Maturational time course of the envelope following response to amplitude-modulated acoustic signals in rats.

OBJECTIVE: The maturation pattern of the envelope following response (EFR) was described using rats as an experimental model. DESIGN: EFRs were recorded in animals at different postnatal ages (15, 20, 25, 35, and 70 postnatal days) in response to broadband noise (BBN) and tones of 8000 and 4000 Hz modulated in amplitude using a continuous sweep of modulation frequencies. Responses were analysed in the 90-190 Hz modulation frequency (MF) range. STUDY SAMPLE: Forty individuals (eight individuals for each age bracket) were included in the present study. RESULTS: During maturation, the MF at which the maximum amplitude was obtained (BMF, best modulation frequency) shifted to higher values when animals were stimulated with tones. At the same time, the amplitude of the response at the BMF increased. For every group of animals, the amplitude of the response continuously decreased for MFs higher than the BMF. However, less steep decreases of amplitude were obtained as animals became adults. CONCLUSIONS: These results provide normative data regarding the maturation of the EFR in rats. They provide information for the development of predictor models to estimate the temporal resolution of the auditory system during maturation.

A 25-Year Review of Cuba's Screening Program for Early Detection of Hearing Loss.

Introduction Early screening for hearing loss is currently recognized as an international healthcare standard. In Cuba, such a program was initiated in the capital, Havana, in 1983 and scaled up to national coverage in 1991. Objective Review the development of Cuba's national hearing screening program over the last 25 years (organizational structure, efficiency, coverage and impact on health), and the science and technology developed to sustain it. Intervention The program was organized in two steps: Step 1-clinical selection of children at different stages of development with multiple high-risk registers; Step 2-referral to territorial, hospitalbased centers for auditory brainstem evoked response (ABR) testing, diagnostic evaluation, and intervention. Prior to national scaling-up, the efficiency of this multiple targeted screening (MTS) protocol was evaluated in Havana. Technology and equipment were then developed, and personnel were trained to set up the national screening network. In 1996, the multiple auditory steady-state evoked response (MSSR) technique for objective audiogram estimation was introduced using AUDIX equipment, designed and produced in Cuba for this program. A semi-automated version for neonatal screening has been developed more recently. Several studies have been conducted to evaluate the program's efficiency, coverage, yield, and impact on health. Results During the first stage of implementation in Havana, the MTS protocol correctly identified 72.5% of children with congenital and preverbal hearing loss. Subsequent studies of different aspects of the program have shown that: 1) the mean age of hearing loss detection/intervention in one municipality was reduced from 4 years to 10 months; 2) hearing-impaired children who were screened showed improved language and cognitive development compared to those who were not screened; 3) the MSSR technique predicted type and severity of hearing loss more accurately than physiological techniques used previously and was also shown to be an effective screening method (92% to 96% sensitivity, 100% specificity); and 4) program coverage (25-86%), though reasonably high in some regions, is not complete and needs improvement, particularly in the country's remote and rural areas. Conclusions The MTS protocol can be considered a valid option for increasing the yield and effectiveness of a hearing screening program operating with limited resources. The MSSR technique provides valuable data for the diagnosis and treatment of children detected through a screening program and, with improvements, may also be useful as a screening method.

Test accuracy and prognostic validity of multiple auditory steady state responses for targeted hearing screening.

The test accuracy and prognostic validity of Multiple Auditory Steady State Responses (MSSR) and click Auditory Brainstem Responses (cABR) was compared within the context of a targeted screening protocol. A sample of 508 high-risk babies was first screened using cABR and MSSR (500 and 2000 Hz). All children (failed/ pass) were called back at three to four years of age to determine their hearing status (pure-tone audiometry). Although both methods showed an equally good test performance in the first screen (sensitivity: 100% and specificity: 92-95%), the MSSR may have some potential advantage to identify low-frequency hearing loss. Furthermore, the confirmatory audiometry with MSSR predicted the child hearing status more accurately than the cABR. In conclusion, the MSSR can provide valuable information for the diagnosis and management of infants earlier detected by a screening protocol and further developed might be also useful as a screening test.