Effect of maternal care on hearing onset induced by developmental changes in the auditory periphery.

Handling (H) and cross-fostering (CF) rodent pups during postnatal development triggers changes in maternal behavior which in turn trigger long-term physiological changes in the offspring. However, less is known about the short-term effects of H and CF on infant development. In this study we hypothesized that manipulations of maternal care affect the onset of hearing in Wistar rats. To test this hypothesis we obtained auditory brainstem responses (ABRs) and micro-CT x-ray scans to measure changes in the development of the auditory periphery in H and CF pups manipulated at postnatal day (P)1, P5, or P9. We found evidence of changes in hearing development in H and CF pups compared with naive pups, including changes in the percentage of animals with ABRs during development, a decrease in ABR thresholds between P13 and P15, and anatomical results consistent with an accelerated formation of the middle ear cavity and opening of the ear canal. Biochemical measurements showed elevated levels of thyroid hormone in plasma from naive and CF pups. These results provide evidence that manipulations of maternal care accelerate hearing onset in Wistar rats. Understanding the mechanisms by which maternal care affects hearing onset opens new opportunities to study experience-dependent development of mammalian hearing.

The efficiency of the single- versus multiple-stimulus auditory steady state responses in infants.

OBJECTIVES: Multiple auditory steady state responses (ASSRs) will likely be included in the diagnostic test battery for estimating infant auditory thresholds in the near future; however, the effects of single- versus multiple-stimulus presentation in infants has never been investigated. In adults, there are no interactions (reduced amplitudes) between responses to multiple simultaneous stimuli presented at 60 dB SPL or lower. Maturational differences, however, may lead to greater interactions in infants; thus, it is unknown whether the single-stimulus technique or the multiple-stimulus technique is more efficient for testing infants. Two studies were carried out to address this issue. DESIGN: All infants in study A participated in three stimulus conditions, which differed in the number of stimuli presented simultaneously. The monotic single (MS) condition consisted of 500, 1000, 2000, and 4000 Hz tones, which were presented singly to one ear. The monotic multiple (MM) condition was composed of four tones (500, 1000, 2000, and 4000 Hz) presented to one ear simultaneously. The dichotic multiple (DM) condition consisted of eight tones presented simultaneously to both ears (four tones to each ear). ASSR amplitudes were obtained from 15 normal infants (mean age: 23.1 wks) in response to multiple (MM, DM) and single (MS) air conduction amplitude-modulated (AM) tones (77 to 105 Hz modulation rates; 60 dB SPL). In study B, ASSR thresholds were determined for 500-Hz stimuli in the single- and DM-stimulus conditions (14 infants; mean age: 20.2 wks). RESULTS: Mean single-stimulus ASSR amplitudes for 500, 1000, 2000, and 4000 Hz were 30, 39, 45 and 43 nV, respectively. Presentation of multiple AM tones (i.e., four octave-spaced frequencies) to one ear resulted in ASSR amplitudes that were 97%, 87%, 82%, and 70% (for 500, 1000, 2000, and 4000 Hz, respectively) of the single-stimulus ASSR amplitudes. Results for the dichotic presentation of eight AM tones show ASSR amplitudes that were 70%, 77%, 67%, and 67% relative to the MS condition. Although decreases in amplitude occurred using multiple stimuli in infants, the multiple ASSR remained more efficient than the single-stimulus ASSR (i.e., multiple-stimulus amplitudes were greater than single-stimulus amplitudes divided by √K, where K is the number of stimuli). Results from study B indicate that ASSR thresholds for 500 Hz presented in the DM condition were elevated 3 dB compared with that obtained in the 500-Hz single-stimulus condition. This statistically nonsignificant difference is within the range of acceptable test-retest variability and is thus not of clinical significance. CONCLUSIONS: The amplitude reductions seen in the multiple-stimulus conditions in infants, not seen in adults, could be related to maturational differences in the ear canal, middle ear, cochlea, and/or brain stem. Because greater interactions occur in the DM-stimulus condition compared with the monotic multiple-stimulus condition and baseline single-stimulus condition, brain stem origins of these interactions are likely. Study B revealed statistically nonsignificant differences between threshold for 500 Hz when presented in the single- and DM-stimulus conditions. In summary, as with adults, multiple-stimulus presentation in infants is more efficient than single AM tones, at least for 60 dB SPL stimuli.

Independent component analysis for robust assessment of auditory system maturation in children with cochlear implants.

The long latency auditory evoked potential (LLAEP) has been used for tracking changes in latency and morphology of the P1 peak in order to evaluate the maturation of the auditory system in children with cochlear implants (CIs). Cochlear implants can induce an artefact in the recordings when sounds are presented, which makes the analysis of LLAEPs much harder. Independent component analysis (ICA) has been used to remove this artefact. In this paper we apply a procedure based on ICA to reduce the CI artefact, to detect the LLAEPs and to use the changes in the spatial projections of their independent components (ICs) for a robust evaluation of the maturation of the auditory system in children with CIs.

Maturation of bone conduction multiple auditory steady-state responses.

The objective of this study was to compare bone-conduction (BC) auditory steady-state responses (ASSR) for infants and adults with normal hearing to investigate the time course of maturation of BC hearing sensitivity. Bone-conduction multiple ASSRs were recorded in 0-11-month-old (n=35), and 12-24-month-old infants (n=13), and adults (n=18). Low-frequency BC ASSR thresholds increased with age, whereas, high-frequency ASSR thresholds were unaffected by age except for a slight improvement at 2000 Hz. Compared to adults, BC ASSR amplitudes for young infants were larger for low frequencies, whereas, their amplitudes were smaller or similar for high frequencies. Compared to adults, young infants are much more sensitive to low-frequency BC stimuli, and probably more sensitive to high-frequency BC stimuli; these differences between infants and adults persist until at least two years of age. Different 'normal levels' for infants of different ages must be used and are proposed in this study.

Musicoterapia para recién nacidos prematuros en cuidados intensivos neonatales* / Music therapy for premature infants in neonatal intensive care

Con las mejoras de la atención médica en Estados Unidos, cada vez sobreviven más recién nacidos críticamente prematuros, de una edad gestacional cada vez más joven, muchos de los cuales pasan todo el último trimestre de su desarrollo en la unidad de cuidados intensivos neonatales. Las técnicas de la musicoterapia son prometedoras para tranquilizar a los recién nacidos, reduciendo el estrés, promoviendo el desarrollo del lenguaje y reforzando su madurez durante estos momentos tan críticos. La música puede también reducir la duración de su estancia en el hospital, y los costes médicos derivados asociados a los cuidados de estos recién nacidos. El objetivo de este artículo es describir las investigaciones que se han realizado en el campo de la musicoterapia con recen nacidos (RN) prematuros y las técnicas recomendadas desde esta modalidad de tratamiento durante su estancia hospitalaria en cuidados intensivos neonatales (AU)

Auditory similarities associated with genetic and experimental acoustic deprivation.

Susceptibility to audiogenic seizures has been produced in otherwise non-susceptible mice by acoustic stress and by conductive hearing loss. Both procedures temporarily elevate the absolute threshold of the auditory evoked potential (AEP) and are maximally effective during a circumscribed period of early development. In the genetically SUSCEPTIBLE DBA/2J mouse, AEP thresholds indicated that its auditory system is functionally less mature during this early period than that of the nonsusceptible C57BL/6Jmouse. It was proposed that innate susceptibility found in the DBA/2J mouse results from auditory disuse supersensitivity during a critical developmental period, in support of Saunders' hypothesis for acoustically primed mice. The increased peak-to-peak AEP amplitudes, however, were not believed to be causally related to the audiogenic seizures.

Albinism and auditory function in the laboratory mouse. I. Effects of single-gene substitutions on auditory physiology, audiogenic seizures, and developmental processes.

The effects of single-gene albino (c/c) mutations on auditory behavior and physiology were examined in congenic C57BL/6J mice. At 16 days of age, the c gene was additively associated with both reduced auditory functioning and lower body weight: 16-day-old c/c mice had higher auditory evoked potential (AEP) thresholds than +/c mice, which, in turn, had higher thresholds than +/+ mice; +/c mice were also intermediate with regard to body weight. Since these differences had nearly disappeared by 21 days of age, it was concluded that the c genes worked in an additive fashion to delay development during the period previously (Henry, 1967) found critical for inducing susceptibility to audiogenic seizures. At 16 days of age, albino mice (c/c) displayed susceptibility to audiogenic seizures, but nonalbino genotypes (+/c and +/+) were immune to the convulsive effects of sound. This behavior appeared to be a recessive trait at this age. But 5 days later, the behavioral phenotype exhibited incomplete dominance, with the +/c genotype displaying audiogenic seizures intermediate to those seen in the susceptible c/c and the nonsusceptible +/+ genotypes. These behaviors were compared to the thresholds and peak-to-peak amplitudes of the AEP, as seen in the input-output functions. It is suggested that differential development of the auditory systems in these genotypes is causally related to susceptibility to audiogenic seizures.