Region of brain 'shorter' in people with hallucinations

Wednesday November 18 2015

"A study of 153 brain scans has linked a particular furrow, near the front of each hemisphere, to hallucinations in schizophrenia," BBC News reports.

While schizophrenia is commonly associated with hallucinations – seeing, hearing and, in some cases, smelling things that are not real – around 3 out of 10 people with schizophrenia do not have them.

Researchers compared the brain scans of people with schizophrenia who have experienced hallucinations with those who have not. They focused on the paracingulate sulcus (PCS) – a fold in the frontal part of the brain – as previous research has associated the PCS with our ability to distinguish between reality and imagination.

The research found the PCS was significantly shorter in people with schizophrenia who've experienced hallucinations, compared with others with schizophrenia who've not had hallucinations, as well as healthy population controls.

The study is undoubtedly of value in furthering our understanding of the brain structure of people who experience abnormal perceptions. However, further research is needed to investigate whether this is a risk factor or a consequence of the condition. As such, at present it has no preventative or therapeutic implications.  

Where did the story come from?

The study was carried out by researchers from the University of Cambridge, Durham University, Trinity College Dublin, and Macquarie University. 

The individual researchers received various sources of financial support, including from the Medical Research Council and the Wellcome Trust. 

The study was published in the peer-reviewed scientific journal Nature Communications on an open access basis, so it is free to read online.

BBC News gives reliable and balanced coverage of this research. 

What kind of research was this?

This was a cross-sectional study comparing the brain scans of people with schizophrenia who have experienced hallucinations with those who have not.

Hallucinations are when a person sees, hears, smells or has other sensory perceptions of something that isn't there. Along with abnormal thought patterns and beliefs (delusions), they are one of the characteristic features of schizophrenia. 

However, not everyone with the condition experiences hallucinations – around a third of people meeting diagnostic criteria for schizophrenia do not report having them.

Various neurological factors are thought to underlie hallucinations. In this study, the researchers focused on examining the structure of the paracingulate sulcus (PCS) in the frontal part of the brain. 

A previous study suggested this part of the brain influences our ability to distinguish between real and imagined events.     

This kind of research design can look to see if there is any link between PCS and hallucinations, but it cannot draw conclusions on the causality.  

What did the research involve?

The research included three groups of people:

  • those with schizophrenia who have experienced hallucinations (n=70)
  • those with schizophrenia who have not (n=34)
  • a control sample of healthy people without schizophrenia or experience of hallucinations (n=40)

Roughly half of those with schizophrenia who'd had hallucinations had experienced auditory ones. The remainder had experienced other sensory hallucinations. The majority of these people were male and had an average age of around 40. 

The other two groups were accordingly matched to give comparative age and gender proportions. They were also all matched by IQ and right- or left-handedness.   

An MRI scanner was used to scan and measure the length of the PCS in both halves of the frontal part of the brain. The PCS was defined as "prominent" if the length was above 40mm, "absent" if the length was below 20mm, and "present" if it fell between the two. 

The measurements were taken by researchers who were unaware of the person's condition. 

What were the basic results?

The researchers found PCS length differed between those who had and had not experienced hallucinations. It was significantly shorter in those with schizophrenia who had hallucinations, compared with people with schizophrenia who hadn't had hallucinations (average 19.2mm shorter) and healthy controls (average 29.2mm shorter).

The difference in PCS length between the latter two groups – those with schizophrenia without hallucinations and healthy controls – was not statistically significant.

In all subjects the PCS in the left half of the frontal lobe was longer than that in the right half. For people with schizophrenia and hallucinations, the PCS was significantly shorter than the healthy controls in both brain halves, but only significantly shorter in the left half than the group with schizophrenia without hallucinations.

Overall, the researchers' modelling suggested a 10mm reduction in PCS length in the left half was associated with 19.9% increased odds the person had experienced hallucinations. 

The type of sensory hallucination did not influence PCS length, suggesting this was an overall association with hallucinations in general, not specific to the nature of the perception. 

No other variables, such as overall brain volume and surface area or other characteristics of the illness, had a significant influence on PCS length. 

Another observation was grey matter volume – which contains the nerve cell bodies – immediately surrounding the PCS was greater in those who had experienced hallucinations.  

How did the researchers interpret the results?

The researchers concluded hallucinations are associated with specific differences in the PCS in the frontal part of the brain. 

They say their findings "suggest a specific morphological basis for a pervasive feature of typical and atypical human experience". 


Previous research suggested the paracingulate sulcus (PCS) – a fold in the frontal part of the brain – may be associated with our ability to distinguish between reality and imagination.

This study found further evidence in support of this association. People with schizophrenia who had experienced hallucinations seemed to have significantly shorter PCS length than people who have not experienced hallucinations – either those with schizophrenia or healthy people.

The samples are relatively small, so it is possible the findings may have been different if it had been possible to study a much larger sample. However, performing MRI scans on extensive numbers of people with and without schizophrenia is unlikely to be feasible, so this is perhaps the best evidence we are likely to get.

What is important to highlight, though, is this is a cross-sectional study taking one-off MRI scans. As such, it can only demonstrate PCS length is associated with the experience of hallucinations. It cannot tell us whether PCS length predicts the risk of hallucinations, or conversely whether PCS length has changed as the result of experiencing hallucinations.

Follow-up studies performing repeated MRI scans over time in people at high risk of, or who have developed, schizophrenia would be valuable to examine if the brain changes during the course of the condition and its development.

Also, as the researchers say, as the PCS develops around birth, it would be valuable to look at any differences in fold length in children and see whether this could be a risk factor.  

At present, though, the findings have no apparent preventative or therapeutic implications for either schizophrenia or the experience of hallucinations.

But despite limited application of these findings, the study is undoubtedly of value in furthering our understanding of the brain structure of people who experience abnormal perceptions.   

Analysis by Bazian
Edited by NHS Choices