Tonotopic Ca2+ dynamics and sound processing in auditory interneurons of the bush-cricket Mecopoda elongata.

Two auditory neurons, TN-1 and ON-1, in the bush-cricket, Mecopoda elongata, have large dendritic arborisations which receive excitatory synaptic inputs from tonotopically organised axonal terminals of auditory afferents in the prothoracic ganglion. By combining intracellular microelectrode recording with calcium imaging we demonstrate that the dendrites of both neurons show a clear Ca2+ signal in response to broad-frequency species-specific chirps. Due to the organisation of the afferents frequency specific auditory activation should lead to local Ca2+ increases in their dendrites. In response to 20 ms sound pulses the dendrites of both neurons showed tonotopically organised Ca2+ increases. In ON-1 we found no evidence for a tonotopic organisation of the Ca2+ signal related to axonal spike activity or for a Ca2+ response related to contralateral inhibition. The tonotopic organisation of the afferents may facilitate frequency-specific adaptation in these auditory neurons through localised Ca2+ increases in their dendrites. By combining 10 and 40 kHz test pulses and adaptation series, we provide evidence for frequency-specific adaptation in TN-1 and ON-1. By reversible deactivating of the auditory afferents and removing contralateral inhibition, we show that in ON-1 spike activity and Ca2+ responses increased but frequency-specific adaptation was not evident.

Phonotactic steering and representation of directional information in the ascending auditory pathway of a cricket.

Directional hearing is crucial for animals depending on acoustic signals to locate a mate. We focused on crickets to explore the reliability of directional information forwarded to the brain by the ascending auditory interneuron AN1, which is crucial for phonotactic behavior. We presented calling song from -45° to +45° in steps of 3° and compared the phonotactic steering of females walking on a trackball with the directional responses of AN1. Forty percent of females showed good steering behavior and changed their walking direction when the speaker passed the body's longitudinal axis. The bilateral latency difference between right and left AN1 responses was small and may not be reliable for auditory steering. In respect to spike count, all AN1 recordings presented significant bilateral differences for angles larger than ±18°, yet 35% showed a mean significant difference of 1-3 action potentials per chirp when the frontal stimulus deviated by 3° from their length axis. For small angles, some females had a very similar AN1 activity forwarded to the brain, but the accuracy of their steering behavior was substantially different. Our results indicate a correlation between directional steering and the response strength of AN1, especially for large angles. The reliable steering of animals at small angles would have to be based on small bilateral differences of AN1 activity, if AN1 is the only source providing directional information. We discuss whether such bilateral response difference at small angles can provide a reliable measure to generate auditory steering commands descending from the brain, as pattern recognition is intensity independent.NEW & NOTEWORTHY The ascending auditory interneuron AN1 has been implicated in cricket auditory steering, but at small acoustic stimulation angles, it does not provide reliable directional information. We conclude that either the small bilateral auditory activity differences of the AN1 neurons are enhanced to generate reliable descending steering commands or, more likely, directional auditory steering is mediated via a thoracic pathway, as indicated by the reactive steering hypothesis.

Substrate texture affects female cricket walking response to male calling song.

Field crickets are extensively used as a model organism to study female phonotactic walking behaviour, i.e. their attraction to the male calling song. Laboratory-based phonotaxis experiments generally rely on arena or trackball-based settings; however, no attention has been paid to the effect of substrate texture on the response. Here, we tested phonotaxis in female Gryllus bimaculatus, walking on trackballs machined from methyl-methacrylate foam with different cell sizes. Surface height variations of the trackballs, due to the cellular composition of the material, were measured with profilometry and characterized as smooth, medium or rough, with roughness amplitudes of 7.3, 16 and 180 µm. Female phonotaxis was best on a rough and medium trackball surface, a smooth surface resulted in a significant lower phonotactic response. Claws of the cricket foot were crucial for effective walking. Females insert their claws into the surface pores to allow mechanical interlocking with the substrate texture and a high degree of attachment, which cannot be established on smooth surfaces. These findings provide insight to the biomechanical basis of insect walking and may inform behavioural studies that the surface texture on which walking insects are tested is crucial for the resulting behavioural response.

Processing of species-specific auditory patterns in the cricket brain by ascending, local, and descending neurons during standing and walking.

The recognition of the male calling song is essential for phonotaxis in female crickets. We investigated the responses toward different models of song patterns by ascending, local, and descending neurons in the brain of standing and walking crickets. We describe results for two ascending, three local, and two descending interneurons. Characteristic dendritic and axonal arborizations of the local and descending neurons indicate a flow of auditory information from the ascending interneurons toward the lateral accessory lobes and point toward the relevance of this brain region for cricket phonotaxis. Two aspects of auditory processing were studied: the tuning of interneuron activity to pulse repetition rate and the precision of pattern copying. Whereas ascending neurons exhibited weak, low-pass properties, local neurons showed both low- and band-pass properties, and descending neurons represented clear band-pass filters. Accurate copying of single pulses was found at all three levels of the auditory pathway. Animals were walking on a trackball, which allowed an assessment of the effect that walking has on auditory processing. During walking, all neurons were additionally activated, and in most neurons, the spike rate was correlated to walking velocity. The number of spikes elicited by a chirp increased with walking only in ascending neurons, whereas the peak instantaneous spike rate of the auditory responses increased on all levels of the processing pathway. Extra spiking activity resulted in a somewhat degraded copying of the pulse pattern in most neurons.

Front leg movements and tibial motoneurons underlying auditory steering in the cricket (Gryllus bimaculatus deGeer).

Front leg movements in the cricket (Gryllus bimaculatus) were measured during phonotactic steering on a trackball together with electromyogram recordings of the tibial extensor and flexor muscles. Up-down leg movements clearly indicated the step cycle and were independent of auditory stimulation. By contrast, left-right movements of the front leg were dependent on sound direction, with crickets performing rapid steering leg movements towards the active speaker. Steering movements were dependent on the phase of sound relative to the step cycle, and were greatest for sounds occurring during the swing phase. During phonotaxis the slow extensor tibiae motoneuron responded to ipsilateral sounds with a latency of 35-40 ms, whereas the fast flexor tibiae motoneurons were excited by contralateral sound. We made intracellular recordings of two tibial extensor and at least eight flexor motoneurons. The fast extensor tibiae, the slow extensor tibiae and one fast flexor tibiae motoneurons were individually identifiable, but a group of at least four fast flexor tibiae as well as at least three slow flexor tibiae motoneurons of highly similar morphology could not be distinguished. Motoneurons received descending inputs from cephalic ganglia and from local prothoracic networks. There was no overlap between the dendritic fields of the tibial motoneurons and the auditory neuropile. They did not respond to auditory stimulation at rest. Neither extracellular stimulation of descending pathways nor pharmacological activation of prothoracic motor networks changed the auditory responsiveness. Therefore, any auditory input to tibial motoneurons is likely to be indirect, possibly via the brain.

Neurite-specific Ca2+ dynamics underlying sound processing in an auditory interneurone.

Concepts on neuronal signal processing and integration at a cellular and subcellular level are driven by recording techniques and model systems available. The cricket CNS with the omega-1-neurone (ON1) provides a model system for auditory pattern recognition and directional processing. Exploiting ON1's planar structure we simultaneously imaged free intracellular Ca(2+) at both input and output neurites and recorded the membrane potential in vivo during acoustic stimulation. In response to a single sound pulse the rate of Ca(2+) rise followed the onset spike rate of ON1, while the final Ca(2+) level depended on the mean spike rate. Ca(2+) rapidly increased in both dendritic and axonal arborizations and only gradually in the axon and the cell body. Ca(2+) levels were particularly high at the spike-generating zone. Through the activation of a Ca(2+)-sensitive K(+) current this may exhibit a specific control over the cell's electrical response properties. In all cellular compartments presentation of species-specific calling song caused distinct oscillations of the Ca(2+) level in the chirp rhythm, but not the faster syllable rhythm. The Ca(2+)-mediated hyperpolarization of ON1 suppressed background spike activity between chirps, acting as a noise filter. During directional auditory processing, the functional interaction of Ca(2+)-mediated inhibition and contralateral synaptic inhibition was demonstrated. Upon stimulation with different sound frequencies, the dendrites, but not the axonal arborizations, demonstrated a tonotopic response profile. This mirrored the dominance of the species-specific carrier frequency and resulted in spatial filtering of high frequency auditory inputs.

Mechanisms underlying phonotactic steering in the cricket Gryllus bimaculatus revealed with a fast trackball system.

Phonotactic steering behaviour of the cricket G. bimaculatus was analysed with a new highly sensitive trackball system providing a spatial and temporal resolution of 127 microm and 0.3 ms, respectively. Orientation to artificial calling songs started at 45 dB SPL, it increased up to 75 dB SPL and then saturated. When exposed to two identical patterns of different intensity, crickets significantly steered towards the louder sound pattern, whenever the intensity difference was greater than 1 dB. Bilateral latency differences in sound presentation did not always cause clear orientation towards the leading side. The overall walking direction depended on the number of sound pulses perceived from the left or right side with the animals turning towards the side providing the larger number of pulses. The recordings demonstrated rapid changes in walking direction performed even during a chirp. These rapid steering responses occurred with a latency of 55-60 ms, well before the central nervous system had time to evaluate the temporal structure of a whole chirp. When every other sound pulse was presented from opposite directions, the crickets followed the temporal pattern of sound presentation and rapidly steered towards the left and right side. Steering towards individual sound pulses does not agree with the proposal that crickets analyse the quality of sound patterns and then steer towards the better pattern. Rather, these experiments suggest that fast steering to single sound pulses determines the lateral deviation of the animals and that complex auditory orientation emerges from this simple mechanism of auditory steering.

Temporal pattern recognition based on instantaneous spike rate coding in a simple auditory system.

Auditory pattern recognition by the CNS is a fundamental process in acoustic communication. Because crickets communicate with stereotyped patterns of constant frequency syllables, they are established models to investigate the neuronal mechanisms of auditory pattern recognition. Here we provide evidence that for the neural processing of amplitude-modulated sounds, the instantaneous spike rate rather than the time-averaged neural activity is the appropriate coding principle by comparing both coding parameters in a thoracic interneuron (Omega neuron ON1) of the cricket (Gryllus bimaculatus) auditory system. When stimulated with different temporal sound patterns, the analysis of the instantaneous spike rate demonstrates that the neuron acts as a low-pass filter for syllable patterns. The instantaneous spike rate is low at high syllable rates, but prominent peaks in the instantaneous spike rate are generated as the syllable rate resembles that of the species-specific pattern. The occurrence and repetition rate of these peaks in the neuronal discharge are sufficient to explain temporal filtering in the cricket auditory pathway as they closely match the tuning of phonotactic behavior to different sound patterns. Thus temporal filtering or "pattern recognition" occurs at an early stage in the auditory pathway.

A corollary discharge mechanism modulates central auditory processing in singing crickets.

Crickets communicate using loud (100 dB SPL) sound signals that could adversely affect their own auditory system. To examine how they cope with this self-generated acoustic stimulation, intracellular recordings were made from auditory afferent neurons and an identified auditory interneuron-the Omega 1 neuron (ON1)-during pharmacologically elicited singing (stridulation). During sonorous stridulation, the auditory afferents and ON1 responded with bursts of spikes to the crickets' own song. When the crickets were stridulating silently, after one wing had been removed, only a few spikes were recorded in the afferents and ON1. Primary afferent depolarizations (PADs) occurred in the terminals of the auditory afferents, and inhibitory postsynaptic potentials (IPSPs) were apparent in ON1. The PADs and IPSPs were composed of many summed, small-amplitude potentials that occurred at a rate of about 230 Hz. The PADs and the IPSPs started during the closing wing movement and peaked in amplitude during the subsequent opening wing movement. As a consequence, during silent stridulation, ON1's response to acoustic stimuli was maximally inhibited during wing opening. Inhibition coincides with the time when ON1 would otherwise be most strongly excited by self-generated sounds in a sonorously stridulating cricket. The PADs and the IPSPs persisted in fictively stridulating crickets whose ventral nerve cord had been isolated from muscles and sense organs. This strongly suggests that the inhibition of the auditory pathway is the result of a corollary discharge from the stridulation motor network. The central inhibition was mimicked by hyperpolarizing current injection into ON1 while it was responding to a 100 dB SPL sound pulse. This suppressed its spiking response to the acoustic stimulus and maintained its response to subsequent, quieter stimuli. The corollary discharge therefore prevents auditory desensitization in stridulating crickets and allows the animals to respond to external acoustic signals during the production of calling song.

Tympanic membrane oscillations and auditory receptor activity in the stridulating cricket Gryllus bimaculatus.

The ears of stridulating crickets are exposed to loud self-generated sounds that might desensitise the auditory system and reduce its responsiveness to environmental sounds. We examined whether crickets prevent self-induced auditory desensitisation, and measured the responsiveness of the peripheral auditory system of the cricket (acoustic spiracle, tympanic membrane and tympanic nerve) during pharmacologically induced sonorous (two-winged) and silent (one-winged) stridulation. The acoustic spiracles remained open during stridulation, so the self-generated auditory signal had full access to both the external side and the internal side of the tympanic membrane. When the spiracles shut in resting crickets, the responsiveness of the tympanic membrane to acoustic stimuli varied according to the phase of ventilation and was minimal during expiration. The tympanic membrane oscillated in phase with the self-generated sounds during sonorous chirps and did not oscillate during silent chirps. In both sonorously and silently singing crickets, the responses of the tympanic membrane to acoustic stimuli were identical during the chirps and the chirp intervals. Bursts of activity were recorded in the tympanic nerve during sonorous chirps; however, activity was minor during silent chirps. In sonorously and in silently singing crickets, the summed nerve response to acoustic stimuli in the chirp intervals was the same as in resting crickets. The response to stimuli presented during the syllable intervals of sonorous chirps was slightly reduced compared with the response in the chirp intervals as a consequence of receptor habituation. In silently singing crickets, acoustic stimuli elicited the same summed nerve response during chirps and chirp intervals. These data indicate that in the cricket no specific mechanism acts to reduce the responsiveness of the peripheral auditory pathway during stridulation.

A highly sensitive opto-electronic system for the measurement of movements.

An opto-electronic system has been developed to measure movements of insect appendages. It is made from a mirror-lens and a linear position-sensitive photodiode. The design of the mirror-lens has been exploited to axially mount a high intensity halogen light source in front of the mirror-lens. The system monitors a reflective marker which is attached to the moving object. Upon illumination by the light source the reflected light is picked up by the optical system and is focussed on the diode. The diode provides a voltage output proportional to the distribution of the light on it's surface. Since the marker is the brightest spot in the image the output of the system corresponds to the position of the marker. At a working distance of 80 cm appendage movements with amplitudes from 10 microm to 20 mm peak-peak amplitude can be recorded. The system accurately detects movements ranging from slow positional changes to 5 kHz oscillations. Currently it used to measure the stridulatory wing movements of crickets but may be applied to a variety of movement recordings.

Control of cricket stridulation by a command neuron: efficacy depends on the behavioral state.

Crickets use different song patterns for acoustic communication. The stridulatory pattern-generating networks are housed within the thoracic ganglia but are controlled by the brain. This descending control of stridulation was identified by intracellular recordings and stainings of brain neurons. Its impact on the generation of calling song was analyzed both in resting and stridulating crickets and during cercal wind stimulation, which impaired the stridulatory movements and caused transient silencing reactions. A descending interneuron in the brain serves as a command neuron for calling-song stridulation. The neuron has a dorsal soma position, anterior dendritic processes, and an axon that descends in the contralateral connective. The neuron is present in each side of the CNS. It is not activated in resting crickets. Intracellular depolarization of the interneuron so that its spike frequency is increased to 60-80 spikes/s reliably elicits calling-song stridulation. The spike frequency is modulated slightly in the chirp cycle with the maximum activity in phase with each chirp. There is a high positive correlation between the chirp repetition rate and the interneuron's spike frequency. Only a very weak correlation, however, exists between the syllable repetition rate and the interneuron activity. The effectiveness of the command neuron depends on the activity state of the cricket. In resting crickets, experimentally evoked short bursts of action potentials elicit only incomplete calling-song chirps. In crickets that previously had stridulated during the experiment, short elicitation of interneuron activity can trigger sustained calling songs during which the interneuron exhibits a spike frequency of approximately 30 spikes/s. During sustained calling songs, the command neuron activity is necessary to maintain the stridulatory behavior. Inhibition of the interneuron stops stridulation. A transient increase in the spike frequency of the interneuron speeds up the chirp rate and thereby resets the timing of the chirp pattern generator. The interneuron also is excited by cercal wind stimulation. Cercal wind stimulation can impair the pattern of chirp and syllable generation, but these changes are not reflected in the discharge pattern of the command neuron. During wind-evoked silencing reactions, the activity of the calling-song command neuron remains unchanged, but under these conditions, its activity is no longer sufficient to maintain stridulation. Therefore stridulation can be suppressed by cercal inputs from the terminal ganglia without directly inhibiting the descending command activity.

[Therapy of headaches in childhood and adolescence]. / Kopfschmerztherapie im Kindes- und Jugendalter.

BACKGROUND: Headaches are one of the most common health problems of children and adolescents, afflicting between 50-90% of the pediatric population in some form sometimes during their first two decades of life. Due to changing prevalence rates, more or less complex classification systems, inconsistent therapy responses with great inter- and intraindividual variabilities and high placebo response rates, pediatric headache syndromes are frequently thought to be too difficult for the outpatient evaluation and treatment in clinical practice. THERAPY AND PROGNOSIS: However, with the introduction of the International Headache Society classification system, the continuously expanding knowledge about the pathophysiology of different headache syndromes and the development of new symptomatic as well as causative treatment options - covering both: pharmacologic and non-pharmacologic approaches - a pragmatic diagnostic work up and the development of specific treatment schedules for pediatric headache patients is now possible.

Neurochemical control of cricket stridulation revealed by pharmacological microinjections into the brain.

Neuroactive substances were administered into the frontal protocerebrum of tethered male Gryllus bimaculatus by pressure injections from microcapillaries. All three types of species-specific song pattern (calling song, rivalry song and courtship song) could be elicited by injection of acetylcholine and cholinergic agonists. Injection of nicotine led to short bouts of calling song that occurred after a short latency. In contrast, muscarine elicited long-lasting stridulation that took longer to develop. The pharmacologically induced song patterns showed transitions from rivalry song to calling song and from calling song to courtship song, which also occur during natural behaviour. Stridulation induced by a cholinergic agonist could be immediately blocked by microinjection of (&ggr;)-aminobutyric acid (GABA) into the same neuropile sites. Administration of picrotoxin in resting crickets led to enhanced motor activity that incorporated the three different song patterns. We propose that, in the brain of the cricket, acetylcholine and GABA are putative transmitters involved in the control of stridulation. Histological analysis located the stimulation sites to an area between the pedunculus and the (&agr;)-lobe of the mushroom body in which the command neurons for calling song have dendritic arborizations.

Forewing movements and intracellular motoneurone stimulation in tethered flying locusts

A new optoelectronic method was used for the measurement of wing movements in tethered flying locusts. The method is based on laser light coupled into a highly flexible optical fibre fastened to a forewing. A dual-axis position-sensing photodiode, aligned to the wing hinge, revealed the flapping, i.e. up-down movement, and lagging, i.e. forward-backward movement, of the wingtip as indicated by the emitted light. Measurements were combined with electromyographic recordings from flight muscles and with intracellular recording and stimulation of flight motoneurones. Compared with muscle recordings, intracellular recordings showed an increase in the variability of motoneurone activity. Stimulation of flight motoneurones reliably caused distinct effects on wing movements. Inhibition of elevator (MN83, MN89) activity led to a decrease in the amplitude of the upstroke. Inhibition of depressor (MN97) activity reduced the amplitude of the downstroke and sometimes stopped flight behaviour. An increase in MN97 activity caused a reduction in the extent of the upward movement and prolonged the flight cycle.

Cholinergic activation of stridulatory behaviour in the grasshopper Omocestus viridulus (L.)

When acetylcholine (ACh) and its agonists are injected into neuropile regions of the protocerebrum and the suboesophageal ganglion of male and female grasshoppers of the species Omocestus viridulus (L.), they elicit stridulation in a pattern no different from that of natural song. Stridulation can even be evoked in mated females which normally do not sing. By choosing suitable ACh agonists, nicotinic and muscarinic ACh receptors can be activated selectively. Activation of nicotinic ACh receptors produces individual song sequences with rapid onset; the stridulation induced by activation of the muscarinic ACh receptors begins after a longer latency, increases slowly in intensity and is maintained for many minutes. The sites within the cephalic ganglia where song can be initiated pharmacologically coincide with regions in which descending stridulatory command neurones arborize.

Presynaptic inhibition of sensory neurons during kicking movements in the locust.

1. Locusts use a distinctive motor pattern to extend the tibia of a hind leg rapidly in a defensive kick, or to extend the tibiae of both hind legs in a jump. The force for the movement is generated by an almost isometric co-contraction of the extensor and flexor tibiae muscles followed by a sudden release of the stored energy when the flexor motor neurons are inhibited. A proprioceptor (the femoral chordotonal organ) spans the femorotibial joint, and at least 50 of its sensory neurons each signal particular features of its movements. Intracellular recordings from these neurons close to their terminals in the CNS show that their spikes during kicking are superimposed on a depolarizing synaptic input generated near their output terminals. The depolarization is linked to the time in the motor pattern when the sensory neurons spike. 2. Flexion-sensitive neurons spike and their terminals are depolarized when the tibia is initially flexed and when the tibia rebounds from the rapid extension of the kick. Some respond phasically, others more tonically and over different ranges of joint angles, but all receive a depolarizing synaptic input when they spike. The depolarization of the terminals precedes the spikes and often occurs concurrently with the changes in the membrane potentials of the motor neurons. The input persists while the tibia is held fully flexed before the kick. 3. Extension-sensitive neurons spike and their terminals are depolarized when the tibia is rapidly extended and this depolarization may outlast the spikes at the completion of a kick. Some of these depolarizing synaptic potentials occur before the movement starts, which suggests that they may result from central elements of the motor pattern; others however are clearly consequent upon joint movements. During the co-contraction that precedes the movement, these neurons do not spike and their membrane potential repolarizes because of a reduction in the synaptic input. 4. The depolarizing synaptic potentials are associated with a fall in the resistance of the membrane and may be attributed to the same gamma-aminobutyric acid-mediated mechanism already identified at the terminals of these sensory neurons. The effect and timing of the depolarization of the terminals during this voluntary movement should be to reduce the effectiveness of the sensory neurons in transmitting signals to their postsynaptic neurons in the CNS. This could therefore be part of a mechanism that allows voluntary movements to proceed in the presence of self-generated sensory feedback which might otherwise impede that movement.

Interneurones involved in stridulatory pattern generation in the grasshopper Chorthippus mollis (Charp.)

In tethered grasshoppers, Chorthippus mollis, stridulatory leg movements were elicited by d.c. brain stimulation. Stridulatory chirps comprise both slow up-and-down movements and rapid oscillations of the hindlegs. Intracellular recording, stimulation and staining of interneurones within the metathoracic ganglion complex were performed simultaneously with recordings of leg movement. Five interneurones were identified in the metathoracic ganglion complex. The branching patterns of these interneurones were typical of stridulatory interneurones. Three of these neurones had a structure very similar to stridulatory interneurones already characterized in the species Omocestus viridulus. During stridulation, the spike activity of all interneurones was phasically coupled to the chirp rhythm; two interneurones additionally exhibited coupling to the rapid leg oscillations. Intracellular stimulation of interneurones A1-AC-2 and A1-AI-1 prolonged the duration of the rapid leg oscillations and influenced the generation of the chirp rhythm. Interneurones T3-LI-2 and T3-LC-4 decreased the amplitude of the slow up-and-down movement. The data indicate that at least part of the metathoracic stridulatory network of C. mollis is organized in a structurally and functionally similar way to that of O. viridulus.

The influence of tracheal pressure changes on the responses of the tympanal membrane and auditory receptors in the locust Locusta migratoria L.

In resting tethered locusts, the effect of slow changes in tracheal air pressure on peripheral auditory information processing was analysed. The tympanal membrane vibrations, the pressure inside the tracheal system and the summed activity of the auditory receptors were measured simultaneously. With the membrane in the resting position, laser vibrometry and Fast Fourier Transformation analysis of sound-induced membrane vibrations demonstrated characteristic power spectra at the attachment sites of the high-frequency and low-frequency receptors. The spectra were different above 9 kHz, but very similar in the range 2­9 kHz. During ventilation, tracheal pressure changed between -500 and 1500 Pa. This caused tympanal membrane peak-to-peak displacements in the range 70­90 µm outwards and 20­30 µm inwards, as measured by means of laser interferometry. For a quantitative analysis, sinusoidal tympanal membrane displacements with amplitudes such as those during natural ventilation could be induced by applying pressure to the tracheal system. There was a sigmoid relationship between the tracheal pressure and the corresponding membrane displacement. Outward displacements of the tympanal membrane at the attachment site of the elevated process (a-cells) attenuated sound-induced membrane vibrations in the ranges 2­10 kHz and 14­22 kHz and increased them in the ranges 10­14 kHz and 22­25 kHz. At the pyriform vesicle (d-cells), the vibration sensitivity was reduced in the frequency range 2­14 kHz. Sensitivity was enhanced in the range 14­25 kHz. As a consequence, the detection of acoustic signals was also influenced at the auditory receptor level. Tympanal membrane displacements during acoustic stimulation with 4 kHz sound pulses decreased the summed receptor response by approximately 15 dB. At 16 kHz, an increase of the response equivalent to 7 dB occurred. The effect on the response to white noise was intermediate.