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PubMed2005

Mapping auditory cortex in the La Plata dolphin (Pontoporia blainvillei).

This study deals with the mapping of the primary and secondary auditory cortex. Due to their important role in echolocation they were the first areas to be examined [P.J. Morgane, M.S. Jacobs, in: R.J. Harrison (Ed.), Functional Anatomy of Marine Mammals, Comparative Anatomy of the Cetacean Nervous System, vol. 1, Academic Press, London, 1972, pp. 117-144]. We analysed the brain of a La Plata dolphin (Pontoporia blainvillei), which had been fixed in formaldehyde, embedded in paraffin, cut in sections of 20mum thickness and stained with cresyl violet. The experimental approach being impossible, we used cytoarchitectonic variations in the neocortex. Former electrophysiological data [T.F. Ladygina, A.Y. Supin, Localization of the projectional sensory areas in the cortex of the porpoise Tursiops truncates, Zh. Evol. Biokhim. Fiziol. 13 (1978) 712-718] [Sokolov, T.F. Ladygina, A.Y. Supin, Location of sensory zones in cerebral cortex of dolphin, Dokl. Biol. Sci., Russian Original 202 (1-6) (1972)] provided the framework for the exact determination of borders between functional cortical areas. We used a stereological observer-independent procedure based on changes in volume density of cell bodies throughout the neocortex [A. Schleicher, et al., Stereological approach to human cortical architecture: Identification and delineation of cortical areas, J. Chem. Neuroanat. 20 (2000) 31-47]. Due to the computer program's high sensitivity to changes in volume density it was possible to analyse the poorly laminated dolphin cortex. The 3D-reconstruction of the auditory cortex was processed using the AMIRA 3.0 Graphics software package comparing the main primary gyri in the histological sections with those in coronal magnetic resonance imaging scans of another intact Pontoporia brain.

Animals↗
PubMed2004

Fish perform spatial pattern recognition and abstraction by exclusive use of active electrolocation.

The field generated by the electric organ of weakly electric fish varies with the electrical properties of nearby objects. Correspondingly, current fluxes in this field differentially stimulate the electroreceptors in the fish's skin. Thus, resistors are to conductors and insulators as gray is to black and white in optics. Additionally, the capacitances of plants and insect larvae contrast with those of water or stones, giving effects comparable to "coloration". Receptors arrayed over a large area of the skin act like a retina upon which the discharge projects "electric images". By further central processing, the fish also discriminate between objects according to their composition, size, or distance, a procedure termed "electrolocation", analogous to echolocation in bats. Here we demonstrate that G. petersii and S. macrurus can also recognize 3D orientations and configurations and extract and generalize spatial features solely with their electrical sense. We presented fish with virtual electrical "objects" formed from electrodes set flush in the inner surface of a Y maze with various patterns of external connectivity. With reward and aversion training, the fish could recognize similar electrode configurations and extract a feature, e.g., a vertical connectivity, present in various novel configurations. Previously, shape recognition has only been shown in electrolocating fish when they are in full mechanical contact with solid objects.

Animals↗
PubMed2000

Corticofugal inhibition compresses all types of rate-intensity functions of inferior collicular neurons in the big brown bat.

Recent studies have shown that the auditory corticofugal system modulates and improves signal processing in the frequency, time and spatial domains. In this study, we examine corticofugal modulation of rate-intensity functions of inferior collicular (IC) neurons of the big brown bat, Eptesicus fuscus, by electrical stimulation in the primary auditory cortex (AC). Cortical electrical stimulation compressed all types of rate-intensity functions so as to increase the slope but decrease the dynamic range of IC neurons. Cortical electrical stimulation also shifts the responsive intensity of IC neurons to higher levels. These data indicate that corticofugal modulation also improves subcortical signal processing in intensity domain. The implication of these findings to bat echolocation is discussed.

Acoustic Stimulation↗
PubMed2003

The effect of bicuculline application on azimuth-dependent recovery cycle of inferior collicular neurons of the big brown bat, Eptesicus fuscus.

The recovery cycle of auditory neurons is an important neuronal property, which determines a neuron's ability to respond to pairs of sounds presented at short inter-sound intervals. This property is particularly important for bats, which rely upon analysis of returning echoes to extract the information about targets after emission of intense orientation sounds. Because target direction often changes throughout the course of hunting, the changing echo direction may affect the recovery cycle and thus temporal processing of auditory neurons. In this study, we examined the effect of sound azimuth on the recovery cycle of inferior collicular (IC) neurons in the big brown bat, Eptesicus fuscus, under free-field stimulation conditions. Our study showed that the recovery cycle of most IC neurons (42/49, 86%) was longer when determined with sounds delivered at 40 degrees ipsilateral (i40 degrees ) than at 40 degrees contralateral (c40 degrees ) to the recording site. To study the contribution of GABAergic inhibition to sound azimuth-dependent recovery cycle, we compared the recovery cycle of IC neurons determined at two sound azimuths before and during iontophoretic application of bicuculline, an antagonist for GABA(A) receptors. Bicuculline application produced a greater decrease of the recovery cycle of these neurons at i40 degrees than at c40 degrees. As a result, the azimuth-dependent recovery cycle of these neurons was abolished or greatly reduced. Possible mechanisms underlying these observations and biological relevance to bat echolocation are discussed.

Acoustic Stimulation↗
PubMed2002

Acoustic sensitivity of fly antennae.

The vast majority of higher flies - the brachycerans - is endowed with strikingly similar antennal morphologies and elaborate antennal mechanosensory organs. Thus far, however, the function of audition has been attributed only to the antennae of Drosophilid and Tephritid flies. Antennal mechanical sensitivity to sound is now documented in a broad range of fly species. These results highlight the wide occurrence of audition in as many as 120,000 species of higher Diptera. Antenna-based audition, as defined by the capacity of sensing the mechanical vibrations of the antenna in response to sound, thus appears to constitute an ubiquitous sensory capacity among higher flies. Functionally, antennal hearing can be used in the contexts of intraspecific acoustic signalling, flight control, and putatively close-range echolocation.

Journal Article↗
PubMed2003

Can dolphins heal by ultrasound?

In recent years, dolphin-assisted therapy has become very popular and an increasing number of facilities offer therapy programs with dolphins worldwide. To this date, there are no studies concerning the behavior of dolphins during these therapies. As a result of speculations that the echolocation of dolphins may play an important role for the success of the therapy and the high publicity of this in the media, people pay much more for dolphin-assisted than for other animal-assisted therapy programs. Based on publications in medicine, we will show that ultrasound emitted by dolphins could have an effect on biological tissue under some circumstances; such as sufficient intensity, repeated application over several days or weeks and a certain application duration per session. We recorded 83 sessions at the "Dolphins Plus", a fenced area with ocean water in the Florida Keys. Our observations demonstrate that only one out of five observed dolphins behave significantly differently towards patients compared to other humans and that the duration of the observed close contacts did not meet the requirements for common ultrasound therapies.

Analysis of Variance↗
PubMedDate not supplied

Neural population coding and auditory temporal pattern analysis.

Over the 2 decades that have elapsed since Robert Erickson first published his pioneering work on across-fiber patterns in the gustatory system, the idea that information is represented by a population code has become almost universally accepted among neuroscientists. Although the concept of a population code is an implicit theoretical assumption underlying most of the work done in neuroscience today, the details of how population codes operate in specific systems remain unclear in many respects. This article reviews electrophysiological studies of the auditory system of echolocating bats that show that information about sound is initially represented across both space and time by relative amounts of activity in populations of excitatory and inhibitory neurons with different discharge patterns, different sensitivity functions, and different latencies. At the next level, each neuron in the auditory midbrain receives convergent input from a specific population of these lower brainstem neurons and acts as a "readout" of activity within this population. As a result, midbrain neurons become selectively tuned to stimulus features, for example, signal duration, to which neurons at lower levels respond indiscriminately. Intracellular recordings from auditory midbrain neurons show some of the mechanisms by which population input is processed. The known projection patterns of the midbrain "readout" neurons indicate that they, in turn, must become part of a new spatio-temporal population code that is transmitted to neurons at the thalamus, where additional forms of selectivity and patterns of output arise.

Animals↗
PubMed2001

Cellular and subcellular distribution of AMPA-type glutamate receptor subunits and metabotropic glutamate receptor 1alpha in the cochlear nucleus of the horseshoe bat (Rhinolophus rouxi).

Ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) selective glutamate receptors (GluRs) are the main mediators of fast excitatory neurotransmission and composed of a variable combination of four different subunits (GluR1-4). The metabotropic glutamate receptor 1alpha (mGluR1alpha) is involved in plastic synaptic events. Since horseshoe bats strongly depend on temporal cues for acoustic imaging by echolocation and exhibit prominent species specific specializations of the cochlear nucleus (CN), the subunit distribution of AMPA selective GluRs and the distribution of mGluR1alpha was studied at the light and electron microscopic level with preembedding immunocytochemistry. Immunoreactivity to GluR1 was low throughout the CN. All types of projection neurons of the ventral CN expressed distinct GluR2/3 and GluR4 immunoreactivity with GluR4-labeling especially prominent in multipolar and octopus cell-like neurons of the posteroventral CN. The AMPA and metabotropic receptor inventory of the laminated ventral subdivision of the dorsal CN (DCNv) agreed with that reported in other mammals, whereas the specialized dorsal non-laminated subdivision of DCN (DCNd) lacked the prominent labeling for GluR2/3 and mGluR1alpha that characterizes cartwheel cells of DCNv. Distinct GluR2/3 and GluR4 immunoreactivity combined with low expression of mGluR1alpha immunoreactivity was characteristic for fusiform cells of DCNv and DCNd. Tuberculoventral cells of both the deep DCNv and the DCNd exhibited light to moderate GluR2/3 and GluR4 immunoreactivity. The staining patterns in DCNd thus indicate a loss of cerebellar-like microcircuits and a conservation of frequency specific circuitry of the deep and fusiform cell layers of the mammalian DCN.

Animals↗
PubMed1997

Audiogram of the big brown bat (Eptesicus fuscus).

The audiograms of three big brown bats (Eptesicus fuscus) were determined using a conditioned avoidance procedure. The average audiogram ranged from 0.850 kHz at 106 dB to 120 kHz at 83 dB SPL, with a best threshold of 7 dB at 20 kHz and a distinct decrease in sensitivity at 45 kHz. The results confirm those of a previous study by Dalland (1965a) that the big brown bat has good high-frequency hearing coupled with poor low-frequency hearing. Comparative analysis suggests that the bat's good high-frequency hearing initially evolved for passive sound localization and that it was later coopted for use in echolocation. In addition, the restricted low-frequency hearing of the big brown bat is typical of mammals with good high-frequency hearing.

Acoustic Stimulation↗
PubMed2002

Seeing and not seeing.

Recent studies revealed that although subterranean mammals inhabit a dark underground environment, they can still perceive light stimuli and use this to entrain their circadian activity rhythm. Regarding spatial orientation, olfactory and tactile cues are employed for short-distance; whereas for long-distance, subterranean mammals employ the earth's magnetic field and self-generated (vestibular and kinestatic) cues. We suggest that seismic signals, utilized for long-distance communication, might also be used as an echolocation mechanism to determine digging depth and presence of obstacles ahead. Taken together, these mechanisms provide an equally efficient means of overall orientation and communication as those found in sighted mammals.

Animals↗
PubMed1998

Hearing in a megachiropteran fruit bat (Rousettus aegyptiacus).

The Egyptian fruit bat (Rousettus aegyptiacus) is one of the few megachiropteran bats capable of echolocation. However, it uses rudimentary tongue clicks rather than laryngeally produced echo calls. We determined the audiogram of 2 bats using a conditioned avoidance procedure with fruit puree reward. At an intensity of 60 dB sound pressure level, the bats' hearing extended from 2.25 kHz to 64 kHz, with a region of good sensitivity between 8 kHz and 45 kHz. A dip in sensitivity at 32 kHz appears to be due to pinna directionality. The hearing of Egyptian fruit bats is typical for a mammal of that size and is not as limited as previously reported. Methodological issues, specifically training an animal to listen for low-intensity signals and imposing a significant cost for failing to report signals (i.e., misses), are discussed as the basis for the discrepancy between our results and earlier reports.

Animals↗
PubMed1999

Sound localization in an Old-World fruit bat (Rousettus aegyptiacus): acuity, use of binaural cues, and relationship to vision.

The passive sound-localization acuity of Egyptian fruit bats (Rousettus aegyptiacus) was determined using a conditioned-avoidance procedure. The mean minimum audible angle for left-right discrimination for 3 bats was 11.6 degrees--very near the mean for terrestrial mammals. The bats also were able to localize low- and high-frequency pure tones, indicating that they can use both binaural phase-difference and binaural intensity-difference cues to localize sound. Moreover, they were able to use the binaural phase-difference cue up to at least 5.6 kHz, which is higher than other mammals yet tested. The width of the Egyptian fruit bats' field of best vision was 27 degrees. This value is consistent with the hypothesis that the role of passive sound localization is to direct the eyes for visual scrutiny of sound sources. Thus, the passive localization abilities of these echolocating megachiropteran fruit bats do not deviate from the patterns established for nonecholocating mammals.

Animals↗
PubMed1999

A neuronal representation of the location of nearby sounds.

Humans can accurately perceive the location of a sound source-not only the direction, but also the distance. Sounds near the head, within ducking or reaching distance, have a special saliency. However, little is known about this perception of auditory distance. The direction to a sound source can be determined by interaural differences, and the mechanisms of direction perception have been studied intensively; but except for studies on echolocation in the bat, little is known about how neurons encode information on auditory distance. Here we describe neurons in the brain of macaque monkeys (Macaca fascicularis) that represent the auditory space surrounding the head, within roughly 30 cm. These neurons, which are located in the ventral premotor cortex, have spatial receptive fields that extend a limited distance outward from the head.

Animals↗
PubMed1993

Revised phylogeny of whales suggested by mitochondrial ribosomal DNA sequences.

Living cetaceans are subdivided into two highly distinct suborders, Odontoceti (the echolocating toothed whales) and Mysticeti (the filter-feeding baleen whales), which are believed to have had a long independent history. Here we report the determination of DNA sequences from two mitochondrial ribosomal gene segments (930 base pairs per species) for 16 species of cetaceans, a perissodactyl and a sloth, and construct the first phylogeny for whales and dolphins based on explicit cladistic methods. Our data (and earlier published myoglobin sequences) confirmed that cetaceans are closely related to artiodactyls and that all families and superfamilies of cetaceans are monophyletic. A surprising finding was that one group of toothed whales, the sperm whales, is more closely related to the baleen whales than to other odontocetes. The common ancestor of baleen whales and sperm whales might have lived only 10-15 million years ago. The suggested paraphyly of toothed whales has many implications for classification, phylogeny and our understanding of the evolutionary history of cetaceans.

Animals↗
PubMed2004

Animal communication: ground squirrel uses ultrasonic alarms.

Apart from echolocation and the pursuit of prey by bats, the function of ultrasound in animal communication is poorly understood. This is mainly because of the broad range of responses that it can evoke and the widely varied contexts in which it is used (for example, in rodents of the Muridae family it may indicate distress in infants or a sexual or predatory encounter in adults). Here we find that a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson's ground squirrel, and show that its function is to warn conspecifics of impending danger. To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators.

Animals↗
PubMed2006

Navigation: bat orientation using Earth's magnetic field.

Bats famously orientate at night by echolocation, but this works over only a short range, and little is known about how they navigate over longer distances. Here we show that the homing behaviour of Eptesicus fuscus, known as the big brown bat, can be altered by artificially shifting the Earth's magnetic field, indicating that these bats rely on a magnetic compass to return to their home roost. This finding adds to the impressive array of sensory abilities possessed by this animal for navigation in the dark.

Animals↗
PubMed2003

Ultraviolet vision in a bat.

Most mammals, with the exception of primates, have dichromatic vision and correspondingly limited colour perception. Ultraviolet vision was discovered in mammals only a decade ago, and in the few rodents and marsupials where it has been found, ultraviolet light is detected by an independent photoreceptor. Bats orient primarily by echolocation, but they also use vision. Here we show that a phyllostomid flower bat, Glossophaga soricina, is colour-blind but sensitive to ultraviolet light down to a wavelength of 310 nm. Behavioural experiments revealed a spectral-sensitivity function with maxima at 510 nm (green) and above 365 nm (ultraviolet). A test for colour vision was negative. Chromatic adaptation had the same threshold-elevating effects on ultraviolet and visible test lights, indicating that the same photoreceptor is responsible for both response peaks (ultraviolet and green). Thus, excitation of the beta-band of the visual pigment is the most likely cause of ultraviolet sensitivity. This is a mechanism for ultraviolet vision that has not previously been demonstrated in intact mammalian visual systems.

Adaptation, Physiological↗
PubMed2006

Ultrasonic communication in frogs.

Among vertebrates, only microchiropteran bats, cetaceans and some rodents are known to produce and detect ultrasounds (frequencies greater than 20 kHz) for the purpose of communication and/or echolocation, suggesting that this capacity might be restricted to mammals. Amphibians, reptiles and most birds generally have limited hearing capacity, with the ability to detect and produce sounds below approximately 12 kHz. Here we report evidence of ultrasonic communication in an amphibian, the concave-eared torrent frog (Amolops tormotus) from Huangshan Hot Springs, China. Males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations that often contain spectral energy in the ultrasonic range. To determine whether A. tormotus communicates using ultrasound to avoid masking by the wideband background noise of local fast-flowing streams, or whether the ultrasound is simply a by-product of the sound-production mechanism, we conducted acoustic playback experiments in the frogs' natural habitat. We found that the audible as well as the ultrasonic components of an A. tormotus call can evoke male vocal responses. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs and that of a sympatric species facing similar environmental constraints. This extraordinary upward extension into the ultrasonic range of both the harmonic content of the advertisement calls and the frog's hearing sensitivity is likely to have co-evolved in response to the intense, predominantly low-frequency ambient noise from local streams. Because amphibians are a distinct evolutionary lineage from microchiropterans and cetaceans (which have evolved ultrasonic hearing to minimize congestion in the frequency bands used for sound communication and to increase hunting efficacy in darkness), ultrasonic perception in these animals represents a new example of independent evolution.

Acoustic Stimulation↗