Incomplete hippocampal inversion in schizophrenia: prevalence, severity, and impact on hippocampal structure

Abstract

Incomplete hippocampal inversion (IHI) is an anatomical variant of the human brain resulting from an arrest in brain development, especially prevalent in the left hemisphere. We hypothesized that IHI is more common in schizophrenia and contributes to the well-known hippocampal structural differences. We studied 199 schizophrenia patients and 161 healthy control participants with 3 T MRI to establish IHI prevalence and the relationship of IHI with hippocampal volume and asymmetry. IHI was more prevalent (left hemisphere: 15% of healthy control participants, 27% of schizophrenia patients; right hemisphere: 4% of healthy control participants, 10% of schizophrenia patients) and more severe in schizophrenia patients compared to healthy control participants. Severe IHI cases were associated with a higher rate of automated segmentation failure. IHI contributed to smaller hippocampal volume and increased R > L volume asymmetry in schizophrenia. The increased prevalence and severity of IHI supports the neurodevelopmental model of schizophrenia. The impact of this developmental variant deserves further exploration in studies of the hippocampus in schizophrenia.

Structural and Functional Deviations of the Hippocampus in Schizophrenia and Schizophrenia Animal Models

“…While former studies mainly focused on total volume changes of the hippocampus in schizophrenic patients, modern high-resolution magnet resonance imaging (MRI) techniques were utilized for a more detailed and region-specific analysis. Interestingly, these techniques contributed to the observation of so-called incomplete inversion patterns which are characterized by a round and verticalized hippocampal morphology with a deep collateral fissure, and a medial positioning in the coronal plane [ 38 , 39 , 40 ]. Surprisingly, this structural deviation can be observed in 18–19% of healthy subjects, predominantly in the left hemisphere, and was primarily suspected to contribute to the pathology of epileptic seizures [ 40 , 41 ].…”

“…Surprisingly, this structural deviation can be observed in 18–19% of healthy subjects, predominantly in the left hemisphere, and was primarily suspected to contribute to the pathology of epileptic seizures [ 40 , 41 ]. Nevertheless, a recently published study showed that incomplete inversion patterns occur, on the one hand in a more severe manner and on the other hand with a higher frequency in schizophrenic patients [ 38 ]. In addition, this study unraveled a link between incomplete inversion patterns and the commonly described reduction of the total hippocampal volume, as well as of the increased volume asymmetry between the left and right hemispheres.…”

Electroacupuncture alleviates orofacial allodynia and anxiety-like behaviors by regulating synaptic plasticity of the CA1 hippocampal region in a mouse model of trigeminal neuralgia

“…However, the analgesic and anxiolytic mechanisms of EA in TN have not yet been fully elucidated. The main function of Hippocampal is to receive complex comprehensive sensory and cognitive information, and it is one of the core regions processing pain, emotion, cognition, and memory signals ( Roeske et al, 2021 ). Synaptic plasticity are closely related to these hippocampal functions.…”

Genetic polymorphism and neuroanatomical changes in schizophrenia

“…As with the pituitary gland, the volume of the hippocampus is lower and normal functioning is affected [ 139 ]. In this case, there is no longer the influence of a direct external factor, but the structural change can be associated with neurodevelopment deficiency [ 140 ]. The changes lead to altered function, and the hippocampus is one of the parts of the limbic system that influences glutamatergic transmission, whose altered functioning is already a constant in schizophrenia [ 141 ].…”