Functional magnetic resonance imaging of inner speech in schizophrenia

[Schizophrenia, cognition and neuroimaging]

Schizophrenia is a complex illness whose mechanisms are still largely unknown. Functional brain imaging, by making the link between psyche and brain, has recently become an indispensable tool to study in vivo the neural bases underlying cognitive dysfunction in this disease. But despite the proliferation of data coming from this approach, the exact impact of functional imaging on our understanding of the disease remains blurry. In general, studies of the brain functioning of patients with schizophrenia found activation abnormalities which vary in nature and localization depending of the cognitive paradigm used. However, it appears that neurofunctional abnormalities observed in patients cannot be reduced to a simple well-localized deficit. It would be rather an alteration of the dynamics of the interactions between different brain regions that underlie the cognitive disturbances encountered in the disease. Functional brain imaging now offers new perspectives to clarify the dynamics of the brain networks, and particularly those involved in high-level cognitive functions, such as cognitive control or social cognition which seem to play a crucial role in the disease. The characterization of these features is an important issue not only to develop new hypotheses on the pathophysiology of the disorder, but also more pragmatically to identify potential therapeutic targets.

Abnormal connectivity between attentional, language and auditory networks in schizophrenia

Brain circuits involved in language processing have been suggested to be compromised in patients with schizophrenia. This does not only include regions subserving language production and perception, but also auditory processing and attention. We investigated resting state network connectivity of auditory, language and attention networks of patients with schizophrenia and hypothesized that patients would show reduced connectivity. Patients with schizophrenia (n = 45) and healthy controls (n = 30) underwent a resting state fMRI scan. Independent components analysis was used to identify networks of the auditory cortex, left inferior frontal language regions and the anterior cingulate region, associated with attention. The time courses of the components where correlated with each other, the correlations were transformed by a Fisher's Z transformation, and compared between groups. In patients with schizophrenia, we observed decreased connectivity between the auditory and language networks. Conversely, patients showed increased connectivity between the attention and language network compared to controls. There was no relationship with severity of symptoms such as auditory hallucinations. The decreased connectivity between auditory and language processing areas observed in schizophrenia patients is consistent with earlier research and may underlie language processing difficulties. Altered anterior cingulate connectivity in patients may be a correlate of habitual suppression of unintended speech, or of excessive attention to internally generated speech. This altered connectivity pattern appears to be present independent of symptom severity, and may be suggestive of a trait, rather than a state characteristic.

Evaluation of state and trait biomarkers in healthy volunteers for the development of novel drug treatments in schizophrenia

Antipsychotic drugs are the mainstay of treatment for schizophrenia but they have little effect on core negative symptoms or cognitive impairment. To meet the deficiencies of current treatments, novel potential compounds are emerging from preclinical research but translation to clinical success has been poor. This article evaluates the possibility that cognitive and physiological abnormalities in schizophrenia can be used as central nervous system biomarkers to predict, in healthy volunteers, the likely efficacy of entirely new pharmacological approaches to treatment. Early detection of efficacy would focus resource on rapidly developing, effective drugs. We review the relevance of selected cognitive and physiological abnormalities as biomarkers in schizophrenia and three of its surrogate populations: (i) healthy volunteers with high trait schizotypy; (ii) unaffected relatives of patients; and (iii) healthy volunteers in a state of cortical glutamate disinhibition induced by low-dose ketamine. Several biomarkers are abnormal in these groups and in some instances there has been exploratory work to determine their sensitivity to drug action. They are generally insensitive to current antipsychotics and therefore their predictive validity cannot be established until novel, therapeutically useful drugs are discovered. Until then such biomarker studies can provide evidence of drugs engaging with the mechanism of interest and encouragement of the concept.

An fMRI study of prefrontal dysfunction and symptomatic recovery in schizophrenia

OBJECTIVE

Prefrontal cortical dysfunction has been implicated in the pathophysiology of schizophrenia but it is unclear to what extent these are related to changes in symptomatology as well as task demand.

METHOD

We examined the neural correlates of symptom change and task demand during a longitudinal functional magnetic resonance imaging (fMRI) study using a verbal fluency task with differential task demands in patients with schizophrenia and matched healthy control subjects. The fMRI data were acquired using clustered acquisition technique, enabling ongoing monitoring of behavioural responses, in the patient group on two occasions separated by 6-8 weeks, and the control group at baseline.

RESULTS

Positive psychotic symptoms were significantly reduced over the 6-8-week duration of the study. This change was associated with increased activation within the left middle frontal gyrus and decreased activation of the left precuneus. An interaction between symptom change and task demand was evident in the activation of the left middle frontal gyrus. The decrease in positive symptoms was associated with normalisation of activation in the dorsolateral prefrontal cortex and a decrease in parietal activation during the verbal fluency task.

CONCLUSION

The data supports the role of dysfunctional prefronto-parietal relationships in the genesis of positive psychotic symptoms.

Qualifying brain functional MRI parameters as endophenotypes in schizophrenia

Although the genetic contribution to schizophrenia pathogenesis has been well established, with an approximate heritability of 81%, the endeavor to elucidate the complex genetic architecture of schizophrenia has met limited success. ‘Endophenotypes’, or ‘intermediate phenotypes’, are more restricted constructs of genetic risk than the clinical manifestations hitherto employed by molecular geneticists. They are, putatively, intermediate in the pathophysiological pathway between genetic variation and clinical phenomenology and can possibly be used to assist in the elucidation of genetic diathesis for schizophrenia. In this article, we present the current evidence that supports functional MRI parameters as promising candidate endophenotypes in schizophrenia.

Functional brain imaging in schizophrenia: selected results and methods

Functional brain imaging studies of patients with schizophrenia may be grouped into those that assume that the signs and symptoms of schizophrenia are due to disordered circuitry within a critical brain region and studies that assume that the signs and symptoms are due to disordered connections among brain regions. Studies have investigated the disordered functional brain anatomy of both the positive and negative symptoms of schizophrenia. Studies of spontaneous hallucinations find that although hallucinations are associated with abnormal brain activity in primary and secondary sensory areas, disordered brain activation associated with hallucinations is not limited to sensory systems. Disordered activation in non-sensory regions appear to contribute to the emotional strength and valence of hallucinations, to be a factor underlying an inability to distinguish ongoing mental processing from memories, and to reflect the brain's attempt to modulate the intensity of hallucinations and resolve conflicts with other processing demands. Brain activation studies support the view that auditory/verbal hallucinations are associated with an impaired ability of internal speech plans to modulate neural activation in sensory language areas. In early studies, negative symptoms of schizophrenia were hypothesized to be associated with impaired function in frontal brain areas. In support of this hypothesis meta-analytical studies have found that resting blood flow or metabolism in frontal cortex is reduced in schizophrenia, though the magnitude of the effect is only small to moderate. Brain activation studies of working memory (WM) functioning are typically associated with large effect sizes in the frontal cortex, whereas studies of functions other than WM generally reveal smaller effects. Findings from some functional connectivity studies have supported the hypothesis that schizophrenia patients experience impaired functional connections between frontal and temporal cortex, although the nature of the disordered connectivity is complex. More recent studies have used functional brain imaging to study neural compensation in schizophrenia, to serve as endophenotypes in genetic studies and to provide biomarkers in drug development studies. These emerging trends in functional brain imaging research are likely to help stimulate the development of a general neurobiological theory of the complex symptoms of schizophrenia.