The posterior cingulate cortex is a highly connected and metabolically active brain region. Recent studies suggest it has an important cognitive role, although there is no consensus about what this is. The region is typically discussed as having a unitary function because of a common pattern of relative deactivation observed during attentionally demanding tasks. One influential hypothesis is that the posterior cingulate cortex has a central role in supporting internally-directed cognition. It is a key node in the default mode network and shows increased activity when individuals retrieve autobiographical memories or plan for the future, as well as during unconstrained ‘rest’ when activity in the brain is ‘free-wheeling’. However, other evidence suggests that the region is highly heterogeneous and may play a direct role in regulating the focus of attention. In addition, its activity varies with arousal state and its interactions with other brain networks may be important for conscious awareness. Understanding posterior cingulate cortex function is likely to be of clinical importance. It is well protected against ischaemic stroke, and so there is relatively little neuropsychological data about the consequences of focal lesions. However, in other conditions abnormalities in the region are clearly linked to disease. For example, amyloid deposition and reduced metabolism is seen early in Alzheimer’s disease. Functional neuroimaging studies show abnormalities in a range of neurological and psychiatric disorders including Alzheimer’s disease, schizophrenia, autism, depression and attention deficit hyperactivity disorder, as well as ageing. Our own work has consistently shown abnormal posterior cingulate cortex function following traumatic brain injury, which predicts attentional impairments. Here we review the anatomy and physiology of the region and how it is affected in a range of clinical conditions, before discussing its proposed functions. We synthesize key findings into a novel model of the region’s function (the ‘Arousal, Balance and Breadth of Attention’ model). Dorsal and ventral subcomponents are functionally separated and differences in regional activity are explained by considering: (i) arousal state; (ii) whether attention is focused internally or externally; and (iii) the breadth of attentional focus. The predictions of the model can be tested within the framework of complex dynamic systems theory, and we propose that the dorsal posterior cingulate cortex influences attentional focus by ‘tuning’ whole-brain metastability and so adjusts how stable brain network activity is over time.

/pdf/the-role-of-the-posterior-cingulate-cortex-in-cognition-and-k3skjitecz.pdf

The role of the posterior cingulate cortex in cognition and disease.

Though only a decade has elapsed since the default network (DN) was first defined as a large-scale brain system, recent years have brought great insight into the network's adaptive functions. A growing theme highlights the DN as playing a key role in internally directed or self-generated thought. Here, we synthesize recent findings from cognitive science, neuroscience, and clinical psychology to focus attention on two emerging topics as current and future directions surrounding the DN. First, we present evidence that self-generated thought is a multifaceted construct whose component processes are supported by different subsystems within the network. Second, we highlight the dynamic nature of the DN, emphasizing its interaction with executive control systems when regulating aspects of internal thought. We conclude by discussing clinical implications of disruptions to the integrity of the network, and consider disorders when thought content becomes polarized or network interactions become disrupted or imbalanced.

/pdf/the-default-network-and-self-generated-thought-component-20rxmb3qvp.pdf

The default network and self-generated thought: component processes, dynamic control, and clinical relevance

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

The role of default network deactivation in cognition and disease.

Resting-state functional magnetic resonance imaging has become a powerful tool for the study of functional networks in the brain. Even “at rest,” the brain's different functional networks spontaneously fluctuate in their activity level; each network's spatial extent can therefore be mapped by finding temporal correlations between its different subregions. Current correlation-based approaches measure the average functional connectivity between regions, but this average is less meaningful for regions that are part of multiple networks; one ideally wants a network model that explicitly allows overlap, for example, allowing a region's activity pattern to reflect one network's activity some of the time, and another network's activity at other times. However, even those approaches that do allow overlap have often maximized mutual spatial independence, which may be suboptimal if distinct networks have significant overlap. In this work, we identify functionally distinct networks by virtue of their temporal independence, taking advantage of the additional temporal richness available via improvements in functional magnetic resonance imaging sampling rate. We identify multiple “temporal functional modes,” including several that subdivide the default-mode network (and the regions anticorrelated with it) into several functionally distinct, spatially overlapping, networks, each with its own pattern of correlations and anticorrelations. These functionally distinct modes of spontaneous brain activity are, in general, quite different from resting-state networks previously reported, and may have greater biological interpretability.

https://www.pnas.org/content/pnas/109/8/3131.full.pdf

Temporally-independent functional modes of spontaneous brain activity

Efforts to understand the functional architecture of the brain have consistently identified multiple overlapping large-scale neural networks that are observable across multiple states. Despite the ubiquity of these networks, it remains unclear how regions within these large-scale neural networks interact to orchestrate behavior. Here, we collected functional magnetic resonance imaging data from 188 human subjects who engaged in three cognitive tasks and a resting-state scan. Using multiple tasks and a large sample allowed us to use split-sample validations to test for replication of results. We parceled the task-rest pairs into functional networks using a probabilistic spatial independent components analysis. We examined changes in connectivity between task and rest states using dual-regression analysis, which quantifies voxelwise connectivity estimates for each network of interest while controlling for the influence of signals arising from other networks and artifacts. Our analyses revealed systematic state-dependent functional connectivity in one brain region: the precuneus. Specifically, task performance led to increased connectivity (compared to rest) between the precuneus and the left frontoparietal network (lFPN), whereas rest increased connectivity between the precuneus and the default-mode network (DMN). The absolute magnitude of this effect was greater for DMN, suggesting a heightened specialization for resting-state cognition. All results replicated within the two independent samples. Our results indicate that the precuneus plays a core role not only in DMN, but also more broadly through its engagement under a variety of processing states.

https://www.jneurosci.org/content/jneuro/34/3/932.full.pdf

Precuneus is a functional core of the default-mode network.

The posterior cingulate cortex (PCC) is a central part of the default mode network (DMN) and part of the structural core of the brain. Although the PCC often shows consistent deactivation when attention is focused on external events, anatomical studies show that the region is not homogeneous, and electrophysiological recordings in nonhuman primates suggest that it is directly involved in some forms of attention. We report a functional magnetic resonance imaging study of an attentionally demanding task (either a zero- or two-back working memory task). Standard subtraction analysis within the PCC shows a relative deactivation as task difficulty increases. In contrast, a dual-regression functional connectivity analysis reveals a clear dissociation between ventral and dorsal parts of the PCC. As task difficulty increases, the ventral PCC shows reduced integration within the DMN and less anticorrelation with the cognitive control network (CCN) activated by the task. The dorsal PCC shows an opposite pattern, with increased DMN integration and more anticorrelation. At rest, the dorsal PCC also shows functional connectivity with both the DMN and attentional networks. As expected, these results provide evidence that the PCC is involved in supporting internally directed thought, as the region is more highly integrated with the DMN at low task demands. In contrast, the task-dependent increases in connectivity between the dorsal PCC and the CCN are consistent with a role for this region in modulating the dynamic interaction between these two networks controlling the efficient allocation of attention.

https://www.jneurosci.org/content/jneuro/31/9/3217.full.pdf

Fractionating the Default Mode Network: Distinct Contributions of the Ventral and Dorsal Posterior Cingulate Cortex to Cognitive Control

Purpose

To quantify fetal cerebellar growth by measuring cerebellar volumes of normal fetuses throughout gestation with MRI.



Materials and Methods

A total of 93 fetuses with normal brains ranging in age from 16 to 40 gestational weeks were included in the study. Standard fetal biometric measurements were made on a three-dimensional postprocessing workstation and included the head circumference, transverse cerebellar diameter, biparietal diameter, occipital-frontal diameter, as well as cerebellar volume. The gestational ages were estimated from fetal head circumference measurements. Regression analysis was used to find the best-fit model.



Results

There is a strong correlation describing cerebellar volume and gestational age in fetuses with normal central nervous systems. A second-order polynomial regression model was found to be the most appropriate descriptor of cerebellar volume in relation to normal fetal growth. In addition, the cerebellar volume was also found to correlate strongly with the common fetal biometric measurements of transverse cerebellar diameter, biparietal diameter, and occipital-frontal diameter.



Conclusion

Nomograms for fetal cerebellar volume with gestational age derived from head circumference measurements are presented for the first time with MRI. A normal fetal cerebellar volume growth chart is established. These results should prove helpful in defining situations of abnormal growth development and dysmorphology. J. Magn. Reson. Imaging 2008. © 2008 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.21290

MR volume of the fetal cerebellum in relation to growth

Remembering what a speaker said depends on attention. During conversational speech, the emphasis is on working memory, but listening to a lecture encourages episodic memory encoding. With simultaneous interference from background speech, the need for auditory vigilance increases. We recreated these context-dependent demands on auditory attention in 2 ways. The first was to require participants to attend to one speaker in either the absence or presence of a distracting background speaker. The second was to alter the task demand, requiring either an immediate or delayed recall of the content of the attended speech. Across 2 fMRI studies, common activated regions associated with segregating attended from unattended speech were the right anterior insula and adjacent frontal operculum (aI/FOp), the left planum temporale, and the precuneus. In contrast, activity in a ventral right frontoparietal system was dependent on both the task demand and the presence of a competing speaker. Additional multivariate analyses identified other domain-general frontoparietal systems, where activity increased during attentive listening but was modulated little by the need for speech stream segregation in the presence of 2 speakers. These results make predictions about impairments in attentive listening in different communicative contexts following focal or diffuse brain pathology.

/pdf/neural-systems-involved-when-attending-to-a-speaker-3bpas2oh1v.pdf

Neural Systems Involved When Attending to a Speaker

Paroxysmal hemicrania (PH) is a rare primary headache disorder characterised by recurrent attacks of severe, strictly unilateral pain, focused around the orbital, supraorbital and temporal regions and associated with autonomic features. Attacks usually occur more than five times a day and last 2–30 min.1 The disorder has an absolute response to indomethacin such that patients are rendered pain-free by therapeutic doses. Between 65% and 88% of patients suffer from the chronic form of PH where the attacks occur for more than 1 year without remission or with remission periods lasting less than 3 months.2 Over 30% of patients report dose-limiting side-effects with indomethacin and approximately 20% discontinue the drug due to tolerability problems.3 Although several other drugs have been reported to have efficacy in PH, none offer the same magnitude of response.

Evidence to support the role of the vagus nerve in trigeminal pain have been identified in prior studies. Inhibition of nociceptive activation of the trigeminocervical neurons have been shown in preclinical animal models, with a dose-dependent effect.4 Non-invasive vagus nerve stimulation (nVNS), using the gammaCore device, has been reported to be beneficial in trigeminal autonomic cephalalgias (TACs). A recent audit looking at 15 patients with indomethacin-responsive headaches, six of whom had PH, concluded that nVNS may be an important adjunct or alternative in those patients with …

https://jnnp.bmj.com/content/jnnp/early/2019/02/01/jnnp-2018-319538.full.pdf

Non-invasive vagus nerve stimulation is beneficial in chronic paroxysmal hemicrania

Granule cell neuronopathy (GCN) is a rare presentation of JC virus (JCV) infection targeting the cerebellum.1 To date, 2 cases have been described in patients prescribed natalizumab for MS.2,3 Recent case reports have acknowledged the importance of controlled reconstitution of host immunity in treating JCV-related neurologic disorders.4 In particular, granulocyte-colony stimulating factor (G-CSF) has emerged as a potential treatment.5

Salwa Kamourieh

Papers

Fractionating the Default Mode Network: Distinct Contributions of the Ventral and Dorsal Posterior Cingulate Cortex to Cognitive Control

MR volume of the fetal cerebellum in relation to growth

Neural Systems Involved When Attending to a Speaker

Non-invasive vagus nerve stimulation is beneficial in chronic paroxysmal hemicrania

Natalizumab granule cell neuronopathy: FDG-PET in diagnosis and immune reconstitution with G-CSF.