Allen F. Marshall

Detection of interaural correlation by neurons in the superior olivary complex, inferior colliculus and auditory cortex of the unanesthetized rabbit

A critical binaural cue important for sound localization and detection of signals in noise is the interaural time difference (ITD), or difference in the time of arrival of sounds at each ear. The ITD can be determined by cross-correlating the sounds at the two ears and finding the ITD where the correlation is maximal. The amount of interaural correlation is affected by properties of spaces and can therefore be used to assess spatial attributes. To examine the neural basis for sensitivity to the overall level of the interaural correlation, we identified subcollicular neurons and neurons in the inferior colliculus (IC) and auditory cortex of unanesthetized rabbits that were sensitive to ITDs and examined their responses as the interaural correlation was varied. Neurons at each brain level could show linear or non-linear responses to changes in interaural correlation. The direction of the non-linearities in most neurons was to increase the slope of the response change for correlations near 1.0. The proportion of neurons with non-linear responses was similar in subcollicular and IC neurons but increased in the auditory cortex. Non-linear response functions to interaural correlation were not related to the type of response as determined by the tuning to ITDs across frequencies. The responses to interaural correlation were also not related to the frequency tuning of the neuron, unlike the responses to ITD, which broadens for neurons tuned to lower frequencies. The neural discriminibility of the ITD using frozen noise in the best neurons was similar to the behavioral acuity in humans at a reference correlation of 1.0. However, for other reference ITDs the neural discriminibility was more linear and generally better than the human discriminibility of the interaural correlation, suggesting that stimulus rather than neural variability is the basis for the decline in human performance at lower levels of interaural correlation.

Behavioral Sensitivity to Interaural Time Differences in the Rabbit

An important cue for sound localization and separation of signals from noise is the interaural time difference (ITD). Humans are able to localize sounds within 1-2 degrees and can detect very small changes in the ITD (10-20micros). In contrast, many animals localize sounds with less precision than humans. Rabbits, for example, have sound localization thresholds of approximately 22 degrees . There is only limited information about behavioral ITD discrimination in animals with poor sound localization acuity that are typically used for the neural recordings. For this study, we measured behavioral discrimination of ITDs in the rabbit for a range of reference ITDs from 0 to +/-300micros. The behavioral task was conditioned avoidance and the stimulus was band-limited noise (500-1500Hz). Across animals, the average discrimination threshold was 50-60micros for reference ITDs of 0 to +/-200micros. There was no trend in the thresholds across this range of reference ITDs. For a reference ITD of +/-300micros, which is near the limit of the physiological window defined by the head width in this species, the discrimination threshold increased to approximately 100micros. The ITD discrimination in rabbits less acute than in cats, which have a similar head size. This result supports the suggestion that ITD discrimination, like sound localization [see Heffner, 1997. Acta Otolaryngol. 532 (Suppl.), 46-53] is determined by factors other than head size.

The TLC: A Novel Auditory Nucleus of the Mammalian Brain

We have identified a novel nucleus of the mammalian brain and termed it the tectal longitudinal column (TLC). Basic histologic stains, tract-tracing techniques and three-dimensional reconstructions reveal that the rat TLC is a narrow, elongated structure spanning the midbrain tectum longitudinally. This paired nucleus is located close to the midline, immediately dorsal to the periaqueductal gray matter. It occupies what has traditionally been considered the most medial region of the deep superior colliculus and the most medial region of the inferior colliculus. The TLC differs from the neighboring nuclei of the superior and inferior colliculi and the periaqueductal gray by its distinct connections and cytoarchitecture. Extracellular electrophysiological recordings show that TLC neurons respond to auditory stimuli with physiologic properties that differ from those of neurons in the inferior or superior colliculi. We have identified the TLC in rodents, lagomorphs, carnivores, nonhuman primates, and humans, which indicates that the nucleus is conserved across mammals. The discovery of the TLC reveals an unexpected level of longitudinal organization in the mammalian tectum and raises questions as to the participation of this mesencephalic region in essential, yet completely unexplored, aspects of multisensory and/or sensorimotor integration.

Auditory response properties of neurons in the tectal longitudinal column of the rat.

The newly-discovered tectal longitudinal column (TLC) spans the paramedian region of the mammalian tectum. It has connections with several nuclei of the auditory system. In this report, we provide the first detailed description of the responses of TLC neurons to auditory stimuli, including monaural and binaural tones and amplitude modulated tones. For comparison, responses in the inferior colliculus (IC) were also recorded. Neurons in the TLC were sensitive to similar ranges of frequency as IC neurons, could have comparably low thresholds, and showed primarily excitatory responses to stimulation of the contralateral ear with either phasic or sustained response patterns. Differences of TLC compared to IC neurons included broader frequency tuning, higher average threshold, longer response latencies, little synchronization or rate tuning to amplitude modulation frequency and a smaller degree of inhibition evoked by stimulation of the ipsilateral ear. These features of TLC neurons suggest a role for the TLC in descending auditory pathways.

Magnetic resonance imaging of guinea pig cochlea after vasopressin-induced or surgically induced endolymphatic hydrops

Objective: To investigate the ability to detect the in vivo cochlear changes associated with vasopressin-induced and surgically induced endolymphatic hydrops using MRI at 3 tesla (T). Study Design: Prospective, animal model. Setting: Animal laboratory. Subjects and Methods: In group 1, five guinea pigs underwent post–gadolinium temporal bone MRI before and after seven and 14 days of chronic systemic administration of vasopressin by osmotic pump. In group 2, five guinea pigs underwent temporal bone MRI eight weeks after unilateral surgical ablation of the endolymphatic sac. Three-tesla high-resolution T1-weighted sequences were acquired pre- and postcontrast administration. Region of interest signal intensities of the perilymph and endolymph were analyzed manually. Quantitative evaluation of hydrops was measured histologically. Results: Gadolinium preferentially concentrated in the perilymph, allowing for distinction of cochlear compartments on 3.0-T MRI. The T1-weighted contrast MRI of vasopressin-induced hydropic cochlea showed significant increases in signal intensity of the endolymph and perilymph. Surgically induced unilateral hydropic cochlea also showed increased signal intensity, compared with the control cochlea of the same animal, but less of an increase than the vasopressin group. The histological degree of hydrops induced in the vasopressin group was comparable to previous studies. Conclusions: In vivo postcontrast MRI of the inner ear demonstrated cochlear changes associated with chronic systemic administration of vasopressin and surgical ablation of the endolymphatic sac. Understanding the MRI appearance of endolymphatic hydrops induced by various methods contributes to the future use of MRI as a possible tool in the diagnosis and treatment of Ménières disease.

Pleomorphic adenoma in the palpebral lobe of the lacrimal gland

Head and neck surgeons commonly manage tumors, lesions, and diseases in and around the orbit. Lesions of the lacrimal gland account for 5% to 15% of all primary orbital tumors. Pleomorphic adenomas comprise 25% of all lacrimal gland tumors and 50% of all epithelial neoplasms involving the lacrimal gland. Pleomorphic adenomas arising in this location are typically slow-growing, painless lesions that require en bloc excision to avoid tumor seeding into the orbit. The lacrimal gland consists of 2 lobes separated by the levator aponeurosis: a deep orbital lobe and a superficial palpebral lobe. While pleomorphic adenomas of the lacrimal gland are commonly located in the orbital lobe, tumors that originate in the palpebral lobe are far less common. While originally thought to be extremely rare, in a review of 36 epithelial lacrimal gland neoplasms, Vangveeravong et al reported that 17% arose from the palpebral lobe. However, upon publication of this manuscript, only 14 cases of pleomorphic adenoma involving the palpebral lobe had been reported. To our knowledge, this is the first such case reported in the otolaryngology–head and neck surgery literature. The purpose of this article is to present a patient with a lacrimal gland mass involving the palpebral lobe and to describe the importance of en bloc excision in the management of these lesions. Additionally, we emphasize the utility of an anteriosupeFrom the Department of Otolaryngology–Head and Neck Surgery, University of North Carolina Hospitals, Chapel Hill, NC. Reprint requests: Allen F. Marshall, MD, Department of Otolaryngology–Head and Neck Surgery, CB#7070, University of North Carolina Hospitals, Chapel Hill, NC 27599-7070; e-mail, allen_marshall@med.unc.edu. Otolaryngol Head Neck Surg 2005;132:141-3. 0194-5998/

10:20: Effect of Vasopressin on Auditory Thresholds in Guinea Pigs

30.00 Copyright

R183: Effect of ETT Size, Cuff, and Steroid on Tracheal Stenosis

recovery). Unpaired t-test was used for statistical analysis. RESULTS: The researchers successfully established a working electrical stimulation model of the injured rat facial nerve. The semi-eyeblink returned significantly earlier (3.71 0.97 vs. 9.57 1.86 days) in stimulated rats (p 0.008). Stimulated rats recovered all functions earlier, and also showed less variability in time to recovery. CONCLUSION: The present study establishes the first model of electrical stimulation of the injured facial nerve in rats. Electrical stimulation significantly reduces recovery time for the semi-eyeblink reflex, a marker of early facial nerve recovery. Electrically stimulated rats have shorter recovery times for all functions. Decreased variability in the recovery period of stimulated animals implies a consistent effect. Electrical stimulation initiates and accelerates facial nerve recovery in the rat model. SIGNIFICANCE: Translational research in accelerating facial nerve recovery in patients with facial nerve paralysis with anatomically contiguous nerve (Bell’s palsy, traumatic paralysis, iatrogenic paralysis). SUPPORT: Department of Otolaryngology Gregory Matz Research Fund, Loyola University Medical Center, Maywood, Illinois 60153, USA.

Behavioral Thresholds to Binaural Cues

PROBLEM: The incidence of iatrogenic subglottic stenosis (SGS) following prolonged intubation in the neonate is 2-4%. The use of cuffed verses uncuffed ETT has recently been revisited in pediatric intensive care. Animal studies using modern low-pressure cuffs are needed. Steroids have been effective therapy for SGS. However, systemic steroids have adverse effects, and local injection is technically difficult. METHODS: A model of SGS was induced in 16 rabbits using a diamond burr to create mucosal trauma. A modified pediatric cuffed or uncuffed ETT was surgically placed into the rabbit airway via tracheotomy. The animals were divided into four groups. In group 1, the ETT cuff was filled with steroid, and in group 2 the cuff was filled with saline. In groups 3 and 4, a 3.0 or 3.5 uncuffed ETT resided in the airway respectively. After 1 week, the ETT was removed via the neck, and the animals were monitored for 2 weeks. The animals were sacrificed, and tracheal and laryngeal cartilages were harvested, analyzed grossly, and graded histologically. RESULTS: All animals developed SGS. Animals with smaller 3.0 uncuffed ETT developed significantly more stenosis than animals with uncuffed 3.5 ETT. Animals with 3.0 cuffed ETT had significantly less stenosis than those with uncuffed 3.0 ETT. Among animals with cuffed ETT, treatment with saline versus steroid resulted in similar degrees of stenosis. The amount of stenosis in animals with uncuffed 3.5 ETT did not differ significantly from animals with 3.0 cuffed ETT filled with saline or steroid. CONCLUSION: The presence of a cuff or larger ETT attenuates SGS. Local steroid administration via endotracheal tube cuff did not significantly decrease degree of stenosis. SIGNIFICANCE: Standard pediatric mechanical ventilation is via uncuffed ETT. These results emphasize the importance of proper tube size selection. Use of monitored modern lowpressure cuffed ETT might be beneficial in the pediatric population.

WT1 modulates apoptosis by transcriptionally upregulating the bcl‐2 proto‐oncogene

Abstract Objectives: There is recent interest in bilateral cochlear implantation to obtain the benefits of binaural hearing. This interest necessitates development of animal models to examine the effects of bilateral implants on the binaural system. Our goal is to develop the unanesthetized rabbit as a model to study behavior and physiology with bilateral implants. This species was chosen because of the wealth of the physiological data from normal animals. However, there is no comparable behavioral data in rabbits. Thus, for this study we behaviorally tested the ability of rabbits to discriminate interaural time differences (ITDs). Methods: Normal hearing Dutch-belted rabbits were trained to discriminate ITDs using conditioned avoidance. A tracking method was used to determine the threshold interaural time difference (ITD) that was discriminable between a reference ITD and a warning ITD. Results: The minimum perceptual threshold was 78 μs at a reference ITD of 100 μs. At 0 μs reference ITD the threshold was 109 μs, increasing to 245 μs at reference ITD of 300 μs. Conclusion: Compared to human beings, the most sensitive region for ITD detection in rabbits is lateralized (100 μs instead of 0 μs) and thresholds are higher (78 μs instead of ∼15 μs). Surprisingly, the rabbit behavioral thresholds are worse than those calculated from physiological responses in neurons, which are comparable to human behavioral thresholds. This study advances the goal of using rabbits as a model system for bilateral cochlear implants.