Neural mechanisms underlying visual and auditory processing impairments in schizophrenia: insight into the etiology and implications for tailoring preventive and therapeutic interventions

Abstract

Schizophrenia is a complex and devastating neuropsychiatric disorder with an unknown etiology. Patients with schizophrenia have a high prevalence of visual disturbances, commonly accompanied by auditory impairments. In recent review articles, the perceptual deficits of visual and auditory sensory processing have been downplayed. However, visual and auditory impairments are associated with hallucinations, which is characteristic of schizophrenia across all cultures. Despite decades of research, the common neural mechanisms underlying hallucinations remain largely unknown. In recent years, neuroimaging technologies have empowered researchers to investigate the underlying neural mechanisms. In this review article, we performed a literature search of studies that assessed visual and auditory processing impairments, along with their relationship to visual disturbances and auditory hallucinations, in schizophrenia. We proposed that the pulvinar may play a critical role. In addition, disrupted visual and auditory projections from the pulvinar to the visual and auditory cortices could be shared pathways in relation to visual disturbances and auditory hallucinations in schizophrenia. Our findings suggest that early visual and auditory processing deficits may occur before the onset of the initial psychotic episode, including hallucinations, and the full manifestation of schizophrenia. Furthermore, we discussed the directions for future studies. Our findings from this review offer unique insights into the distinct underlying neural mechanisms of schizophrenia, which may help develop tailored preventive and therapeutic interventions in the future.

Keywords: Schizophrenia; auditory hallucinations; fMRI; pulvinar; visual disturbances; visual hallucinations.

Figure 1

Schematic illustration of structural and functional impairments in the central auditory system and the correlation with auditory hallucinations in schizophrenia. Main structural and functional impairments in the central auditory processing system in patients with schizophrenia are schematically illustrated. The deficits in both structure and function of the central auditory system directly contribute to auditory hallucinations in schizophrenia patients.

Figure 2

Hypothetical pathways in relation to both visual disturbances and auditory hallucinations in schizophrenia. The pulvinar nucleus/LP directly modulates the primary auditory cortex activity through layer 1 (L1) neurons and layers 2/3 (L2/3) pyramidal neurons, and it exerts a net inhibitory effect in normal conditions. The abnormal alterations of the pulvinar nucleus in schizophrenia include low metabolic rate, decreased volume, and conformational change, which may reduce the suppression and induce the activation of the primary auditory cortex, while also contributing to the development of auditory hallucinations. Compared with the new role of the pulvinar nucleus in the modulation of the primary auditory cortex, there are the reciprocal connections between the pulvinar and visual cortices in visual processing. These disruptions contribute to visual disturbances in schizophrenia. The pulvinar may play a critical role, and the disrupted visual and hearing projections from the pulvinar to the visual and auditory cortices could be a common pathway associated with visual disturbances and auditory hallucinations in schizophrenia. LP, the lateral posterior nucleus, is the homolog in rodents of the pulvinar in mammals.