E. Covey - Academia.edu (original) (raw)

Papers by E. Covey

European Journal of Neuroscience, 1991

This study investigates the role of the pontine grey as a link between the auditory system and th... more This study investigates the role of the pontine grey as a link between the auditory system and the cerebellum in the bat, Rhinolophus rouxi. We recorded response properties of single neurons in the pontine grey and, in the same preparation, injected wheat germ agglutinin ‐ horseradish peroxidase (WGA‐HRP) in areas responsive to sound. Thus the functional evidence was correlated with retrograde and anterograde transport. The main results are: (i) all auditory neurons in the pontine grey are tuned within one of two harmonically related frequency ranges of the echolocation call. The upper range corresponds to the constant frequency and frequency modulated components of the second harmonic, but the lower range corresponds only to the frequency modulated component of the first harmonic. There is no systematic tonotopic organization; (ii) discharge patterns are extremely variable, latencies cover a wide range, and about half of the neurons are binaurally responsive with excitation from bo...

The Mammalian Cochlear Nuclei, 1993

The mammalian cochlear nucleus is made up of several different divisions, each of which receives ... more The mammalian cochlear nucleus is made up of several different divisions, each of which receives input from the fibers of the auditory nerve, and each of which performs some different transformation of this input. These different divisions of the cochlear nucleus in turn give rise to different parallel pathways. Some of these pathways ascend directly to the midbrain, some provide interconnections among the divisions of the cochlear nucleus, and others innervate cell groups in the brainstem where the signals originating in the cochlear nucleus undergo further transformation. These transformations may be accomplished through various mechanisms, for example, different patterns of axonal termination on cell bodies or dendrites, different biophysical properties of the target cells, or convergence of inputs from more than one pathway. The present review focuses on the transformations that occur in one system of brainstem auditory nuclei, the intermediate (INLL) and ventral (VNLL) nuclei of the lateral lemniscus.

The Senses: A Comprehensive Reference, 2008

The inferior colliculus (IC) receives multiple inputs from a variety of sources. These include th... more The inferior colliculus (IC) receives multiple inputs from a variety of sources. These include the ascending pathways from the lower brainstem as well as intrinsic, descending, motor-related, polysensory, and modulatory inputs. There is evidence that subsets of inputs form density gradients across one or more dimensions of the IC, but that the graded projections overlap throughout much of the IC. The two main gradient-based systems are: (1) the ventral cochlear nucleus (VCN) system which comprises pathways that are most dense ventrolaterally, decreasing ventromedially; (2) the dorsal cochlear nucleus (DCN) system, comprising pathways that are most dense dorsomedially, decreasing ventrolaterally. There is some evidence that projections from different sources may terminate in different, or partially overlapping, regions within a fibrodendritic lamina, forming functional domains. There is also some evidence that functional properties of neurons, such as latency or best modulation rate, may be distributed in gradients that are related to the anatomical gradient systems.

Journal of neurophysiology, Jan 15, 2014

Neurons with responses selective for the duration of an auditory stimulus are called duration-tun... more Neurons with responses selective for the duration of an auditory stimulus are called duration-tuned neurons (DTNs). Temporal specificity in their spiking suggests that one function of DTNs is to encode stimulus duration; however, the efficacy of duration encoding by DTNs has yet to be investigated. Herein, we characterize the information content of individual cells and a population of DTNs from the mammalian inferior colliculus (IC) by measuring the stimulus-specific information (SSI) and estimated Fisher information (FI) of spike count responses. We found that SSI was typically greatest for those stimulus durations that evoked maximum spike counts, defined as best duration (BD) stimuli, and that FI was maximal for stimulus durations off BD where sensitivity to a change in duration was greatest. Using population data, we demonstrate that a maximum likelihood estimator (MLE) can accurately decode stimulus duration from evoked spike counts. We also simulated a two-alternative forced c...

Journal of Neurophysiology, 2000

In the inferior colliculus (IC) of the big brown bat, a subpopulation of cells (∼35%) are tuned t... more In the inferior colliculus (IC) of the big brown bat, a subpopulation of cells (∼35%) are tuned to a narrow range of sound durations. Band-pass tuning for sound duration has not been seen at lower levels of the auditory pathway. Previous work suggests that it arises at the IC through the interaction of sound-evoked, temporally offset, excitatory and inhibitory inputs. To test this hypothesis, we recorded from duration-tuned neurons in the IC and examined duration tuning before and after iontophoretic infusion of antagonists to γ-aminobutyric acid-A (GABAA) (bicuculline) or glycine (strychnine). The criterion for duration tuning was that the neuron's spike count as a function of duration had a peak value at one duration or a range of durations that was ≥2 times the lowest nonzero value at longer durations. Out of 21 units tested with bicuculline, duration tuning was eliminated in 15, broadened in two, and unaltered in four. Out of 10 units tested with strychnine, duration tuning ...

Animal Sonar, 1988

In all species of mammals a number of parallel auditory pathways ascend to the inferior colliculu... more In all species of mammals a number of parallel auditory pathways ascend to the inferior colliculus, but the relationships among these pathways at their targets are poorly understood. The pathways which project via the medial and lateral nuclei of the superior olivary complex (MSO and LSO) receive extensive bilateral input from the cochlear nuclei. For this reason they are probably the first stage in processing binaural cues for localizing sound in space. The projection area of MSO and LSO in the inferior colliculus can therefore be considered to be a structural definition of the binaural region of the inferior colliculus. In this study we sought to define the binaural region in the inferior colliculus of Rhinolophus rouxii by the method of anterograde axonal transport from physiologically defined areas within the superior olivary complex.

Hearing by Bats, 1995

In the auditory system, more than any other sensory modality, extensive processing of incoming si... more In the auditory system, more than any other sensory modality, extensive processing of incoming signals occurs in the brainstem. In all vertebrates, the auditory pathways below the inferior colliculus consist of a complex system of parallel pathways, each with its own centers for signal processing. The auditory structures of the lower brainstem act as filters to selectively enhance specific stimulus features and as computational centers to add, subtract, or compare signals in different channels. Some brainstem structures, such as the superior olive, have been studied extensively, and their function is at least partially understood. Others, such as the nuclei of the lateral lemniscus, have been largely ignored, and their functional roles are just beginning to be discovered.

Journal of Neurophysiology, 1997

Ehrlich, Daphna, John H. Casseday, and Ellen Covey. Neural tuning to sound duration in the inferi... more Ehrlich, Daphna, John H. Casseday, and Ellen Covey. Neural tuning to sound duration in the inferior colliculus of the big brown bat, Eptesicus fuscus. J. Neurophysiol. 77: 2360–2372, 1997. Neural tuning to different sound durations may be a useful filter for identification of certain sounds, especially those that are biologically important. The auditory midbrains of mammals and amphibians contain neurons that appear to be tuned to sound duration. In amphibians, neurons are tuned to durations of sound that are biologically important. The purpose of this study was to characterize responses of neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, to sounds of different durations. Our aims were to determine what percent of neurons are duration tuned and how best durations are correlated to durations of echolocation calls, and to examine response properties that may be relevant to the mechanism for duration tuning, such as latency and temporal firing pattern; we...

The Journal of Comparative Neurology, 1989

T o determine the sources and targets of auditory pathways that bypass the inferior colliculus in... more T o determine the sources and targets of auditory pathways that bypass the inferior colliculus in the mustache bat, we injected WGA-HRP in the medial geniculate body and related auditory nuclei of the thalamus as well as in the lower brainstem. We used electrophysiological methods to verify that the injection electrode was in an area responsive to sound. The only thalamic injections that produced retrograde transport to cells in auditory nuclei caudal to the inferior colliculus were those that included the suprageniculate nucleus. These injections labeled a group of large multipolar cells lying between the ventral nucleus of the lateral lemniscus and the superior olivary complex. Neurons in this cell group have also been shown to project to the deep layers of the superior colliculus in the mustache bat. The pathway revealed by these studies is almost identical to the "central acoustic tract" in which fibers course medial to the lateral lemniscus and bypass the inferior colliculus to reach the deep superior colliculus and the suprageniculate nucleus.

The Journal of …, 2009

To identify sounds as novel, there must be some neural representation of commonly occurring sound... more To identify sounds as novel, there must be some neural representation of commonly occurring sounds. Stimulus-specific adaptation (SSA) is a reduction in neural response to a repeated sound. Previous studies using an oddball stimulus paradigm have shown that SSA occurs ...

Frontiers in Human Neuroscience, 2009

Acoustical Signal Processing in the Central Auditory System, 1997

Serotonin (5-hydroxytryptamine. 5-HTl is a neuroactive substance that is widely distributed in bo... more Serotonin (5-hydroxytryptamine. 5-HTl is a neuroactive substance that is widely distributed in both invertebrates and vertebrates. In vertebrates. 5-HT neurons are located mainly in the raphe nuclei along the midline of the brainstem. Neurons of the raphe nuclei project ...

The Journal of neuroscience : the official journal of the Society for Neuroscience, 1986

To study the role of the lateral lemniscus as a link in the ascending auditory pathway, injection... more To study the role of the lateral lemniscus as a link in the ascending auditory pathway, injections of neuronal tracers were placed in the anteroventral cochlear nucleus (AVCN) and in the inferior colliculus of the bat Eptesicus fuscus. To correlate the anatomical results with tonotopic organization, the characteristic frequency of cells at each injection site was determined electrophysiologically. Pathways from AVCN diverge to 3 major targets in the lateral lemniscus, the intermediate nucleus and 2 divisions of the ventral nucleus (VNLL). Projections from these 3 nuclei then converge at the inferior colliculus. One cell group is particularly notable for its cytoarchitectural appearance. It is referred to here as the columnar area of VNLL because its cells are organized as a tightly packed matrix of columns and rows. The connections of the columnar area are organized in sheets that are precisely related to the tonotopic organization of both AVCN and the inferior colliculus. Sheets of...

Journal of neurophysiology, 1991

1. Previous studies of the superior olive of echolocating bats suggest that the lateral superior ... more 1. Previous studies of the superior olive of echolocating bats suggest that the lateral superior olive (LSO) retains the same structure and function as in other mammals but that the medial superior olive (MSO) is different in structure and possibly also in function. The present study is an examination of this idea in Pteronotus parnellii, a bat that has a large and well-defined MSO. 2. Using pure tones presented via earphones, we obtained data on frequency tuning for 60 single units and 96 multiunits in LSO and 94 single units and 154 multiunits in MSO. Of these we also obtained binaural response characteristics from 55 single units in LSO and 72 single units in MSO. 3. LSO and MSO each have a complete tonotopic representation, arranged in a sequence similar to that of other mammals studied. However, in both LSO and MSO there is an expanded representation of the frequencies around 60 kHz, the main frequency component of the bat's echolocation call; there is another expanded repr...

Speech Communication, 2003

Because of their stereotyped audio-vocal behavior and highly accessible brainstem circuitry, echo... more Because of their stereotyped audio-vocal behavior and highly accessible brainstem circuitry, echolocating bats provide a good model system in which to study the neural mechanisms that underlie the analysis of temporal features of sound. This paper reviews the lower brainstem auditory circuitry and describes selected forms of information processing that are performed in the pathways of the lower brainstem and auditory midbrain (inferior colliculus (IC)). Several examples of neural circuits in echolocating bats point out the ways in which inputs with different properties converge on IC neurons to create selectivity for specific temporal features of sound that are common to speech and echolocation. The initial transformations of auditory nerve input that occur in the lower brainstem pathways include a change in sign from excitatory input to inhibitory output, changes in discharge pattern, and the creation of delay lines. Convergence of multiple inputs on neurons in the IC produces tuning for temporal features of sound including duration, the direction of frequency sweeps, modulation rate, and interstimulus interval. The auditory cortex exerts control over some of this processing by sharpening or shifting neuronal filter properties. The computational processes that occur in the IC result in integration across a time scale that is consistent with the rate at which biological sounds are produced, whether they be echolocation signals or human speech components.

The Journal of Comparative Neurology, 1987

The mustache bat, Pteronotus parnellii, depends on echolocation to navigate and capture prey. Thi... more The mustache bat, Pteronotus parnellii, depends on echolocation to navigate and capture prey. This adaptation is reflected in the large size and elaboration of brainstem auditory structures and in the minimal development of visual structures. The superior colliculus, usually associated with orienting the eyes, is nevertheless large and well developed in Pteronotus. This observation raises the question of whether the superior colliculus in the echolocating bat has evolved to play a major role in auditory rather than visual orientation. The connections of the superior colliculus in Pteronotus were studied with the aid of anterograde and retrograde transport of wheat germ agglutinin conjugated to HRP. These results indicate that the superior colliculus of Pteronotus is composed almost entirely of the layers beneath stratum opticum. The retinal projection is restricted to a very thin zone just beneath the pial surface. Prominent afferent pathways originate in motor structures, particularly the substantia nigra and the deep nuclei of the cerebellum. Sensory input from the auditory system originates in three brainstem nuclei: the inferior colliculus, the anterolateral periolivary nucleus, and the dorsal nuclei of the lateral lemniscus. The projections from these auditory structures terminate mainly in the central tier of the deep layer. The most prominent efferent pathways are those to medial motor structures of the contralateral brainstem via the predorsal bundle and to the ipsilateral midbrain and pontine tegmentum via the lateral efferent bundle. Ascending projections to the diencephalon are mainly to the medial dorsal nucleus and zona incerta. Thus, the superior colliculus in Pteronotus possesses well-developed anatomical connections that could mediate reflexes for orienting its ears, head, or body toward objects detected by echolocation.

Springer Handbook of Auditory Research, 2002

ABSTRACT

Experimental Brain Research Supplementum, 1985