Paracingulate Sulcus Morphology and Hallucinations in Clinical and Nonclinical Groups

Abstract

Hallucinations are a characteristic symptom of psychotic mental health conditions that are also experienced by many individuals without a clinical diagnosis. Hallucinations in schizophrenia have been linked to differences in the length of the paracingulate sulcus (PCS), a structure in the medial prefrontal cortex which has previously been associated with the ability to differentiate perceived and imagined information. We investigated whether this putative morphological basis for hallucinations extends to individuals without a clinical diagnosis, by examining whether nonclinical individuals with hallucinations have shorter PCS than nonclinical individuals without hallucinations. Structural MRI scans were examined from 3 demographically matched groups of individuals: 50 patients with psychotic diagnoses who experienced auditory verbal hallucinations (AVHs), 50 nonclinical individuals with AVHs, and 50 healthy control subjects with no life-time history of hallucinations. Results were verified using automated data-driven gyrification analyses. Patients with hallucinations had shorter PCS than both healthy controls and nonclinical individuals with hallucinations, with no difference between nonclinical individuals with hallucinations and healthy controls. These findings suggest that the association of shorter PCS length with hallucinations is specific to patients with a psychotic disorder. This presents challenges for full-continuum models of psychosis and suggests possible differences in the mechanisms underlying hallucinations in clinical and nonclinical groups.

Keywords: clinical; hallucinations; nonclinical; paracinguate sulcus.

Fig. 1.

Paracingulate sulcus (PCS) measurement for 2 example images. Note: The PCS lies dorsal and parallel to the cingulate sulcus (CS). (a) The PCS is continuous and is measured from its origin in the first quadrant (cross-hairs at y = 0 and z = 0) to its end. (b) The PCS is noncontinuous, and is measured from its start in the first quadrant with subsequent segments included such that the total distance between them is less than 20 mm.

Fig. 2.

Possible mechanisms underlying hallucinations in clinical and nonclinical groups.

Fig. 3.

Paracingulate sulcus (PCS) length by group. (a) Total PCS length across both hemispheres, (b) PCS length in the left hemisphere, and (c) PCS length in the right hemisphere. ***P < .001, **P < .01, *P < .05. Error bars represent standard error of the mean. Variation is also seen between the groups for the proportions of absent PCS. Taking an earlier definition of an absent PCS to be one of length <20 mm,^, 11% of the brain hemispheres measured in control subjects had no PCS compared with 20% for nonclinical individuals with hallucinations, and 33% for individuals in the clinical group.

Fig. 4.

Cortical gyrification differentiates patients with auditory verbal hallucinations (AVHs), but not nonclinical individuals with hallucinations, from healthy controls. (a) Mean lGI in bilateral regions surrounding the paracingulate sulcus (PCS) is lower in patients with hallucinations than in healthy controls, *P < .05, error bars represent standard error of the mean. (b) Local gyrification index around posterior PCS significantly differentiates clinical individuals with AVHs from healthy controls. There were no significant differences in lGI between nonclinical individuals with AVHs and either healthy controls, or patients with hallucinations.