Sound environment is a prime source of conscious and unconscious information which allows listeners to place themselves, to communicate, to feel, to remember. The author describes the process of designing a new audio interactive apparatus for Alzheimer's care, in the context of an active multidisciplinary research project led by the author in collaboration with a longterm care centre (EHPAD) in Burgundy (France), a geriatrician, a gerontologist, psychologists and caregivers. The apparatus, named Madeleines Sonores in reference to Proust's madeleine, have provided virtual soundscapes sounding for a year for 14 elderly people hosted in the dedicated Alzheimer's unit of the care centre, 24/7. Empiric aspects of sonic interactivity are discussed in relation to dementia and to the activity of caring. Scientific studies are initiated to evaluate the benefits of such a disposal in Alzheimer's disease therapy and in caring dementia.