Auditory Research publications

Objective Traumatic brain injury (TBI) significantly reduces the quality of life for millions of survivors worldwide, causing persistent brain tissue damage and cognitive impairments, with no established therapeutic interventions currently available. Slow‐wave activity, a hallmark of deep sleep, has been implicated in recovery after TBI, but pharmacological approaches to enhance it lack specificity and scalability, complicating efforts to identify slow‐wave activity as a direct mechanistic contributor and severely limiting clinical translation. Methods To overcome these limitations, we developed a preclinical closed‐loop auditory stimulation (CLAS) paradigm that targets sleep's slow waves, enabling highly specific and temporally precise enhancement of slow‐wave activity. Therefore, we delivered 30‐ms sound triggers targeting the up‐phase of real‐time detected slow‐waves (upCLAS: TBI n = 8), or no sound stimulation (mockCLAS: non‐TBI n = 8, TBI n = 7) during sleep to healthy controls (non‐TBI) or brain injured (TBI) rats. Concomitantly, we assessed the ability of upCLAS‐enhanced sleep to counteract brain tissue damage (primary outcome) and symptomatic sequelae (secondary outcome) of TBI. Results Bayesian analysis revealed that sound‐mediated slow‐wave activity enhancement: (1) reduces diffuse axonal injury, with TBI mockCLAS posterior estimates falling outside the 95% confidence intervals of both other groups, whereas the posterior distributions of TBI upCLAS and non‐TBI groups largely overlapped (~13% posterior differences >0), consistent with a negligible effect size between groups; (2) decreases demyelination, with approximately 97% posterior differences >0 between TBI mockCLAS and TBI upCLAS groups, compared to approximately 60% between non‐TBI and TBI upCLAS groups; and (3) preserves cognitive ability, with recognition indexes in the novel object recognition test significantly above chance level in non‐TBI (* p = 0.031) and TBI upCLAS (* p = 0.026) groups, in contrast to mockCLAS‐treated TBI rats ( p = 0.156), presenting pronounced cognitive deficit. Furthermore, microglial response to brain injury was increased by deep sleep enhancement, with reduced ionized calcium‐binding adaptor molecule 1+ area coverage in TBI upCLAS rats (* p = 0.0445) compared to non‐TBI ones. Interpretation These results unambiguously demonstrate slow‐wave activity enhancement confers robust disease modification following TBI while overcoming major limitations of other preclinical approaches. Our findings constitute proof‐of‐concept that boosted sleep intensity mitigates histopathological and cognitive sequelae of brain trauma, suggesting that a clinically relevant, nonobtrusive, sleep‐based therapy may represent a novel therapeutic intervention for TBI survivors. ANN NEUROL 2026;100:242–254

Aging and noise over-exposure lead to complex mixtures of cochlear degradation that impair the structure and function of outer hair cells, inner hair cells (IHCs), and the cochlear nerve. However, IHC damage and cochlear synaptopathy (CS) remain pathologies “hidden” from the audiogram. This study aimed to identify and differentiate the physiological signatures of these two distinct pathologies using promising non-invasive assays: Envelope Following Responses (EFRs), Auditory Brainstem Response (ABRs), Wideband middle-ear reflexes (WB-MEMRs), and Distortion Product Otoacoustic Emissions (DPOAEs). We utilized chinchilla models of carboplatin-induced (CA) IHC damage (N = 4) and temporary threshold shift (TTS) noise-induced CS (N = 4) to compare the physiological signatures of each pathology. While both groups showed unchanged ABR thresholds two weeks after exposure, EFRs, ABR Wave V/I ratios, and MEMRs showed distinct effects of exposure. Despite non-elevated ABR-derived audiometric thresholds after exposure, both CA and TTS exposure resulted in severe in EFR “peakiness”, particularly for sharp, short-duty-cycle stimuli and significant elevations in ABR Wave V/I ratios. However, these findings were less-pronounced in the TTS-exposed animals. WB-MEMR amplitudes were decreased with elevated thresholds in both groups; this effect was more pronounced in the TTS group. Opposite trends in DPOAE amplitudes indicated that while both IHC damage and CS result in similar suprathreshold temporal coding deficits, effects on outer-hair-cell integrity and auditory efferent physiology may differ between the two pathologies. Future work and novel diagnostics should aim to distinguish these specific cochlear pathologies in clinical populations, or at the very least consider their overlap. Highlights A multi-metric diagnostic approach was used with chinchilla models of inner-hair-cell (IHC) damage and cochlear synaptopathy (CS). IHC damage and synaptopathy both cause suprathreshold deficits “hidden” from the audiogram. IHC damage results in more severe temporal envelope coding degradation than does synaptopathy. A combination of EFR “peakiness”, ABR Wave V/I ratio, and Wideband Middle Ear Muscle Reflex (WB-MEMR) appear to be useful measures for profiling IHC damage and CS.

Everyday listening often requires the auditory system to move beyond the perception of individual sound sources towards a more global representation of acoustic scenes. While auditory behaviour has been well characterised for one or a few sources, it remains unclear how listeners perceive scenes containing many simultaneous sounds. As multiple sound sources combine into a single acoustic mixture, separating individual sources becomes increasingly difficult, potentially requiring listeners to rely on summary representations rather than discrete object-based parsing. Auditory numerosity judgement , the ability to estimate how many distinct sound sources are present, can provide a way to probe how listeners perceive such complex acoustic scenes. Here, we measured numerosity judgements along the three dimensions of auditory space: azimuth, elevation, and distance, allowing each spatial axis to be examined in isolation. As these dimensions rely on markedly different spatial cues and differ strongly in spatial acuity, this design enabled the dissociation of spatial and non-spatial contributions to numerosity perception. Across dimensions, numerosity judgements showed no systematic relationship with individual spatial hearing performance. Speech intelligibility likewise exerted only a weak influence. In contrast, perceived numerosity was significantly modulated by the spectrotemporal coverage of the acoustic mixture, a summary statistic independent of spatial dimension or higher-lever linguistic factors. Together, these findings suggest that auditory numerosity judgement is largely insensitive to spatial hearing precision and instead reflects more general principles of how complex sound mixtures are represented at the scene level.

There is ample evidence from cognitive sciences and neurosciences studies that multisensory stimuli are detected better and faster than their unisensory counterparts. Yet, most of this work has been conducted in settings and with protocols within which participants had the sole detection task to perform. In realistic and complex environments, such as military ones, detection of critical information has to be performed while the operator is concurrently managing several others tasks and processing a vast amount of sensory inputs. To date, it remains to determine whether multisensory benefits for detection hold true in complex multitasking situations. In the present study, we compared the detection performance of healthy participants when the target was only auditory, only tactile, or both auditory and tactile. Detection performance was measured in a simple detection task condition and in a multitasking condition. In the latter, participants had to detect the targets while concurrently performing the subtasks of the MATB-II environment, designed in the 90s by NASA to simulate piloting tasks. Multisensory acceleration of reaction times was larger during multitasking compared to single-task conditions. Crucially, participants detected auditory–tactile targets faster than their unisensory counterparts. While previous studies have reported such facilitation effects in single-task contexts, our results show that multisensory facilitation of detection speed does occur in a realistic multitasking environment and is larger than in simple task conditions. Auditory-tactile displays seem to have the potential to enhance information presentation and could be used in applied settings like military aviation.

The superior para-olivary nucleus (SPN or SPON) is a prominent nucleus in the superior olivary complex of the auditory brainstem. The cellular composition of the nucleus reportedly differs between species, but a prominent recurring feature is the unusual characteristic to not respond during a sound but at its offset. Blocking glycine has shown that sound-induced inhibition is the mechanism, but the time course of the responsible synaptic events has not been directly measured in vivo. We obtained intracellular recordings in the Mongolian gerbil (meriones unguiculatus) with patch electrodes containing biocytin, and retrieved 12 labeled neurons with large dendritic trees within and around the SPN region. We found that these neurons could be categorized into three classes that show consistency along multiple dimensions like ultrastructure, spontaneous activity, and responses to current injection and a variety of ipsi- and contralateral sounds. Fast cells fire at onset of depolarizing current, generate short-latency rebound spikes to sound or hyperpolarizing current, and show dense synaptic coverage. Slow cells show sparse synaptic coverage, sustained responses to depolarization, and inhibition with a slow time course to hyperpolarizing current or sound. Uninhibited cells form a third class which profoundly differ in their responses to sound, lacking rebound spiking. We propose that fast cells project to the inferior colliculus, and slow cells to the cochlear nucleus.

We aimed to test whether hearing speech in phonetic categories (as opposed to a continuous/gradient fashion) affords benefits to “cocktail party” speech perception. We measured speech perception performance (recognition, localization, and source monitoring) in a simulated 3D cocktail party environment. We manipulated task difficulty by varying the number of additional maskers presented at other spatial locations in the horizontal soundfield (1–4 talkers) and via forward vs. time-reversed maskers, the latter promoting a release from masking. In separate tasks, we measured isolated phoneme categorization using two-alternative forced choice (2AFC) and visual analog scaling (VAS) tasks designed to promote more/less categorical hearing and thus test putative links between categorization and real-world speech-in-noise skills. We first show cocktail party speech recognition accuracy and speed decline with additional competing talkers and amidst forward compared to reverse maskers. Dividing listeners into “discrete” vs. “continuous” categorizers based on their VAS labeling (i.e., whether responses were binary or continuous judgments), we then show the degree of release from masking experienced at the cocktail party is predicted by their degree of categoricity in phoneme labeling and not high-frequency audiometric thresholds; more discrete listeners make less effective use of time-reversal and show less release from masking than their gradient responding peers. Our results suggest a link between speech categorization skills and cocktail party processing, with a gradient (rather than discrete) listening strategy benefiting degraded speech perception. These findings suggest that less flexibility in binning sounds into categories may be one factor that contributes to figure-ground deficits.

Binaural speech intelligibility in rooms is a complex process that is affected by many factors including room acoustics, hearing loss, and hearing aid (HA) signal processing. Intelligibility is evaluated in this paper for a simulated room combined with a simulated hearing aid. The test conditions comprise three spatial configurations of the speech and noise sources, simulated anechoic and concert hall acoustics, three amounts of multitalker babble interference, the hearing status of the listeners, and three degrees of simulated HA processing provided to compensate for the noise and/or hearing loss. The impact of these factors and their interactions is considered for normal-hearing (NH) and hearing-impaired (HI) listeners for sentence stimuli. Both listener groups showed a significant reduction in intelligibility as the signal-to-noise ratio (SNR) decreased, and showed a reduction in intelligibility in reverberation when compared to anechoic listening. There was no significant improvement in intelligibility for the NH group for the noise suppression algorithm used here, and no significant improvement in intelligibility for the HI group for more advanced HA processing algorithms as opposed to linear amplification in either of the two acoustic spaces or at any of the three SNRs.

Acoustic displays are conspicuous behaviors common across diverse animal taxa. They have long been studied in behavioral ecology, evolutionary biology, and neuroscience. Most of these investigations, however, have focused on male display. For species in which both sexes display, correcting this bias will lead to a fuller understanding of the evolution and function of these behaviors. In this study, we investigated the role of vocal advertisement display in female Alston’s singing mice ( Scotinomys teguina ). Singing mice are small muroid rodents of the family Cricetidae, native to high altitude cloud forests of Central America. Females and males both produce elaborate advertisement songs used in mate attraction and intra-sexual competition. Prior studies have largely focused on male behavior, though we recently found that both sexes dramatically increase their rate of singing and song duration in response to playback of conspecific male song. Here, we tested how mice of both sexes adjust their song effort in response to female song playback. Our results show that, like male song, female song elicits robust increases in song effort from both female and male mice. This study reveals additional social contexts that promote high song effort in this species, while raising additional questions about the role of song in communication within and between the sexes.

Sensory-motor interactions in the auditory system play an important role in vocal self-monitoring and control. These result from top-down corollary discharges, relaying predictions about vocal timing and acoustics. Recent evidence suggests such signals may be two distinct processes, one suppressing neural activity during vocalization and another enhancing sensitivity to sensory feedback, rather than a single mechanism. Single-neuron recordings have been unable to disambiguate due to overlap of motor signals with sensory inputs. Here, we sought to disentangle these processes in marmoset auditory cortex during production of multi-phrased ‘twitter’ vocalizations. Temporal responses revealed two timescales of vocal suppression: temporally-precise phasic suppression during phrases and sustained tonic suppression. Both components were present within individual neurons, however, phasic suppression presented broadly regardless of frequency tuning (gating), while tonic was selective for vocal frequencies and feedback (prediction). This suggests that auditory cortex is modulated by concurrent corollary discharges during vocalization, with different computational mechanisms.

Our perceptual system bins elements of the speech signal into categories to make speech perception manageable. Here, we aimed to test whether hearing speech in categories (as opposed to a continuous/gradient fashion) affords yet another benefit to speech recognition: parsing noisy speech at the “cocktail party.” We measured speech recognition in a simulated 3D cocktail party environment. We manipulated task difficulty by varying the number of additional maskers presented at other spatial locations in the horizontal soundfield (1-4 talkers) and via forward vs. time-reversed maskers, promoting more and less informational masking (IM), respectively. In separate tasks, we measured isolated phoneme categorization using two-alternative forced choice (2AFC) and visual analog scaling (VAS) tasks designed to promote more/less categorical hearing and thus test putative links between categorization and real-world speech-in-noise skills. We first show that listeners can only monitor up to ∼3 talkers despite up to 5 in the soundscape and streaming is not related to extended high-frequency hearing thresholds (though QuickSIN scores are). We then confirm speech streaming accuracy and speed decline with additional competing talkers and amidst forward compared to reverse maskers with added IM. Dividing listeners into “discrete” vs. “continuous” categorizers based on their VAS labeling (i.e., whether responses were binary or continuous judgments), we then show the degree of IM experienced at the cocktail party is predicted by their degree of categoricity in phoneme labeling; more discrete listeners are less susceptible to IM than their gradient responding peers. Our results establish a link between speech categorization skills and cocktail party processing, with a categorical (rather than gradient) listening strategy benefiting degraded speech perception. These findings imply figure-ground deficits common in many disorders might arise through a surprisingly simple mechanism: a failure to properly bin sounds into categories.

Introduction: Spatial hearing is most accurate using both ears, but accuracy decreases in persons with asymmetrical hearing between ears. In participants with deafness in one ear but normal hearing in the other ear (single-sided deafness [SSD]), this difference can be compensated by a unilateral cochlear implant (CI). It has been shown that a CI can restore sound localization performance, but it is still unclear to what extent auditory spatial discrimination can be improved. Methods: The present study investigated auditory spatial discrimination using minimum audible angles (MAAs) in 18 CI-SSD participants. Results were compared to 120 age-matched normal-hearing (NH) listeners. Low-frequency (LF) and high-frequency (HF) noise bursts were presented from 4°, 30°, and 60° azimuth on the CI side and on the NH side. MAA thresholds were tested for correlation with localization performance in the same participants. Results: There were eight good performers and ten poor performers. There were more poor performers for LF signals than for HF signals. Performance on the CI side was comparable to performance on the NH side. Most difficulties occurred at 4° and at 30°. Eight of the good performers in the localization task were also good performers in the MAA task. Only the localization ability at 4° on the CI side was positively correlated with the MAA at that location. Conclusion: Our data suggest that a CI can restore localization ability but not necessarily auditory spatial discrimination at the same time. The ability to discriminate between adjacent locations may be trainable during rehabilitation to enhance important auditory skills.

Priming, a change in the mental processing of a stimulus as a result of prior encounter with a related stimulus, has been observed repeatedly and studied extensively in humans. Yet currently, there is no behavioral model of short-term priming in lab animals, precluding research on the neurobiological basis of priming. Here, we describe an auditory discrimination paradigm for studying response priming in freely moving mice. We find a priming effect in success rate in all mice tested on the task. In contrast, we do not find a priming effect in response times. Compared to non-primed discrimination trials, the addition of incongruent prime stimuli reduces success rate more than congruent prime stimuli, suggesting a cognitive mechanism based on differential interference. The results establish the short-term priming phenomenon in rodents, and the paradigm opens the door to studying the cellular-network basis of priming.

Background Behavior consists of the interaction between an organism and its environment, and is controlled by the brain. Brain activity varies at sub-second time scales, but behavioral measures are usually coarse (often consisting of only binary trial outcomes). Results To overcome this mismatch, we developed the Rat Interactive Foraging Facility (RIFF): a programmable interactive arena for freely moving rats with multiple feeding areas, multiple sound sources, high-resolution behavioral tracking, and simultaneous electrophysiological recordings. The paper provides detailed information about the construction of the RIFF and the software used to control it. To illustrate the flexibility of the RIFF, we describe two complex tasks implemented in the RIFF, a foraging task and a sound localization task. Rats quickly learned to obtain rewards in both tasks. Neurons in the auditory cortex as well as neurons in the auditory field in the posterior insula had sound-driven activity during behavior. Remarkably, neurons in both structures also showed sensitivity to non-auditory parameters such as location in the arena and head-to-body angle. Conclusions The RIFF provides insights into the cognitive capabilities and learning mechanisms of rats and opens the way to a better understanding of how brains control behavior. The ability to do so depends crucially on the combination of wireless electrophysiology and detailed behavioral documentation available in the RIFF.

Syllables are an essential building block of speech. We recently showed that tactile stimuli linked to the perceptual centers of syllables in continuous speech can improve speech comprehension. The rate of syllables lies in the theta frequency range, between 4 and 8 Hz, and the behavioural effect appears linked to multisensory integration in this frequency band. Because this neural activity may be oscillatory, we hypothesized that a behavioural effect may also occur not only while but also after this activity has been evoked or entrained through vibrotactile pulses. Here we show that audiotactile integration regarding the perception of single syllables, both on the neural and on the behavioural level, is consistent with this hypothesis. We first stimulated subjects with a series of vibrotactile pulses and then presented them with a syllable in background noise. We show that, at a delay of 200 ms after the last vibrotactile pulse, audiotactile integration still occurred in the theta band and syllable discrimination was enhanced. Moreover, the dependence of both the neural multisensory integration as well as of the behavioral discrimination on the delay of the audio signal with respect to the last tactile pulse was consistent with a damped oscillation. In addition, the multisensory gain is correlated with the syllable discrimination score. Our results therefore evidence the role of the theta band in audiotactile integration and provide evidence that these effect may involve oscillatory activity that still persists after the tactile stimulation.

Introduction: Competing noise in the environment negatively affects speech intelligibility, particularly when listening at a distance. This is especially true for children with hearing loss in classroom environments where the signal-to-noise ratio is often poor. Remote microphone technology has been shown to be highly beneficial at improving the signal-to-noise ratio in hearing device users. Children with bone conduction devices, however, often must rely on indirect transmission of the acoustic signal for commonly used classroom-based remote microphone listening (e.g., digital adaptive microphone) which may negatively affect speech intelligibility. There are no studies on the effectiveness of using a relay method of signal delivery using remote microphone technology to improve speech intelligibility in adverse listening environments in bone conduction device users. Methods: Nine children with irresolvable conductive hearing loss and 12 adult controls with normal hearing were included for study. Controls were bilaterally plugged to simulate conductive hearing loss. All testing was conducted using the Cochlear™ Baha® 5 standard processor coupled with either the Cochlear™ Mini Microphone 2+ digital remote microphone or the Phonak Roger™ adaptive digital remote microphone. Speech intelligibility in noise was evaluated in the (1) bone conduction device processor alone, (2) bone conduction device + personal remote microphone, and (3) bone conduction device + personal remote microphone + adaptive digital remote microphone listening conditions at −10 dB, 0 dB, and +5 dB signal-to-noise ratios. Results and Conclusions: Speech intelligibility in noise improved significantly in the bone conduction device + personal remote microphone condition over the bone conduction device alone, demonstrating significant benefit for listening at poor signal-to-noise ratios in children with conductive hearing loss using bone conduction devices with personal remote microphone use. Experimental findings demonstrate poor signal transparency when using the relay method. Coupling of the adaptive digital remote microphone technology to the personal remote microphone negatively affects signal transparency, and no hearing in noise improvements are observed. Significant gains in speech intelligibility are consistently observed for direct streaming methods and are confirmed in adult controls. Behavioral findings are supported by objective verification of the signal transparency between the remote microphone and the bone conduction device.

Evoked neural responses to sensory stimuli have been extensively investigated in humans and animal models both to enhance our understanding of brain function and to aid in clinical diagnosis of neurological and neuropsychiatric conditions. Recording and imaging techniques such as electroencephalography (EEG), magnetoencephalography (MEG), local field potentials (LFPs), and calcium imaging provide complementary information about different aspects of brain activity at different spatial and temporal scales. Modeling and simulations provide a way to integrate these different types of information to clarify underlying neural mechanisms. In this study, we aimed to shed light on the neural dynamics underlying auditory evoked responses by fitting a rate-based model to LFPs recorded via multi-contact electrodes which simultaneously sampled neural activity across cortical laminae. Recordings included neural population responses to best-frequency (BF) and non-BF tones at four representative sites in primary auditory cortex (A1) of awake monkeys. The model considered major neural populations of excitatory, parvalbumin-expressing (PV), and somatostatin-expressing (SOM) neurons across layers 2/3, 4, and 5/6. Unknown parameters, including the connection strength between the populations, were fitted to the data. Our results revealed similar population dynamics, fitted model parameters, predicted equivalent current dipoles (ECD), tuning curves, and lateral inhibition profiles across recording sites and animals, in spite of quite different extracellular current distributions. We found that PV firing rates were higher in BF than in non-BF responses, mainly due to different strengths of tonotopic thalamic input, whereas SOM firing rates were higher in non-BF than in BF responses due to lateral inhibition. In conclusion, we demonstrate the feasibility of the model-fitting approach in identifying the contributions of cell-type specific population activity to stimulus-evoked LFPs across cortical laminae, providing a foundation for further investigations into the dynamics of neural circuits underlying cortical sensory processing.

The human brain networks responsible for selectively listening to a voice amid other talkers remain to be clarified. The present study aimed to investigate relationships between cortical activity and performance in a speech-in-speech task, before (Experiment I) and after training-induced improvements (Experiment II). In Experiment I, 74 participants performed a speech-in-speech task while their cortical activity was measured using a functional near infrared spectroscopy (fNIRS) device. One target talker and one masker talker were simultaneously presented at three different target-to-masker ratios (TMRs): adverse, intermediate and favorable. Behavioral results show that performance may increase monotonically with TMR in some participants and failed to decrease, or even improved, in the adverse-TMR condition for others. On the neural level, an extensive brain network including the frontal (left prefrontal cortex, right dorsolateral prefrontal cortex and bilateral inferior frontal gyri) and temporal (bilateral auditory cortex) regions was more solicited by the intermediate condition than the two others. Additionally, bilateral frontal gyri and left auditory cortex activities were found to be positively correlated with behavioral performance in the adverse-TMR condition. In Experiment II, 27 participants, whose performance was the poorest in the adverse-TMR condition of Experiment I, were trained to improve performance in that condition. Results show significant performance improvements along with decreased activity in bilateral inferior frontal gyri, the right dorsolateral prefrontal cortex, the left inferior parietal cortex and the right auditory cortex in the adverse-TMR condition after training. Arguably, lower neural activity reflects higher efficiency in processing masker inhibition after speech-in-speech training. As speech-in-noise tasks also imply frontal and temporal regions, we suggest that regardless of the type of masking (speech or noise) the complexity of the task will prompt the implication of a similar brain network. Furthermore, the initial significant cognitive recruitment will be reduced following a training leading to an economy of cognitive resources.

There is a weak relationship between clinical and self-reported speech perception outcomes in cochlear implant (CI) listeners. Such poor correspondence may be due to differences in clinical and “real-world” listening environments and stimuli. Speech in the real world is often accompanied by visual cues, background environmental noise, and is generally in a conversational context, all factors that could affect listening demand. Thus, our objectives were to determine if brain responses to naturalistic speech could index speech perception and listening demand in CI users. Accordingly, we recorded high-density electroencephalogram (EEG) while CI users listened/watched a naturalistic stimulus (i.e., the television show, “The Office”). We used continuous EEG to quantify “speech neural tracking” (i.e., TRFs, temporal response functions) to the show’s soundtrack and 8–12 Hz (alpha) brain rhythms commonly related to listening effort. Background noise at three different signal-to-noise ratios (SNRs), +5, +10, and +15 dB were presented to vary the difficulty of following the television show, mimicking a natural noisy environment. The task also included an audio-only (no video) condition. After each condition, participants subjectively rated listening demand and the degree of words and conversations they felt they understood. Fifteen CI users reported progressively higher degrees of listening demand and less words and conversation with increasing background noise. Listening demand and conversation understanding in the audio-only condition was comparable to that of the highest noise condition (+5 dB). Increasing background noise affected speech neural tracking at a group level, in addition to eliciting strong individual differences. Mixed effect modeling showed that listening demand and conversation understanding were correlated to early cortical speech tracking, such that high demand and low conversation understanding occurred with lower amplitude TRFs. In the high noise condition, greater listening demand was negatively correlated to parietal alpha power, where higher demand was related to lower alpha power. No significant correlations were observed between TRF/alpha and clinical speech perception scores. These results are similar to previous findings showing little relationship between clinical speech perception and quality-of-life in CI users. However, physiological responses to complex natural speech may provide an objective measure of aspects of quality-of-life measures like self-perceived listening demand.

Jet lag, shift work, and the extended light hours of modern life disrupt the regular light-dark cycle, affecting the menstrual cycle and decreasing fertility. The circadian pacemaker, the suprachiasmatic nucleus (SCN), is known to modulate ovulation, but the exact mechanism is not understood. Here we explore this connection by imaging neuronal activity in freely-behaving mice following extrinsic (jet lag) and intrinsic circadian circuit perturbations. We show that retina-connected vasoactive intestinal peptide (VIP)-expressing neurons in the SCN directly relay light information to gonadotropin-releasing hormone (GnRH)-expressing neurons to gate ovulation, as measured by recording calcium-sensitive activity of SCNVIP neurons over days in freely behaving mice. We show with machine-learning-based discriminations that the neuronal light-synchronized activity is primarily sex-dependent, and estrous-dependent in the late afternoon. Consistent with such a light-driven switch, we find that a pulse of light in this critical period could rescue estrous cycle regularity and the number of eggs released by animals kept in limited-light conditions. Our in vivo approach thus reveals the dynamic mechanism by which SCNVIP neurons trigger ovulation and demonstrates light-induced rescue of fertility, a finding with potential therapeutic implications for humans struggling with infertility due to shift work or jet lag.

Brain region size generally scales allometrically with brain size, but mosaic shifts in brain region size independent of brain size have been found in several lineages and may be related to the evolution of behavioral novelty. African weakly electric fishes (Mormyroidea) evolved a mosaically enlarged cerebellum and hindbrain, yet the relationship to their behaviorally novel electrosensory system remains unclear. We addressed this by studying South American weakly electric fishes (Gymnotiformes) and weakly electric catfishes ( Synodontis spp.), which evolved varying aspects of electrosensory systems, independent of mormyroids. If the mormyroid mosaic increases are related to evolving an electrosensory system, we should find similar mosaic shifts in gymnotiforms and Synodontis . Using micro-computed tomography scans, we quantified brain region scaling for multiple electrogenic, electroreceptive, and non-electrosensing species. We found mosaic increases in cerebellum in all three electrogenic lineages relative to non-electric lineages and mosaic increases in torus semicircularis and hindbrain associated with the evolution of electrogenesis and electroreceptor type. These results show that evolving novel electrosensory systems is repeatedly and independently associated with changes in the sizes of individual major brain regions independent of brain size, suggesting that selection can impact structural brain composition to favor specific regions involved in novel behaviors.