Efferent unmasking of speech-in-noise encoding?

OBJECTIVE: The medial olivocochlear (MOC) reflex provides efferent feedback from the brainstem to cochlear outer hair cells. Physiologic studies have demonstrated that the MOC reflex is involved in "unmasking" of signals-in-noise at the level of the auditory nerve; however, its functional importance in human hearing remains unclear. DESIGN: This study examined relationships between pre-neural measurements of MOC reflex strength (click-evoked otoacoustic emission inhibition; CEOAE) and neural measurements of speech-in-noise encoding (speech frequency following response; sFFR) in four conditions (Quiet, Contralateral Noise, Ipsilateral Noise, and Ipsilateral + Contralateral Noise). Three measures of CEOAE inhibition (amplitude reduction, effective attenuation, and input-output slope inhibition) were used to quantify pre-neural MOC reflex strength. Correlations between pre-neural MOC reflex strength and sFFR "unmasking" (i.e. response recovery from masking effects with activation of the MOC reflex in time and frequency domains) were assessed. STUDY SAMPLE: 18 young adults with normal hearing. RESULTS: sFFR unmasking effects were insignificant, and there were no correlations between pre-neural MOC reflex strength and sFFR unmasking in the time or frequency domain. CONCLUSION: Our results do not support the hypothesis that the MOC reflex is involved in speech-in-noise neural encoding, at least for features that are represented in the sFFR at the SNR tested.

Efferent modulation of pre-neural and neural distortion products.

Distortion product otoacoustic emissions (DPOAEs) and distortion product frequency following responses (DPFFRs) are respectively pre-neural and neural measurements associated with cochlear nonlinearity. Because cochlear nonlinearity is putatively linked to outer hair cell electromotility, DPOAEs and DPFFRs may provide complementary measurements of the human medial olivocochlear (MOC) reflex, which directly modulates outer hair cell function. In this study, we first quantified MOC reflex-induced DPOAE inhibition at spectral fine structure peaks in 22 young human adults with normal hearing. The f1 and f2 tone pairs producing the largest DPOAE fine structure peak for each subject were then used to evoke DPFFRs with and without MOC reflex activation to provide a related neural measure of efferent inhibition. We observed significant positive relationships between DPOAE fine structure peak inhibition and inhibition of DPFFR components representing neural phase locking to f2 and 2f1-f2, but not f1. These findings may support previous observations that the MOC reflex inhibits DPOAE sources differentially. That these effects are maintained and represented in the auditory brainstem suggests that the MOC reflex may exert a potent influence on subsequent subcortical neural representation of sound.

Gastrointestinal Mucormycosis After Orthotopic Liver Transplantation Presenting as Femoral Nerve Palsy: A Case Report and Review of the Literature.

Mucormycosis has emerged as a major threat to transplant recipients with high morbidity and mortality. This infection most commonly presents with rhino-sino-orbital localization. Gastrointestinal mucormycosis is uncommon, with presenting symptoms usually abdominal in nature. Here, we describe the case of a liver transplant recipient who developed gastrointestinal mucormycosis with an initial manifestation of femoral nerve palsy, ultimately resulting in fungal dissemination and patient demise. This case highlights the challenges in making a timely diagnosis of mucormycosis, particularly in immunocompromised patients.

Prognostic importance of brainstem auditory evoked responses after asphyxia.

Brainstem auditory evoked responses were recorded after acute asphyxia in 126 infants, ages birth through 18 months. Of these, 21 had markedly abnormal amplitude ratios, and all infants with abnormal amplitude ratios had severe neurologic handicaps. An abnormal amplitude ratio predicts long-term neurologic sequelae of acute asphyxia in infants. Normal amplitude ratios did not, however, ensure normal neurologic outcome; 10 infants with normal responses were severely handicapped.

Brainstem auditory evoked response in the diagnosis of pediatric neurologic diseases.

Brainstem auditory evoked responses (BAERs) were measured in pediatric patients with neurologic diseases. Abnormalities of interwave intervals, amplitude ratios, and response to changing rate of stimulation were found in patients with tumors, myelin disorders, anoxic-ischemic encephalopathy, trauma, and neurodegenerative disorders. Reversibility of brainstem abnormalities (excluding multiple sclerosis) and sensitivity to toxic-metabolic disorders are features of the response not previously described in adults with neurologic disorders. The BAER is a promising new tool for the investigation of pediatric neurologic disease.

Brain stem auditory evoked potentials in patients with congenital atresia.

The purpose of this paper is to illustrate the value of the brain stem auditory evoked response in the definitive assessment of newborn and older infants with congenital malformations of the auditory system. Clinical cases selected illustrate the methodology required in the evaluation and demonstrate how the technique can facilitate immediate and appropriate medical and habilitative services.