Salience processing and insular cortical function and dysfunction (original) (raw)
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Abstract Insular cortex is one of the brain regions that show consistent abnormalities in both structural and functional neuroimaging studies in schizophrenia. In healthy individuals insula has been implicated in a myriad of physiological functions. Anterior cingulate cortex and insula together constitute the Salience Network (SN), an intrinsic large-scale network showing strong functional connectivity. Considering insula as a functional unit along with anterior cingulate cortex provides an integrated understanding of the role of insula in information processing. In this review, we bring together evidence from imaging studies to understand the role of salience network in schizophrenia, and propose a model of insular dysfunction in psychosis.
Abstract: Background: Schizophrenia is characterised by both electrophysiological abnormalities and consistent changes in the structure of cortical grey matter. But the relationship between these two observations is largely unknown. Structural changes reported in schizophrenia include reduced grey matter volume, thickness and surface area in several cortical regions, but most frequently in the insula and anterior cingulate cortex. These two regions together constitute an intrinsic brain circuit known as the ‘Salience Network’, which has a key role in stimulus processing. During stimulus processing tasks, evoked activity is noted using electroencephalography (EEG). Phase resetting of ongoing oscillations contributes to this evoked activity. Methods: In this study, we investigated the relationship between the cortical thickness in the Salience Network (measured using MRI) and the degree of phase resetting observed during an oddball task (measured using EEG) in 18 patients with schizophrenia and 20 healthy controls. Results: In patients with schizophrenia the reduced thickness in the Salience Network was associated with the inefficient phase resetting of theta oscillations. Conclusions: Our findings suggest that the grey matter reduction seen in the Salience Network in patients with schizophrenia has substantial functional consequences. In particular, the structural defect of the insula that is seen in schizophrenia is likely to be associated with less efficient recruitment of brain circuits for processing information. This implies a possible mechanism by which disruptions in the intrinsic Salience Network can result in a general disturbance in salience detection seen in schizophrenia.
"Abstract A large body of neuroimaging literature suggests that distributed regions in the brain form coordinated large scale networks that show reliable patterns of connectivity when observed using either functional or structural magnetic resonance imaging (MRI) methods. Functional activation within these networks provides a robust and reliable representation of dynamic brain states observed during information processing. One such network comprised of anterior fronto-insular cortex (aFI) and anterior cingulate cortex (ACC) is called the Salience Network (SN). SN has been identified as a system that enables the switch between various dynamic brain states. SN dysfunction has been proposed as a mechanistic model for several core symptoms of schizophrenia. In this review, we explore how various risk factors of schizophrenia could operate through the dysfunctional SN to generate symptoms of psychosis. We also consider the putative neurochemical basis for the SN dysfunction in schizophrenia, and suggest that the SN dysfunction is a viable therapeutic target for a combined pharmacological and cognitive training treatment approach. This combination approach, termed as Brain Network Modulation, could exploit neuronal plasticity to reverse a key pathophysiological deficit in schizophrenia. "
Brain Sciences
Recent evidence suggests that the aberrant signaling of salience is associated with psychotic illness. Salience, however, can take many forms in task environments. For example, salience may refer to any of the following: (1) the valence of an outcome, (2) outcomes that are unexpected, called reward prediction errors (PEs), or (3) cues associated with uncertain outcomes. Here, we measure brain responses to different forms of salience in the context of a passive PE-signaling task, testing whether patients with schizophrenia (SZ) showed aberrant signaling of particular types of salience. We acquired event-related MRI data from 29 SZ patients and 23 controls during the performance of a passive outcome prediction task. Across groups, we found that the anterior insula and posterior parietal cortices were activated to multiple different types of salience, including PE magnitude and heightened levels of uncertainty. However, BOLD activation to salient events was not significantly different ...
Reality Distortion is related to the structure of Salience Network in schizophrenia
"Abstract BACKGROUND: An intrinsic cerebral network comprising the anterior cingulate and anterior insula (the salience network) is considered to play an important role in salience detection in healthy volunteers. Aberrant salience has been proposed as an important mechanism in the production of psychotic symptoms such as delusions and hallucinations (reality distortion). We investigated whether structural deficits in the salience network are associated with the reality distortion seen in schizophrenia.MethodA sample of 57 patients in a clinically stable state of schizophrenia and 41 controls were studied with high-resolution magnetic resonance imaging. RESULTS: Bilateral volume reduction was seen in the anterior cingulate and anterior insula in patients with schizophrenia. Reduced volume in the two left-sided regions of the salience network was significantly correlated with the severity of reality distortion. CONCLUSIONS: These findings suggest that a deficit of grey matter in the salience network leads to an impaired attribution of salience to stimuli that is associated with delusions and hallucinations in schizophrenia."