Neural delays shape selectivity to interaural intensity differences in the lateral superior olive

Neurons in the lateral superior olive (LSO) respond selectively to interaural intensity differences (IIDs), one of the chief cues used to localize sounds in space. LSO cells are innervated in a characteristic pattern: they receive an excitatory input from the ipsilateral ear and an inhibitory input from the contralateral ear. Consistent with this pattern, LSO cells generally are excited by sounds that are more intense at the ipsilateral ear and inhibited by sounds that are more intense at the contralateral ear. Despite their relatively homogeneous pattern of innervation, IID selectivity varies substantially from cell to cell, such that selectivities are distributed over the range of IIDs that would be encountered in nature. For some time, researchers have speculated that the relative timing of the excitatory and inhibitory inputs to an LSO cell might shape IID selectivity. To test this hypothesis, we recorded from 50 LSO cells in the free-tailed bat while presenting stimuli that varied in interaural intensity and in interaural time of arrival. The results suggest that, for more than half of the cells, the latency of inhibition was several hundred microseconds longer than the latency of excitation. Increasing the intensity to the inhibitory ear shortened the latency of inhibition and brought the timing of the inputs from the two ears into register. Thus, a neural delay of the inhibition helped to define the IID selectivity of these cells, accounting for a significant part of the variation in selectivity among LSO cells

Variations in Overhead and Fundraising Efficiency Measures

The desire of individual donors and institutional funders to know how their money is spent, along with the increasing availability of financial information on nonprofit organizations has increased the use and abuse of financial measures of nonprofit efficiency. We focus on two measures: the proportion of budget spent on non-program expenses and the ratio of fundraising expenses to contributions. We hypothesize variations in these measures by organizational size, age, and subsector, and we test these hypothesis with data reported by the organizations to the Internal Revenue Service. We conclude that the ratio measures vary by organizational characteristics, a factor both widely cited by watchdog groups and overlooked by agents that attempt to apply the measures to nonprofit organizations without regard for systematic variation. We also conclude that other basic factors besides size, age, and subsector are important in explaining the relative efficiencies of nonprofit organizations

Understanding Management and General Expenses in Nonprofits

There has been growing coverage by the press and the accounting profession about how nonprofits report their management and general costs. There has also been growing attention by some donors, perhaps made most famously by claims by some donors that nothing should go to administration. While this area of nonprofit management has caught the attention of the public, it has largely escaped the research lens of scholars. This paper is a first step to understanding and explaining what management and general costs look like in the nonprofit sector and whether or not various institutional characteristics such as mission, size, age, sources of revenues, and/or accounting practices can help explain some of the variation in management and general expenses. We find that these institutional characteristics do matter quite a bit in explaining differences in management and general costs in nonprofits

Distinct firing patterns of identified basket and dendrite-targeting interneurons in the prefrontal cortex during hippocampal theta and local spindle oscillations

The medial prefrontal cortex is involved in working memory and executive control. However, the collective spatiotemporal organization of the cellular network has not been possible to explain during different brain states.Weshow that pyramidal cells in the prelimbic cortex fire synchronized to hippocampal theta and local spindle oscillations in anesthetized rats. To identify which types of interneurons contribute to the synchronized activity, we recorded and juxtacellularly labeled parvalbumin- and calbindin-expressing (PV+/CB+) basket cells and CB-expressing, PV-negative (CB+/PV-) dendrite-targeting interneurons during both network oscillations. All CB+/PV- dendrite-targeting cells strongly decreased their firing rate during hippocampal theta oscillations. Most PV+/CB+ basket cells fired at the peak of dorsalCA1theta cycles, similar to prefrontal pyramidal cells.Weshow that pyramidal cells in the ventral hippocampus also fire around the peak of dorsal CA1 theta cycles, in contrast to previously reported dorsal hippocampal pyramidal cells. Therefore, prefrontal neurons might be driven by monosynaptic connections from the ventral hippocampus during theta oscillations. During prefrontal spindle oscillations, the majority of pyramidal cells and PV+/CB+ basket cells fired preferentially at the trough and early ascending phase, but CB+/PV- dendrite-targeting cells fired uniformly at all phases.Weconclude thatPV+/CB+ basket cells contribute to rhythmic responses of prefrontal pyramidal cells in relation to hippocampal and thalamic inputs and CB+/PV-dendrite-targeting cells modulate the excitability of dendrites and spines regardless of these field rhythms. Distinct classes of GABAergic interneuron in the prefrontal cortex contribute differentially to the synchronization of pyramidal cells during network oscillations. Copyright © 2009 Society for Neuroscience

Interneurons in the medial prefrontal cortex

In Aufgaben, die eine Entscheidungsfindung unter Mitwirkung des Arbeitsgedächtnisses erfordern, tritt verstärkt korreliertes Feuerungsverhalten von Neuronen im Hippocampus und im medialen, präfrontalen Kortex (mPFC) auf und Neurone im mPFC feuern zu einer bestimmten Phase von Theta-Oszillationen im Hippocampus. Um zu verstehen welche Rolle Interneurone im mPFC bei diesem Phänomen spielen, wurde das Feuerungsmuster von einzelnen Interneuronen im mPFC aufgezeichnet und deren Soma, Dendriten und Axons mit Neurobiotin angefärbt (durchgeführt von Katja Hartwich). In dieser Diplomarbeit habe ich die molekularen Expressionsmuster und postsynaptischen Zielzellen dieser angefärbten Interneurone untersucht. Der Großteil dieser angefärbten Zellen exprimiert entweder Parvalbumin (PV) oder Calbindin (CB) oder beide dieser Calcium-bindenden Proteine. Zellen, die nur PV exprimieren oder PV und CB co-exprimieren bilden Synapsen an kleinen und apikalen Dendriten, dendritischen Dornen und Zellkörpern von Pyramidenzellen und konnten daher als Korbzellen identifiziert werden. Im Gegensatz dazu bilden CB-exprimierende Zellen Synapsen ausschließlich an kleinen Dendriten und dendritischen Dornen von Pyramidenzellen aus. Außerdem wurde noch ein Zelltyp identifiziert, der ausschließlich Synapsen an initialen Axonhügeln ausbildet und weder PV noch CB exprimiert. Um zukünftig die Charakterisierung von Interneuronklassen durch neue molekulare Marker zu unterstützen, habe ich auch diverse Antikörper getestet, die es erlauben zwischen Zelltypen zu unterscheiden. Als Fazit, in einer Subpopulation von GABAergen Interneuronen im mPFC scheint das molekulare Expressionsmuster mit der Spezifität von postsynaptischen Zielzellen korreliert zu sein: PV-exprimierende aber auch PV und CB co-exprimierende Zellen konnten als Korbzellen und Zellen, die nur CB exprimieren, als Dendriten innervierende Interneurone identifiziert werden.During working memory/decision making tasks correlated firing between the hippocampus and the medial prefrontal cortex (mPFC) of rats is enhanced and neurons in the mPFC are phase-locked to hippocampal theta oscillations. In order to understand the contribution of GABAergic interneurons of the mPFC to temporal network organisation, the firing patterns of single interneurons in the mPFC were recorded in anaesthetized rats and their soma, dendrites and axons specifically labelled with neurobiotin (done by Katja Hartwich). In this diploma thesis, I have investigated the molecular expression profile and postsynaptic targets of the recorded and labelled interneurons. Most of the cells expressed either parvalbumin (PV), or Calbindin (CB) or both calcium-binding proteins. Cells expressing PV only and cells expressing PV and CB target small and apical dendrites, dendritic spines and somata of pyramidal cells, and could therefore be identified as basket cells. In contrast, CB only expressing cells exclusively terminate on small dendrites and spines. Additionally, an axo-axonic cell was identified, which targets exclusively axon initial segments and does not express PV or CB. In order to support future characterization of interneuron classes using novel molecular markers, I have also tested several antibodies against molecules that could further distinguish between cell classes. In conclusion, in a subset of GABAergic interneurons in the mPFC, molecular expression profile and postsynaptic target-specificity seems to be correlated: PV expressing, but also PV/CB co-expressing interneurons could be identified as basket cells and CB only expressing cells as dendrite targeting interneurons

Response Rates for Mail Surveys of Nonprofit Organizations: A Review and Empirical Test

The failure of a substantial portion of mail survey recipients to respond to invitations to participate in research projects raises issues of nonresponse error. Because this error is difficult to quantify, survey researchers seek high rates of return to signal legitimacy and reduce questions regarding nonresponse bias. Research on survey method indicates that the design of the survey research process has a measurable influence on the rate of survey returns. This article focuses on three aspects of research design that are expected to influence mail survey returns in surveys of nonprofit organizations: questionnaire complexity, use of Federal Express versus standard mail, and the use of monetary incentives. Using an experimental design, the research concludes that questionnaire complexity and the use of monetary incentives generate no difference in returns, whereas the use of Federal Express to deliver the survey to nonprofit executives has a measurable positive effect

The Transition State in a Noisy Environment

Transition State Theory overestimates reaction rates in solution because conventional dividing surfaces between reagents and products are crossed many times by the same reactive trajectory. We describe a recipe for constructing a time-dependent dividing surface free of such recrossings in the presence of noise. The no-recrossing limit of Transition State Theory thus becomes generally available for the description of reactions in a fluctuating environment

Inhibiting the inhibition

The precedence effect describes the phenomenon whereby echoes are spatially fused to the location of an initial sound by selectively suppressing the directional information of lagging sounds (echo suppression). Echo suppression is a prerequisite for faithful sound localization in natural environments but can break down depending on the behavioral context. To date, the neural mechanisms that suppress echo directional information without suppressing the perception of echoes themselves are not understood. We performed in vivo recordings in Mongolian gerbils of neurons of the dorsal nucleus of the lateral lemniscus (DNLL), a GABAergic brainstem nucleus that targets the auditory midbrain, and show that these DNLL neurons exhibit inhibition that persists tens of milliseconds beyond the stimulus offset, so-called persistent inhibition (PI). Using in vitro recordings, we demonstrate that PI stems from GABAergic projections from the opposite DNLL. Furthermore, these recordings show that PI is attributable to intrinsic features of this GABAergic innervation. Implementation of these physiological findings into a neuronal model of the auditory brainstem demonstrates that, on a circuit level, PI creates an enhancement of responsiveness to lagging sounds in auditory midbrain cells. Moreover, the model revealed that such response enhancement is a sufficient cue for an ideal observer to identify echoes and to exhibit echo suppression, which agrees closely with the percepts of human subjects

Monte-Carlo Simulations of the Dynamical Behavior of the Coulomb Glass

We study the dynamical behavior of disordered many-particle systems with long-range Coulomb interactions by means of damage-spreading simulations. In this type of Monte-Carlo simulations one investigates the time evolution of the damage, i.e. the difference of the occupation numbers of two systems, subjected to the same thermal noise. We analyze the dependence of the damage on temperature and disorder strength. For zero disorder the spreading transition coincides with the equilibrium phase transition, whereas for finite disorder, we find evidence for a dynamical phase transition well below the transition temperature of the pure system.Comment: 10 pages RevTeX, 8 Postscript figure