Our brain works as an information-processing system; it receives external and internal signals that comprise multiple sensory modalities, evaluate them in a context-dependent manner, and makes a right choice. To understand the logic how such computation is achieved in the brain is a fundamental question in the field of neuroscience. The fruit fly Drosophila melanogaster is an ideal model organism that allows sophisticated genetic manipulations to analyze neurons and neural circuits in the brain. The aim of our research group is to understand how sound signals are detected, processed, and integrated in the fly brain, by identifying the functional elements in the brain to process auditory information.
　Hearing is an important sensory modality for most animals to detect sound as they mate, look for food, or fend off prey. The fruit fly, with its rather simple nervous system and a large variety of molecular and genetic tools available, is an ideal model organism for dissecting mechanisms underlying sound sensing, perception, and evaluation.
　During courtship, Drosophila males produce an acoustic signal (so-called the "love song") that has a species-specific temporal pattern. By combining molecular neurogenetics, calcium imaging and behavioral analyses, we found that the internal sensory neurons of the fly ear are comprised of specialized clusters that are each required for sound and gravity sensing (Kamikouchi et al 2006; 2009). Systematic identification of higher-order interneurons that feed into the primary auditory and gravity centres revealed the characteristic of the auditory and gravity pathways, which is reminiscent of the cochlear and vestibular pathways in our brain. Such anatomical similarity predicts that the logic to process sound and gravity information would be conserved between flies and mammals.
How, then, these signals are processed in the downstream neural circuit of the brain? To discover general principles underlying how the species-specific sounds are represented and evaluated within the fly brain, we had started a systematic analysis of the structural and functional organization of the higher-order auditory neural circuits by using state-of-the-art technologies. The aim of our research is (1) to establish the comprehensive map of the auditory neural circuit in the fly brain, and (2) to clarify the function of identified neural circuits, and by doing so, (3) to understand the neural basis of sound perception and evaluation in the brain.