http://nwkpsych.rutgers.edu/~jose/courses/578_mem_learn/2012/readings/Broyd_2009.pdf

Default-mode brain dysfunction in mental disorders: A systematic review

We examined the status of the neural network mediating the default mode of brain function, which typically exhibits greater activation during rest than during task, in patients in the early phase of schizophrenia and in young first-degree relatives of persons with schizophrenia. During functional MRI, patients, relatives, and controls alternated between rest and performance of working memory (WM) tasks. As expected, controls exhibited task-related suppression of activation in the default network, including medial prefrontal cortex (MPFC) and posterior cingulate cortex/precuneus. Patients and relatives exhibited significantly reduced task-related suppression in MPFC, and these reductions remained after controlling for performance. Increased task-related MPFC suppression correlated with better WM performance in patients and relatives and with less psychopathology in all 3 groups. For WM task performance, patients and relatives had greater activation in right dorsolateral prefrontal cortex (DLPFC) than controls. During rest and task, patients and relatives exhibited abnormally high functional connectivity within the default network. The magnitudes of default network connectivity during rest and task correlated with psychopathology in the patients. Further, during both rest and task, patients exhibited reduced anticorrelations between MPFC and DLPFC, a region that was hyperactivated by patients and relatives during WM performance. Among patients, the magnitude of MPFC task suppression negatively correlated with default connectivity, suggesting an association between the hyperactivation and hyperconnectivity in schizophrenia. Hyperactivation (reduced task-related suppression) of default regions and hyperconnectivity of the default network may contribute to disturbances of thought in schizophrenia and risk for the illness.

https://www.pnas.org/content/pnas/106/4/1279.full.pdf

Hyperactivity and hyperconnectivity of the default network in schizophrenia and in first-degree relatives of persons with schizophrenia

Neuropsychiatric disorders are associated with abnormal function of the default mode network (DMN), a distributed network of brain regions more active during rest than during performance of many attention-demanding tasks and characterized by a high degree of functional connectivity (i.e., temporal correlations between brain regions). Functional magnetic resonance imaging studies have revealed that the DMN in the healthy brain is associated with stimulus-independent thought and self-reflection and that greater suppression of the DMN is associated with better performance on attention-demanding tasks. In schizophrenia and depression, the DMN is often found to be hyperactivated and hyperconnected. In schizophrenia this may relate to overly intensive self-reference and impairments in attention and working memory. In depression, DMN hyperactivity may be related to negative rumination. These findings are considered in terms of what is known about psychological functions supported by the DMN, and alteration of the DMN in other neuropsychiatric disorders.

Default Mode Network Activity and Connectivity in Psychopathology

http://johndmurray.org/papers/anticevic_2012_tics.pdf

The role of default network deactivation in cognition and disease.

Models of Network Growth All networks, whether they are social, technological, or biological, are the result of a growth process. Many of these networks continue to grow for prolonged periods of time, continually modifying their connectivity structure throughout their entire existence. For example, the World Wide Web has grown from a small number of cross-linked documents in the early 1 990s to an estimated 30 billion indexed web pages in 2009.3 The extraordinary growth of the Web continues unabated and has occurred without any top-down design, yet the topology of its hyperlink structure exhibits characteristic statistical patterns (Pastor-Satorras and Vespig­ nani, 2004). Other technological networks such as the power grid, global transportation networks, or mobile communication networks continue to grow and evolve, each displaying characteristic patterns of expansion and elaboration. Growth and change in social and organizational

Networks of the Brain

BackgroundFunctional imaging studies using working memory tasks have documented both prefrontal cortex (PFC) hypo- and hyperactivation in schizophrenia. However, these studies have often failed to consider the potential role of task-related deactivation.MethodThirty-two patients with chronic schizophrenia and 32 age- and sex-matched normal controls underwent functional magnetic resonance imaging (fMRI) scanning while performing baseline, 1-back and 2-back versions of the n-back task. Linear models were used to obtain maps of activations and deactivations in the groups.ResultsThe controls showed activation in the expected frontal regions. There were also clusters of deactivation, particularly in the anterior cingulate/ventromedial PFC and the posterior cingulate cortex/precuneus. Compared to the controls, the schizophrenic patients showed reduced activation in the right dorsolateral prefrontal cortex (DLPFC) and other frontal areas. There was also an area in the anterior cingulate/ventromedial PFC where the patients showed apparently greater activation than the controls. This represented a failure of deactivation in the schizophrenic patients. Failure to activate was a function of the patients' impaired performance on the n-back task, whereas the failure to deactivate was less performance dependent.ConclusionsPatients with schizophrenia show both failure to activate and failure to deactivate during performance of a working memory task. The area of failure of deactivation is in the anterior prefrontal/anterior cingulate cortex and corresponds to one of the two midline components of the ‘default mode network’ implicated in functions related to maintaining one's sense of self.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033291708003565

Failure to deactivate in the prefrontal cortex in schizophrenia: dysfunction of the default mode network?

Validation of the Word Accentuation Test (TAP) as a means of estimating premorbid IQ in Spanish speakers

Background Cognitive impairment is an established feature of schizophrenia. However, little is known about its relationship to the structural and functional brain abnormalities that characterise the disorder.

Aims To identify structural and/or functional brain abnormalities associated with schizophrenic cognitive impairment.

Method We carried out structural magnetic resonance imaging (MRI) and voxel-based morphometry in 26 participants who were cognitively impaired and 23 who were cognitively preserved, all with schizophrenia, plus 39 matched controls. Nineteen of those who were cognitively impaired and 18 of those who were cognitively preserved plus 34 controls also underwent functional MRI during performance of a working memory task.

Results No differences were found between the participants who were cognitively intact and those who were cognitively impaired in lateral ventricular volume or whole brain volume. Voxel-based morphometry also failed to reveal clusters of significant difference in grey and white matter volume between these two groups. However, during performance of the n-back task, the participants who were cognitively impaired showed hypoactivation compared with those who were cognitively intact in the dorsolateral prefrontal cortex among other brain regions.

Conclusions Cognitive impairment in schizophrenia is not a function of the structural brain abnormality that accompanies the disorder but has correlates in altered brain function.

/pdf/neural-correlates-of-cognitive-impairment-in-schizophrenia-1f8w3sotnh.pdf

Neural correlates of cognitive impairment in schizophrenia

COMT Val158Met polymorphism in relation to activation and de-activation in the prefrontal cortex: A study in patients with schizophrenia and healthy subjects

A. Guerrero

Papers

Failure to deactivate in the prefrontal cortex in schizophrenia: dysfunction of the default mode network?

Validation of the Word Accentuation Test (TAP) as a means of estimating premorbid IQ in Spanish speakers

Neural correlates of cognitive impairment in schizophrenia

COMT Val158Met polymorphism in relation to activation and de-activation in the prefrontal cortex: A study in patients with schizophrenia and healthy subjects

IgG anti-ganglioside antibodies and their subclass distribution in two patients with acute and chronic motor neuropathy