Abnormal Anatomy of the Auditory Cortex in Schizophrenic Brains with Auditory Hallucinations: A Systematic Review

Abstract

Background: Due to the high prevalence of auditory hallucinations in schizophrenic individuals (60-80%; Lim et al., 2016), this review will focus on evidence of neuroanatomical abnormalities found in key auditory structures of this clinical population. Identifying atypical anatomy of these areas can inform our understanding of the mechanisms underlying the experience of auditory hallucinations as well as potential deficits in central auditory processing, providing a rationale for the involvement of audiologists in diagnosis and treatment of auditory hallucinations. Purpose: The goal of this review is to describe the auditory neuroanatomical differences in schizophrenic individuals who experience auditory hallucinations compared to normal individuals who do not. Further, it will also explore how these differences in neuroanatomy may be related to central auditory processing dysfunction and auditory hallucinations. Methods: A review of existing literature published from 1960-2020 was conducted to summarize and compare neuroanatomical abnormalities of key auditory structures in schizophrenic brains. Relevant studies published between the years of 1960 and 2020 were identified using the following online databases: Google Scholar, PubMed, PSYCnet, and Mendeley, as well as books, chapters, and bibliographies. For each of the listed databases, search terms included “schizophrenia” AND “auditory hallucinations” AND “auditory cortex” AND “anatomy” AND “Sylvian fissure” OR “superior temporal gyrus” OR “Heschl’s gyrus” OR “planum temporale” OR “(central) auditory processing dysfunction” OR “dichotic listening”. Results: Findings from previous anatomical studies are in strong agreement, having identified structural abnormalities of Heschl’s gyrus, planum temporale, and the Sylvian fissure in schizophrenic brains, suggesting that these auditory structures potentially play a role in the experience of auditory hallucinations. Conclusion/Discussion: This review summarizes and compares available evidence of neuroanatomical abnormalities in the auditory cortex of individuals with schizophrenia who experience auditory hallucinations. Anatomical studies investigating auditory structures in schizophrenic brains indicate abnormalities of Heschl’s gyrus, planum temporale, and the Sylvian fissure, particularly a reduction in hemispheric asymmetries. These anatomical deviations have implications for functional auditory processing. Evidence of the involvement of these key auditory structures provides rationale for audiologists to collaborate with psychiatrists in the diagnosis and treatment of auditory hallucinations. This review also suggests the need for future research to investigate potential correlations between neuroanatomical variances in schizophrenic brains and audiological findings. Key Words: Auditory Hallucinations, schizophrenia, auditory cortex, structure, anatomy, superior temporal gyrus, Heschl’s gyrus, planum temporale, Sylvian fissure, central auditory processing, dichotic listening Abbreviations: Auditory hallucinations (AH), auditory verbal hallucinations (AVH), central auditory nervous system (CANS), inner speech model (ISM), corpus callosum (CC), superior temporal gyrus (STG), Heschl’s gyrus (HG), planum temporale (PT), gray matter (GM), gray matter volume (GMV), white matter (WM), white matter volume (WMV), anterior cingulate cortex (ACC), temporo-parietal junction (TPJ), right ear advantage (REA)