Imaging the neural correlates of tinnitus: a comparison between animal models and human studies

Tinnitus is the perception of a sound, a so-called “phantom sound,” in the absence of a physical sound. The phantom perception persists after transection of the auditory nerve, indicating that the site of tinnitus manifestation is in the central nervous system. Imaging studies in tinnitus sufferers have revealed increased neuronal activity—hyperactivity—in subcortical and cortical auditory centers. These studies have demonstrated that non-auditory brain areas, such as the limbic system, are involved in the neural basis of tinnitus, Finally human imaging studies have led to novel hypotheses for the generation of tinnitus, such as the thalamocortical dysrhythmia hypothesis. Imaging in animal models of tinnitus exhibit similarities to results from human studies and have revealed hyperexcitability of auditory brain centers as a neural correlate of tinnitus. We propose that the comparison between animal model and human studies will aid in the design of appropriate experimental paradigms aimed at elucidating the cellular and circuit mechanisms underlying tinnitus

Cardiac arrest-induced global brain hypoxia-ischemia during development affects spontaneous activity organization in rat sensory and motor thalamocortical circuits during adulthood

Normal maturation of sensory information processing in the cortex requires patterned synaptic activity during developmentally regulated critical periods. During early development, spontaneous synaptic activity establishes required patterns of synaptic input, and during later development it influences patterns of sensory experience-dependent neuronal firing. Thalamocortical neurons occupy a critical position in regulating the flow of patterned sensory information from the periphery to the cortex. Abnormal thalamocortical inputs may permanently affect the organization and function of cortical neuronal circuits, especially if they occur during a critical developmental window. We examined the effect of cardiac arrest (CA)-associated global brain hypoxia-ischemia in developing rats on spontaneous and evoked firing of somatosensory thalamocortical neurons and on large-scale correlations in the motor thalamocortical circuit. The mean spontaneous and sensory-evoked firing rate activity and variability were higher in CA injured rats. Furthermore, spontaneous and sensory-evoked activity and variability were correlated in uninjured rats, but not correlated in neurons from CA rats. Abnormal activity patterns of ventroposterior medial nucleus (VPm) neurons persisted into adulthood. Additionally, we found that neurons in the entopeduncular nucleus (EPN) in the basal ganglia had lower firing rates yet had higher variability and higher levels of burst firing after injury. Correlated levels of power in local field potentials (LFPs) between the EPN and the motor cortex (MCx) were also disrupted by injury. Our findings indicate that hypoxic-ischemic injury during development leads to abnormal spontaneous and sensory stimulus-evoked input patterns from thalamus to cortex. Abnormal thalamic inputs likely permanently and detrimentally affect the organization of cortical circuitry and processing of sensory information. Hypoxic-ischemic injury also leads to abnormal single neuron and population level activity in the basal ganglia that may contribute to motor dysfunction after injury. Combination of deficits in sensory and motor thalamocortical circuit function may negatively impact sensorimotor integration in CA survivors. Modulation of abnormal activity patterns post-injury may represent a novel therapeutic target to improve neurologic function in survivors

A Process of Original Cataloging of Theses and Dissertations

The purpose of this paper is to describe the reasoning, methodology, and impact behind a semi-automated cataloging process for electronic theses and dissertations, including explanations of the importance of retention and addition of cataloger created metadata. The authors explain an automated process that is generated by ProQuest and student entered data, and also the addition of metadata including the subject headings, classification number, etc. The study includes a survey of the public service librarians’ perceived usefulness of the cataloger and ProQuest generated metadata to describe theses and dissertations

Long-term deficits in cortical circuit function after asphyxial cardiac arrest and resuscitation in developing rats

AbstractCardiac arrest is a common cause of global hypoxic-ischemic brain injury. Poor neurologic outcome among cardiac arrest survivors results not only from direct cellular injury but also from subsequent long-term dysfunction of neuronal circuits. Here, we investigated the long-term impact of cardiac arrest during development on the function of cortical layer IV (L4) barrel circuits in the rat primary somatosensory cortex. We used multielectrode single-neuron recordings to examine responses of presumed excitatory L4 barrel neurons to controlled whisker stimuli in adult (8 ± 2-mo-old) rats that had undergone 9 min of asphyxial cardiac arrest and resuscitation during the third postnatal week. Results indicate that responses to deflections of the topographically appropriate principal whisker (PW) are smaller in magnitude in cardiac arrest survivors than in control rats. Responses to adjacent whisker (AW) deflections are similar in magnitude between the two groups. Because of a disproportionate decrease in PW-evoked responses, receptive fields of L4 barrel neurons are less spatially focused in cardiac arrest survivors than in control rats. In addition, spiking activity among L4 barrel neurons is more correlated in cardiac arrest survivors than in controls. Computational modeling demonstrates that experimentally observed disruptions in barrel circuit function after cardiac arrest can emerge from a balanced increase in background excitatory and inhibitory conductances in L4 neurons. Experimental and modeling data together suggest that after a hypoxic-ischemic insult, cortical sensory circuits are less responsive and less spatially tuned. Modulation of these deficits may represent a therapeutic approach to improving neurologic outcome after cardiac arrest.</jats:p

Using Self-Organizing Maps to Recognize Acoustic Units Associated with Information Content in Animal Vocalizations

Kohonen self-organizing neural networks, also called self-organizing maps (SOMs), have been used successfully to recognize human phonemes and in this way to aid in human speech recognition. This paper describes how SOMS also can be used to associate specific information content with animal vocalizations. A SOM was used to identify acoustic units in Gunnison’s prairie dog alarm calls that were vocalized in the presence of three different predator species. Some of these acoustic units and their combinations were found exclusively in the alarm calls associated with a particular predator species and were used to associate predator species information with individual alarm calls. This methodology allowed individual alarm calls to be classified by predator species with an average of 91% accuracy. Furthermore, the topological structure of the SOM used in these experiments provided additional insights about the acoustic units and their combinations that were used to classify the target alarm calls. An important benefit of the methodology developed in this paper is that it could be used to search for groups of sounds associated with information content for any animal whose vocalizations are composed of multiple simultaneous frequency components

Where the Deer and The Antelope Play:Conserving Big Game Migrations As an Endangered Phenomena

In the American West, high-profile big game species including mule deer, antelope, elk, moose, bison and bighorn sheep use large landscapes to migrate between winter and summer habitats to obtain the resources they need to survive. The big game species are a vital part of the West’s ecology, economy, and culture and are valued by local, national, and international stakeholders. Thanks to large parcels of private and public land and a low human population, many parts of the American West still provide some of the best big game habitats in the world. But these vast, intact landscapes are under threat by ongoing habitat loss and disturbances to seasonal and migratory habitats that result in declines in big game population and the disappearance of migrations. Addressing the challenge of conserving big game populations and the endangered phenomena of seasonal migration across large landscapes in the American West will require dynamic, innovative, and flexible legal approaches. Those legal approaches should recognize the biological needs of the species themselves and reflect economic policy analysis of conservation in landscapes with multiple land managers. Considering both integrated biological and economic decision frameworks and incentive-based tools to define and implement legal and policy structures can produce migratory species conservation more efficiently than less integrated approaches. Conservation of big game migrations is now a growing priority and initial conservation efforts are beginning to emerge, including the Department of Interior Secretarial Order 3362 “Improving Habitat Quality in Western Big-Game Winter Range and Migration Corridors” and state policies including the Wyoming Game and Fish Department Ungulate Migration Corridor Strategy. This interdisciplinary paper evaluates those emerging policies and finds that the policies miss opportunities to provide higher levels of conservation of migratory species by failing to address key ecological characteristics of migratory species and to incorporate economically efficient hierarchies of management and policy. We conclude by offering thoughts on how future conservation polices might be designed to incorporate both ecology and economics to better conserve migrations

Cell-specific activity-dependent fractionation of layer 2/3→5B excitatory signaling in mouse auditory cortex

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Neuroscience 35 (2015): 3112-3123, doi:10.1523/JNEUROSCI.0836-14.2015.Auditory cortex (AC) layer 5B (L5B) contains both corticocollicular neurons, a type of pyramidal-tract neuron projecting to the inferior colliculus, and corticocallosal neurons, a type of intratelencephalic neuron projecting to contralateral AC. Although it is known that these neuronal types have distinct roles in auditory processing and different response properties to sound, the synaptic and intrinsic mechanisms shaping their input–output functions remain less understood. Here, we recorded in brain slices of mouse AC from retrogradely labeled corticocollicular and neighboring corticocallosal neurons in L5B. Corticocollicular neurons had, on average, lower input resistance, greater hyperpolarization-activated current (Ih), depolarized resting membrane potential, faster action potentials, initial spike doublets, and less spike-frequency adaptation. In paired recordings between single L2/3 and labeled L5B neurons, the probabilities of connection, amplitude, latency, rise time, and decay time constant of the unitary EPSC were not different for L2/3→corticocollicular and L2/3→corticocallosal connections. However, short trains of unitary EPSCs showed no synaptic depression in L2/3→corticocollicular connections, but substantial depression in L2/3→corticocallosal connections. Synaptic potentials in L2/3→corticocollicular connections decayed faster and showed less temporal summation, consistent with increased Ih in corticocollicular neurons, whereas synaptic potentials in L2/3→corticocallosal connections showed more temporal summation. Extracellular L2/3 stimulation at two different rates resulted in spiking in L5B neurons; for corticocallosal neurons the spike rate was frequency dependent, but for corticocollicular neurons it was not. Together, these findings identify cell-specific intrinsic and synaptic mechanisms that divide intracortical synaptic excitation from L2/3 to L5B into two functionally distinct pathways with different input–output functions.This work was supported by National Institutes of Health grants DC013272 (T.T. and G.M.G.S.), DC007905 (T.T.), NS061963 (G.M.G.S), R03DC012585 (J.W.M.), T32DC011499 (C.T.A.), and F32DC013734 (C.T.A), and by the Albert and Ellen Grass Faculty Award (T.T. and G.M.G.S.) and Charles Evans Foundation Award (T.T. and G.M.G.S.).2015-08-1

Remarkable resilience of forest structure and biodiversity following fire in the peri-urban bushland of Sydney, Australia

In rapidly urbanizing areas, natural vegetation becomes fragmented, making conservation planning challenging, particularly as climate change accelerates fire risk. We studied urban forest fragments in two threatened eucalypt‐dominated (scribbly gum woodland, SGW, and ironbark forest, IF) communities across ~2000 ha near Sydney, Australia, to evaluate effects of fire frequency (0– 4 in last 25 years) and time since fire (0.5 to >25 years) on canopy structure, habitat quality and biodiversity (e.g., species richness). Airborne lidar was used to assess canopy height and density, and ground‐based surveys of 148 (400 m2) plots measured leaf area index (LAI), plant species com‐ position and habitat metrics such as litter cover and hollow‐bearing trees. LAI, canopy density, litter, and microbiotic soil crust increased with time since fire in both communities, while tree and mistletoe cover increased in IF. Unexpectedly, plant species richness increased with fire frequency, owing to increased shrub richness which offset decreased tree richness in both communities. These findings indicate biodiversity and canopy structure are generally resilient to a range of times since fire and fire frequencies across this study area. Nevertheless, reduced arboreal habitat quality and subtle shifts in community composition of resprouters and obligate seeders signal early concern for a scenario of increasing fire frequency under climate change. Ongoing assessment of fire responses is needed to ensure that biodiversity, canopy structure and ecosystem function are maintained in the remaining fragments of urban forests under future climate change which will likely drive hotter and more frequent fires

Saliva microRNA Biomarkers of Cumulative Concussion

Recurrent concussions increase risk for persistent post-concussion symptoms, and may lead to chronic neurocognitive deficits. Little is known about the molecular pathways that contribute to persistent concussion symptoms. We hypothesized that salivary measurement of microribonucleic acids (miRNAs), a class of epitranscriptional molecules implicated in concussion pathophysiology, would provide insights about the molecular cascade resulting from recurrent concussions. This hypothesis was tested in a case-control study involving 13 former professional football athletes with a history of recurrent concussion, and 18 age/sex-matched peers. Molecules of interest were further validated in a cross-sectional study of 310 younger individuals with a history of no concussion (n = 230), a single concussion (n = 56), or recurrent concussions (n = 24). There was no difference in neurocognitive performance between the former professional athletes and their peers, or among younger individuals with varying concussion exposures. However, younger individuals without prior concussion outperformed peers with prior concussion on three balance assessments. Twenty salivary miRNAs differed (adj. p \u3c 0.05) between former professional athletes and their peers. Two of these (miR-28-3p and miR-339-3p) demonstrated relationships (p \u3c 0.05) with the number of prior concussions reported by younger individuals. miR-28-3p and miR-339-5p may play a role in the pathophysiologic mechanism involved in cumulative concussion effects