Studies of auditory neurophysiology in non-echolocating bats, and adaptations for echolocation in one genus, Rousettus (original) (raw)

Neurobiological specializations in echolocating bats

The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology, 2005

Although the bat's nervous system follows the general mammalian plan in both its structure and function, it has undergone a number of modifications associated with flight and echolocation. The most obvious neuroanatomical specializations are seen in the cochleas of certain species of bats and in the lower brainstem auditory pathways of all microchiroptera. This article is a review of peripheral and central auditory neuroanatomical specializations in echolocating bats. Findings show that although the structural features of the central nervous system of echolocating microchiropteran bats are basically the same as those of more generalized mammals, certain pathways, mainly those having to do with accurate processing of temporal information and auditory control of motor activity, are hypertrophied and/or organized somewhat differently from those same pathways in nonecholocating species. Through the resulting changes in strengths and timing of synaptic inputs to neurons in these pathways, bats have optimized the mechanisms for analysis of complex sound patterns to derive accurate information about objects in their environment and direct behavior toward those objects.

Neurobiology of echolocation in bats

Current Opinion in Neurobiology, 2003

Echolocating bats (sub-order: Microchiroptera) form a highly successful group of animals, comprising approximately 700 species and an estimated 25% of living mammals. Many echolocating bats are nocturnal predators that have evolved a biological sonar system to orient and forage in three-dimensional space. Acoustic signal processing and vocal-motor control are tightly coupled, and successful echolocation depends on the coordination between auditory and motor systems. Indeed, echolocation involves adaptive changes in vocal production patterns, which, in turn, constrain the acoustic information arriving at the bat's ears and the time-scales over which neural computations take place. Abbreviations 3-D three-dimensional ACC anterior cingulate cortex BD best duration BF best frequency CF constant frequency DNLL dorsal nucleus of the lateral lemniscus EI binaural response profile created with excitatory/inhibitory contralateral/ipsilateral inputs FM frequency modulated GABA g-amino butyric acid IC inferior colliculus ILD interaural level difference PAG periaqueductal gray PB parabrachial nucleus PLa paralemniscal tegmentum area PLS paradoxical latency shift

Neural processing mechanisms in echolocating bats, correlated with differences in emitted sounds

Journal of the Acoustical Society of America, 1973

Bats that emit pulses containing constant wavelength (CW) components preceding an FM sweep show neural adaptations that differ conspicuously from those of bats emitting purely FM pulses. In contrast to "FM bats," which have sharply tuned units distributed broadly throughout the range of their emitted pulses, "CW bats" have auditory systems tuned predominantly to a much smaller range corresponding to the restricted range of emitted frequencies. There is an "off"-response sharply tuned to the emitted CW frequencies. "On"response sensitivity is greater at just lower frequencies (CW component of less than 8-msec duration) or on either side of the "off"-frequency, with a null at that point (CW component of 10-20 msec or longer). The "off"-response, which is present at the level of the auditory nerve, apparently represents rebound excitation following non-neural suppression peripheral to the primary afferent fibers. It reflects a mechanism for increasing frequency discrimination and has the effect as well of enhancing response to the FM portion of the emitted pulses. High sensitivity to frequencies above that of the emitted CW, in "long CW" bats, is apparently tied to a use of the Doppler-shifted echo CW to detect and determine the angle and/or relative velocity of echo sources. CW bats show much less dramatic temporal resolution ability than FM bats, although it seems probable that the same mechanism of distance determination-measurement of elapsed time between emitted and returning FM sweeps-is used by both. CW bats, on the other hand, appear to have more units that are sharply sensitive to signal angle, showing strong binaural interaction. The consistent and conspicuous differences in neurophysiology in different species indicates not only that central analytic mechanisms are highly adaptable, but that these adaptations are important and closely tied to the types of orientation sounds used.

Peripheral control of acoustic signals in the auditory system of echolocating bats

Journal of Experimental Biology, 1975

Many species of echolocating bats emit intense orientation sounds. If such intense sounds directly stimulated their ears, detection of faint echoes would be impaired. Therefore, possible mechanisms for the attenuation of selfstimulation were studied with Myotis lucifugus. The acoustic middle-earmuscle reflex could perfectly and transiently regulate the amplitude of an incoming signal only at its beginning. However, its shortest latency in terms of electromyograms and of the attenuation of the cochlear microphonic was 3-4 and 4-8 msec, respectively, so that these muscles failed to attenuate orientation signals by the reflex. The muscles, however, received a message from the vocalization system when the bat vocalized, and contracted synchronously with vocalization. The duration of the contraction-relaxation was so short that the self-stimulation was attenuated, but the echoes were not. The tetanus-fusion frequency of the stapedius muscle ranged between 260 and 32o/sec. Unlike the efferent fibres in the lateral-line and vestibular systems, the olivo-cochlear bundle showed no sign of attenuation of self-stimulation.

Suga, N. & Jen, P. H. Peripheral control of acoustic signals in the auditory system of echolocating bats. J. Exp. Biol. 62, 277-311

Journal of Experimental Biology

Auditory scene analysis by echolocation in bats

The Journal of the Acoustical Society of America, 2001

Echolocating bats transmit ultrasonic vocalizations and use information contained in the reflected sounds to analyze the auditory scene. Auditory scene analysis, a phenomenon that applies broadly to all hearing vertebrates, involves the grouping and segregation of sounds to perceptually organize information about auditory objects. The perceptual organization of sound is influenced by the spectral and temporal characteristics of acoustic signals. In the case of the echolocating bat, its active control over the timing, duration, intensity, and bandwidth of sonar transmissions directly impacts its perception of the auditory objects that comprise the scene. Here, data are presented from perceptual experiments, laboratory insect capture studies, and field recordings of sonar behavior of different bat species, to illustrate principles of importance to auditory scene analysis by echolocation in bats. In the perceptual experiments, FM bats ͑Eptesicus fuscus͒ learned to discriminate between systematic and random delay sequences in echo playback sets. The results of these experiments demonstrate that the FM bat can assemble information about echo delay changes over time, a requirement for the analysis of a dynamic auditory scene. Laboratory insect capture experiments examined the vocal production patterns of flying E. fuscus taking tethered insects in a large room. In each trial, the bats consistently produced echolocation signal groups with a relatively stable repetition rate ͑within 5%͒. Similar temporal patterning of sonar vocalizations was also observed in the field recordings from E. fuscus, thus suggesting the importance of temporal control of vocal production for perceptually guided behavior. It is hypothesized that a stable sonar signal production rate facilitates the perceptual organization of echoes arriving from objects at different directions and distances as the bat flies through a dynamic auditory scene. Field recordings of E. fuscus, Noctilio albiventris, N. leporinus, Pippistrellus pippistrellus, and Cormura brevirostris revealed that spectral adjustments in sonar signals may also be important to permit tracking of echoes in a complex auditory scene.

Adaptations of the auditory nervous system for echolocation

Zeitschrift f�r Vergleichende Physiologie, 1972

1. Seven species of paleotropica] echolocating bats were studied in an effort to correlate differences in emitted orientation pulses with differences in neural analysis mechanisms. Major emphasis was on species of the genus Hippo-sidero~, which emit extremely high frequencies in pulses consisting of a constant frequency for several msec followed by a fast downward sweep in frequency.

Studies of auditory neurophysiology in non-echolocating bats, and adaptations for echolocation in one genus, Rousettus (original) (raw)

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