Biology subjects

Greene, N. T.

Publications and source records attributed to Greene, N. T..

8 recordsLinked to original sources

bioRxiv2025

Intracochlear pressure measurements quantify overall noise exposure to the inner ear during mastoidectomy

IntroductionThe acoustic trauma patients are exposed to during otologic surgery is unclear, as previous studies have not captured the effects of vibrational noise on the inner ear. To fill this knowledge gap, we examined inner ear noise directly via intracochlear pressure changes during a mastoidectomy and cochleostomy. MethodsInner ear stimulation was measured using fiber optic pressure sensors inserted into the cochlea of cadaveric heads using a trans-canal approach. A tympanomeatal flap was elevated, cochleostomies were made into scala vestibuli and tympani, and sensors placed and secured to the cochlear promontory, and the flap resecured. Intracochlear pressures were measured with different drill bits, speeds, and during mastoidectomy and cochleostomy. The equivalent sound pressure level in the ear canal (LEq) was calculated using the middle ear transfer function. Microphones were also placed in the surgeons ear, cadaver ear, and approximately three feet away. ResultsResults show sound pressure levels that could exceed 120 dBA (A-weighted dB SPL LEq), with the highest levels observed during cochleostomy. Results showed broad band exposure, with a distinct peak at 1.33 kHz during the 80k RPM drill speed. Importantly, SPLs in the surgeons ear did not always predict patient noise exposure. ConclusionSurgically induced cochlear noise revealed levels high enough to potentially induce acoustic trauma, and sometimes at frequencies that may cause hearing loss not captured by a traditional audiogram (i.e. 1.33 kHz). This data characterizes surgical noise exposures, and will lead to permissible noise exposure guidelines and durations for both patients and surgeons.

bioengineering↗

bioRxiv2025

Spatial hearing and temporal processing ability of the Mongolian gerbil (Meriones unguiculatus) measured using prepulse inhibition of acoustic startle

The Mongolian gerbil is a common model organism for studying the neural and behavioral mechanisms of binaural and spatial hearing, largely because of its ability to hear lower frequencies than other rodents and thus utilize both interaural time and level difference cues for sound localization. Prior spatial hearing studies in gerbils have relied on operant conditioning paradigms, requiring large amounts of time-consuming training and testing on multiple different tasks needed to make a comprehensive assessment of spatial hearing ability (including temporal processing, spatial acuity and spatial unmasking). This limits the ability of researchers to thoroughly assess behavioral performance in individual animals. In this study, we used the reflexive prepulse inhibition of the acoustic startle reflex (PPI) to extensively assess spatial hearing and temporal processing abilities in individual gerbils of both sexes. Results show that gerbils inhibit a startle response to a brief loud sound based on prepulse acoustical cues consisting of a 1) temporal gap in ongoing sounds, 2) change in sound source location, and 3) target sound in the presence of a masker. In each test, the magnitude of the suppression of startle increased monotonically as a function of the magnitude of the acoustical prepulse, not unlike a psychometric function, from which threshold performance could be measured. Thresholds in the gerbils in each task measured using PPI matched those acquired using operant conditioning methods.

animal behavior and cognition↗

bioRxiv2024

VARIATION IN HEAD AND PINNA MORPHOLOGY OF PRESERVED PEROMYSCUS SPP. SPECIMENS AND IMPLICATIONS FOR AUDITORY FUNCTION

The characteristics of an animals head and pinna mark the beginning of auditory communication. Auditory communication is broadly achieved by receiving sounds from the environment and plays a vital role in an animals ability to perceive and localize sounds. Natural history museums and collections along with their vast repositories of specimens provide a unique resource for examining how the variability in both the size and shape of the head and pinna cause variability in the detection of acoustic signals across species. Using this approach, we measured the dimensions of the head and pinna of over 1,200 preserved specimens of Peromyscus boylii, P. californicus, P. gossypinus, P. leucopus, P. maniculatus, and P. truei, followed by a series of head-related transfer functions (HRTFs) on several individuals to study the relationship between morphology and available auditory information. Our morphological results show significant variation in pinna length and width, as well as in the distance between the two ears across the six species. ITDs and ILDs were calculated and demonstrated consistent results across species, suggesting the differences in head and pinna size do not significantly modify these cues. Not only does this study contribute to existing research on external morphology and auditory function, but it also provides valuable insight into the use of preserved specimens in auditory research, an area that is currently understudied. Summary statementThis work aims to provide insight into using natural history museum specimens for morphological research pertaining to the auditory system in small mammals.

evolutionary biology↗

bioRxiv2024

Degradation in Binaural and Spatial Hearing and Auditory Temporal Processing Abilities as a Function of Aging

ObjectivesSensorineural hearing loss is common with advancing age, but even with normal or near-normal hearing in older persons, performance deficits are often seen for suprathreshold listening tasks such as understanding speech in background noise or localizing sound direction. This suggests there is also a more central source of the problem. Objectives of this study were to examine as a function of age (young adult to septuagenarian) performance on: 1) a spatial acuity task examining localization ability, and a spatial speech-in-noise (SSIN) recognition task, both measured in a hemi-anechoic sound field using a circular horizontal-plane loudspeaker array, and 2) a suprathreshold auditory temporal processing task and a spectro-temporal processing task, both measured under headphones. Further, we examined any correlations between age, hearing thresholds including extended high frequency (EHF: >8000 Hz), and these measures. DesignSubjects were 48 adults, aged 21 to 78, with either normal hearing or only a mild sensorineural hearing loss through 4000 Hz. The localization task measured minimum audible angle (MAA) for 500 and 4000 Hz 1/3rd octave narrowband noise (NBN) in diffuse background noise for both an on-axis (reference source 0{degrees}) and off-axis (reference source 45{degrees}) listening condition at signal-to-noise ratios (SNRs) of -3, -6, -9, and -12 dB. SSIN testing was also completed for key word recognition in sentences in multi-talker babble noise; specifically, the separation between speech and noise loudspeakers was adaptively varied to determine the difference needed for 40% and 80% correct performance levels. Finally, auditory temporal processing ability was examined using the Temporal Fine Structure (TFS) test, and the Spectro-Temporal Modulation (STM) test. ResultsSpatial acuity was poorer (larger MAAs) in older compared to younger subjects, particularly in the more adverse listening conditions (off-axis, and poorer SNRs). The SSIN data also showed declining mean performance with age at both criterion levels, emerging in the middle age group (> 40 years), but was not correlated with standard audiometric hearing thresholds. Decreased performance on the TFS and STM tasks was dependent on age, emerging only in the older (> 60 years) and middle (>40 years) age groups, respectively; neither was dependent on hearing thresholds. Results of multiple regression analyses suggest that SSIN recognition scales with the ability of the subjects to use both low-frequency binaural temporal fine structure as well as higher-frequency binaural envelope cues, both of which are impacted by aging but not necessarily audiometric hearing thresholds. Finally, EHF range hearing thresholds significantly decreased with age, but performance on tasks remained significantly correlated with age when controlled for EHF hearing. ConclusionsParticularly for more adverse listening conditions, age-related deficits, but not hearing-threshold-related deficits, were found on both of the spatial hearing tasks and in temporal and spectro-temporal processing abilities. It may be that deficits in temporal processing ability contribute to poorer spatial hearing performance in older subjects due to inaccurate coding of binaural/interaural timing information sent from the periphery to the binaural brainstem. In addition, EHF hearing loss may be a coexisting factor in the reduced performance seen in older subjects.

neuroscience↗

bioRxiv2024

Unilateral auditory deprivation reveals brainstem origin of a sensitive period for spatial hearing

Early sensory experience can exert lasting perceptual consequences. For example, a brief period of auditory deprivation early in life can lead to persistent spatial hearing deficits. Some forms of hearing loss (i.e., conductive; CHL) can distort acoustical cues needed for spatial hearing, which depend on inputs from both ears. We hypothesize that asymmetric acoustic input during development disrupts auditory circuits that integrate binaural information. Here, we identify prolonged maturation of the binaural auditory brainstem in the guinea pig by tracking auditory evoked potentials across development. Using this age range, we induce a reversible unilateral CHL and ask whether behavioral and neural maturation are disrupted. We find that developmental CHL alters a brainstem readout of binaural function which is not observed when the CHL is induced in adulthood. Startle-based behavioral measures reveal poorer spatial resolution of sound sources, but only for high-frequency sound stimuli. Finally, single-unit recordings of auditory midbrain neurons reveal significantly poorer neural acuity to a sound location cue that largely depends on high-frequency sounds. Thus, these findings show that unilateral deprivation can disrupt developing auditory circuits that integrate binaural information and may give rise to lingering spatial hearing deficits.

neuroscience↗

bioRxiv2019

Auditory binaural and spatial hearing impairments in a Fragile X Syndrome mouse model

The auditory brainstem compares sound-evoked excitation and inhibition from both ears to compute sound source location. Although alterations to the anatomy and physiology of the auditory brainstem have been demonstrated in Fragile X Syndrome (FXS) it is not known whether these changes cause sound localization impairments in FXS. To test the hypothesis that FXS-related alterations to brainstem circuits impair spatial hearing abilities, a reflexive prepulse inhibition (PPI) task, with sound source location as the prepulse stimulus, was used to show that Fmr1 knockout mice have decreased inhibition of their startle responses. Specifically, Fmr1 mice show decreased PPI compared to wildtype during gap detection, changes in sound source location, and spatial release from masking with no alteration to their overall startle thresholds compared to wildtype. Lastly, Fmr1 mice have increased latency to respond in these tasks suggesting additional impairments in the pathway responsible for reacting to a startling sound.

neuroscience↗

bioRxiv2019

Sensitivity of single units in the LSO of decerebrate cat to sinusoidally amplitude modulated tones

Fluctuations in amplitude are a common component of behaviorally important sound stimuli. Amplitude modulation (AM) is encoded by the peripheral auditory system in the timing of discharge spikes, and, more centrally, in the discharge rate. The mechanism producing this transformation from a time- to rate-based code is not known, but recent modeling efforts have suggested a role for neurons with response characteristics consistent with cells in the lateral superior olive (LSO). The responses of single units in the LSO of unanesthetized decerebrate cat were recorded to monaural sinusoidally amplitude modulated (SAM) tones by systematically varying sound level and modulation frequency (fm), and are described in terms of synchronization to the envelope and average discharge rate as a function of fm. LSO units typically synchronize strongly to low fm, and discharge preferentially (i.e. more strongly) over a small range of fm in response to low level SAM tones. At higher sound levels synchronization decreases and response rate increases until most or all modulation in the response is lost. These results contrast with responses recorded in the barbiturate-anesthetized cat, which tend to respond to most low-frequency modulations, and are consistent with LSO as an intermediate processing stage between the peripheral temporal- and central rate-based code for AM sounds.

neuroscience↗

bioRxiv2019

Evidence of a Functionally Segregated Pathway from Lateral Superior Olive to Inferior Colliculus

Neurons in the central nucleus of the inferior colliculus (ICC) of decerebrate cats show three major response patterns when tones of different frequencies and levels are presented to the contralateral ear. The frequency response maps of type I units uniquely exhibit a narrowly tuned I-shaped area of excitation around best frequency (the most sensitive frequency) and flanking regions of inhibition at lower and higher frequencies. Type I units receive ipsilateral inhibition, and show binaural excitatory/inhibitory interactions. Lateral superior olive (LSO) principal cells display a similar receptive field organization and sensitivity to interaural level differences (ILDs) and project directly to the ICC, therefore are supposed to be the dominant source of excitatory input for type I units. To test this hypothesis, the responses of ICC units were compared before and after reversible inactivation of the LSO by injection of the non-specific excitatory amino-acid antagonist kynurenic acid. When excitatory activity within the LSO was blocked, many ICC type I units (~50%) were silenced or showed substantially decreased activitycomparable. By contrast, the responses of the other two ICC unit types were largely unaffected. With regard to the origins of unaffected ICC type I units, evidence indicates that the LSO was inactivated in an incomplete, anisotropic manner, and the monaural and binaural responses of such units are similar to those of affected type I units. Taken together, these results support the interpretation that most type I units are the midbrain components of a functionally segregated ILD processing pathway initiated by the LSO.

neuroscience↗