Neural responses in the inferior colliculus of echolocating bats to artificial orientation sounds and echoes

The responses of single units and evoked potentials to a pair of artificial sounds, mimicking theorientation sound and echo, and to tape recorded actual orientation sounds were studied in terms of recovery cycle. the recovery cycle of single units could be classified into four groups: (1) short suppression (4%), (2) delayed inhibition (11%), (3) temporal recovery with or without a supernormal phase (7%), and (4) undelayed inhibition (78%) lasting 4 to 26 msec. therefore the majority of neurons were not excited by the second sound (echo) of a pair when it was delivered within several milliseconds after the first (out-going orientation sound). the duration of the recovery cycle was a function of the intensity of a pair of sounds. the weaker the first tone pulse relative to the second, the more rapid the recovery to the second. therefore, the reception of echoes is probably improved by contraction of middle ear muscles resulting in attenuation of self-stimulation by the out-going pulse. The collicular evoked potential consisted of two components, a fast one mainly due to the incoming fibers from lower levels and a slow one due to the main body of the inferior colliculus. The slow component showed slow recovery cycles as did the majority of single units while the fast one recovered very quickly. No noticeable difference in recovery cycles was found between awake and anesthetized animals. The functional meaning of inhibitory periods in the recovery cycle and role of the inferior colliculus in echo-location are discussed.     

Echolocation behavior of the Japanese horseshoe bat in pursuit of fluttering prey

Echolocation sounds of Rhinolophus ferrumequinum nippon as they approached a fluttering moth (Goniocraspidum pryeri) were investigated using an on-board telemetry microphone (Telemike). In 40?% of the successful moth-capture flights, the moth exhibited distinctive evasive flight behavior, but the bat pursued the moth by following its flight path. When the distance to the moth was approximately 3-4?m, the bats increased the duration of the pulses to 65-95?ms, which is 2-3 times longer than those during landing flight (30-40?ms). The mean of 5.8 long pulses were emitted before the final buzz phase of moth capture, without strengthening the sound pressure level. The mean duration of long pulses (79.9?±?7.9?ms) corresponded to three times the fluttering period of G. pryeri (26.5?×?3?=?79.5?ms). These findings indicate that the bats adjust the pulse duration to increase the number of temporal repetitions of fluttering information rather than to produce more intense sonar sounds to receive fine insect echoes. The bats exhibited Doppler-shift compensation for echoes returning from large static objects ahead, but not for echoes from target moths, even though the bats were focused on capturing the moths. Furthermore, the echoes of the Telemike recordings from target moths showed spectral glints of approximately 1-1.5?kHz caused by the fluttering of the moths but not amplitude glints because of the highly acoustical attenuation of ultrasound in the air, suggesting that spectral information may be more robust than amplitude information in echoes during moth capturing flight.     

COMPARATIVE ANALYSIS OF SWIMBLADDER (DRUMMING) AND PECTORAL (STRIDULATION) SOUNDS IN THREE FAMILIES OF CATFISHES

ABSTRACT

Among teleosts, only representatives of several tropical catfish families have evolved two sonic organs: pectoral spines for stridulation and swimbladder drumming muscles. Pectoral mechanisms differ in relative size between pimelodids, mochokids and doradids, whereas swimbladder mechanisms exhibit differences in origin and insertion of extrinsic muscles. Differences in vocalization among families were investigated by comparing distress calls in air and underwater. High frequency broad-band pulsed sounds of similar duration were emitted during abduction of pectoral spines in all three families. Adduction sounds were similar to abduction signals in doradids, shorter and of lower sound pressure in mochokids, and totally lacking in pimelodids. Simultaneously or successively with pectoral sounds, low frequency harmonic drumming sounds were produced by representatives of two families. Drumming sounds were of similar intensity as stridulatory sounds in pimelodids, fainter in doradids, and not present in mochokids. Swimbladder sounds were frequency modulated and the fundamental frequency was similar in pimelodids and doradids. The ratio of stridulatory to drumming sound amplitude was higher in air than underwater in both doradids and one of the pimelodids. Also, overall duration of pectoral sounds, compared to swimbladder sounds, was longer in air than underwater in one doradid and pimelodid species. This first comparison of vocalization within one major teleost order demonstrates a wide variation in occurrence, duration, intensity and spectral content of sounds and indicates family- and species-specific as well as context- (receiver-) dependent patterns of vocalization.     

Adaptive mechanisms underlying the bat biosonar behavior

For survival, bats of the suborder Microchiropetra emit intense ultrasonic pulses and analyze the weak returning echoes to extract the direction, distance, velocity, size, and shape of the prey. Although these bats and other mammals share the common layout of the auditory pathway and sound coding mechanism, they have highly developed auditory systems to process biologically relevant pulses at the expense of a reduced visual system. During this active biosonar behavior, they progressively shorten the pulse duration, decrease the amplitude and pulse-echo gap as they search, approach and finally intercept the prey. Presumably, these changes in multiple pulse parameters throughout the entire course of hunting enable them to extract maximal information about localized prey from the returning echoes. To hunt successfully, the auditory system of these bats must be less sensitive to intense emitted pulses but highly sensitive to weak returning echoes. They also need to recognize and differentiate the echoes of their emitted pulses from echoes of pulses emitted by other conspecifics. Past studies have shown the following mechanical and neural adaptive mechanisms underlying the successful bat biosonar behavior: (1) Forward orienting and highly mobile pinnae for effective scanning, signal reception, sound pressure transformation and mobile auditory sensitivity; (2) Avoiding and detecting moving targets more successfully than stationary ones; (3) Coordinated activity of highly developed laryngeal and middle ear muscles during pulse emission and reception; (4) Mechanical and neural attenuation of intense emitted pulses to prepare for better reception of weak returning echoes; (5) Increasing pulse repetition rate to improve multiple-parametric selectivity to echoes; (6) Dynamic variation of duration selectivity and recovery cycle of auditory neurons with hunting phase for better echo analysis; (7) Maximal multiple-parametric selectivity to expected echoes returning within a time window after pulse emission; (8) Pulse-echo delaysensitive neurons in higher auditory centers for echo ranging; (9) Corticofugal modulation to improve on-going multiple-parametric signal processing and reorganize signal representation, and (10) A large area of the superior colliculus, pontine nuclei and cerebellum that is sensitive to sound for sensori-motor integration. All these adaptive mechanisms facilitate the bat to effectively extract prey features for successful hunting.     

Effect of the stage of the reproductive cycle on vocalization and behaviour in female bank voles

Females of several species of rodents are known to emit audible and ultrasonic sounds during same-sex encounters. There is very little information about factors affecting this vocalization. The present study was undertaken to investigate the effect of the stage of the reproductive cycle on vocalization and behaviour of adult bank vole females during various same-sex encounters. Pregnancy and lactation were studied as important phases of female life. The possible role of ovarian hormones in the emission of acoustic signals was also investigated as these hormones are known to be important in the regulation of other female social behaviour. The behaviour and vocalization of sexually naive, ovariectomized, pregnant and lactating females were studied using 10-min confrontation tests. The results demonstrate that the behaviour displayed and the emission of sounds in female–female bank vole encounters depend on the phase of reproductive cycle. Ultrasounds are produced more often by sexually naive and ovariectomized females which present mainly non-aggressive behaviour than by more aggressive lactating females. Audible sounds are emitted only occasionally by naive and by ovariectomized females but pregnant and especially lactating females emitted such calls more often, with shorter latencies and for longer than the unmated groups. Ultrasonic vocalization therefore seems to be related to non-aggressive behaviour and audible vocalization to aggression.     

Complex sound analysis in the lesser bulldog bat: evidence for a mechanism for processing frequency elements of frequency modulated signals over restricted time intervals

A stereotypical approach phase vocalization response of the lesser bulldog bat, Noctilio albiventris, to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bat was not significantly different when presented with naturally structured CF/FM echoes containing FM elements that sweep continuously from about 75-55 kHz in 4 ms or with CF/FM echoes containing FM components constructed from a series of 98 pure tone frequency steps, each with a duration of 0.04 ms. The performance of the bat remained unchanged when the duration of the tone steps was increased up to 0.08 ms but declined sharply to a level that was significantly below that seen with a naturally structured echo when the steps were 0.09 ms or longer. The performance of the bat depended on the duration of the individual tone steps, which could not exceed a specific upper limit of about 0.08 ms. The study suggests that the bats have adaptations for processing individual narrow band segments of FM signals over specific time intervals.Abbreviations CF constant frequency - FM frequency modulation     

Attenuation of reflex pressor and ventilatory responses to static muscular contraction by intrathecal opioids

We have tested the hypothesis that intrathecal injections of opioid peptides attenuate the reflex pressor and ventilatory responses to static contraction of the triceps surae muscles of chloralose-anesthetized cats. We found that before intrathecal injections of [D-Ala2]Met-enkephalinamide (100 micrograms in 0.2 ml), static contraction increased mean arterial pressure and ventilation by 32 +/- 5 (SE) mmHg and 227 +/- 61 (SE) ml/min, whereas after injection of this opioid peptide, static contraction increased mean arterial pressure and ventilation by only 15 +/- 5 mmHg and 37 +/- 33 ml/min, respectively. The attenuation of both the pressor and ventilatory responses to static contraction by [D-Ala2]Met-enkephalinamide were statistically significant (P less than 0.05). Moreover, the attenuation was probably not caused by an opioid-induced withdrawal of sympathetic outflow because [D-Ala2]Met-enkephalinamide had no effect on the pressor and ventilatory responses evoked by high-intensity electrical stimulation of the central cut end of the sciatic nerve. In addition, intrathecal injection of peptides that were highly selective agonists for either the opioid mu- or delta-receptor attenuated the reflex responses to static contraction. Naloxone (1,000 micrograms), injected intrathecally, prevented the attenuation of the reflex responses to contraction by opioid peptides. We speculate that the opioid-induced attenuation of the reflex pressor and ventilatory responses to static contraction may have been due to suppression of substance P release from group III and IV muscle afferents.     

Qualities and drawbacks of radiotransmitted vocalizations of monkeys through laryngophones: new perspectives in analysis

Radiotransmitted (RT) calls of monkeys equipped with laryngeal microtransmitters are compared with those recorded by an external microphone (AT). Sharp attenuation of background noise and echoes results in better sonograms with RT than AT sounds. Sensitive detection of unvoiced calls or phonatory noises leads to knowledge of the motivational state of the animals and the mechanisms of their vocal production. However, the laryngophone acts as a low pass filter which limits RT spectra below 3 kHz. Constant distance and orientation between sound source and microphone permit us to get absolute (low-pitched call) or relative (high-pitched call) intensity measurements. Their generalization should be possible with the use of a specific weighting filter which would reconstitute the original energy of calls. The system has interesting applications in behavioral and ecological studies.     

Action of naloxone on emotionally positive and antinociceptive effects of hypothalamic stimulation in rats

Naloxone (5 mg/kg subcutaneously) failed to effect significantly the reaction of electric self-stimulation in rats with electrodes implanted into lateral hypothalamic area. In 3 rats the analgesic effect manifested in an increase of the threshold of painful vocalization under electrostimulation of the tail was revealed. The antinociceptive effect was abolished with naloxone. Morphine (3 mg/kg) potentiated self-stimulation while naloxone antagonized this action. The role of opiate receptors in effects of self-stimulation and centrally produced analgesia is discussed.     

Estrogen's attenuating effect on the exercise pressor reflex is more opioid dependent in gonadally intact than in ovariectomized female cats.

Using gonadally intact female cats, we showed previously that estrogen, applied topically to the spinal cord, attenuated the exercise pressor reflex. Although the mechanism by which estrogen exerted its attenuating effect is unknown, this steroid hormone has been shown to influence spinal opioid pathways, which in turn have been implicated in the regulation of the exercise pressor reflex. These findings prompted us to test the hypothesis that opioids mediate the attenuating effect of estrogen on the exercise pressor reflex in both gonadally intact female and ovariectomized cats. We therefore applied 200 microl of 17beta-estradiol (0.01 microg/ml) with and without the addition of 1,000 microg naloxone, a mu- and delta-opioid antagonist, to a spinal well covering the L6-S1 spinal cord in decerebrated female cats that were either gonadally intact or ovariectomized. The exercise pressor reflex was evoked by electrical stimulation of the L7 or S1 ventral root, a maneuver that caused the hindlimb muscles to contract statically. We found that, in gonadally intact cats, the attenuating effect of estrogen was more pronounced than that in ovariectomized cats. We also found that, in gonadally intact female cats, naloxone partly reversed the attenuation of the pressor response to static contraction caused by spinal estrogen application. For example, in intact cats, the pressor response to contraction before estrogen application averaged 39 +/- 4 mmHg (n = 10), whereas the pressor response 60 min afterward averaged only 18 +/- 4 mmHg (P < 0.05). In contrast, the pressor response to contraction before estrogen and naloxone application averaged 33 +/- 5 mmHg (n = 11), whereas afterward it averaged 27 +/- 6 mmHg (P < 0.05). In ovariectomized cats, naloxone was less effective in reversing the attenuating effect of estrogen on the exercise pressor reflex.     

Influence of Proprioceptive Signals from the Neck Muscles on the Organization of Vestibuloocular Reactions

To gain insight into the influence of the cervical proprioceptive factor on the organization of vestibuloocular reactions, the oculomotor reflexes were studied in patients with asymmetrically increased tone of the neck muscles. It was established that, in the absolute majority of these spasmodic torticollis patients, the active cervicoocular reflex (a-COR) was more intense than the vestibuloocular reflex (VOR). The a-COR was predominant in the direction to the side opposite to the forced turn of the head; i.e., when the head is turned by overcoming the force of the tense cervical muscles, the most powerful nystagmic reaction takes place.     

Frequency modulated sound pattern analysis in the lesser bulldog bat: the role of interactions between adjacent frequency elements of complex sounds

A stereotyped approach phase vocalization response of Noctilio albiventris to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bats depended on the temporal pattern of frequency change of the continuously sweeping frequency modulated (FM) component of the signals. When the bats were presented with a CF/FM signal containing a time-reversed upward FM sweep, they responded with approach phase behavior at a performance level that was significantly below that seen with a CF/FM signal containing a naturally structured downward FM sweep. When the FM sweep was divided into a series of brief pure tone steps, the extent to which the bats showed a difference in their capability to process upward versus downward FM sweeps depended on the difference in frequency between the pure tone steps. The bats effectively processed downward but not upward FM sweeps when the difference in frequency between pure tone frequency elements of the FM sweeps was from about 100–200 Hz, but they effectually processed both downward and upward FM sweeps when the tonal elements composing the FM sweeps were separated by more than about 200 Hz. This suggests that the ability of the bats to effectively process downward but not upward FM sweeps is based on local interactions between adjacent frequency elements of the complex sounds.Abbreviations CF constant frequency - FM frequency modulated     

Ranging in Human Sonar: Effects of Additional Early Reflections and Exploratory Head Movements

Many blind people rely on echoes from self-produced sounds to assess their environment. It has been shown that human subjects can use echolocation for directional localization and orientation in a room, but echo-acoustic distance perception - e.g. to determine one''s position in a room - has received little scientific attention, and systematic studies on the influence of additional early reflections and exploratory head movements are lacking. This study investigates echo-acoustic distance discrimination in virtual echo-acoustic space, using the impulse responses of a real corridor. Six blindfolded sighted subjects and a blind echolocation expert had to discriminate between two positions in the virtual corridor, which differed by their distance to the front wall, but not to the lateral walls. To solve this task, participants evaluated echoes that were generated in real time from self-produced vocalizations. Across experimental conditions, we systematically varied the restrictions for head rotations, the subjects'' orientation in virtual space and the reference position. Three key results were observed. First, all participants successfully solved the task with discrimination thresholds below 1 m for all reference distances (0.75–4 m). Performance was best for the smallest reference distance of 0.75 m, with thresholds around 20 cm. Second, distance discrimination performance was relatively robust against additional early reflections, compared to other echolocation tasks like directional localization. Third, free head rotations during echolocation can improve distance discrimination performance in complex environmental settings. However, head movements do not necessarily provide a benefit over static echolocation from an optimal single orientation. These results show that accurate distance discrimination through echolocation is possible over a wide range of reference distances and environmental conditions. This is an important functional benefit of human echolocation, which may also play a major role in the calibration of auditory space representations.     

Effects of exercise on muscle transverse relaxation determined by MR imaging and in vivo relaxometry.

The purpose of this study was to determine the effects of intense exercise on the proton transverse (T(2)) relaxation of human skeletal muscle. The flexor digitorium profundus muscles of 12 male subjects were studied by using magnetic resonance imaging (MRI; 6 echoes, 18-ms echo time) and in vivo magnetic resonance relaxometry (1,000 echoes, 1.2-ms echo time), before and after an intense handgrip exercise. MRI of resting muscle produced a single T(2) value of 32 ms that increased by 19% (P < 0.05) with exercise. In vivo relaxometry showed at least three T(2) components (>5 ms) for all subjects with mean values of 21, 40, and 137 ms and respective magnitudes of 34, 49, and 14% of the total magnetic resonance signal. These component magnitudes changed with exercise by -44% (P < 0.05), +52% (P < 0.05), and +23% (P < 0.05), respectively. These results demonstrate that intense exercise has a profound effect on the multicomponent T(2) relaxation of muscle. Changes in the magnitudes of all the T(2) components synergistically increase MRI T(2), but changes in the two shortest T(2) components predominate.     

Topographic representation of vocal frequency demonstrated by microstimulation of anterior cingulate cortex in the echolocating bat,Pteronotus parnelli parnelli

1. A midline region of brain dorsal and anterior to the corpus callosum, presumably anterior cingulate cortex, has been explored for its role in the production of vocalization in the mustached bat, Pteronotus p. parnelli. 2. Vocalizations elicited by microstimulation were virtually indistinguishable from natural biosonar sounds. The spectral content, relative intensity of harmonic components, and durations of emitted pulses are comparable to spontaneous emissions. 3. The frequencies of elicited vocalizations were within the range typically used by the mustached bat during Doppler-shift compensation. The frequency of the second-harmonic constant-frequency component (CF2) covered the range from 57-62 kHz, but was most commonly emitted at frequencies of 59-61 kHz. 4. An increase in the frequency of vocalizations over a number of consecutive pulses towards a steady-state plateau is evident in both spontaneous vocalizations and emissions elicited by microstimulation just above threshold. Increasing the stimulus intensity caused the frequency of emissions to approach the steady state more rapidly. 5. The anterior cingulate cortex appears to be organized topographically for increasing frequency of elicited biosonar sounds along a rostrocaudal axis. The area from which biosonar emissions were elicited was overrepresented for a 2 kHz band of frequencies just below the bats' CF2 resting frequency. Audible vocalizations with a complex spectrum resembling social cries can also be elicited by microstimulation, but only in an area that is adjacent and posterior to the biosonar region. 6. Some examples of both elicited and spontaneous vocalizations contained a relative intensity pattern of the harmonic components which deviated from the typical pattern. This suggests that mustached bats are capable of actively altering the spectrum of their pulses to subserve different tasks in echolocation.     

Neonates' vocal and facial expressions and their changes during experimental playbacks of intra-uterine sounds

The present study was conducted to describe neonates' vocalizations and facial expressions in crying states, and to examine the effects of intra-uterine sounds on neonates' vocal and facial behaviors. Based on 22 h taped data taken from 4 healthy full-term neonates ranging in ages of 10–168 h, a total of 1020 samples of vocalization and their accompanying facial expressions were analyzed, and 12 categories of vocalizations and 8 categories of facial expressions were classified. In the playback experiments, it was shown that presentation of intra-uterine sounds changed the fundamental frequencies of infant cry vocalizations. Furthermore, it was found that the intra-uterine sounds elicited a progenitor of the facial expression of “affection” which mainly occurred accompanying the emission of short and low vocalizations.     

Analysis of control strategies for VIVA OpenHBM with active reflexive neck muscles

Modeling muscle activity in the neck muscles of a finite element (FE) human body model can be based on two biological reflex systems. One approach is to approximate the Vestibulocollic reflex (VCR) function, which maintains the head orientation relative to a fixed reference in space. The second system tries to maintain the head posture relative to the torso, similar to the Cervicocolic reflex (CCR). Strategies to combine these two neck muscle controller approaches in a single head-neck FE model were tested, optimized, and compared to rear-impact volunteer data. The first approach, Combined-Control, assumed that both controllers simultaneously controlled all neck muscle activations. In the second approach, Distributed-Control, one controller was used to regulate activation of the superficial muscles while a different controller acted on deep neck muscles. The results showed that any muscle controller that combined the two approaches was less effective than only using one of VCR- or CCR-based systems on its own. A passive model had the best objective rating for cervical spine kinematics, but the addition of a single active controller provided the best response for both head and cervical spine kinematics. The present study demonstrates the difficulty in completely capturing representative head and cervical spine responses to rear-impact loading and identified a controller capturing the VCR reflex as the best candidate to investigate whiplash injury mechanisms through FE modeling.

     

Reflex muscle contractions can be elicited by valgus positional perturbations of the human knee

Experimental evidence on the reflex responses of thigh muscles to valgus mechanical perturbations at the human knee are presented. Random step positional deflections, ranging from 5 degrees to 12 degrees at 60 degrees /s, were applied to the fully extended knees of seven healthy subjects. Subjects were instructed to maintain a constant background co-activation ( approximately 2-11% MVC) of the quadriceps and hamstring muscles prior to and during the mechanical stimulus. We found that the reflex response to sustained valgus joint deflection in the vasti muscles had longer onset latencies (range: 83-92ms) than did the stretch reflex in the same muscles (latencies: 29-31ms). This reflex EMG response consisted typically of a peak followed by sustained muscle activity throughout the step perturbation. The sustained EMG activity was dependent on the amplitude of the perturbing stimulus, but in a nonlinear manner. The long latency of the valgus response suggests that the reflex originates in nonmuscular sensory pathways, potentially from mechanoreceptors lying in periarticular tissues such as joint ligaments and capsule. Analysis of the spatial distribution of reflex responses showed an asymmetrical pattern with preferential activation of medial vs. lateral muscles of the knee. We assess whether these asymmetric reflex contractions could promote joint stability, either by inducing generalized joint stiffening, or by preferential activation of those muscles that are best suited to resist induced ligament strain.     

Control of echolocation pulses by neurons of the nucleus ambiguus in the rufous horseshoe bat,Rhinolophus rouxi

The vocal motor control of the larynx was studied with single unit recordings from the efferent motor nucleus (nucleus ambiguus) in the CF-FM-bat Rhinolophus rouxi, spontaneously emitting echolocation sounds. The experiments were performed in a stereotaxic apparatus that allowed differentiation of activities in the recorded nucleus depending on the electrode position (Fig. 1). Echolocation calls and respiration activity were monitored simultaneously, thus it was possible to compare the time course of the motor control activity during respiration with and without concurrent vocalization. Unit discharges were classified as laryngeal motoneuron activity according to their correlation with the time course (onset and end) of echolocation calls and their discharge rate as: Pre-off-tonic, pre-off-phasic, off-pauser, off-tonic, on-chopper, on-tonic, prior-tonic and inhibitory (Fig. 4). The on-chopper and on-tonic discharge patterns were assigned to the motor activity of the lateral cricoarytenoid muscle and the off-pauser and off-tonic discharge patterns to the motor activity of the posterior cricoarytenoid muscle controlling the time course of vocal pulses. Motoneuron activities recorded under the condition of systematically shifted frequencies in the emitted echolocation calls were investigated in Doppler-shift compensating bats responding to electronically simulated echoes. Of all neurons classified as motor control, only units of the pre-off-tonic discharge type (cricothyroid muscle) changed their activity with frequency shifts in the vocalized pulses; they showed a positive linear correlation with the emitted sound frequency (Fig. 6). In addition, single unit activities in strict synchronization to vocalization were recorded, that by their low discharge rate were not valid as motor control, and were considered to represent activities of interneurons or internuclear neurons connecting the nucleus ambiguus with other vocalization- and respiration-centers (Fig. 3c). Electric lesions in the brain stem and iontophoretically applied horseradish peroxidase (HRP) served as references for localization and morphological identification of the recording sites in cell stained brain slices.     

Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii.

Pteronotus parnellii uses the second harmonic (61-62 kHz) of the CF component in its orientation sounds for Doppler-shift compensation. The bat's inner ear is mechanically specialized for fine analysis of sounds at about 61-62 kHz. Because of this specialization, cochlear microphonics (CM) evoked by 61-62 kHz tone bursts exhibit prominent transients, slow increase and decrease in amplitude at the onset and cessation of these stimuli. CM-responses to 60-61 kHz tone bursts show a prominent input-output non-linearity and transients. Accordingly, a summated response of primary auditory neurones (N1) appears not only at the onset of the stimuli, but also at the cessation. N1-off is sharply tuned at 60-61 kHz, while N1-on is tuned at 63-64 kHz, which is 2 kHz higher than the best frequency of the auditory system because of the envelope-distortion originating from sharp mechanical tuning. Single peripheral neurones sensitive to 61-62 kHz sounds have an unusually sharp tuning curve and show phase-locked responses to beats of up to 3 kHz. Information about the frequencies of Doppler-shifted echoes is thus coded by a set of sharply tuned neurones and also discharges phase-locked to beats. Neurones with a best frequency between 55 and 64 kHz show not only tonic on-responses but also off-responses which are apparently related to the mechanical off-transient occuring in the inner ear and not to a rebound from neural inhibition.