Publications using TDT

Human perception requires the many-to-one mapping between continuous sensory elements and discrete categorical representations. This grouping operation underlies the phenomenon of categorical perception (CP)-the experience of perceiving discrete categories rather than gradual variations in signal input. Speech perception requires CP because acoustic cues do not share constant relations with perceptual-phonetic representations. Beyond facilitating perception of unmasked speech, we reasoned CP might also aid the extraction of target speech percepts from interfering sound sources (i.e., noise) by generating additional perceptual constancy and reducing listening effort. Specifically, we investigated how noise interference impacts cognitive load and perceptual identification of unambiguous (i.e., categorical) vs. ambiguous stimuli. Listeners classified a speech vowel continuum (/u/-/a/) at various signal-to-noise ratios (SNRs [unmasked, 0 and -5 dB]). Continuous recordings of pupil dilation measured processing effort, with larger, later dilations reflecting increased listening demand. Critical comparisons were between time-locked changes in eye data in response to unambiguous (i.e., continuum endpoints) tokens vs. ambiguous tokens (i.e., continuum midpoint). Unmasked speech elicited faster responses and sharper psychometric functions, which steadily declined in noise. Noise increased pupil dilation across stimulus conditions, but not straightforwardly. Noise-masked speech modulated peak pupil size (i.e., [0 and -5 dB] > unmasked). In contrast, peak dilation latency varied with both token and SNR. Interestingly, categorical tokens elicited earlier pupil dilation relative to ambiguous tokens. Our pupillary data suggest CP reconstructs auditory percepts under challenging listening conditions through interactions between stimulus salience and listeners' internalized effort and/or arousal.

Sleep-wake transitions are modulated through extensive subcortical networks although the precise roles of their individual components remain elusive. Using forward genetics and in vivo electrophysiology, we identified a recessive mouse mutant line characterised by a reduced propensity to transition between all sleep states while a profound loss in total REM sleep time was evident. The causative mutation, an Ile102Asn substitution in VAMP2, was associated with substantial synaptic changes while in vitro electrophysiological investigations with fluorescence imaging revealed a diminished probability of vesicular release in mutants. We conclude that the synaptic efficiency of the entire subcortical brain network determines the likelihood that an animal transitions from one vigilance state to the next.

Age-related hearing loss (ARHL) is one of the most common disorders affecting elderly individuals. There is an urgent need for effective preventive measures for ARHL because none are currently available. Cockayne syndrome (CS) is a premature aging disease that presents with progressive hearing loss at a young age, but is otherwise similar to ARHL. There are two human genetic complementation groups of CS, A and B. While the clinical phenotypes in patients are similar, the proteins have very diverse functions, and insight into their convergence is of great interest. Here, we use mouse models for CS ( CSA − /− and CSB m/m ) that recapitulate the hearing loss in human CS patients. We previously showed that NAD + , a key metabolite with various essential functions, is reduced in CS and associated with multiple CS phenotypes. In this study, we report that NAD + levels are reduced in the cochlea of CSB m/m mice and that short-term treatment (10 days) with the NAD + precursor nicotinamide riboside (NR), prevents hearing loss, restores outer hair cell loss, and improves cochlear health in CSB m/m mice. Similar, but more modest effects were observed in CSA − /− mice. Remarkably, we observed a reduction in synaptic ribbon counts in the presynaptic zones of inner hair cells in both CSA −/− and CSB m/m mice, pointing to a converging mechanism for cochlear defects in CS. Ribbon synapses facilitate rapid and sustained synaptic transmission over long periods of time. Ribeye, a core protein of synaptic ribbons, possesses an NAD(H) binding pocket which regulates its activity. Intriguingly, NAD + supplementation rescues reduced synaptic ribbon formation in both CSA −/− and CSB m/m mutant cochleae. These findings provide valuable insight into the mechanism of CS- and ARHL-associated hearing loss, and suggest a possible intervention.

Background Impaired neurological function affects 85% to 90% of cardiac arrest ( CA ) survivors. Pulsatile blood flow may play an important role in neurological recovery after CA . Cerebral blood flow ( CBF ) pulsatility immediately, during, and after CA and resuscitation has not been investigated. We characterized the effects of asphyxial CA on short‐term (<2 hours after CA ) CBF and femoral arterial blood pressure ( ABP ) pulsatility and studied their relationship to cerebrovascular resistance ( CVR ) and short‐term neuroelectrical recovery. Methods and Results Male rats underwent asphyxial CA followed by cardiopulmonary resuscitation. A multimodal platform combining laser speckle imaging, ABP , and electroencephalography to monitor CBF , peripheral blood pressure, and brain electrophysiology, respectively, was used. CBF and ABP pulsatility and CVR were assessed during baseline, CA , and multiple time points after resuscitation. Neuroelectrical recovery, a surrogate for neurological outcome, was assessed using quantitative electroencephalography 90 minutes after resuscitation. We found that CBF pulsatility differs significantly from baseline at all experimental time points with sustained deficits during the 2 hours of postresuscitation monitoring, whereas ABP pulsatility was relatively unaffected. Alterations in CBF pulsatility were inversely correlated with changes in CVR , but ABP pulsatility had no association to CVR . Interestingly, despite small changes in ABP pulsatility, higher ABP pulsatility was associated with worse neuroelectrical recovery, whereas CBF pulsatility had no association. Conclusions Our results reveal, for the first time, that CBF pulsatility and CVR are significantly altered in the short‐term postresuscitation period after CA . Nevertheless, higher ABP pulsatility appears to be inversely associated with neuroelectrical recovery, possibly caused by impaired cerebral autoregulation and/or more severe global cerebral ischemia.

Anurans (frogs and toads) are the most vocal amphibians. In most species, only males produce advertisement calls for defending territories and attracting mates. Female vocalizations are the exceptions among frogs, however in the African clawed frog (Xenopus laevis) both males and females produce distinct vocalizations. The matched filter hypothesis predicts a correspondence between peripheral auditory tuning of receivers and properties of species-specific acoustic signals, but few studies have assessed this relationship between the sexes. Measuring hearing sensitivity with a binaural recording of distortion product otoacoustic emissions, we have found that the ears of the males of this species are tuned to the dominant frequency of the female's calls, whereas the ears of the females are tuned close to the dominant frequency of the male's calls. Our findings provide support for the matched filter hypothesis extended to include male-female calling. This unique example of reciprocal matched filtering ensures that males and females communicate effectively in high levels of background noise, each sex being most sensitive to the frequencies of the other sex's calls.

Background: Digital noise reduction (DNR) processing is used in hearing aids to enhance perception in noise by classifying and suppressing the noise acoustics. However, the efficacy of DNR processing is not known under reverberant conditions where the speech-in-noise acoustics are further degraded by reverberation. Purpose: The purpose of this study was to investigate acoustic and perceptual effects of DNR processing across a range of reverberant conditions for individuals with hearing impairment. Research Design: This study used an experimental design to investigate the effects of varying reverberation on speech-in-noise processed with DNR. Study Sample: Twenty-six listeners with mild-to-moderate sensorineural hearing impairment participated in the study. Data Collection and Analysis: Speech stimuli were combined with unmodulated broadband noise at several signal-to-noise ratios (SNRs). A range of reverberant conditions with realistic parameters were simulated, as well as an anechoic control condition without reverberation. Reverberant speech-in-noise signals were processed using a spectral subtraction DNR simulation. Signals were acoustically analyzed using a phase inversion technique to quantify improvement in SNR as a result of DNR processing. Sentence intelligibility and subjective ratings of listening effort, speech naturalness, and background noise comfort were examined with and without DNR processing across the conditions. Results: Improvement in SNR was greatest in the anechoic control condition and decreased as the ratio of direct to reverberant energy decreased. There was no significant effect of DNR processing on speech intelligibility in the anechoic control condition, but there was a significant decrease in speech intelligibility with DNR processing in all of the reverberant conditions. Subjectively, listeners reported greater listening effort and lower speech naturalness with DNR processing in some of the reverberant conditions. Listeners reported higher background noise comfort with DNR processing only in the anechoic control condition. Conclusions: Results suggest that reverberation affects DNR processing using a spectral subtraction algorithm in such a way that decreases the ability of DNR to reduce noise without distorting the speech acoustics. Overall, DNR processing may be most beneficial in environments with little reverberation and that the use of DNR processing in highly reverberant environments may actually produce adverse perceptual effects. Further research is warranted using commercial hearing aids in realistic reverberant environments.

Diving birds spend up to several minutes underwater during pursuit-dive foraging. To find and capture prey, like fish and squid, they probably need several senses in addition to vision. Cormorants, very efficient predators of fishes, have unexpectedly low visual acuity underwater. So, underwater hearing may be an important sense, as for other diving animals. We measured auditory thresholds and eardrum vibrations in air and underwater of the great cormorant (Phalacrocorax carbo sinensis). Wild-caught cormorant fledglings were anesthetized, and their auditory brainstem response (ABR) and eardrum vibrations to clicks and tone bursts were measured, first in an anechoic box in air and then in a large water-filled tank, with their head and ears submerged 10 cm below the surface. Both the ABR-response waveshape and latency, as well as the ABR-thresholds, measured in units of sound pressure, were similar in air and water. The best average sound pressure sensitivity was found at 1 kHz, both in air (53 dB re. 20 µPa) and underwater (58 dB re. 20 µPa). When thresholds were compared in units of intensity, however, the sensitivity underwater was higher than in air. Eardrum vibration amplitudes in both media reflected the ABR-threshold curves. These results suggest that cormorants have in-air hearing abilities comparable to similar-sized diving birds, and that their underwater hearing sensitivity is at least as good as their aerial sensitivity. This together with the morphology of the outer ear (collapsible meatus) and middle ear (thickened eardrum), suggest that cormorants may have anatomical and physiological adaptations for amphibious hearing.

Hypothesis: Local administration of the calcium-channel blocker (CCB), diltiazem, via intratympanic (IT) chitosan-glycerophosphate (CGP) hydrogel will protect against cisplatin-induced ototoxicity. Background: Cisplatin induces calcium-mediated apoptosis of cochlear outer hair cells (OHCs). Previous work demonstrated otoprotection and reduced auditory brainstem response (ABR) threshold shifts in a cisplatin-induced ototoxicity mouse model treated with multiple doses of IT diltiazem given in solution. Here, we evaluated the role of a single dose of IT CGP-diltiazem as a novel otoprotectant against cisplatin-induced ototoxicity. Methods: Baseline pure-tone and click-evoked ABRs were performed in control (IT CGP-saline, n = 13) and treatment (IT CGP-diltiazem 2 mg/kg, n = 9) groups of female CBA/J mice. A single dose of IT CGP hydrogel was administered just before intraperitoneal injection of cisplatin (14 mg/kg). On Day 7 posttreatment, ABRs were performed and cochleae were harvested. Hair cells were quantified using anti-myosin VIIa immunostaining and inner hair cell ribbon synapses were quantified using Ctbp2 immunostaining. Results: There was a statistically significant effect of treatment on click- and tone-evoked ABRs between groups. The mean threshold shifts were significantly reduced in both click- and tone-evoked ABRs on Day 7 in IT CGP-diltiazem treated mice compared with CGP-saline control mice. There were no significant differences in OHC counting between groups, but there appears to be an otoprotection against loss of synapses in the apical turn from IT CGP-diltiazem treated mice ( p < 0.05). Conclusions: This preliminary work suggests that IT CGP-diltiazem reduces ABR threshold shifts with possible mechanisms of protecting ribbon synapses in the setting of cisplatin-induced ototoxicity. More work is necessary to determine the mechanism underlying this otoprotection.

Focused attention on expected voice features, such as fundamental frequency (F0) and spectral envelope, may facilitate segregation and selection of a target talker in competing talker backgrounds. Age-related declines in attention may limit these abilities in older adults, resulting in poorer speech understanding in complex environments. To test this hypothesis, younger and older adults with normal hearing listened to sentences with a single competing talker. For most trials, listener attention was directed to the target by a cue phrase that matched the target talker’s F0 and spectral envelope. For a small percentage of randomly occurring probe trials, the target’s voice unexpectedly differed from the cue phrase in terms of F0 and spectral envelope. Overall, keyword recognition for the target talker was poorer for older adults than younger adults. Keyword recognition was poorer on probe trials than standard trials for both groups, and incorrect responses on probe trials contained keywords from the single-talker masker. No interaction was observed between age-group and the decline in keyword recognition on probe trials. Thus, reduced performance by older adults overall could not be attributed to declines in attention to an expected voice. Rather, other cognitive abilities, such as speed of processing and linguistic closure, were predictive of keyword recognition for younger and older adults. Moreover, the effects of age interacted with the sex of the target talker, such that older adults had greater difficulty understanding target keywords from female talkers than male talkers.

Background: Combined electrical-acoustical stimulation (EAS) has gained popularity as patients with residual hearing are increasingly undergoing cochlear implantation. Preservation of residual hearing correlates with hearing outcomes, but loss of hearing occurs in a subset of these patients. Several mechanisms have been proposed as causing this hearing loss; we have previously described high amplitude pressure transients, equivalent to high-level noise exposures, in the inner ear during electrode insertion. The source of these transients has not been identified. Methods: Cadaveric human heads were prepared with an extended facial recess. Fiber-optic pressure sensors were inserted into the scala vestibuli and scala tympani to measure intracochlear pressures. Two cochlear implant (CI) electrode styles (straight and perimodiolar) were inserted during time-synced intracochlear pressures and video fluoroscopy measurements. Results: CI electrode insertions produced pressure transients in the cochlea up to 160 to 170 dB pSPL equivalent for both styles, consistent with previous results. However, the position of the electrode within the cochlea when transients were generated differed (particularly contact with the medial or lateral walls). Conclusions: These results begin to elucidate the insertion pressure profiles of CI electrodes, which can be used to improve CI electrode designs and facilitate “silent-insertions” to improve chances of hearing preservation.

Introduction The vestibular system is essential for normal postural control and balance. Because of their proximity to the cochlea, the otolith organs are vulnerable to noise. We previously showed that head jerks that evoke vestibular nerve activity were no longer capable of inducing a response after noise overstimulation. The present study adds a greater range of jerk intensities to determine if the response was abolished or required more intense stimulation (threshold shift). Materials and Methods Vestibular short-latency evoked potential (VsEP) measurements were taken before noise exposure and compared to repeated measurements taken at specific time points for 28 days after noise exposure. Calretinin was used to identify changes in calyx-only afferents in the sacculus. Results Results showed that more intense jerk stimuli could generate a VsEP, although it was severely attenuated relative to prenoise values. When the VsEP was evaluated 4 weeks after noise exposure, partial recovery was observed. Conclusion These data suggest that noise overstimulation, such as can occur in the military, could introduce an increased risk of imbalance that should be evaluated before returning a subject to situations that require normal agility and motion. Moreover, although there is recovery with time, some dysfunction persists for extended periods.

The perception of spectrotemporal changes is crucial for distinguishing between acoustic signals, including vocalizations. Temporal modulation transfer functions (TMTFs) have been measured in many species and reveal that the discrimination of amplitude modulation suffers at rapid modulation frequencies. TMTFs were measured in six CBA/CaJ mice in an operant conditioning procedure, where mice were trained to discriminate an 800 ms amplitude modulated white noise target from a continuous noise background. TMTFs of mice show a bandpass characteristic, with an upper limit cutoff frequency of around 567 Hz. Within the measured modulation frequencies ranging from 5 Hz to 1280 Hz, the mice show a best sensitivity for amplitude modulation at around 160 Hz. To look for a possible parallel evolution between sound perception and production in living organisms, we also analyzed the components of amplitude modulations embedded in natural ultrasonic vocalizations (USVs) emitted by this strain. We found that the cutoff frequency of amplitude modulation in most of the individual USVs is around their most sensitive range obtained from the psychoacoustic experiments. Further analyses of the duration and modulation frequency ranges of USVs indicated that the broader the frequency ranges of amplitude modulation in natural USVs, the shorter the durations of the USVs.

Speech audiometry in noise based on sentence tests is an important diagnostic tool to assess listeners’ speech recognition threshold (SRT), i.e., the signal-to-noise ratio corresponding to 50% intelligibility. The clinical standard measurement procedure requires a professional experimenter to record and evaluate the response (expert-conducted speech audiometry). The use of automatic speech recognition enables self-conducted measurements with an easy-to-use speech-based interface. This article compares self-conducted SRT measurements using smart speakers with expert-conducted laboratory measurements. With smart speakers, there is no control over the absolute presentation level, potential errors from the automated response logging, and room acoustics. We investigate the differences between highly controlled measurements in the laboratory and smart speaker-based tests for young normal-hearing (NH) listeners as well as for elderly NH, mildly and moderately hearing-impaired listeners in low, medium, and highly reverberant room acoustics. For the smart speaker setup, we observe an overall bias in the SRT result that depends on the hearing loss. The bias ranges from +0.7 dB for elderly moderately hearing-impaired listeners to +2.2 dB for young NH listeners. The intrasubject standard deviation is close to the clinical standard deviation (0.57/0.69 dB for the young/elderly NH compared with 0.5 dB observed for clinical tests and 0.93/1.09 dB for the mild/moderate hearing-impaired listeners compared with 0.9 dB). For detecting a clinically elevated SRT, the speech-based test achieves an area under the curve value of 0.95 and therefore seems promising for complementing clinical measurements.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive loss of memory and cognitive decline. Over the last decade, it has been found that defects in sensory systems could be highly associated with AD. Hearing is an important neural sense. However, little is known about hearing functional changes in AD. In this study, APP/PS1 AD mice (Jackson Lab: Stack No. 004462) were used. Hearing function was assessed by auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and cochlear microphonics (CM) recordings. Wild-type (WT) littermates served as control. We found that APP/PS1 AD mice measured as ABR threshold had hearing loss. The hearing loss appeared at high frequency as early as 2 months old, prior to the reported occurrence of spatial learning deficit at 6-7 months of age in this AD mouse model. The hearing loss was progressive and extended from high frequency to low frequency. At 3-4 months old, the hearing loss appeared in the whole-frequency range. Moreover, the wave IV and V in the super-threshold ABR were eliminated, indicating substantial impairment in inferior colliculus, nuclei of lateral lemniscus, and medial geniculate body in the upper brainstem. DPOAE in APP/PS1 AD mice was also reduced. However, there was no reduction in CM in APP/PS1 mice. These data demonstrate that unlike age-related hearing loss APP/PS1 AD mice have early onset of hearing loss. These data also suggest that hearing function testing could provide a simple, sensitive, non-invasive screen-tool for early detecting AD and localizing lesion.

The formation of reactive oxygen species (ROS) is a well-documented process in noise-induced hearing loss (NIHL). We have also previously shown that activation of 5' adenosine monophosphate (AMP)-activated protein kinase (AMPKα) at its catalytic residue T172 is one of the key reactions triggering noise-induced outer hair cell (OHC) death. In this study, we are addressing the link between ROS formation and activation of AMPKα in OHCs after noise exposure. In-vivo treatment of CBA/J mice with the antioxidant N-acetyl cysteine (NAC) reduced noise-induced ROS formation (as assessed by the relative levels of 4-hydroxynonenal and 3-nitrotyrosine) and activation of AMPKα in OHCs. Forskolin, an activator of adenylyl cyclase (AC) and an antioxidant, significantly increased cyclic adenosine monophosphate (cAMP) and decreased ROS formation and noise-induced activation of AMPKα. Consequently, treatment with forskolin attenuated noise-induced losses of OHCs and NIHL. In HEI-OC1 cells, H2O2-induced activation of AMPKα and cell death were inhibited by the application of forskolin. The sum of our data indicates that noise activates AMPKα in OHCs through formation of ROS and that noise-exposure-induced OHC death is mediated by a ROS/AMPKα-dependent pathway. Forskolin may serve as a potential compound for prevention of NIHL.

Premotor areas of primates are specialized cortical regions that can contribute to hand movements by modulating the outputs of the primary motor cortex (M1). The goal of the present work was to study how the supplementary motor area (SMA) located within the same hemisphere [i.e., ipsilateral SMA (iSMA)] or the opposite hemisphere [i.e., contralateral (cSMA)] modulate the outputs of M1. We used paired-pulse protocols with intracortical stimulations in sedated capuchin monkeys. A conditioning stimulus in iSMA or cSMA was delivered simultaneously or before a test stimulus in M1 with different interstimulus intervals (ISIs) while electromyographic activity was recorded in hand and forearm muscles. The pattern of modulation from iSMA and cSMA shared some clear similarities. In particular, both areas predominantly induced facilitatory effects on M1 outputs with shorter ISIs and inhibitory effects with longer ISIs. However, the incidence and strength of facilitatory effects were greater for iSMA than cSMA. We then compared the pattern of modulatory effects from SMA to the ones from the dorsal and ventral premotor cortexes (PMd and PMv) collected in the same series of experiments. Among premotor areas, the impact of SMA on M1 outputs was always weaker than the one of either PMd or PMv, and this was regardless of the hemisphere, or the ISI, tested. These results show that SMA exerts a unique set of modulations on M1 outputs, which could support its specific function for the production of hand movements. NEW & NOTEWORTHY We unequivocally isolated stimulation to either the ipsilateral or contralateral supplementary motor area (SMA) using invasive techniques and compared their modulatory effects on the outputs of primary motor cortex (M1). Modulations from both SMAs shared many similarities. However, facilitatory effects evoked from ipsilateral SMA were more common and more powerful. This pattern differs from the ones of other premotor areas, which suggests that each premotor area makes unique contributions to the production of motor outputs.

We examined the sensitivity of the neurons in the mouse inferior colliculus (IC) to the interaural time differences (ITD) conveyed in the sound envelope. Utilizing optogenetic methods, we compared the responses to the ITD in the envelope of identified glutamatergic and GABAergic neurons. More than half of both cell types were sensitive to the envelope ITD, and the ITD curves were aligned at their troughs. Within the physiological ITD range of mice (±50 μs), the ITD curves of both cell types had a higher firing rate when the contralateral envelope preceded the ipsilateral envelope. These results show that the circuitry to process ITD persists in the mouse despite its lack of low-frequency hearing. The sensitivity of IC neurons to ITD is most likely to be shaped by the binaural interaction of excitation and inhibition in the lateral superior olive.

The effects of noise-induced hearing loss have yet to be studied for the Dutch-belted strain of rabbits, which is the only strain that has been used in studies of the central auditory system. We measured auditory brainstem responses (ABRs), 2f1-f2 distortion product otoacoustic emissions (DPOAEs), and counts of cochlear inner and outer hair cells (IHCs and OHCs, respectively) from confocal images of Myo7a-stained cochlear whole-mounts in unexposed and noise-overexposed, Dutch-belted, male and female rabbits in order to characterize cochlear function and structure under normal-hearing and hearing-loss conditions. Using an octave-band noise exposure centered at 750 Hz presented under isoflurane anesthesia, we found that a sound level of 133 dB SPL for 60 min was minimally sufficient to produce permanent ABR threshold shifts. Overexposure durations of 60 and 90 min caused median click-evoked ABR threshold shifts of 10 and 50 dB, respectively. Susceptibility to overexposure was highly variable across ears, but less variable across test frequencies within the same ear. ABR and DPOAE threshold shifts were smaller, on average, and more variable in male than female ears. Similarly, post-exposure survival of OHCs was higher, on average, and more variable in male than female ears. We paired post-exposure ABR and DPOAE threshold shift data with hair cell count data measured in the same ear at the same frequency and cochlear frequency location. ABR and DPOAE threshold shifts exhibited critical values of 46 and 18 dB, respectively, below which the majority of OHCs and IHCs survived and above which OHCs were wiped out while IHC survival was variable. Our data may be of use to researchers who wish to use Dutch-belted rabbits as a model for the effects of noise-induced hearing loss on the central auditory system.

Speech is our most important form of communication, yet we have a poor understanding of how communication sounds are processed by the brain. Mice make great model organisms to study neural processing of communication sounds because of their rich repertoire of social vocalizations and because they have brain structures analogous to humans, such as the auditory midbrain nucleus inferior colliculus (IC). Although the combined roles of GABAergic and glycinergic inhibition on vocalization selectivity in the IC have been studied to a limited degree, the discrete contributions of GABAergic inhibition have only rarely been examined. In this study, we examined how GABAergic inhibition contributes to shaping responses to pure tones as well as selectivity to complex sounds in the IC of awake mice. In our set of long-latency neurons, we found that GABAergic inhibition extends the evoked firing rate range of IC neurons by lowering the baseline firing rate but maintaining the highest probability of firing rate. GABAergic inhibition also prevented IC neurons from bursting in a spontaneous state. Finally, we found that although GABAergic inhibition shaped the spectrotemporal response to vocalizations in a nonlinear fashion, it did not affect the neural code needed to discriminate vocalizations, based either on spiking patterns or on firing rate. Overall, our results emphasize that even if GABAergic inhibition generally decreases the firing rate, it does so while maintaining or extending the abilities of neurons in the IC to code the wide variety of sounds that mammals are exposed to in their daily lives. NEW & NOTEWORTHY GABAergic inhibition adds nonlinearity to neuronal response curves. This increases the neuronal range of evoked firing rate by reducing baseline firing. GABAergic inhibition prevents bursting responses from neurons in a spontaneous state, reducing noise in the temporal coding of the neuron. This could result in improved signal transmission to the cortex.