Aging in the Neuropil of Cerebral Cortex– A Quantitative Ultrastructural Study

Ikari, Koichi; Hayashi, Michihiko

doi:10.1111/j.1440-1819.1981.tb00245.x

Cited by 6 publications

(9 citation statements)

References 22 publications

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“…In gray matter, “stick” fractions between 10 and 20% are consistent with previous findings . However, the findings are not consistent with interpreting “sticks” as neurites, because the combined (neurite) density of axons and dendrites is approximately 60% according to histology . We hypothesize, as in Lampinen, that this discrepancy is due to dendrites not exhibiting "stick‐like" diffusion, due to, for example, exchange with soma or between short segments with different orientations.…”

Section: Discussionsupporting

confidence: 61%

Towards unconstrained compartment modeling in white matter using diffusion‐relaxation MRI with tensor‐valued diffusion encoding

Lampinen

Szczepankiewicz

Mårtensson

et al. 2020

Magnetic Resonance in Med

111

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This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Purpose:To optimize diffusion-relaxation MRI with tensor-valued diffusion encoding for precise estimation of compartment-specific fractions, diffusivities, and T 2 values within a two-compartment model of white matter, and to explore the approach in vivo. Methods: Sampling protocols featuring different b-values (b), b-tensor shapes (b Δ ), and echo times (TE) were optimized using Cramér-Rao lower bounds (CRLB).Whole-brain data were acquired in children, adults, and elderly with white matter lesions. Compartment fractions, diffusivities, and T 2 values were estimated in a model featuring two microstructural compartments represented by a "stick" and a "zeppelin." Results: Precise parameter estimates were enabled by sampling protocols featuring seven or more "shells" with unique b/b Δ /TE-combinations. Acquisition times were approximately 15 minutes. In white matter of adults, the "stick" compartment had a fraction of approximately 0.5 and, compared with the "zeppelin" compartment, featured lower isotropic diffusivities (0.6 vs. 1.3 μm 2 /ms) but higher T 2 values (85 vs. 65 ms). Children featured lower "stick" fractions (0.4). White matter lesions exhibited high "zeppelin" isotropic diffusivities (1.7 μm 2 /ms) and T 2 values (150 ms). Conclusions: Diffusion-relaxation MRI with tensor-valued diffusion encoding expands the set of microstructure parameters that can be precisely estimated and therefore increases their specificity to biological quantities. K E Y W O R D Sbrain microstructure, diffusion-relaxation MRI, Fisher information, tensor-valued diffusion encoding 1606 | LAMPINEN Et AL. S (u) = (K ⊛ P) (u) = ∫ |n|=1 K(u ⋅ n) P(n) dn,(2) K(u ⋅ n) = S 0 J

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Section: Discussionsupporting

confidence: 61%

Towards unconstrained compartment modeling in white matter using diffusion‐relaxation MRI with tensor‐valued diffusion encoding

Lampinen

Szczepankiewicz

Mårtensson

et al. 2020

Magnetic Resonance in Med

111

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“…If this is the case, their respective prevalence should contribute similarly to microscopic diffusion anisotropy in the brain, and we would expect a contrast in MK A that bears similarity to the contrast in neurite density. In cortical gray matter, histology studies in mice have reported a rather even split between axons and dendrites and a neurite volume fraction of approximately 60% (Braitenberg & Schüz, ; Chklovskii, Schikorski, & Stevens, ; Ikari & Hayashi, ). In white matter, histology studies have reported a neurite density (intra‐axonal volume fraction) of 30–50% in the corpus callosum of macaque (Stikov et al, ) and mice (Jelescu et al, ) and in the rat spinal cord (Xu et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…In cortical gray matter, histology studies in mice have reported a rather even split between axons and dendrites and a neurite volume fraction of approximately 60% (Braitenberg & Schüz, 1998;Chklovskii, Schikorski, & Stevens, 2002;Ikari & Hayashi, 1981). In white matter, histology studies have reported a neurite density (intra-axonal volume fraction) of 30-50% in the corpus callosum of macaque (Stikov et al,FIGURE 4 Compartment densities could be estimated independently from T2 relaxation in white matter lesions, but not in the healthy brain.…”

Section: Discussionmentioning

confidence: 99%

Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling

Lampinen

Szczepankiewicz

Novén

et al. 2019

Human Brain Mapping

116

137

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In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high but challenging aim. First, it is unknown whether all neurites exhibit completely anisotropic (“stick‐like”) diffusion. Second, the “density” of tissue components may be confounded by non‐diffusion properties such as T2 relaxation. Third, the domain of validity for the estimated parameters to serve as indices of neurite density is incompletely explored. We investigated these challenges by acquiring data with “b‐tensor encoding” and multiple echo times in brain regions with low orientation coherence and in white matter lesions. Results showed that microscopic anisotropy from b‐tensor data is associated with myelinated axons but not with dendrites. Furthermore, b‐tensor data together with data acquired for multiple echo times showed that unbiased density estimates in white matter lesions require data‐driven estimates of compartment‐specific T2 values. Finally, the “stick” fractions of different biophysical models could generally not serve as neurite density indices across the healthy brain and white matter lesions, where outcomes of comparisons depended on the choice of constraints. In particular, constraining compartment‐specific T2 values was ambiguous in the healthy brain and had a large impact on estimated values. In summary, estimating neurite density generally requires accounting for different diffusion and/or T2 properties between axons and dendrites. Constrained “index” parameters could be valid within limited domains that should be delineated by future studies.

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“…In particular, areas located in the frontal and temporal cortex show a strong correlation of grey matter thickness and functional activation with IQ scores: individuals with high IQ show larger grey matter volume of, for instance, Brodmann areas 21 and 38 (Choi et al 2008;Deary et al 2010;Karama et al 2009;Narr et al 2007). Cortical grey matter consists for a substantial part of dendrites (Chklovskii et al 2002;Ikari & Hayashi 1981), which receive and integrate synaptic information and strongly affect functional properties of neurons (Bekkers & Häusser 2007;Eyal et al 2014;Vetter et al 2001). Especially high-order association areas in temporal and frontal lobes in humans harbor pyramidal neurons of extraordinary dendritic size and complexity (Elston 2003;Mohan et al 2015) that may constitute variation in cortical thickness, neuronal function, and ultimately IQ.…”

Section: Introductionmentioning

confidence: 99%

“…IQ scores positively correlate with dendritic structure of temporal cortical pyramidal cells Cortical association areas in temporal lobes play a key role in high-level integrative neuronal processes and its superficial layers harbor neurons of increased neuronal complexity (DeFelipe et al 2002;Elston 2003;Scholtens et al 2014;van den Heuvel et al 2015). In rodents, the neuropil of cortical association areas consists for over 30% of dendritic structures (Ikari & Hayashi 1981). To test the hypothesis that human temporal cortical thickness is associated with dendrite size, we used 72 full reconstructions of biocytin-labelled temporal cortical pyramidal neurons from human layer 2, 3 and 4 part of which was previously reported (Mohan et al 2015 Figs 1&2).…”

mentioning

confidence: 99%

Large and fast human pyramidal neurons associate with intelligence

Goriounova

Heyer

Wilbers

et al. 2018

Preprint

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It is generally assumed that human intelligence relies on efficient processing by neurons in our brain. Although gray matter thickness and activity of temporal and frontal cortical areas correlate with IQ scores, no direct evidence exists that links structural and physiological properties of neurons to human intelligence. Here, we find that high IQ scores and large temporal cortical thickness associate with larger, more complex dendrites of human pyramidal neurons. We show in silico that larger dendritic trees enable pyramidal neurons to track activity of synaptic inputs with higher temporal precision, due to fast action potential kinetics. Indeed, we find that human pyramidal neurons of individuals with higher IQ scores sustain fast action potential kinetics during repeated firing. These findings provide the first evidence that human intelligence is associated with neuronal complexity, action potential kinetics and efficient information transfer from inputs to output within cortical neurons.All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

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Aging in the Neuropil of Cerebral Cortex– A Quantitative Ultrastructural Study

Cited by 6 publications

References 22 publications

Towards unconstrained compartment modeling in white matter using diffusion‐relaxation MRI with tensor‐valued diffusion encoding

Towards unconstrained compartment modeling in white matter using diffusion‐relaxation MRI with tensor‐valued diffusion encoding

Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling

Large and fast human pyramidal neurons associate with intelligence

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