Microscopic Quantification of Oxygen Consumption across Cortical Layers

The cerebral cortex is organized in cortical layers that differ in their cellular density, composition, and wiring. Cortical laminar architecture is also readily revealed by staining for cytochrome oxidase – the last enzyme in the respiratory electron transport chain located in the inner mitochondrial membrane. It has been hypothesized that a high-density band of cytochrome oxidase in cortical layer IV reflects higher oxygen consumption under baseline (unstimulated) conditions. Here, we tested the above hypothesis using direct measurements of the partial pressure of O 2 (pO 2 ) in cortical tissue by means of 2-photon phosphorescence lifetime microscopy (2PLM). We revisited our previously developed method for extraction of the cerebral metabolic rate of O 2 (CMRO 2 ) based on 2-photon pO 2 measurements around diving arterioles and applied this method to estimate baseline CMRO 2 in awake mice across cortical layers. To our surprise, our results revealed a decrease in baseline CMRO 2 from layer I to layer IV . This decrease of CMRO 2 with cortical depth was paralleled by an increase in tissue oxygenation. Higher baseline oxygenation and cytochrome density in layer IV may serve as an O 2 reserve during surges of neuronal activity or certain metabolically active brain states rather than baseline energy needs. Our study provides the first quantification of microscopically resolved CMRO 2 across cortical layers as a step towards informed interpretation and modeling of cortical-layer-specific Blood Oxygen Level Dependent (BOLD) fMRI signals.

Early Cortical Laminar Necrosis on MRI

An 80-year-old man with chronic hypertension was admitted to the emergency department with consciousness disorders. The evolution was marked by a rapid worsening of his neurological condition. The patient was intubated and ventilated. The biological check-up revealed a blood glucose level of 0.2g/l. A brain scan was performed which was without abnormality. Two days after the normalization of the blood sugar level, the patient presented a late awakening. A brain MRI was performed which showed bilateral fronto-parietal laminar cortical areas in T2, Flair and diffusion hypersignal, T1 iso signal, and no hyposignal on T2 gradient echo sequence (Figure 1). The diagnostic of Cortical Laminar Necrosis was retained.

Prolonged Hemiplegic Migraine Associated with Irreversible Neurological Deficit and Cortical Laminar Necrosis in a Patient with Patent Foramen Ovale ：A case report

Background: Aura symptoms of hemiplegic migraine (HM) usually resolve completely, permanent attack-related deficit and radiographic change are rare. Case presentation: We reported a HM case presented with progressively aggravated hemiplegic migraine episodes refractory to medication. He experienced two prolonged hemiplegic migraine attacks that led to irreversible visual impairment and cortical laminar necrosis (CLN) on brain MRI. Patent foramen ovale (PFO) was found on the patient. PFO closure resulted in a significant reduction of HM attacks. Conclusions: Prolonged hemiplegic migraine attack could result in irreversible neurological deficit with neuroimaging changes manifested as CLN. We recommend screening for PFO in patients with prolonged or intractable hemiplegic migraine, for that closure of PFO might alleviate the attacks thus preventing patient from disabling sequelae.

Time-dependent diffusion MRI probes cerebellar microstructural alterations in a mouse model of Down syndrome

The cerebellum is a complex system with distinct cortical laminar organization. Alterations in cerebellar microstructure are common and associated with many factors such as genetics, cancer and ageing. Diffusion MRI (dMRI) provides a non-invasive tool to map the brain structural organization, and the recently proposed diffusion-time (td)-dependent dMRI further improves its capability to probe the cellular and axonal/dendritic microstructures by measuring water diffusion at multiple spatial scales. The td-dependent diffusion profile in the cerebellum and its utility in detecting cerebellar disorders, however, are not yet elucidated. Here, we first deciphered the spatial correspondence between dMRI contrast and cerebellar layers, based on which the cerebellar layer-specific td-dependent dMRI patterns were characterized in both euploid and Ts65Dn mice, a mouse model of Down syndrome. Using oscillating gradient dMRI, which accesses diffusion at short td’s by modulating the oscillating frequency, we detected subtle changes in the apparent diffusivity coefficient of the cerebellar internal granular layer and Purkinje cell layer of Ts65Dn mice that were not detectable by conventional pulsed gradient dMRI. The detection sensitivity of oscillating gradient dMRI increased with the oscillating frequency at both the neonatal and adult stages. The td-dependence, quantified by ΔADC map, was reduced in Ts65Dn mice, likely associated with the reduced granule cell density and abnormal dendritic arborization of Purkinje cells as revealed from histological evidence. Our study demonstrates superior sensitivity of short-td diffusion using oscillating gradient dMRI to detect cerebellar microstructural changes in Down syndrome, suggesting the potential application of this technique in cerebellar disorders.

Exploring the laminar connectome

The human connectome is the complete structural description of the network of connections and elements that form the wiring diagram of the brain. Because of the current scarcity of information regarding laminar end points of white matter tracts inside cortical grey matter, tractography remains focused on cortical partitioning into regions, while ignoring radial partitioning into laminar components. To overcome this biased representation of the cortex as a single homogenous unit, we use a recent data-derived model of cortical laminar connectivity, which has been further explored and corroborated in the macaque brain by comparison to published studies. The model integrates multimodal MRI imaging datasets regarding both white matter connectivity and grey matter laminar composition into a laminar-level connectome. In this study we model the laminar connectome of healthy human brains (N=20) and explore them via a set of neurobiologically meaningful complex network measures. Our analysis demonstrates a subdivision of network hubs that appear in the standard connectome into each individual component of the laminar connectome, giving a fresh look into the role of laminar components in cortical connectivity and offering new prospects in the fields of both structural and functional connectivity.