Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8986.1997.tb02140.x

Heart rate variability: Origins, methods, and interpretive caveats

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...

Spinal and Supraspinal Factors in Human Muscle Fatigue

1. In ten normal volunteers, a transcranial magnetic or electric stimulus that was subthreshold for evoking an EMG response in relaxed muscles was used to condition responses evoked by a later, suprathreshold magnetic or electric test shock. In most experiments the test stimulus was given to the lateral part of the motor strip in order to evoke EMG responses in the first dorsal interosseous muscle (FDI). 2. A magnetic conditioning stimulus over the hand area of cortex could suppress responses produced in the relaxed FDI by a suprathreshold magnetic test stimulus at interstimulus intervals of 1-6 ms. At interstimulus intervals of 10 and 15 ms, the test response was facilitated. 3. Using a focal magnetic stimulus we explored the effects of moving the conditioning stimulus to different scalp locations while maintaining the magnetic test coil at one site. If the conditioning coil was moved anterior or posterior to the motor strip there was less suppression of test responses in the FDI. In contrast, stimulation at the vertex could suppress FDI responses by an amount comparable to that seen with stimulation over the hand area. With the positions of the two coils reversed, conditioning stimuli over the hand area suppressed responses evoked in leg muscles by vertex test shocks. 4. The intensity of both conditioning and test shocks influenced the amount of suppression. Small test responses were more readily suppressed than large responses. The best suppression was seen with small conditioning stimuli (0.7-0.9 times motor threshold in relaxed muscle); increasing the intensity to motor threshold or above resulted in less suppression or even facilitation. 5. Two experiments suggested that the suppression was produced by an action on cortical, rather than spinal excitability. First, a magnetic conditioning stimulus over the hand area failed to produce any suppression of responses evoked in active hand muscles by a small (approximately 200 V, 50 microsecond time constant) anodal electric test shock. Second, a vertex conditioning shock had no effect on forearm flexor H reflexes even though responses in the same muscles produced by magnetic cortical test shocks were readily suppressed at appropriate interstimulus intervals. 6. Small anodal electric conditioning stimuli were much less effective in suppressing magnetic test responses than either magnetic or cathodal electric conditioning shocks.(ABSTRACT TRUNCATED AT 400 WORDS)

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1993.sp019912

Corticocortical inhibition in human motor cortex.

Altered peripheral nerve excitability depends on severity of multiple sclerosis.

Abstract. We examined the effects of soil chemistry on the herbaceous forest wildflower Podophyllum peltatum (Mayapple) in an existing large-scale ecosystem level experiment that raised soil pH by two units (from ∼ 4 to ∼ 6) and increased available phosphorus (P) at least sevenfold. Plant leaf tissue was monitored for four years, and we began detailed plant measurements after we observed changes in leaf P content. Plant nutrient content, reproductive allocation, and the extent of root colonization by arbuscular mycorrhizal fungi were determined. We found no effect of changing soil chemistry on P. peltatum reproductive allocation. Addition of P resulted in significant increases in leaf P content, but also marginally reduced leaf N and C content. Increases in pH had no effect on leaf N or P, but there was a significant interaction between P addition and pH elevation on leaf C content. Root colonization by arbuscular mycorrhizal fungi was significantly affected by soil treatment; our data suggest that pH elevation and P addition may have opposite effects on mycorrhizal colonization in forest herbs, with pH increasing and P addition decreasing root colonization. Our study has important implications for how forest wildflowers may respond to anthropogenic changes in soil nutrient content and chemistry.

Increases in soil pH and P availability in a temperate hardwood forest affect mycorrhizal colonization and nutrient content of the herbaceous wildflower Podophyllum peltatum (Mayapple)

Preservation of Ia afferent function in peripheral neuropathies.

ABSTRACT White-tailed deer (Odocoileus virginianus) impact the ecological integrity of eastern deciduous forests by modifying plant community composition and structure. Previous studies have shown that overabundant deer can negatively impact the recruitment and persistence of both woody and herbaceous plants. However, the strength and nature of these interactions can depend on habitat context. Forest edges provide favorable habitat for deer along with many introduced plant species, and have the potential to modify the nature of deer impacts. Here, we explore whether forest edges shape the impacts of deer on plant communities within the forest landscape. Specifically, we excluded deer, or, alternatively, allowed deer access, in plots along the edge and within the interior of two northern hardwood forests. Background deer abundance in these forests was approximately 6–12 individuals per km2. After eight years of exclusion, we surveyed plant communities within plots to assess the impacts of deer on plant community composition across the forested landscape. We found that the impacts of deer were robust across habitat context within the forest, with relatively weak impacts on cover and richness of both native and introduced species. Edge habitat, on the other hand, had strong impacts on cover of both native and introduced species, as well as woody and herbaceous species, but the magnitude of these impacts was variable across the two forest sites. This work suggests that deer can have modest impacts when at relatively low densities, and that these effects can be consistent across forest habitat types, while forest fragmentation and subsequent generation of edge habitat can be an important driver of composition in the forest understory.

Effect of Deer and Forest Edge on Understory Plant Communities

Peripheral nerve injuries caused by focal constriction are characterised by local nerve ischaemia, axonal degeneration, demyelination, and neuroinflammation. The aim of this study was to understand temporal changes in the excitability properties of injured motor axons in a mouse model of nerve constriction injury (NCI). The excitability of motor axons following unilateral sciatic NCI was studied in male C57BL/6J mice distal to the site of injury at the acute (6 hours-1 week) and chronic (up to 20 weeks) phases of injury, using threshold tracking. Multiple measures of nerve excitability, including strength-duration properties, threshold electrotonus, current-threshold relationship, and recovery cycle were examined using the automated nerve excitability protocol (TRONDNF). Acutely, injured motor axons developed a pattern of excitability characteristic of ischemic depolarisation. In most cases, the sciatic nerve became transiently inexcitable. When a liminal compound muscle action potential could again be recorded, it had an increase in threshold and latency, compared to both pre-injury baseline and sham-injured groups. These axons showed a greater threshold change in response to hyperpolarising threshold electrotonus and a significant upward shift in the recovery cycle. Mathematical modelling suggested that the changes seen in chronically injured axons involve shortened internodes, reduced myelination, and exposed juxtaparanodal fast K+ conductances. The findings of this study demonstrate long-term changes in motor excitability following NCI (involving alterations in axonal properties and ion channel activity) and are important for understanding the mechanisms of neurapraxic injuries and traumatic mononeuropathies.

David Burke

Papers

Altered peripheral nerve excitability depends on severity of multiple sclerosis.

Increases in soil pH and P availability in a temperate hardwood forest affect mycorrhizal colonization and nutrient content of the herbaceous wildflower Podophyllum peltatum (Mayapple)

Preservation of Ia afferent function in peripheral neuropathies.

Effect of Deer and Forest Edge on Understory Plant Communities

Electrophysiological investigation of motor axonal excitability in a mouse model of nerve constriction injury.