scholarly journals Axon Diameter Measurements using Diffusion MRI are Infeasible

2020 ◽  
Author(s):  
Michael Paquette ◽  
Cornelius Eichner ◽  
Thomas R. Knösche ◽  
Alfred Anwander
Keyword(s):  
Diffusion Mri ◽  
Signal Transmission ◽  
Effective Diameter ◽  
Axon Diameter ◽  
Non Invasive ◽  
Signal Decay ◽  
Axonal Diameter ◽  
The Brain ◽  
Transmission Speed ◽  
Minimal Diameter

AbstractThe feasibility of non-invasive axonal diameter quantification with diffusion MRI is a strongly debated topic due to the neuroscientific potential of such information and its relevance for the axonal signal transmission speed. It has been shown that under ideal conditions, the minimal diameter producing detectable signal decay is bigger than most human axons in the brain, even using the strongest currently available MRI systems. We show that resolving the simplest situations including multiple diameters is unfeasible even with diameters much bigger than the diameter limit. Additionally, the recently proposed effective diameter resulting from fitting a single value over a distribution is almost exclusively influenced by the biggest axons. We show how impractical this metric is for comparing different distributions. Overall, axon diameters currently cannot be quantified by diffusion MRI in any relevant way.

scholarly journals A time-dependent diffusion MRI signature of axon caliber variations and beading

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Hong-Hsi Lee ◽  
Antonios Papaioannou ◽  
Sung-Lyoung Kim ◽  
Dmitry S. Novikov ◽  
Els Fieremans
Keyword(s):  
Time Dependence ◽  
Diffusion Mri ◽  
Cellular Level ◽  
3 Dimensional ◽  
Non Invasive ◽  
Brain White Matter ◽  
Cell Dimensions ◽  
Micrometer Scale ◽  
Exciting Possibility ◽  
The Brain

AbstractMRI provides a unique non-invasive window into the brain, yet is limited to millimeter resolution, orders of magnitude coarser than cell dimensions. Here, we show that diffusion MRI is sensitive to the micrometer-scale variations in axon caliber or pathological beading, by identifying a signature power-law diffusion time-dependence of the along-fiber diffusion coefficient. We observe this signature in human brain white matter and identify its origins by Monte Carlo simulations in realistic substrates from 3-dimensional electron microscopy of mouse corpus callosum. Simulations reveal that the time-dependence originates from axon caliber variation, rather than from mitochondria or axonal undulations. We report a decreased amplitude of time-dependence in multiple sclerosis lesions, illustrating the potential sensitivity of our method to axonal beading in a plethora of neurodegenerative disorders. This specificity to microstructure offers an exciting possibility of bridging across scales to image cellular-level pathology with a clinically feasible MRI technique.

Tractography of White Matter Fibers Using Diffusion MRI

2022 ◽  
pp. 98-112
Author(s):  
Strivathsav Ashwin Ramamoorthy
Keyword(s):  
White Matter ◽  
Human Brain ◽  
Diffusion Mri ◽  
Neural Circuits ◽  
Water Molecules ◽  
Neural Connectivity ◽  
Non Invasive ◽  
Diffusion Weighted Images ◽  
Different Types ◽  
The Brain

To understand more about the human brain and how it works, it is vital to understand how the neural circuits connect different regions of the brain. The human brain is filled predominantly with water and the majority of the water molecules undergo diffusion which can be captured with the help of diffusion MRI. Diffusion weighted images enable us to reconstruct the neural circuits in a non-invasive manner, and this procedure is referred to as tractography. Tractography aids neurosurgeons to understand the neural connectivity of the patient. This chapter attempts to explain the procedure of tractography and different types of algorithms.

NON-INVASIVE BCI METHOD: EEG - ELECTROENCEPHALOGRAPHY

2019 ◽  
pp. 139-145
Author(s):  
Selma Büyükgöze
Keyword(s):  
Brain Computer Interface ◽  
Computer Interface ◽  
Electrode Placement ◽  
Eeg Signals ◽  
Non Invasive ◽  
Brain Signals ◽  
Brain States ◽  
The Brain

Brain Computer Interface consists of hardware and software that convert brain signals into action. It changes the nerves, muscles, and movements they produce with electro-physiological signs. The BCI cannot read the brain and decipher the thought in general. The BCI can only identify and classify specific patterns of activity in ongoing brain signals associated with specific tasks or events. EEG is the most commonly used non-invasive BCI method as it can be obtained easily compared to other methods. In this study; It will be given how EEG signals are obtained from the scalp, with which waves these frequencies are named and in which brain states these waves occur. 10-20 electrode placement plan for EEG to be placed on the scalp will be shown.

Differences in the brain stem terminations of large- and small-diameter vestibular primary afferents

1995 ◽  
Vol 74 (3) ◽  
pp. 1362-1366 ◽  
Author(s):  
J. A. Huwe ◽  
E. H. Peterson
Keyword(s):  
Brain Stem ◽  
Large Diameter ◽  
Small Diameter ◽  
Movement Control ◽  
Three Dimensions ◽  
Significant Shift ◽  
Axon Diameter ◽  
Vestibular Complex ◽  
The Brain ◽  
Adjacent Brain

1. We visualized the central axons of 32 vestibular afferents from the posterior canal by extracellular application of horseradish peroxidase, reconstructed them in three dimensions, and quantified their morphology. Here we compare the descending limbs of central axons that differ in parent axon diameter. 2. The brain stem distribution of descending limb terminals (collaterals and associated varicosities) varies systematically with parent axon diameter. Large-diameter afferents concentrate their terminals in rostral regions of the medial/descending nuclei. As axon diameter decreases, there is a significant shift of terminal concentration toward the caudal vestibular complex and adjacent brain stem. 3. Rostral and caudal regions of the medial/descending nuclei have different labyrinthine, cerebellar, intrinsic, commissural, and spinal connections; they are believed to play different roles in head movement control. Our data help clarify the functions of large- and small-diameter afferents by showing that they contribute differentially to rostral and caudal vestibular complex.

In vivo exploration of brain phosphorus 31 metabolism in patients with senile dementia of Alzheimer type

1994 ◽  
Vol 9 (2) ◽  
pp. 105-109
Author(s):  
G Mecheri ◽  
Y Bissuel ◽  
J Dalery ◽  
JL Terra ◽  
G Balvay ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Senile Dementia ◽  
Phospholipid Metabolism ◽  
Alzheimer Type ◽  
Dementia Of Alzheimer Type ◽  
Non Invasive ◽  
Significant Difference ◽  
The Brain

SummaryIn vivo NMR 31p spectroscopy is a non invasive, non ionizing method of exploration of energy and phospholipid metabolism in the brain. This study consisted of comparing 31p spectra in five patients with Senile Dementia of Alzheimer Type (SDAT) with those of four controls of similar ages. Abnormal phosphonionocsters (PME) concentrations, either high or low, were found in the patients, but statistical analysis did not elicit any significant difference relative to controls.

scholarly journals The brain timewise: how timing shapes and supports brain function

2015 ◽  
Vol 370 (1668) ◽  
pp. 20140170 ◽  
Author(s):  
Riitta Hari ◽  
Lauri Parkkonen
Keyword(s):  
Human Brain ◽  
Brain Imaging ◽  
Brain Function ◽  
Temporal Dynamics ◽  
Generative Models ◽  
Network Activity ◽  
Brain Diseases ◽  
Specific Information ◽  
Non Invasive ◽  
The Brain

We discuss the importance of timing in brain function: how temporal dynamics of the world has left its traces in the brain during evolution and how we can monitor the dynamics of the human brain with non-invasive measurements. Accurate timing is important for the interplay of neurons, neuronal circuitries, brain areas and human individuals. In the human brain, multiple temporal integration windows are hierarchically organized, with temporal scales ranging from microseconds to tens and hundreds of milliseconds for perceptual, motor and cognitive functions, and up to minutes, hours and even months for hormonal and mood changes. Accurate timing is impaired in several brain diseases. From the current repertoire of non-invasive brain imaging methods, only magnetoencephalography (MEG) and scalp electroencephalography (EEG) provide millisecond time-resolution; our focus in this paper is on MEG. Since the introduction of high-density whole-scalp MEG/EEG coverage in the 1990s, the instrumentation has not changed drastically; yet, novel data analyses are advancing the field rapidly by shifting the focus from the mere pinpointing of activity hotspots to seeking stimulus- or task-specific information and to characterizing functional networks. During the next decades, we can expect increased spatial resolution and accuracy of the time-resolved brain imaging and better understanding of brain function, especially its temporal constraints, with the development of novel instrumentation and finer-grained, physiologically inspired generative models of local and network activity. Merging both spatial and temporal information with increasing accuracy and carrying out recordings in naturalistic conditions, including social interaction, will bring much new information about human brain function.

Chronic stress and brain-derived neurotrophic factor

2021 ◽  
Vol 19 (2) ◽  
pp. 19-27
Author(s):  
A. V. DUBOVAYA ◽  
◽  
S. Ya. IAROSHENKO ◽  
O. A. PRILUTSKAYA ◽  
◽  
...  
Keyword(s):  
Neurotrophic Factor ◽  
Signal Transmission ◽  
Active Agent ◽  
Brain Derived Neurotrophic Factor ◽  
Relationship Of ◽  
The Relationship ◽  
The Brain ◽  
Pituitary Adrenal Axis ◽  
Transmission Information ◽  
Class Representative

The article discusses the influence of stress on the development of nervous tissue, in particular, on the synthesis of neurotrophins (by the example of the brain-derived neurotrophic factor (BDNF), as the most studied class representative). The biological functions of BDNF are discussed as well as its influence on neuroplasticity and the mechanisms by which the protection of neurons is carried out. The article covers the relationship of the stress-implementing system (hypothalamic-pituitary-adrenal axis) and its main active agent (cortisol) with the BDNF synthesis system at its various levels: from the inhibition of mRNA formation to the mechanisms of postsynaptic signal transmission. Information is also provided on changes of BDNF levels due to the maternal deprivation. Epigenetic changes under the influence of glucocorticoids are also reported. However, it is not only glucocorticoids that alter the functioning of the neurotrophin system. The article provides examples of the reverse effect, enabling to consider neurotrophins as a substance with an anti-stress function. In conclusion, the authors give examples of activities that, according to research, can stimulate the synthesis of neurotrophic factor in the brain.

scholarly journals Contrast and stability of the axon diameter index from microstructure imaging with diffusion MRI

2012 ◽  
Vol 70 (3) ◽  
pp. 711-721 ◽  
Author(s):  
Tim B. Dyrby ◽  
Lise V. S⊘gaard ◽  
Matt G. Hall ◽  
Maurice Ptito ◽  
Daniel. C. Alexander
Keyword(s):  
Diffusion Mri ◽  
Axon Diameter ◽  
Microstructure Imaging

scholarly journals Brain–Computer Interfacing Using Functional Near-Infrared Spectroscopy (fNIRS)

Biosensors ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 389
Author(s):  
Kogulan Paulmurugan ◽  
Vimalan Vijayaragavan ◽  
Sayantan Ghosh ◽  
Parasuraman Padmanabhan ◽  
Balázs Gulyás
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Brain Function ◽  
Near Infrared ◽  
Functional Near Infrared Spectroscopy ◽  
Non Invasive ◽  
Neuron Function ◽  
Brain Computer Interfacing ◽  
The Brain ◽  
Computer Interfacing

Functional Near-Infrared Spectroscopy (fNIRS) is a wearable optical spectroscopy system originally developed for continuous and non-invasive monitoring of brain function by measuring blood oxygen concentration. Recent advancements in brain–computer interfacing allow us to control the neuron function of the brain by combining it with fNIRS to regulate cognitive function. In this review manuscript, we provide information regarding current advancement in fNIRS and how it provides advantages in developing brain–computer interfacing to enable neuron function. We also briefly discuss about how we can use this technology for further applications.

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