SU79. The Pathway to Hearing Voices? The Arcuate Fasciculus in Adolescents Reporting Psychotic Experiences

Abstract

Background: The arcuate fasciculous (AF) is a large bundle of association fbers in the white matter of each cerebral hemisphere that bidirection-ally connects caudal temporal cortex and inferior parietal cortex to locations in the frontal lobe and it is one of 4 subdivisions of the SLF. The AF connects 2 important areas for language use, Broca's area in the inferior frontal gyrus and Wernicke's area in the posterior superior temporal gyrus and abberant connectivity of this tract has been previously implicated in the presence of auditory hallucinations, especially in the left hemisphere where speech-relevant areas are predominantly located. Discrepancies in the directionality of the integrity of the AF have been observed with both increased and decreased FA identifed depending on the DTI methodology and disease state investigated. Methods: We used High Angular Resolution Diffusion Imaging (HARDI)-based data in conjunction with advanced constrained spherical deconvolu-tion (CSD)-based fber tractography to examine the ability of advanced modeling tractography to delineate the arcuate fasciculous. Following extraction of the tract formations, we compared standard diffusion metrics (fractional anisotrophy [FA] and diffusivity measures MD, AD, and RD), to assess white matter structural connectivity differences between adolescents experiencing subclinical auditory hallucinations and those who do not. Results: Our results agreed with recent studies of the AF (Fernandes-Miranda et al, 2015) and revealed a pattern of asymmetry of the AF with more extensive tract bundles being consistently identifed in the left hemi-sphere compared to the right. Statistical examination of FA, MD, AD, and RD failed to identify any signifcant between-group differences between controls and those experiencing subclinical psychotic symptoms (auditory hallucinations). Conclusion: Discrepancies within the AF could refect dysfunctional con-nectivity between frontal and parieto-temporal speech-related areas contributing to the pathogenesis of auditory hallucinations. Abnormal activation in regions that normally process external language stimuli could relate to the inability of people with psychotic disorders to distinguish self-generated thoughts from external stimulation. Our pilot investigation identifes no white matter structural differences in the A F. This could indi-cate that possible disturbances in the developmental trajectory of the AF implicated in hallucinatory experiences in psychotic disorders may appear later in the brains maturation process and closer to timeframe of the frst episode of psychotic disorder. Developmental disruption within these networks leading to cognitive dysfunction during the generation and monitoring of inner speech, which may affect how internally generated language is perceived to be generated externally may be targeted in late adolescence and early adulthood.