Large-Scale Distributed Networks and Cerebral Hemispheres

Elkhonon Goldberg, Jaan Tulviste

The two main large-scale distributed networks, Central Executive (CEN) and Default Mode (DMN) have been extensively studied, but their relationship to hemispheric specialization has not been comprehensively addressed. We present evidence that they are neuroanatomically asymmetric: the CEN components are volumetrically larger in the right hemisphere, and DMN components are volumetrically larger in the left hemisphere. Based on this, the possibility that CEN and DMN are also functionally asymmetric is introduced and implications of the putative functional asymmetry of large-scale distributed networks for refining our understanding of hemispheric specialization are examined.

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Multiple Neuroinvasive Pathways in COVID-19

Dmitri Bougakov, Kenneth Podell, Elkhonon Goldberg
Molecular Neurobiology 58, 564–575 (2021)

COVID-19 is a highly infectious viral disease caused by the novel coronavirus SARS-CoV-2. While it was initially regarded as a strictly respiratory illness, the impact of COVID-19 on multiple organs is increasingly recognized. The brain is among the targets of COVID-19, and it can be impacted in multiple ways, both directly and indirectly. Direct brain infection by SARS-CoV-2 may occur via axonal transport via the olfactory nerve, eventually infecting the olfactory cortex and other structures in the temporal lobe, and potentially the brain stem. A hematogenous route, which involves viral crossing of blood–brain barrier, is also possible. Secondary mechanisms involve hypoxia due to respiratory failure, as well as aberrant immune response leading to various forms of encephalopathy, white matter damage, and abnormal blood clotting resulting in stroke. Multiple neurological symptoms of COVID-19 have been described. These involve anosmia/ageusia, headaches, seizures, mental confusion and delirium, and coma. There is a growing concern that in a number of patients, long-term or perhaps even permanent cognitive impairment will persist well after the recovery from acute illness. Furthermore, COVID-19 survivors may be at increased risk for developing neurodegenerative diseases years or decades later. Since COVID-19 is a new disease, it will take months or even years to characterize the exact nature, scope, and temporal extent of its long-term neurocognitive sequelae. To that end, rigorous and systematic longitudinal follow-up will be required. For this effort to succeed, appropriate protocols and patient registries should be developed and put in place without delay now.

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Schizophrenia and frontotemporal dementia: Shared causation?

The relationship between specific genes and particular diseases in neuropsychiatry is unclear, and newer studies focus on shared domains of neurobiological and cognitive pathology across different disorders. This paper reviews the evidence for an association between schizophrenia and frontotemporal dementia, including symptom similarity, familial co-morbidity, and neuroanatomical changes. Genetic as well as epigenetic findings from both schizophrenia and frontotemporal dementia are also discussed. As a result, we introduce the hypothesis of a shared susceptibility for certain subgroups of schizophrenia and frontotemporal dementia. This common causation may involve the same gene(s) at different stages of life: early in schizophrenia and late in frontotemporal dementia. Additionally, we provide a rationale for future research that should emphasize both genetic and cognitive parallels between certain forms of schizophrenia and frontotemporal dementia in a synergistic, coordinated way, placing both in the context of aberrant lateralization patterns.
International Review of Psychiatry. International Review of Psychiatry, April 2013; 25(2): 168–177.

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Hemispheric asymmetries of cortical volume in the human brain

Hemispheric asymmetry represents a cardinal feature of cerebral organization, but the nature of structural and functional differences between the hemispheres is far from fully understood. Using Magnetic Resonance Imaging morphometry, we identified several volumetric differences between the two hemispheres of the human brain. Heteromodal inferoparietal and lateral prefrontal cortices are more extensive in the right than left hemisphere, as is visual cortex. Heteromodal mesial and orbital prefrontal and cingulate cortices are more extensive in the left than right hemisphere, as are somatosensory, parts of motor, and auditory cortices. Thus, heteromodal association cortices are more extensively represented on the lateral aspect of the right than in the left hemisphere, and modality-specific cortices are more extensively represented on the lateral aspect of the left than in the right hemisphere. On the mesial aspect heteromodal association cortices are more extensively represented in the left than right hemisphere.
Cortex, 2013, 49, 200-210.

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