Basic maps in the auditory midbrain

Topologic maps at consecutive levels of sensory pathways indicate behaviorally relevant features of stimuli at increasing degrees of complexity. In the auditory system, except for tonotopic maps, the nature of represented features is unknown. In a model analogous to visual map formation we show that in the auditory midbrain, layers of neurons with preference to the same frequency (isofrequency planes) may hold maps of two basic, mutually orthogonal parameters--instantaneous amplitude and phase--of basilar membrane displacement at the cochlear location responding to that frequency. The proposed neural tuning to frequency, amplitude, and phase implies that sound is transformed into specific temporal trajectories of neural activation, with consequences for experimental design and interpretation of neural response behavior.