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Synopsis of Scientific Activities

Studying the vestibular system with all its related reflexes and motor functions provides an avenue to the understanding of how the brain processes inputs from different sensory modalities (vestibular, visual, proprioceptive, etc.), and how a subsequent coordinated motor response results from this processing (eye movements, head movements, etc.). These functions imply complicated calculations for coordinate transformations between sensory and motor systems with various degrees of freedom and apparent overcompleteness. One way for the brain to deal with multi-dimensional systems is to employ constraints within reference frame systems. A physical representation of such an intrinsic reference frame is constituted by the three-dimensional geometry of the semicircular canals of the labyrinth. Furthermore, the extraocular muscle system and the visually driven cells of the accessory optic system are organized around distinct coordinate axes which reflect the basic geometry of the semicircular canal system. The neuronal networks interconnecting these sensory and motor systems can be modeled in a meaningful fashion, and indeed they coincide with experimental results. Finally, coordinate transformations either in a physiological context or subsequent to adaptive pressures are an integral part of this conceptual framework.

My recent scientific studies have mainly investigated the eye and head movement systems of vertebrates in order to describe and demonstrate common principles of the physical and intrinsic neuronal organization of these systems. Across the vertebrate species studied, the abovementioned intrinsic reference frame systems are functionally identical. Species-specific specializations may occur, however, overall geometrical and functional principles are preserved. The presence of clearly defined intrinsic reference frame systems within vestibulo-motor systems signals a principle of brain function, namely to reduce the degrees of freedom of a system and to shift a substantial amount of necessary sensory-motor transformation to the sensory and motor periphery. These mechanisms are thought to simplify neuronal operations and thereby economize neuronal operations.