinations by nearly 20 per cent.

The effect was observed regardless of whether hallucinations were auditory or visual in nature, consistent with a reality monitoring explanation.

"By comparing brain structure in a large number of people diagnosed with schizophrenia with and without the experience of hallucinations, we have been able to identify a particular brain region that seems to be associated with a key symptom of the disorder," said Simons.

The researchers believe that changes in other areas of the brain are likely also important in generating the complex phenomena of hallucinations, possibly including regions that process visual and auditory perceptual information.

In people who experience hallucinations, these areas may produce altered perceptions which, due to differences in reality monitoring processes supported by regions around the PCS, may be misattributed as being real.

For example, a person may vividly imagine a voice but judge that it arises from the outside world, experiencing the voice as a hallucination.

"We think that the PCS is involved in brain networks that help us recognise information that has been generated ourselves," said first author Jane Garrison, from University of Cambridge.

"People with a shorter PCS seem less able to distinguish the origin of such information, and appear more likely to experience it as having been generated externally," Garrison said.

The study was published in the journal Nature Communications.