Paracingulate sulcus length is shorter in voice-hearers regardless of need for care

While hallucinations are often considered to be the sine qua non of serious mental illness, they are commonly experienced by those without a need for care. Such non-clinical, hallucinating individuals offer a window into the etiology of hallucinations. Garrison et al. (2015) recently assessed structural variability in paracingulate sulcus (PCS) of medial prefrontal cortex. They found a reduction of 10mm in left hemisphere PCS length increased the likelihood of hallucinations by 19.9%. However, these findings were in clinical hallucinators, and reduced leftward asymmetry in PCS has been repeatedly demonstrated in schizophrenia and associated with reduced reality monitoring. Similar analyses have been conducted in non-clinical voice hearers and in those particpants, no reduction in PCS length was reported. However, there is considerable variability in the voice experiences of non-clinical voice hearers. Put simply, some may be more clinical than others. We recently identified a relatively homogenous group of non-clinical voice hearers who identify as clairaudient psychics. Their voice experiences are extremely redolent of those reported by a matched patient voice hearing group and their brain and behavioral responses to a perceptual inference task were, at least at the level of prior beliefs, similarly perturbed to patients who hear voices. These observations are consistent with a continuum model of voice hearing, along which clairaudient voice hearers are nearer to patients with schizophrenia in some respects. The PCS data reported by Garrison et al would militate against such a continuum. Before rejecting the continuum model, we sought to determine if the differences in PCS length also applied to the clairaudient non-clinical voice hearers. If PCS length is to be developed as a biomarker for clinical hallucination risk, then it is important to demonstrate that it is not similarly reduced in non-clinical voice hearers. We find that it is reduced, both in clinical and non-clinical voice-hearers.