Neurosciences Commons^™

Restructuring Of The Axon Initial Segment In Mouse Models Of Neurodevelopmental Disorders, Rachel Ali Rodriguez

UNLV Theses, Dissertations, Professional Papers, and Capstones

Neurodevelopmental disorders (NDDs) affect more than 36% of children in countries with low- and middle- incomes (Boivin, 2015; McCoy, 2016). Interestingly, these heterogeneous disorders share a high incidence of epileptic seizures, suggesting a shared pathology. Seizures result when neuronal firing activity becomes disturbed and neurons fire excessively or in unregulated patterns. A key site in the control of neuronal firing patterns is the axon initial segment (AIS), where the local density of proteins and the morphology of the AIS in part determine the firing of neurons. We hypothesized that a disruption in the morphology and/or composition of the AIS can …

Reattachment Of The Multifidus Tendon In Lumbar Surgery To Decrease Postoperative Back Pain: A Technical Note., Neil Klinger, Emre Yilmaz, Dia R Halalmeh, R Shane Tubbs, Marc D Moisi

Articles, Abstracts, and Reports

The posterior midline approach to the lumbar spine requires significant manipulation of the paraspinal muscles. Muscle detachment and retraction results in iatrogenic damage such as crush injury, devascularization, and denervation, all of which have been associated with postoperative pain. The muscle most directly affected by the posterior approach is the lumbar multifidus (LM), the largest and most medial of the deep lumbar paraspinal muscles. The effects of the posterior approach on the integrity of the LM is concerning, as multiple studies have demonstrated that intraoperative injuries sustained by the LM lead to postoperative muscle atrophy and potentially worsening low back …

Ultrafast Two-Photon Imaging Of A High-Gain Voltage Indicator In Awake Behaving Mice, Vincent Villette, Mariya Chavarha, Ivan K Dimov, Jonathan Bradley, Lagnajeet Pradhan, Benjamin Mathieu, Stephen W Evans, Simon Chamberland, Dongqing Shi, Renzhi Yang, Benjamin B Kim, Annick Ayon, Abdelali Jalil, François St-Pierre, Mark J Schnitzer, Guoqiang Bi, Katalin Toth, Jun Ding, Stéphane Dieudonné, Michael Z Lin

Faculty, Staff and Students Publications

Optical interrogation of voltage in deep brain locations with cellular resolution would be immensely useful for understanding how neuronal circuits process information. Here, we report ASAP3, a genetically encoded voltage indicator with 51% fluorescence modulation by physiological voltages, submillisecond activation kinetics, and full responsivity under two-photon excitation. We also introduce an ultrafast local volume excitation (ULoVE) method for kilohertz-rate two-photon sampling in vivo with increased stability and sensitivity. Combining a soma-targeted ASAP3 variant and ULoVE, we show single-trial tracking of spikes and subthreshold events for minutes in deep locations, with subcellular resolution and with repeated sampling over days. In the …

Memantine: Can It Be Used To Treat Children With Autism Spectrum Disorder?, Austin Brown, Katherine Liu, Pul Lee, Rachel Muhlenkamp, Manoranjan D'Souza

Pharmacy and Wellness Review

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairment in social, behavior and communicative skills. The current therapy for ASD only targets the associated symptoms such as aggression, self-harming acts or temper tantrums but not the core symptoms of social dysfunction. The pathology of ASD is not fully understood. Interestingly, imaging studies in ASD patients have reported abnormal high levels of glutamate in certain brain regions that play an important role in social interaction and communication. Thus, it has been hypothesized that medications attenuating glutamate transmission may be used as treatment for some of the core symptoms of …

Cannabinoids For The Treatment Of Chronic Headaches, Kevin Krivanek, Lucy K. Wagala, Brian Heilbronner, Kimberly Loughlin, David Kinder

Pharmacy and Wellness Review

Species of the Cannabis plant genus were among the earliest medicinal plants cultivated by man, with historical accounts of their medicinal uses dating back before the Common Era. Despite its current legal status, Cannabis has garnered nationwide attention as a therapeutic agent for various disease states, including chronic headaches, due to its medical indications as an antispastic, analgesic, antiemetic, neuroprotective and anti-inflammatory agent. Since headaches have a high prevalence in the American population and greatly impair simple daily aspects of living, chronic headaches have become a particular point of interest in regard to the therapeutic potential of Cannabis. Clinical trials …

Alzheimer's And Amyloid Beta: Amyloidogenicity And Tauopathy Via Dyshomeostatic Interactions Of Amyloid Beta, Jordan Tillinghast

Senior Honors Theses

This paper reviews functions of Amyloid-β (Aβ) in healthy individuals compared to the consequences of aberrant Aβ in Alzheimer’s disease (AD). As extraneuronal Aβ accumulation and plaque formation are characteristics of AD, it is reasonable to infer a pivotal role for Aβ in AD pathogenesis. Establishing progress of the disease as well as the mechanism of neurodegeneration from AD have proven difficult (Selkoe, 1994). This thesis provides evidence suggesting the pathogenesis of AD is due to dysfunctional neuronal processes involving Aβ’s synaptic malfunction, abnormal interaction with tau, and disruption of neuronal homeostasis. Significant evidence demonstrates that AD symptoms are partially …

Are Specific Learning Disorders Truly Specific, And Are They Disorders?, Lien Peters, Daniel Ansari

Brain and Mind Institute Researchers' Publications

© 2019 The Authors Specific learning disorders, such as dyslexia and dyscalculia, are frequently studied to inform our understanding of cognitive development, genetic mechanisms and brain function. In this Opinion Paper, we discuss limitations of this research approach, including the use of arbitrary criteria to select groups of children, heterogeneity within groups and overlap between domains of learning. By drawing on evidence from cognitive science, neuroscience and genetics, we propose an alternative, dimensional framework. We argue that we need to overcome the problems associated with a categorical approach by taking into account interacting factors at multiple levels of analysis that …

Altered Motor, Anxiety-Related And Attentional Task Performance At Baseline Associate With Multiple Gene Copies Of The Vesicular Acetylcholine Transporter And Related Protein Overexpression In Chat::Cre+ Rats, Craig P. Mantanona, Johan Alsiö, Joanna L. Elson, Beth M. Fisher, Jeffrey W. Dalley, Timothy Bussey, Ilse S. Pienaar

Brain and Mind Institute Researchers' Publications

© 2019, The Author(s). Transgenic rodents expressing Cre recombinase cell specifically are used for exploring mechanisms regulating behavior, including those mediated by cholinergic signaling. However, it was recently reported that transgenic mice overexpressing a bacterial artificial chromosome containing choline acetyltransferase (ChAT) gene, for synthesizing the neurotransmitter acetylcholine, present with multiple vesicular acetylcholine transporter (VAChT) gene copies, resulting in altered cholinergic tone and accompanying behavioral abnormalities. Since ChAT::Cre+ rats, used increasingly for understanding the biological basis of CNS disorders, utilize the mouse ChAT promotor to control Cre recombinase expression, we assessed for similar genotypical and phenotypical differences in such rats compared …

A Macaque Connectome For Large-Scale Network Simulations In Thevirtualbrain, Kelly Shen, Gleb Bezgin, Michael Schirner, Petra Ritter, Stefan Everling, Anthony R. Mcintosh

Brain and Mind Institute Researchers' Publications

© 2019, The Author(s). Models of large-scale brain networks that are informed by the underlying anatomical connectivity contribute to our understanding of the mapping between the structure of the brain and its dynamical function. Connectome-based modelling is a promising approach to a more comprehensive understanding of brain function across spatial and temporal scales, but it must be constrained by multi-scale empirical data from animal models. Here we describe the construction of a macaque (Macaca mulatta and Macaca fascicularis) connectome for whole-cortex simulations in TheVirtualBrain, an open-source simulation platform. We take advantage of available axonal tract-tracing datasets and enhance the existing …

Predator-Induced Fear Causes Ptsd-Like Changes In The Brains And Behaviour Of Wild Animals, Liana Y. Zanette, Emma C. Hobbs, Lauren E. Witterick, Scott A. Macdougall-Shackleton, Michael Clinchy

Brain and Mind Institute Researchers' Publications

© 2019, The Author(s). Predator-induced fear is both, one of the most common stressors employed in animal model studies of post-traumatic stress disorder (PTSD), and a major focus of research in ecology. There has been a growing discourse between these disciplines but no direct empirical linkage. We endeavoured to provide this empirical linkage by conducting experiments drawing upon the strengths of both disciplines. Exposure to a natural cue of predator danger (predator vocalizations), had enduring effects of at least 7 days duration involving both, a heightened sensitivity to predator danger (indicative of an enduring memory of fear), and elevated neuronal …

Consciousness-Specific Dynamic Interactions Of Brain Integration And Functional Diversity, Andrea I. Luppi, Michael M. Craig, Ioannis Pappas, Paola Finoia, Guy B. Williams, Judith Allanson, John D. Pickard, Adrian M. Owen, Lorina Naci, David K. Menon, Emmanuel A. Stamatakis

Brain and Mind Institute Researchers' Publications

Prominent theories of consciousness emphasise different aspects of neurobiology, such as the integration and diversity of information processing within the brain. Here, we combine graph theory and dynamic functional connectivity to compare resting-state functional MRI data from awake volunteers, propofol-anaesthetised volunteers, and patients with disorders of consciousness, in order to identify consciousness-specific patterns of brain function. We demonstrate that cortical networks are especially affected by loss of consciousness during temporal states of high integration, exhibiting reduced functional diversity and compromised informational capacity, whereas thalamo-cortical functional disconnections emerge during states of higher segregation. Spatially, posterior regions of the brain’s default mode …

Influence Of Metabolic Capacity On The Consequences Of Spreading Depolarization, Katelyn M. Reinhart

Biomedical Sciences ETDs

In the United States, stroke is the fifth leading cause of death and stroke survivors often face long-term disability. After ischemic stroke, the ischemic territory can expand and recruit previously viable tissues into the lesioned area. During this critical period, there is an unsettling lack of interventions that prevent or treat secondary neuronal loss and cognitive decline. Clinical subdural recordings have revealed a close link between infarct progression and waves of spreading depolarizations (SD) in the acutely injured brain. SD is a slowly progressing wave of near-complete neuroglia depolarization that is extremely energetically demanding and this additional metabolic ‘hit’ …

Gna11 Brain Somatic Pathogenic Variant In An Individual With Phacomatosis Pigmentovascularis, Joseph M Sliepka, Sarah C Mcgriff, Linda Z Rossetti, Peyman Bizargity, Haley Streff, Yi-Shan Lee, Hongzheng Dai, Satyamaanasa Polubothu, Grace Lee, Vicky Ren, Jill V Hunter, Daniel J Curry, Fernando Scaglia, Adekunle M Adesina, Irfan Ali, Veronica Kinsler, Lindsay C Burrage, Dana Marafi

Faculty, Staff and Students Publications

OBJECTIVE: To describe the findings of histopathology and genotyping studies in affected brain tissue from an individual with phacomatosis pigmentovascularis (PPV).

METHODS: A retrospective chart review of a 2-year 10-month-old male with a clinical diagnosis of PPV cesiomarmorata (or type V) was performed. Clinical features, brain imaging and histopathology findings, and genotyping studies in his affected brain tissue are summarized.

RESULTS: The proband had a clinically severe neurologic phenotype characterized by global developmental delay, generalized hypotonia, and recurrent episodes of cardiac asystole in the setting of status epilepticus. A somatic pathogenic variant in

CONCLUSIONS: The finding of this variant in …

Seasonal Plasticity In GabaA Signaling Is Necessary For Restoring Phase Synchrony In The Master Circadian Clock Network, Kayla Rohr, Harshida Pancholi, Shabi Haider, Christopher Karow, David Modert, Nicholas J. Raddatz, Jennifer A. Evans

Biomedical Sciences Faculty Research and Publications

Annual changes in the environment threaten survival, and numerous biological processes in mammals adjust to this challenge via seasonal encoding by the suprachiasmatic nucleus (SCN). To tune behavior according to day length, SCN neurons display unified rhythms with synchronous phasing when days are short, but will divide into two sub-clusters when days are long. The transition between SCN states is critical for maintaining behavioral responses to seasonal change, but the mechanisms regulating this form of neuroplasticity remain unclear. Here we identify that a switch in chloride transport and GABA_A signaling is critical for maintaining state plasticity in the SCN …

Interleukin 1 Alpha Administration Is Neuroprotective And Neuro-Restorative Following Experimental Ischemic Stroke, Kathleen E. Salmeron, Michael E. Maniskas, Danielle N. Edwards, Raymond Wong, Ivana Rajkovic, Amanda L. Trout, Abir A. Rahman, Samantha Hamilton, Justin F. Fraser, Emmanuel Pinteaux, Gregory J. Bix

Sanders-Brown Center on Aging Faculty Publications

BACKGROUND: Stroke remains a leading cause of death and disability worldwide despite recent treatment breakthroughs. A primary event in stroke pathogenesis is the development of a potent and deleterious local and peripheral inflammatory response regulated by the pro-inflammatory cytokine interleukin-1 (IL-1). While the role of IL-1β (main released isoform) has been well studied in stroke, the role of the IL-1α isoform remains largely unknown. With increasing utilization of intravenous tissue plasminogen activator (t-PA) or thrombectomy to pharmacologically or mechanically remove ischemic stroke causing blood clots, respectively, there is interest in pairing successful cerebrovascular recanalization with neurotherapeutic pharmacological interventions (Fraser et …

Functional Localization Of The Frontal Eye Fields In The Common Marmoset Using Microstimulation, Janahan Selvanayagam, Kevin D. Johnston, David J. Schaeffer, Lauren K. Hayrynen, Stefan Everling

Brain and Mind Institute Researchers' Publications

Copyright © 2019 the authors. The frontal eye field (FEF) is a critical region for the deployment of overt and covert spatial attention. Although investigations in the macaque continue to provide insight into the neural underpinnings of the FEF, due to its location within a sulcus, the macaque FEF is virtually inaccessible to electrophysiological techniques such as high-density and laminar recordings. With a largely lissencephalic cortex, the common marmoset (Callithrix jacchus) is a promising alternative primate model for studying FEF microcircuitry. Putative homologies have been established with the macaque FEF on the basis of cytoarchitecture and connectivity; however, physiological investigation …

Method Of Predicting Obesity Comprising Measuring Neurotensin, B. Mark Evers, Jing Li, Paul Dobner, Olle Melander

Surgery Faculty Patents

The presently disclosed subject matter relates to a method for predicting increased risk of obesity on a non-obese subject. More particularly, the presently disclosed subject matter relates to a method of predicting increased risk of obesity in a non-obese subject by determining a level of neurotensin expression in a biological sample from the subject and comparing the level of neurotensin expression in the sample with a control level. The presently disclosed subject matter further relates to a method of preventing and/or treating obesity in a subject in need thereof by administering to the subject an effective amount of an agent …

Sign And Speech Share Partially Overlapping Conceptual Representations, Samuel Evans, Cathy J. Price, Jörn Diedrichsen, Eva Gutierrez-Sigut, Mairéad Macsweeney

Brain and Mind Institute Researchers' Publications

© 2019 The Author(s) Conceptual knowledge is fundamental to human cognition. Yet, the extent to which it is influenced by language is unclear. Studies of semantic processing show that similar neural patterns are evoked by the same concepts presented in different modalities (e.g., spoken words and pictures or text) [1–3]. This suggests that conceptual representations are “modality independent.” However, an alternative possibility is that the similarity reflects retrieval of common spoken language representations. Indeed, in hearing spoken language users, text and spoken language are co-dependent [4, 5], and pictures are encoded via visual and verbal routes [6]. A parallel approach …

Variational Representational Similarity Analysis, Karl J. Friston, Jörn Diedrichsen, Emma Holmes, Peter Zeidman

Brain and Mind Institute Researchers' Publications

© 2019 The Authors This technical note describes a variational or Bayesian implementation of representational similarity analysis (RSA) and pattern component modelling (PCM). It considers RSA and PCM as Bayesian model comparison procedures that assess the evidence for stimulus or condition-specific patterns of responses distributed over voxels or channels. On this view, one can use standard variational inference procedures to quantify the contributions of particular patterns to the data, by evaluating second-order parameters or hyperparameters. Crucially, this allows one to use parametric empirical Bayes (PEB) to infer which patterns are consistent among subjects. At the between-subject level, one can then …

Using Spatial Release From Masking To Estimate The Magnitude Of The Familiar-Voice Intelligibility Benefit, Ysabel Domingo, Emma Holmes, Ewan Macpherson, Ingrid S. Johnsrude

Brain and Mind Institute Researchers' Publications

© 2019 Acoustical Society of America. The ability to segregate simultaneous speech streams is crucial for successful communication. Recent studies have demonstrated that participants can report 10%-20% more words spoken by naturally familiar (e.g., friends or spouses) than unfamiliar talkers in two-voice mixtures. This benefit is commensurate with one of the largest benefits to speech intelligibility currently known - that which is gained by spatially separating two talkers. However, because of differences in the methods of these previous studies, the relative benefits of spatial separation and voice familiarity are unclear. Here, the familiar-voice benefit and spatial release from masking are …

Estimating Cognitive Workload In An Interactive Virtual Reality Environment Using Eeg, Christoph Tremmel, Christain Herff, Tetsuya Sato, Krzysztof Rechowicz, Yusuke Yamani, Dean J. Krusienski

Electrical & Computer Engineering Faculty Publications

With the recent surge of affordable, high-performance virtual reality (VR) headsets, there is unlimited potential for applications ranging from education, to training, to entertainment, to fitness and beyond. As these interfaces continue to evolve, passive user-state monitoring can play a key role in expanding the immersive VR experience, and tracking activity for user well-being. By recording physiological signals such as the electroencephalogram (EEG) during use of a VR device, the user's interactions in the virtual environment could be adapted in real-time based on the user's cognitive state. Current VR headsets provide a logical, convenient, and unobtrusive framework for mounting EEG …

A Sound-Sensitive Source Of Alpha Oscillations In Human Non-Primary Auditory Cortex, Alexander J. Billig, Björn Herrmann, Ariane E. Rhone, Phillip E. Gander, Kirill V. Nourski, Beau F. Snoad, Christopher K. Kovach, Hiroto Kawasaki, Matthew A. Howard, Ingrid S. Johnsrude

Brain and Mind Institute Researchers' Publications

Copyright © 2019 Billig, Herrmann et al. The functional organization of human auditory cortex can be probed by characterizing responses to various classes of sound at different anatomical locations. Along with histological studies this approach has revealed a primary field in posteromedial Heschl's gyrus (HG) with pronounced induced high-frequency (70-150 Hz) activity and short-latency responses that phase-lock to rapid transient sounds. Low-frequency neural oscillations are also relevant to stimulus processing and information flow, however, their distribution within auditory cortex has not been established. Alpha activity (7-14 Hz) in particular has been associated with processes that may differentially engage earlier versus …

Burden Of Relapsing-Remitting Multiple Sclerosis On Workers In The Us: A Cross-Sectional Analysis Of Survey Data., Jacqueline A Nicholas, Batul Electricwala, Lulu K Lee, Kristen M Johnson

Neuroscience Articles

BACKGROUND: Multiple sclerosis (MS) is prevalent among working age individuals (20-60 years), leading to high burden on work productivity. Few data are available about the absenteeism and presenteeism in employed individuals with MS in comparison to non-MS personnel. This study aimed to quantify the burden of illness of employed US adults with relapsing-remitting multiple sclerosis (RRMS) and examine burden by levels of work impairment.

METHODS: A retrospective cross-sectional analysis was conducted using patient-reported responses from the US National Health and Wellness Survey (NHWS). Data from NHWS 2015-2016 were analyzed from 196 employed RRMS respondents who were matched 1:4 to employed …

Alpha Synuclein In Hematopoiesis And Immunity, Robert W. Maitta

Faculty Scholarship

Parkinson's disease (PD) is the second most common neurodegenerative condition and intracellular deposition of Lewy bodies in the substantia nigra (SN), which can cause dopaminergic neuronal death, is the hallmark of this syndrome. α-synuclein (syn) is a small protein expressed mainly in neurons but can also be found in a number of tissues. It can be present as a soluble monomer under normal physiological conditions, but can be toxic in its oligomeric or fibrillary forms. Most of the available literature has focused on the effects of α-syn pathology in the mechanisms leading to PD. However, the normal functions of α-syn …

An Accurate Registration Of The Bigbrain Dataset With The Mni Pd25 And Icbm152 Atlases., Yiming Xiao, Jonathan C Lau, Taylor Anderson, Jordan Dekraker, D Louis Collins, Terry Peters, Ali R Khan

Brain and Mind Institute Researchers' Publications

Brain atlases that encompass detailed anatomical or physiological features are instrumental in the research and surgical planning of various neurological conditions. Magnetic resonance imaging (MRI) has played important roles in neuro-image analysis while histological data remain crucial as a gold standard to guide and validate such analyses. With cellular-scale resolution, the BigBrain atlas offers 3D histology of a complete human brain, and is highly valuable to the research and clinical community. To bridge the insights at macro- and micro-levels, accurate mapping of BigBrain and established MRI brain atlases is necessary, but the existing registration is unsatisfactory. The described dataset includes …

Sex, Drugs, And Seizures: Subarachnoid Hemorrhage In A Young Patient., Alex Davis, Eric Cortez, Andrew Kalnow

Neuroscience Articles

A 17-year-old male patient presented to the emergency department (ED) with seizures after sexual intercourse. The patient was found to have an intracerebral hemorrhage (ICH) likely secondary to sexual intercourse and concomitant amphetamine use, an extremely rare finding in this patient population. In this case review, we will discuss the presentation, management, and disposition of subarachnoid hemorrhage (SAH), a well-known emergency diagnosis within the ED, while highlighting a case that is clearly uncommon. In addition, we discuss the etiology of ICH in the setting of intercourse and amphetamine use with the ultimate goal of understanding the interdisciplinary care of a …

Visualization And Quantification Of Post-Stroke Neural Connectivity And Neuroinflammation Using Serial Two-Photon Tomography In The Whole Mouse Brain, Katherine Poinsatte, Dene Betz, Vanessa O. Torres, Apoorva D. Ajay, Shazia Mirza, Uma M. Selvaraj, Erik J. Plautz, Xiangmei Kong, Sankalp Gokhale, Julian P. Meeks, Denise M. O. Ramirez, Mark P. Goldberg, Ann M. Stowe

Neurology Faculty Publications

Whole-brain volumetric microscopy techniques such as serial two-photon tomography (STPT) can provide detailed information on the roles of neuroinflammation and neuroplasticity throughout the whole brain post-stroke. STPT automatically generates high-resolution images of coronal sections of the entire mouse brain that can be readily visualized in three dimensions. We developed a pipeline for whole brain image analysis that includes supervised machine learning (pixel-wise random forest models via the “ilastik” software package) followed by registration to a standardized 3-D atlas of the adult mouse brain (Common Coordinate Framework v3.0; Allen Institute for Brain Science). These procedures allow the detection of cellular fluorescent …

A Framework For Evaluating Correspondence Between Brain Images Using Anatomical Fiducials., Jonathan C Lau, Andrew G Parrent, John Demarco, Geetika Gupta, Jason Kai, Olivia W Stanley, Tristan Kuehn, Patrick J Park, Kayla Ferko, Ali R Khan, Terry M Peters

Brain and Mind Institute Researchers' Publications

Accurate spatial correspondence between template and subject images is a crucial step in neuroimaging studies and clinical applications like stereotactic neurosurgery. In the absence of a robust quantitative approach, we sought to propose and validate a set of point landmarks, anatomical fiducials (AFIDs), that could be quickly, accurately, and reliably placed on magnetic resonance images of the human brain. Using several publicly available brain templates and individual participant datasets, novice users could be trained to place a set of 32 AFIDs with millimetric accuracy. Furthermore, the utility of the AFIDs protocol is demonstrated for evaluating subject-to-template and template-to-template registration. Specifically, …

Big Spine Data Put To Good Use: The Nhs Sets An Example., Jens R Chapman, Jeffrey C Wang, Karsten Wiechert

Articles, Abstracts, and Reports

No abstract provided.

Voltage-Gated Potassium Channels Are Critical For Infrared Inhibition Of Action Potentials: An Experimental Study, Junqi Zhuo, Matthew T. Mcpheeters, Michael W. Jenkins, Hillel J. Chiel

Faculty Scholarship

Thermal block of unmyelinated axons may serve as a modality for control, suggesting a means for providing therapies for pain. Computational modeling predicted that potassium channels are necessary for mediating thermal block of propagating compound action potentials (CAPs) with infrared (IR) light. Our study tests that hypothesis. Results suggest that potassium channel blockers disrupt the ability of IR to block propagating CAPs in Aplysia californica nerves, whereas sodium channel blockers appear to have no significant effect. These observations validate the modeling results and suggest potential applications of thermal block to many other unmyelinated axons.