Schizophrenia: Functional imaging and cognitive abnormalities
Department of Cognitive Neurology, Hammersmith Hospital, London, UK. The Lancet
(Impact Factor: 45.22).
10/1995; 346(8975):615-20. DOI: 10.1016/S0140-6736(95)91441-2
From its initial labelling as dementia praecox, the disorder we now call schizophrenia has always been associated with cognitive impairments. While there was a time when these deficits were believed to be secondary to treatment and institutionalisation, there is now overwhelming evidence that cognitive impairments are an essential feature of schizophrenia. Precise specification of the form of these impairments has important implications for the nature of the underlying brain malfunction.
Available from: Ganesan Venkatasubramanian
- "Positive symptoms such as hallucinations may thus be interpreted as a deficit of self-monitoring associated with a kind of over-activity of mental imagery: Patients’ inner life is particularly intense and vivid and the patients are unable to realize that their mental images come from themselves rather from the external world. This function is impaired in patients with schizophrenia and underlies several positive and negative symptoms see. It has been proposed that episodic memory and source monitoring are closely interlinked so much so that brain structures implicated in the former (for the encoding process, storage and retrieval of memory trace) are also associated with the latter vouching for a central role of the hippocampus in the entire process. "
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ABSTRACT: Hippocampal deficits are an established feature of schizophrenia and are complementary with recent evidences of marked allocentric processing deficits being reported in this disorder. By "Cognitive mapping" we intend to refer to the concepts from the seminal works of O'Keefe and Nadel (1978) that led to the development of cognitive map theory of hippocampal function. In this review, we summarize emerging evidences and issues that indicate that "Cognitive mapping deficits" form one of the important cognitive aberrations in schizophrenia. The importance has been placed upon hippocampally mediated allocentric processing deficits and their role in pathology of schizophrenia, for spatial/representational cognitive deficits and positive symptoms in particular. It is modestly summarized that emerging evidences point toward a web of spatial and cognitive representation errors concurrent with pronounced hippocampal dysfunction. In general, it can be stated that there are clear and consistent evidences that favor the cognitive mapping theory in explaining certain deficits of schizophrenia and for drawing out a possible and promising endophenotype/biomarkers. Further research in this regard demands attention.
Available from: Fereshteh Momeni
- "The source memory includes monitoring to distinguish the events made by persons in their minds from what is occurring in the real world. Frith (1995) has found this deficit in schizophrenic patients with positive symptoms. According to Frith and Done (1998), a deficit in corollary discharge networks, which distinguishes self-generated perceptions from the external ones, provokes a defect in self-attribution, and therefore one attributes his/her activities to others. "
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ABSTRACT: The most important speech disorder in schizophrenic patients with positive symptoms is incoherency, which has a wide spectrum depending on various factors. The present paper examines the relationship between incoherency of speech, delusions and hallucinations by investigating the discourse characteristics of the spontaneous speech of 18 Persian-speaking schizophrenics with positive symptoms. Based on the analysis of the data, two types of delusions: variable (VD) and invariable (ID), and two types of hallucinations: synchronic (SH) and diachronic (DH) were identified, and their relationships were discussed. The findings reveal that there is a strong correlation between the incoherency of speech and VD in these patients, and VD itself seems to result from SH.
Available from: Joseph F X DeSouza
- "This implies that while regional specialization in areas such as DLPFC might be disrupted, it is likely related to broader deficits in functional integration across cortical areas. The results of frontotemporal and fronto-parietal dysconnectivity have been found using prefrontally mediated tasks, both with normal DLPFC activation as well as hypoactivation, but most importantly they have been found in patients with both negative and positive symptoms (Allen, Liddle, & Frith, 1993; Crossley et al., 2009; Fletcher, McKenna, Friston, Frith & Dolan, 1999; Friston et al., 1991; Frith, 1995; Lawrie et al., 2002), including those with auditory hallucinations and no impairments in verbal fluency. Additionally, patients with passivity symptoms and hyperactivity in parietal cortex also appear hypofrontal, and to a greater degree when most symptomatic (Allen, Liddle, & Frith, 1993; Frith, 1995; Fletcher et al., 1999; Spence et al., 1997). "
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ABSTRACT: Efference copy signals are used to reduce cognitive load by decreasing sensory processing of reafferent information (those incoming sensory signals that are produced by an organism's own motor output). Attenuated sensory processing of self-generated afferents is seen across species and in multiple sensory systems involving many different neural structures and circuits including both cortical and subcortical structures with thalamic nuclei playing a particularly important role. It has been proposed that the failure to disambiguate self-induced from externally generated sensory input may cause some of the positive symptoms in schizophrenia such as auditory hallucinations and delusions of passivity. Here, we review the current data on the role of efference copy signals within different sensory modalities as well as the behavioural, structural and functional abnormalities in clinical groups that support this hypothesis.
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