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Information processing in the nervous system critically relies on temporally precise spiking activity. In the auditory system, various degrees of phase-locking can be observed from the auditory nerve to cortical neurons. The classical metric for quantifying phase-locking is the vector strength (VS), which captures the periodicity in neuronal spiking. More recently, another metric, called the correlation index (CI), was proposed to quantify the temporally reproducible response characteristics of a neuron. The CI is defined as the peak value of a normalized shuffled autocorrelogram (SAC). Both VS and CI have been used to investigate how temporal information is processed and propagated along the auditory pathways. While previous analyses of physiological data in cats suggested covariation of these two metrics, general characterization of their connection has never been performed. In the present study, we derive a rigorous relationship between VS and CI. To model phase-locking, we assume Poissonian spike trains with a temporally changing intensity function following a von Mises distribution. We demonstrate that VS and CI are mutually related via the so-called concentration parameter that determines the degree of phase-locking. We confirm that these theoretical results are largely consistent with physiological data recorded in the auditory brainstem of various animals. In addition, we generate artificial phase-locked spike sequences, for which recording and analysis parameters can be systematically manipulated. Our analysis results suggest that mismatches between empirical data and the theoretical prediction can often be explained with deviations from the von Mises distribution, including skewed or multimodal period histograms. Furthermore, temporal relations of spike trains across trials can contribute to higher CI values than predicted mathematically based on the VS. We find that, for most applications, a SAC bin width of 50 ms seems to be a favorable choice, leading to an estimated error below 2.5% for physiologically plausible conditions. Overall, our results provide general relations between the two measures of phase-locking and will aid future analyses of different physiological datasets that are characterized with these metrics.

Scientists have long sought to explain how fish can sense the direction of sound, given the challenges that hearing underwater poses. An experimental study testing a variety of models now provides some answers. Experimental evidence for how directional hearing occurs in fish.

Background Arts therapies are widely but inconsistently provided in community mental health. Whilst they are appealing to patients, evidence for their effectiveness is mixed. Trials to date have been limited to one art-form or diagnosis. Patients may hold strong preferences for or against an art-form whilst group therapies rely on heterogeneity to provide a range of learning experiences. This study will test whether manualised group arts therapies (art therapy, dance movement therapy and music therapy) are effective in reducing psychological distress for diagnostically heterogeneous patients in community mental health compared to active group counselling control. Methods A pragmatic multi-centre 2-arm randomised controlled superiority trial with health economic evaluation and nested process evaluation. Adults aged ≥ 18, living in the community with a primary diagnosis of psychosis, mood, or anxiety disorder will be invited to participate and provide written informed consent. Participants are eligible if they score ≥ 1.65 on the Global Severity Index of the Brief Symptom Inventory. Those eligible will view videos of arts therapies and be asked for their preference. Participants are randomised to either their preferred type of group arts therapy or counselling. Groups will run twice per week in a community venue for 20 weeks. Our primary outcome is symptom distress at the end of intervention. Secondary outcomes include observer-rated symptoms, social situation and quality of life. Data will be collected at baseline, post-intervention and 6 and 12 months post-intervention. Outcome assessors and trial statisticians will be blinded. Analysis will be intention-to-treat. Economic evaluation will assess the cost-effectiveness of group arts therapies. A nested process evaluation will consist of treatment fidelity analysis, exploratory analysis of group process measures and qualitative interviews with participants and therapists. Discussion This will be the first trial to account for patient preferences and diagnostic heterogeneity in group arts therapies. As with all group therapies, there are a number of logistical challenges to which we have had to further adapt due to the COVID-19 pandemic. Overall, the study will provide evidence as to whether there is an additive benefit or not to the use of the arts in group therapy in community mental health care. Trial registration ISRCTN, ISRCTN88805048 . Registered on 12 September 2018.

Animals, including humans, use interaural time differences (ITDs) that arise from different sound path lengths to the two ears as a cue of horizontal sound source location. The nature of the neural code for ITD is still controversial. Current models differentiate between two population codes: either a map-like rate-place code of ITD along an array of neurons, consistent with a large body of data in the barn owl, or a population rate code, consistent with data from small mammals. Recently, it was proposed that these different codes reflect optimal coding strategies that depend on head size and sound frequency. The chicken makes an excellent test case of this proposal because its physical prerequisites are similar to small mammals, yet it shares a more recent common ancestry with the owl. We show here that, like in the barn owl, the brainstem nucleus laminaris in mature chickens displayed the major features of a place code of ITD. ITD was topographically represented in the maximal responses of neurons along each isofrequency band, covering approximately the contralateral acoustic hemisphere. Furthermore, the represented ITD range appeared to change with frequency, consistent with a pressure gradient receiver mechanism in the avian middle ear. At very low frequencies, below 400Hz, maximal neural responses were symmetrically distributed around zero ITD and it remained unclear whether there was a topographic representation. These findings do not agree with the above predictions for optimal coding and thus revive the discussion as to what determines the neural coding strategies for ITDs.

Turtles, like other amphibious animals, face a trade-off between terrestrial and aquatic hearing. We used laser vibrometry and auditory brainstem responses to measure their sensitivity to vibration stimuli and to airborne versus underwater sound. Turtles are most sensitive to sound underwater, and their sensitivity depends on the large middle ear, which has a compliant tympanic disc attached to the columella. Behind the disc, the middle ear is a large air-filled cavity with a volume of approximately 0.5 ml and a resonance frequency of approximately 500 Hz underwater. Laser vibrometry measurements underwater showed peak vibrations at 500–600 Hz with a maximum of 300 µm s−1 Pa−1, approximately 100 times more than the surrounding water. In air, the auditory brainstem response audiogram showed a best sensitivity to sound of 300–500 Hz. Audiograms before and after removing the skin covering reveal that the cartilaginous tympanic disc shows unchanged sensitivity, indicating that the tympanic disc, and not the overlying skin, is the key sound receiver. If air and water thresholds are compared in terms of sound intensity, thresholds in water are approximately 20–30 dB lower than in air. Therefore, this tympanic ear is specialized for underwater hearing, most probably because sound-induced pulsations of the air in the middle ear cavity drive the tympanic disc.

The position of testudines in vertebrate phylogeny is being re-evaluated. At present, testudine morphological and molecular data conflict when reconstructing phylogenetic relationships. Complicating matters, the ecological niche of stem testudines is ambiguous. To understand how turtles have evolved to hear in different environments, we examined middle ear morphology and scaling in most extant families, as well as some extinct species, using 3-dimensional reconstructions from micro magnetic resonance (MR) and submillimeter computed tomography (CT) scans. All families of testudines exhibited a similar shape of the bony structure of the middle ear cavity, with the tympanic disk located on the rostrolateral edge of the cavity. Sea Turtles have additional soft tissue that fills the middle ear cavity to varying degrees. When the middle ear cavity is modeled as an air-filled sphere of the same volume resonating in an underwater sound field, the calculated resonances for the volumes of the middle ear cavities largely fell within testudine hearing ranges. Although there were some differences in morphology, there were no statistically significant differences in the scaling of the volume of the bony middle ear cavity with head size among groups when categorized by phylogeny and ecology. Because the cavity is predicted to resonate underwater within the testudine hearing range, the data support the hypothesis of an aquatic origin for testudines, and function of the middle ear cavity in underwater sound detection.

Lungless salamanders (Family Plethodontidae) form a highly speciose group that has undergone spectacular adaptive radiation to colonize a multitude of habitats. Substantial morphological variation in the otic region coupled with great ecological diversity within this clade make plethodontids an excellent model for exploring the ecomorphology of the amphibian ear. We examined the influence of habitat, development, and vision on inner ear morphology in 52 plethodontid species. We collected traditional and 3D geometric morphometric measurements to characterize variation in size and shape of the otic endocast and peripheral structures of the salamander ear. Phylogenetic comparative analyses demonstrate structural convergence in the inner ear across ecologically similar species. Species that dwell in spatially complex microhabitats exhibit robust, highly curved semicircular canals suggesting enhanced vestibular sense, whereas species with reduced visual systems demonstrate reduced canal curvature indicative of relaxed selection on the vestibulo-ocular reflex. Cave specialists show parallel enlargement of auditory-associated structures. The morphological correlates of ecology among diverse species reveal underlying evidence of habitat specialization in the inner ear and suggest that there exists physiological variation in the function of the salamander ear even in the apparent absence of selective pressures on the auditory system to support acoustic behavior.

  GKLT activates with only small depolarization [26] and sets the time constant of the membrane by reducing the membrane resistance to unusually low values. Because of the GKLT, coincidence detectors typically have very low input resistances and thus very rapid responses to changes in voltage (τ of 0.3-1.5 ms). The longer the initial rise of the compound synaptic potential, the more time GKLT has to activate, the larger the conductance will be at the time of the peak in the EPSP, suppressing the voltage response, and reducing the likelihood of firing an action potential. [...]although the source(s) of the asymmetry in medial superior olive inputs remains open to debate, one major point emerges from the Jercog et al. study, which is that asymmetry in bilateral EPSP shapes could greatly influence coincidence detection and neural codes for ITD.

A wide variety of neurons encode temporal information via phase-locked spikes. In the avian auditory brainstem, neurons in the cochlear nucleus magnocellularis (NM) send phase-locked synaptic inputs to coincidence detector neurons in the nucleus laminaris (NL) that mediate sound localization. Previous modeling studies suggested that converging phase-locked synaptic inputs may give rise to a periodic oscillation in the membrane potential of their target neuron. Recent physiological recordings in vivo revealed that owl NL neurons changed their spike rates almost linearly with the amplitude of this oscillatory potential. The oscillatory potential was termed the sound analog potential, because of its resemblance to the waveform of the stimulus tone. The amplitude of the sound analog potential recorded in NL varied systematically with the interaural time difference (ITD), which is one of the most important cues for sound localization. In order to investigate the mechanisms underlying ITD computation in the NM-NL circuit, we provide detailed theoretical descriptions of how phase-locked inputs form oscillating membrane potentials. We derive analytical expressions that relate presynaptic, synaptic, and postsynaptic factors to the signal and noise components of the oscillation in both the synaptic conductance and the membrane potential. Numerical simulations demonstrate the validity of the theoretical formulations for the entire frequency ranges tested (1-8 kHz) and potential effects of higher harmonics on NL neurons with low best frequencies (<2 kHz).

Arts therapies are widely but inconsistently provided in community mental health. Whilst they are appealing to patients, evidence for their effectiveness is mixed. Trials to date have been limited to one art-form or diagnosis. Patients may hold strong preferences for or against an art-form whilst group therapies rely on heterogeneity to provide a range of learning experiences. This study will test whether manualised group arts therapies (art therapy, dance movement therapy and music therapy) are effective in reducing psychological distress for diagnostically heterogeneous patients in community mental health compared to active group counselling control. A pragmatic multi-centre 2-arm randomised controlled superiority trial with health economic evaluation and nested process evaluation. Adults aged [greater than or equal to] 18, living in the community with a primary diagnosis of psychosis, mood, or anxiety disorder will be invited to participate and provide written informed consent. Participants are eligible if they score [greater than or equal to] 1.65 on the Global Severity Index of the Brief Symptom Inventory. Those eligible will view videos of arts therapies and be asked for their preference. Participants are randomised to either their preferred type of group arts therapy or counselling. Groups will run twice per week in a community venue for 20 weeks. Our primary outcome is symptom distress at the end of intervention. Secondary outcomes include observer-rated symptoms, social situation and quality of life. Data will be collected at baseline, post-intervention and 6 and 12 months post-intervention. Outcome assessors and trial statisticians will be blinded. Analysis will be intention-to-treat. Economic evaluation will assess the cost-effectiveness of group arts therapies. A nested process evaluation will consist of treatment fidelity analysis, exploratory analysis of group process measures and qualitative interviews with participants and therapists. This will be the first trial to account for patient preferences and diagnostic heterogeneity in group arts therapies. As with all group therapies, there are a number of logistical challenges to which we have had to further adapt due to the COVID-19 pandemic. Overall, the study will provide evidence as to whether there is an additive benefit or not to the use of the arts in group therapy in community mental health care.