Hitting the right note at the right time: Circadian control of audibility in Anopheles mosquito mating swarms is mediated by flight tones

By beating their wings faster around sunset, male Anopheles mosquitoes sensitize their auditory system to female flight tones.

Forward masking in a bottlenose dolphin Tursiops truncatus : Dependence on azimuthal positions of the masker and test sources

Forward masking was investigated by the auditory evoked potentials (AEP) method in a bottlenose dolphin Tursiops truncatus using stimulation by two successive acoustic pulses (the masker and test) projected from spatially separated sources. The positions of the two sound sources either coincided with or were symmetrical relative to the head axis at azimuths from 0 to ±90°. AEPs were recorded either from the vertex or from the lateral head surface next to the auditory meatus. In the last case, the test source was ipsilateral to the recording side, whereas the masker source was either ipsi- or contralateral. For lateral recording, AEP release from masking (recovery) was slower for the ipsi- than for the contralateral masker source position. For vertex recording, AEP recovery was equal both for the coinciding positions of the masker and test sources and for their symmetrical positions relative to the head axis. The data indicate that at higher levels of the auditory system of the dolphin, binaural convergence makes the forward masking nearly equal for ipsi- and contralateral positions of the masker and test.

The Rare Cry For Help: First Record of An Agonistic Call From A Snake In South America

Discussions about auditory systems and sound dynamics in snakes are frequent. The known frequency of sounds produced by snakes ranges from 0.2 - 7.5 KHz, ranging from imperceptible sounds to humans to audible and observable squeaks. The hiss and whistles are the most common sound and are not considered vocalizations. During a nocturnal survey on June 13, 2021, in the northern Brazilian Amazon, we observed the first record of vocalization in a South American snake. Emitted by the individual from Dipsas catesbyi has a duration of 0.06 seconds, reaching 3036 Hz in its peak frequency, with an amplitude of 2761 to 4152 Hz of frequency in its main emission. Vocalizations were made during the exhalation of air through the larynx. The modulation differs from all patterns observed for snakes resembling the agonistic call of anuran amphibians, which could characterize an evolutionary mimicry of this behavior. Vocal emission via the larynx can generate internal vibrations perceptible to the auditory system of snakes, which, when vocalizing, vibrate the laryngeal cartilage and vocal cord. Our hypothesis is that structured vocal emission through laryngeal air exhalation may be a characteristic shared by other species of the Colubridae family.

Molecular and Clinical Significance of Fibroblast Growth Factor 2 in Development and Regeneration of the Auditory System

The fibroblast growth factor 2 (FGF2) is a member of the FGF family which is involved in key biological processes including development, cellular proliferation, wound healing, and angiogenesis. Although the utility of the FGF family as therapeutic agents has attracted attention, and FGF2 has been studied in several clinical contexts, there remains an incomplete understanding of the molecular and clinical function of FGF2 in the auditory system. In this review, we highlight the role of FGF2 in inner ear development and hearing protection and present relevant clinical studies for tympanic membrane (TM) repair. We conclude by discussing the future implications of FGF2 as a potential therapeutic agent.

Detecting Noise-Induced Cochlear Synaptopathy by Auditory Brainstem Response in Tinnitus Patients With Normal Hearing Thresholds: A Meta-Analysis

Noise-induced cochlear synaptopathy (CS) is defined as a permanent loss of synapses in the auditory nerve pathway following noise exposure. Several studies using auditory brainstem response (ABR) have indicated the presence of CS and increased central gain in tinnitus patients with normal hearing thresholds (TNHT), but the results were inconsistent. This meta-analysis aimed to review the evidence of CS and its pathological changes in the central auditory system in TNHT. Published studies using ABR to study TNHT were reviewed. PubMed, EMBASE, and Scopus databases were selected to search for relevant literature. Studies (489) were retrieved, and 11 were included for meta-analysis. The results supported significantly reduced wave I amplitude in TNHT, whereas the alternations in wave V amplitude were inconsistent among the studies. Consistently increased V/I ratio indicated noise-induced central gain enhancement. The results indicated the evidence of noise-induced cochlear synaptopathy in tinnitus patients with normal hearing. However, inconsistent changes in wave V amplitude may be explained by that the failure of central gain that triggers the pathological neural changes in the central auditory system and/or that increased central gain may be necessary to generate tinnitus but not to maintain tinnitus.

A toy model for the auditory system that exploits stochastic resonance

The transduction process that occurs in the inner ear of the auditory system is a complex mechanism which requires a non-linear dynamical description. In addition to this, the stochastic phenomena that naturally arise in the inner ear during the transduction of an external sound into an electro-chemical signal must also be taken into account. The presence of noise is usually undesirable, but in non-linear systems a moderate amount of noise can improve the system's performance and increase the signal-to-noise ratio. The phenomenon of stochastic resonance combines randomness with non-linearity and is a natural candidate to explain at least part of the hearing process which is observed in the inner ear. In this work, we present a toy model of the auditory system which shows how stochastic resonance can be instrumental to sound perception, and suggests an explanation of the frequency dependence of the hearing threshold.

Cortical Temporal Integration Window for Binaural Cues accounts for Sluggish Auditory Spatial Perception

The auditory system has exquisite temporal coding in the periphery which is transformed into a rate-based code in central auditory structures like auditory cortex. However, the cortex is still able to synchronize, albeit at lower modulation rates, to acoustic fluctuations. The perceptual significance of this cortical synchronization is unknown. We estimated physiological synchronization limits of cortex (in humans with electroencephalography) and brainstem neurons (in chinchillas) to dynamic binaural cues using a novel system-identification technique, along with parallel perceptual measurements. We find that cortex can synchronize to dynamic binaural cues up to approximately 10 Hz, which aligns well with our measured limits of perceiving dynamic spatial information and utilizing dynamic binaural cues for spatial unmasking, i.e. measures of binaural sluggishness. We also find the tracking limit for frequency modulation (FM) is similar to the limit for spatial tracking, demonstrating that this sluggish tracking is a more general perceptual limit that can be accounted for by cortical temporal integration limits.

Emergence and function of cortical offset responses in sound termination detection

Offset responses in auditory processing appear after a sound terminates. They arise in neuronal circuits within the peripheral auditory system, but their role in the central auditory system remains unknown. Here, we ask what the behavioral relevance of cortical offset responses is and what circuit mechanisms drive them. At the perceptual level, our results reveal that experimentally minimizing auditory cortical offset responses decreases the mouse performance to detect sound termination, assigning a behavioral role to offset responses. By combining in vivo electrophysiology in the auditory cortex and thalamus of awake mice, we also demonstrate that cortical offset responses are not only inherited from the periphery but also amplified and generated de novo. Finally, we show that offset responses code more than silence, including relevant changes in sound trajectories. Together, our results reveal the importance of cortical offset responses in encoding sound termination and detecting changes within temporally discontinuous sounds crucial for speech and vocalization.