The Effects of Normal Aging on Nerve Fibers and Neuroglia in the Central Nervous System
David R. Riddle in Brain Aging, 2007
The anterior commissure is another well-circumscribed bundle of white matter in which the total numbers of nerve fibers can be accurately determined [55]. In the anterior commissures of young monkeys, the mean number of nerve fibers is 2.2 × 106, while in monkeys over 25 years of age the mean number is reduced to 1.2 × 106. This loss of fibers is accompanied by a 25% reduction in the cross-sectional area of the anterior commissure. Some middle-aged monkeys, 12 to 20 years of age, also were available for study and it became evident that, in terms of the total numbers of nerve fibers, middle-aged monkeys resemble young ones, so most of the loss of nerve fibers appears to occur after middle age. Nerve fibers with abnormal myelin sheaths are evident at all ages, but there is a progressive, age-related increase in their frequency, such that in young monkeys only 0.4% of profiles of nerve fibers show alterations in myelin, while the number increases to 1.8% in middle-aged monkeys, and reaches 5.4% in old monkeys. Similarly, as would be expected from the loss of nerve fibers, there is a significant increase in the numbers of axons that show degenerative changes with age. Because most of the monkeys used in this study had been behaviorally tested, it was possible to correlate the data with a decline in their cognitive status. A positive correlation was found between the reduction in the total numbers of nerve fibers and cognitive impairment, but there was not a strong correlation between myelin sheath abnormalities and cognitive status.
Introduction: Background Material
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
There are several classifications and names for the various brain structures, which is somewhat confusing. Conventionally, the brain may be divided into four major subdivisions, as indicated in Figure 1.7 and are illustrated in Figure 1.8 in a midsagittal section that divides the brain into right and left halves. These two halves of the brain are interconnected by a massive fiber tract, the corpus callosum, having a cross-sectional area of about 700 mm2 and consisting of about 200 million fibers. A smaller tract, the anterior commissure, also connects the two hemispheres. The four major subdivisions will be described very briefly in what follows. More details about the structure of these subdivisions, their substructures, and their functions will be presented in future chapters as needed for our discussion of the neuromuscular system.
Biological Predictions from the Conduction Delay Hypothesis of Cerebral Lateralization
Robert Miller in Axonal Conduction Time and Human Cerebral Laterality, 2019
It is likely that there are lateral differences in other regions of the hemisphere, about which very little is known at present. Kopp et al. (1977) give some clues to lateral differences in parts of the temporal lobe other than the posterior speech area. The “bridge” between the first and second temporal gyri was commoner on the left (especially in brains from male subjects). The second temporal gyrus had a greater maximum width on the right, and the fusiform gyrus (at the base of the temporal lobe) was wider on the left in the majority of cases. The larger planum temporale on the left correlated with the size of the anterior commissure. All these differences were highly significant statistically. Jack et al. (1989) found, from MRI studies, that the right hippocampus was significantly larger than the left (mean difference 0.3 cm3; p < 0.001). Weis et al. (1989) found from study of post mortem brains that the cortex of the parahippocampal gyrus and in the basal temporal region was thicker on the right than the left (p < 0.01) and that the frontal orbital cortex was larger on the right (p < 0.01). Kopp et al. (1977) comment: “Anatomical asymmetries of the two cerebral hemisphere in man seem to be numerous. The interpretation of these asymmetries is difficult.”
Seizure and cognitive outcomes of posterior quadrantic disconnection: a series of 12 pediatric patients
Published in British Journal of Neurosurgery, 2020
Yao Wang, Chao Zhang, Xiu Wang, Lin Sang, Feng Zhou, Jian-Guo Zhang, Wen-Han Hu, Kai Zhang
After this procedure, the fibres mentioned in 1)–3) above were disconnected with remaining fibres as follows: 5) hippocampal efferent fibres; 6) projection fibres from the amygdala; 7) fibres through the anterior commissure between the anterior temporal lobe and limbic cortex; and 8) projection fibres from the insula to the basal ganglia, thalamus, hypothalamus and brain stem.(3) Stage III: Mesial temporal resection: After the opening of the temporal horn, the amygdala was revealed in the anteromedial part. The amygdala was removed along with resection of the subdural uncinate gyrus. The superior boundary of the amygdala resection was located at the top of the temporal horn of the lateral ventricle. The hippocampus was exposed and resected along the temporal horn and choroid fissure.
Altered dynamic parahippocampus functional connectivity in patients with post-traumatic stress disorder
Published in The World Journal of Biological Psychiatry, 2021
Hui Juan Chen, Rongfeng Qi, Jun Ke, Jie Qiu, Qiang Xu, Zhiqiang Zhang, Yuan Zhong, Guang Ming Lu, Feng Chen
Magnetic resonance imaging scans were conducted at Hainan General Hospital using a 3 Tesla MR scanner (Skyra, Siemens Medical Solutions, Erlangen, Germany) equipped with a 32 channel standard head coil. Subjects’ heads were immobilised using a foam pad and a Plexiglas head cradle. Whole brain resting-state functional images were obtained using an echo-planar imaging sequence with the following parameters: TR/TE = 2000/30 ms, flip angle = 90°, FOV = 230 × 230 mm2, matrix = 64 × 64, 35 slices, slice thickness = 3.6 mm, no intersection gap, and total volume number = 250. The sections were placed approximately parallel to the anterior commissure-posterior commissure line. High resolution T1-weighted 3 D anatomical images were also acquired with a sagittal magnetization-prepared rapid gradient echo sequence for later co-registration and normalisation (TR/TE = 2300/1.97 ms, flip angle = 9°, FOV = 256 × 256 mm2, matrix = 256 × 256, 176 slices, slice thickness = 1 mm). Each fMRI scan lasted for 500 seconds. During the functional scanning, subjects were instructed to lie quietly, keep their eyes closed, and let their mind wander without falling asleep.
Cortical Visual Connections via the Corpus Callosum are Asymmetrical in Human Infantile Esotropia
Published in Strabismus, 2018
Marcel P. M. ten Tusscher, Anne Cees Houtman, Johan De Mey, Peter Van Schuerbeek
The abnormalities found in visual callosal interhemispheric connections in patients with IE strongly suggest that interhemispheric pathways are involved in human binocular development. In cats, transection of the CC before the age of 19 days causes a reduction of binocularly activated neurons in the striate cortex and a larger amount of neurons is dominated by the contralateral eye.23 In an earlier paper, the authors suggested that this change in dominance would explain the typical motor phenomena of IE.24 Moreover, the role of the CC is supposed to play in binocularity made the authors wonder if callosal agenesis with normal binocularity could be explained by a different interhemispheric connection. In such a case, the authors showed a connection through the anterior commissure.25
Related Knowledge Centers
- Axon
- Cerebral Hemisphere
- Corpus Callosum
- Nerve Tract
- Nociception
- Olfactory Tract
- Posterior Commissure
- Temporal Lobe
- White Matter
- Fornix