Rapid advances have occurred in the field of regenerative medicine due to progress in stem-cell and developmental biology. Even organs that were never considered as having the potential to naturally regenerate have become targets in regenerative medicine. Such organs include the inner ear and auditory nerve, causal organs of sensorineural hearing loss. In this review, a general overview of the current status of regenerative medicine is presented first. Then, the history and current status of regenerative medicine to treat hair cell loss are reviewed from the aspects of three important factors in regenerative medicine: 1) cells (including stem cells); 2) growth factors and other important factors for the development; 3) stem cells in situ and their niche. Several promising methods to regenerate hair cells have been reported, however, most are far from being sufficiently developed for clinical application. This is a different situation from that for the retina, because a clinical trial of stem cell therapy for the retinal disease has already started. One of the reasons for this difference is the lack of thorough knowledge of inner ear development. To achieve more efficient regeneration of hair cells, more progress in the developmental biology of the inner ear is required.

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　In subjects who did not purchase hearing aids, we examined the reasons for the reluctance to buy hearing aids and examined the measures that could be taken to improve the quality of life of persons with hearing loss who require hearing aids and of those around them. The major factor for not purchasing hearing aids was the lack of disease awareness in persons with hearing loss, indicating the existence of persons with hearing loss who do not feel the need to make efforts to compensate hearing. To improve the quality of communication during hearing aid purchase, the acceptance and awareness of hearing loss by the persons themselves and also by those around them are necessary. Moreover, staff should possess the skills to actively recommend the management of hearing loss from a specialist point of view.

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　The effects of aging on high-frequency hearing sensitivity and distortion product otoacoustic emissions (DPOAE) were investigated in 14 normal hearing persons aged 20-41 years. High-frequency hearing sensitivity was studied using the buzzing sound of a mosquito (sound A: 12.5kHz, sound B: 16kHz, sound C: 20kHz). DPOAE was recorded with an Otodynamic Analyzer ( ILO292-USB). The F₂/F₁ ratio was fixed at 1.2 and the DP level of 2F₂- F₁ was investigated at 9 points between 793 and 7,966Hz. The stimulus intensity of F1 and F2 was fixed at 70dBSPL.
　Results: All 14 persons could hear sound A, but none heard sound C. Sound B was audible to 7 persons, but not to the other 7 persons. The hearing group was 10.9 years younger than the non-hearing group.
　In regard to the DPOAE, the DP increased with from 5,042Hz to 6,348Hz in the hearing group. On the other hand, it decreased in the non-hearing group.
　Our conclusion is that the cochlear dysfunction for high frequencies already begins in younger than 41 year old group before the age of 41 years and it was presented with hearing audibility and DPOAE.

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　We conducted articulation training at 9 years old for a child who had received his first cochlear implant at the age of 3 years and 8 months and the second cochlear implant at the age of 8 years and 8 months. After the cochlear implantation surgery, while the child's speech perception ability improved, his articulation errors of velar plosive (/k/, /g/), affricate (/dz/, /ts/), fricative (/s/) and flapped (/r/) remained. By 6 months after the start of the articulation training, the articulation errors were almost fully resolved and the speech intelligibility score was approximately 100%. We speculated on the cause of the articulation errors as follows. 1) The movements of his incorrect articulations were obscured. 2) The incorrect articulations acquired after unilateral cochlear implantation became a habit. 3) The listening discrimination between correct and incorrect articulations after unilateral cochlear implantation alone was difficult. We propose the following as the factors responsible for his articulation improvement within a short time after the start of articulation training. 1) After wearing bilateral cochlear implants, the listening discrimination between correct and incorrect articulations became easy. 2) In articulation training, we promoted control of his speech rate and voice loudness, and his becoming aware of self-sound feedback. 3) We used not only auditory, but also visual, tactile, and motor sensory modalities in the articulation training. 4) He had acquired adequate language ability to comprehend the therapist's verbal explanation of the articulation movements.

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　A conditioned orientation response audiometry (COR) was performed in infants not suffering from any developmental or motor disorders, and the response format was then classified by the presence or absence of conditioning by auditory stimuli and visual stimuli, and by the sense of direction in response to the auditory stimuli. The objective was to analyze the results of 99 COR tests carried out in infants aged 4 to 35 months old.
　 Infants under 12 months without any formed conditioning were comparatively common (8- to 11- month old infants 37%, 4- to 7-month old infants 63%). These test results are due to Behavioral Observation Audiometry, and it was considered that the results of the COR should be clearly distinguished. Infants older than 12 months had mostly formed conditioning (12- to 17-month old infants 95%, 18- to 23-month old infants 89%, and 24- to 35-month old infants, 94%), and the COR adaptation was good.
　 The response format for a typical COR (turning reaction to the auditory stimulus side) was frequently present, showing that many infants had normal hearing ability. The sense of direction was inaccurate in infants with hearing difficulties, leading to many atypical results; this was particularly prominent among infants with unilateral hearing loss.

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