155 research outputs found
Timescale-invariant representation of acoustic communication signals by a bursting neuron
No full textAcoustic communication often involves complex sound motifs in which the relative durations of individual elements, but not their absolute durations, convey meaning. Decoding such signals requires an explicit or implicit calculation of the ratios between time intervals. Using grasshopper communication as a model, we demonstrate how this seemingly difficult computation can be solved in real time by a small set of auditory neurons. One of these cells, an ascending interneuron, generates bursts of action potentials in response to the rhythmic syllable-pause structure of grasshopper calls. Our data show that these bursts are preferentially triggered at syllable onset; the number of spikes within the burst is linearly correlated with the duration of the preceding pause. Integrating the number of spikes over a fixed time window therefore leads to a total spike count that reflects the characteristic syllable-to-pause ratio of the species while being invariant to playing back the call faster or slower. Such a timescale-invariant recognition is essential under natural conditions, because grasshoppers do not thermoregulate; the call of a sender sitting in the shade will be slower than that of a grasshopper in the sun. Our results show that timescale-invariant stimulus recognition can be implemented at the single-cell level without directly calculating the ratio between pulse and interpulse durations
A species-specific frequency filter through specific inhibition, not specific excitation
No full textMany bushcrickets produce specific song spectra for acoustic communication. Song detection and/or recognition may make use of such specificity. Where in the nervous system are the filters for song frequency situated? A peripheral tuning for song frequency typically does not exist. Auditory receptor cells of bushcrickets connect to local and ascending neurons in the prothoracic ganglion. One of the ascending neurons (1) may function as a frequency filter in a group of four related bushcrickets (genera Ancistrura, Barbitistes). The frequency response of ascending neuron 1 is species-specific roughly corresponding to the frequency of the conspecific male song. The species-specific tuning of the neuron is not brought about by specific excitation, but by specific inhibition. By eliminating this frequency-dependent and species-specific inhibition the former filter neuron is transformed into an unspecific broad-band neuron in all four species. Its tuning then does not differ from omega neuron 1, a local neuron which is rather unspecific for frequency. Also, the supra-threshold responses of ascending neuron 1, which are different in intact animals, are similar to each other and similar to omega neuron 1 following elimination of inhibition. Only ascending neuron I of Ancistrura retains some species-specific features at low frequencies. In conclusion, evolution changed inhibition, not excitation of a species-specific neuron
Songs and the function of song elements in four duetting bushcricket species (ensifera, phaneropteridae, Barbitistes)
No full textThe structure of male songs and the timing of female replies with respect to the male songs are described for four species of the palaearctic bushcricket genus Barbitistes (B. constrictus, B. ocskayi, B. serricauda, B. yersini). In a male song, 3 to 16 syllables form a chirp followed by a "trigger syllable" after a longer interval. The trigger syllable releases a female reply with a latency of 30 to 50 ms in all four species. In B. serricauda songs, there is no clearly separated trigger syllable. Instead, the first syllable of a chirp functions as a trigger syllable. Some B. serricauda males may produce a short female-type syllable just at the moment, when a female would reply. The possible function of such a syllable is acoustical mimicry. When comparing at least two song parameters, each species occupies a specific combination of values. According to the overlap of parameters a close phylogenetic relationship between B. constrictus and B. serricauda and between B. ocskayi and B. yersini is assumed. This interpretation is compared with a hypothesis based on morphological investigations
Evolution and function of auditory systems in insects
No full textWhile the sensing of substrate vibrations is common among arthropods, the reception of sound pressure waves is an adaptation restricted to insects, which has arisen independently several times in different orders. Wherever studied, tympanal organs were shown to derive from chordotonal precursors, which were modified such that mechanosensitive scolopidia became attached to thin cuticular membranes backed by air-filled tracheal cavities (except in lacewings). The behavioural context in which hearing has evolved has strongly determined the design and properties of the auditory system. Hearing organs which have evolved in the context of predator avoidance are highly sensitive, preferentially in a broad range of ultrasound frequencies, which release rapid escape manoeuvres. Hearing in the context of communication does not only require recognition and discrimination of highly specific song patterns but also their localisation. Typically, the spectrum of the conspecific signals matches the best sensitivity of the receiver. Directionality is achieved by means of sophisticated peripheral structures and is further enhanced by neuronal processing. Side-specific gain control typically allows the insect to encode the loudest signal on each side. The filtered information is transmitted to the brain, where the final steps of pattern recognition and localisation occur. The outputs of such filter networks, modulated or gated by further processes (subsumed by the term motivation), trigger command neurones for specific behaviours. Altogether, the many improvements opportunistically evolved at any stage of acoustic information-processing ultimately allow insects to come up with astonishing acoustic performances similar to those achieved by vertebrates
Evolution and function of auditory systems in insects
No full textWhile the sensing of substrate vibrations is common among arthropods, the reception of sound pressure waves is an adaptation restricted to insects, which has arisen independently several times in different orders. Wherever studied, tympanal organs were shown to derive from chordotonal precursors, which were modified such that mechanosensitive scolopidia became attached to thin cuticular membranes backed by air-filled tracheal cavities (except in lacewings). The behavioural context in which hearing has evolved has strongly determined the design and properties of the auditory system. Hearing organs which have evolved in the context of predator avoidance are highly sensitive, preferentially in a broad range of ultrasound frequencies, which release rapid escape manoeuvres. Hearing in the context of communication does not only require recognition and discrimination of highly specific song patterns but also their localisation. Typically, the spectrum of the conspecific signals matches the best sensitivity of the receiver. Directionality is achieved by means of sophisticated peripheral structures and is further enhanced by neuronal processing. Side-specific gain control typically allows the insect to encode the loudest signal on each side. The filtered information is transmitted to the brain, where the final steps of pattern recognition and localisation occur. The outputs of such filter networks, modulated or gated by further processes (subsumed by the term motivation), trigger command neurones for specific behaviours. Altogether, the many improvements opportunistically evolved at any stage of acoustic information-processing ultimately allow insects to come up with astonishing acoustic performances similar to those achieved by vertebrates
Sex-specific spectral tuning for the partner's song in the duetting bushcricket Ancistrura nigrovittata (Orthoptera: Phaneropteridae)
No full textThe song of the male bushcricket Ancistrura nigrovittata consists of a sequence of verses. Each verse comprises a syllable group, plus, after about 400 ms a single syllable serving as a trigger for the female response song. The carrier frequency of the male song spectrum peaks at around 15 kHz, while the female song peaks at around 27 kHz. The thresholds of female responses to models of male songs are lowest for song frequencies between 12 and 16 kHz and therefore correspond to the male song spectrum. The threshold curve of the female response to the trigger syllable at different frequencies has the same shape as the tuning for the syllable group. Phonotactic thresholds of male Ancistrura nigrovittata to synthetic female responses at different frequencies are lowest between 24 and 28 kHz and thereby correspond to the female song spectrum and clearly differ from female response thresholds. Activity of the tympanic fibre bundle of both sexes is most sensitive between 15 and 35 kHz and therefore not specifically tuned to the partner's song. Individual behavioural thresholds have their minimum within 10 dB of the values of tympanic thresholds
Processing of ultrasound in a bush cricket's brain
No full textThe processing and categorization of conspecific and heterospecific acoustic signals is an important task of the central nervous system. In orthopteran species, carrier frequency (besides temporal cues) is one of the major discriminators. In the bush cricket species Ancistrura nigrovittata Brunner von Wattenwyl (Phaneropteridae, Barbitistini), ultrasound has potentially different meanings and may elicit vastly different behaviours depending on the context it is perceived in. In the present study, data are presented of the morphology and neuronal responses of three local brain neurones (LBNs) that respond best to ultrasound. All neurones show dense arborizations in the lateral protocerebrum, where ascending interneurones terminate. The LBN2 and LBN9 neurones are entirely restricted to one side of the brain, whereas LBN5 crosses the midline, thereby linking both hemispheres. The response maxima for LBN2 overlap closely with the peak carrier frequencies found in a species-specific duet, which consists of sonic (16 kHz, male), as well as ultrasonic (2428 kHz, female) sound. By contrast, LBN9 responds only to ultrasound in the range of the female reply, whereas the male song induces exceptionally long-lasting inhibition. The LBN5 neurone shows strongest spike activity to a broad range of ultrasonic frequencies, as long as the pulse duration remains short. All three brain neurones respond to ultrasound in a unique way and may be involved in the shaping of different behavioural outcomes
GABA-like immunoreactivity suggests an inhibitory function of the thoracic low-frequency neuron (TN1) in acridid grasshoppers
No full textA new biophysical method to determine the gain of the acoustic trachea in bushcrickets
No full textA method is described for measuring the gain (i.e., the change of amplitude and phase angle) for sounds that propagate to the internal surface of the tympana in ears working as pressure difference receivers. The gain of the acoustic trachea has been measured in two similarly sized and closely related species of bushcrickets, in which the acoustic spiracles and tracheae differ markedly in size. The amplitude part of the gain is much larger in the species with the larger acoustic spiracle, whereas the phase part is very similar in the two species. The method is compared with other methods, which in the past have been used for estimating the gain of sound pathways inside animal bodies
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