title: A Neuroimaging Investigation into Hallucination Proneness in a Healthy Population
Creators: name: Alotaibi, Abdullah
Publisher: name: University of Liverpool Repository
Year: 2021

description: The experience of hallucinations is one of the symptoms used in the diagnosis of a psychiatric disorders such as schizophrenia. Functional and structural neuroimaging studies consistently link hallucinatory experience with abnormalities in brain areas supporting normal processing such language areas in auditory verbal hallucinations (AVH) and visual sensory areas in visual hallucinations (VH). Hallucinations are not confined to clinical populations, but are also relatively frequent in the general population. Finding that healthy individuals experience hallucinations without distress has led to models proposing that hallucinatory experiences lie on a continuum, which spans healthy and clinical populations. Continuum models (e.g., Baumeister et al., 2017) provide a theoretical framework with testable hypotheses, that predict brain functional activation, morphometrics or microstructural alterations in the healthy hallucinator group from existing data in the clinical group. Healthy hallucinators therefore may be a key resource in informing transdiagnostic research into the neurological cause of hallucinations. The aim of the current study is to test whether hallucination proneness predict a wide range of multi-modal neuroimaging measures in a large, healthy population. The Launay-Slade Hallucination Scale modified by Morrison’s et al. (2000) LSHS(M) scale as well as auditory (LSHS(A)) and visual (LSHS(V)) subscales were used as a regressors in structural (VBM and FreeSurfer based morphometrics), functional (fMRI) and microstructural (DTI diffusivity and tractography) neuroimaging experiments to test whether alterations seen in patients translate into the healthy population. The morphometric analysis of structural data showed a significant positive correlation between brain thickness in the temporal cortex (bilateral transverse temporal gyrus) (TTG) and LSHS(M) scores. Functional activation data shows a significant positive correlation between LSHS(A) scores and activation in irrelevant task activation (audio/visual) in right (inferior frontal gyrus, superior temporal gyrus and middle temporal gyrus). DTI diffusivity analysis showed that reduced mean diffusivity (MD) in the right inferior longitudinal fasciculus (ILF), superior longitudinal fasciculus (SLF) and occipital lobe (OL), also reduced axial diffusivity (AD) in the bilateral (SLF) and (OL) were linked to higher LSHS(M) scores. The arcuate fasciculus (AF) analysis showed that reduced diffusivity in the left (MD) and left (AD) were linked to high LSHS(M) scores. It is striking that, for this healthy population, the effects observed are the opposite of what might have been expected (continuum theory) for brain pathology and contrasts with previously published data for schizophrenia patients suffering from hallucinations. Finding consistent results using multiple imaging modalities in overlapping brain areas and for a relatively large population makes methodological differences or sampling effects an unlikely explanation for the results. The continuum hypothesis of hallucination assumes that psychotic symptoms, such as AVH and VH, which are experienced in clinical and non-clinical populations, have a common cause. In neuroimaging terms this means that similar functional, structural, and microstructural parameters would be expected for clinical and non-clinical populations show the same direction of differences. Our data does not fit well with this model. However, the results failed to prove that. Studying hallucinatory experiences in a healthy population is attractive because it avoids confounding effects, ranging from childhood trauma, medication or hospitalization. Our data suggests that studies in healthy individuals may not provide data that easily extrapolates to the causes underlying schizophrenic hallucinations.