Responses to Sounds in the Central Auditory System of the Frog: An Advanced Electrophysiology Laboratory in Sensory Processing

Frogs rely upon vocal communication to advertise for potential mates, to defend territory and to alarm neighbors of danger. Cells in the auditory midbrain of an awake frog display tuning to the spectral energy present in calls based upon discharge rate and encode the temporal properties of calls in the timing of their discharges. This laboratory experiment is designed to allow students to explore the relationship between stimulus amplitude or frequency and response rate, and how the timing of responses can also be used to encode behaviorally relevant features of the stimulus. Action potentials in the midbrain auditory nucleus, the torus semicularis, are evoked by delivery of free field sounds and recorded. Most cells are broadly tuned to frequency, yet some can be fairly precise in preserving periodic structure. The use of a comparative model of study should help students understand principles common among all sensory systems, and an appreciation that the architecture of each system is adaptively matched to the ethological task at hand.