The Effects of Normal Aging on Nerve Fibers and Neuroglia in the Central Nervous System
David R. Riddle in Brain Aging, 2007
There is also MRI data from humans (e.g., [36, 37]) and from monkeys ([38]; see also [39]) supporting the conclusion that there is a loss of white matter from the cerebral hemispheres with increasing age, and especially from the frontal lobes (e.g., [40, 41]). In addition, there are MRI studies that show that the signal characteristics of white matter alter in normal human aging. These changes are considered to indicate that white matter is undergoing degenerative changes, which result in disconnections between parts of the brain (e.g., [42, 43]). The study by De Groot et al. [44] indicates that the most common locations for white matter lesions in the aging human brain are the subcortical and periventricular white matter. The subcortical fibers mainly consist of short U-fibers that connect adjacent areas of the cortex, while the periventricular fibers are mainly long association fibers. After analyzing the frequency of occurrence of lesions and correlating the data with the cognitive status of the subjects examined, De Groot et al. [44] conclude that it is the lesions of the long association fibers that play a dominant role in bringing about cognitive decline.
Brain Injury and Infant Cardiac Surgery: Overview
Richard A. Jonas, Jane W. Newburger, Joseph J. Volpe, John W. Kirklin in Brain Injury and Pediatric Cardiac Surgery, 2019
The neurological features of this lesion, i.e., particularly spastic diplegia, relate to the topography of the injury.18,19 Thus, in spastic diplegia, the lower extremity is involved more than the upper extremity. Because of the focal necrosis in the periventricular white matter, the motor fibers emanating from the cerebral cortex and subserving lower extremity function are preferentially affected. Fibers subserving the function of upper extremities course more laterally and thus are less likely to be injured or are injured less. However, because there is also more diffuse injury to cerebral white matter, association fibers are affected, and this involvement may account for at least some of the cognitive deficits that one sees on follow-up in affected infants.
Disruptions in physical substrates of vision following traumatic brain injury
Mark J. Ashley, David A. Hovda in Traumatic Brain Injury, 2017
These linkages are carried out by numerous axonal pathways located both in the cortex and subcortical white matter. These pathways consist of large groups of axons covered with a myelin coat and are identified as fasciculi, tracts, or bundles. Vision is created by the simultaneous integration of neural networks modulated by attention. These connections are bidirectional and multidirectional. They can converge or diverge from lower to higher centers, higher to lower centers, or can be collateral or spread out at the same level. This results in “top to bottom” or “bottom to top” processing. The organization of the white matter pathways begins in the cerebral cortex. Neurons within a specific cortical area give rise to three distinct categories of fiber systems that can be distinguished within the white matter beneath the gyrus. They are association fibers, striatal fibers, or subcortically directed fibers.13 The association fiber tract can be divided into three categories: local, neighborhood, and long association fibers. The local association fiber system, or the U system, leaves a given area of the cortex and travels to an adjacent gyrus running in a thin identifiable band beneath the sixth layer of the neocortex. The neighborhood association fiber system arises from a given cortical area and is directed to nearby regions but is distinguished from the U fiber system that runs immediately beneath the cortex. The long association fiber system emanates from a given cortical point and travels in a distinct bundle leading to other cortical areas in the same hemisphere. The operation of long association bundles are mandatory for specific domains of vision. The locations of the more prominent fasciculi are shown in Figure 9.5. Their connectivity in the distributed neural networks is shown in Table 9.1. These are outlined in Filley’s textbook, The Behavioral Neurology of White Matter.14
Nineteenth- and twentieth-century brain maps relating to locations and constructions of brain functions
Published in Journal of the History of the Neurosciences, 2022
Wernicke (1874) did not accept the functional equivalence of the cerebral surface as promoted by Flourens. Nor did he accept the localized, arbitrarily defined mental functions of the phrenologists, which were based on common sense distinctions. Wernicke believed that only the most elementary of mental functions, such as perceptual functions, could be associated with certain parts of the cortex. He believed that the brain was a mosaic of simple functions related to sensory information from the external world. Anything beyond these simple elements was the result of the links provided by the association fibers of the brain. He conceptualized these connections as analogous to connections among nervous elements in reflexes. His brain maps were line-drawings,9A line-drawing may appear crudely drawn, a shorthand way of depicting something, but it is designed to show only enough of known information to illustrate the point. The information it does include is crucial to orient the viewer. By its nature, it is a straightforward yet abstract illustration. with hypothetical pathways drawn on them.
The role of diffusion tensor imaging in characterizing injury patterns on athletes with concussion and subconcussive injury: a systematic review
Published in Brain Injury, 2021
Maryam Tayebi, Samantha J. Holdsworth, Allen A. Champagne, Douglas J. Cook, Poul Nielsen, Tae-Rin Lee, Alan Wang, Justin Fernandez, Vickie Shim
Several studies examined the whole regions of the brain, while others just focused on specific white matter tracts of association fibers, projection fibers, commissural fibers, or gray matter (GM). Figures 9 and 10 illustrate the number of papers which reported significant differences between the athletes with concussion and control group according to the name of white matter tracts. Based on this figure, the genu of the corpus callosum (CC) (Nstudies = 21 out of 39), superior longitudinal fasciculus (N studies = 15 out of 39), and anterior corona radiata (Nstudies = 13 out of 39) were the most remarkable fibers which showed substantial alterations. Among the studies conducted on the subconcussed players (Figure 11), splenium of CC (Nstudies = 10 out of 19), genu of CC (Nstudies = 8 out of 19), and posterior internal capsule (N studies = 7 out of 19) were found to be the most vulnerable tracts.
Acute symptomatic neonatal seizures, brain injury, and long-term outcome: The role of neuroprotective strategies
Published in Expert Review of Neurotherapeutics, 2021
Francesco Pisani, Carlo Fusco, Lakshmi Nagarajan, Carlotta Spagnoli
The main predisposing factors to IVH are the immaturity of the vasculature of the germinal matrix and its passivity to systemic blood pressure changes, which are typical of preterm newborns. White matter injury can be favored by cerebral oxygenation changes, infection, and inflammation, but also by intrinsic vulnerability to oxidative stress under hypoxic-ischemic conditions [40,41], which are in turn favored by immature vascular supply and autoregulation mechanisms [40,42]. In the acute phase, injury to the subplate neurons can transiently increase cortical excitability [43], resulting in acute seizures. The ensuing disruption of projection and association fibers and the secondary effects on the cortical plate and its connections to the thalamus are thought to be key determinants for long-term outcomes, especially relating to epilepsy and cognition [44].
Related Knowledge Centers
- Axon
- Cerebral Cortex
- Cerebral Hemisphere
- Diffusion Mri
- Gyrus
- Interneuron
- Projection Fiber
- Tractography
- Commissural Fiber