Albert S. Feng and Peter M. Narins (2008): Ultrasonic communication in concave-eared torrent frogs ( Amolops tormotus ). J. Comp. Physiol. A 194(2), 159-167.
Abstract: The concave-eared torrent frogs (Amolops tormotus) have highly unusual ear morphology-in males the eardrums are embedded deep inside ear cavities. In collaboration with our colleagues we investigated the functional significance of this morphological feature in hearing. Sound recordings in the field showed that males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations and non-linear phenomena (e.g., frequency jumps, different orders of subharmonics, and chaos) that often contain spectral energy in the ultrasonic range. The audible as well as the ultrasonic components of the species call could effectively evoke males' vocal responses, demonstrating that they can hear and respond to ultrasound. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs. The recessed tympana and extremely thin tympanic membranes are adaptations for hearing ultrasound-this sensitivity may have evolved in response to the intense, predominately low-frequency ambient noise from local streams. Finally, results from the isolated laryngeal preparation in euthanized frogs revealed that the origin of call complexity and diversity lies with having a vocal system with nonlinear properties. URL: http://www.springerlink.com/content/j682q3443392u5m2/ For reprints please contact Albert S. Feng (Email: [EMAIL PROTECTED]) Nobuo Suga (2008): Role of corticofugal feedback in hearing. J. Comp. Physiol. A 194(2),169-183. Abstract: The auditory system consists of the ascending and descending (corticofugal) systems. The corticofugal system forms multiple feedback loops. Repetitive acoustic or auditory cortical electric stimulation activates the cortical neural net and the corticofugal system and evokes cortical plastic changes as well as subcortical plastic changes. These changes are short-term and are specific to the properties of the acoustic stimulus or electrically stimulated cortical neurons. These plastic changes are modulated by the neuromodulatory system. When the acoustic stimulus becomes behaviorally relevant to the animal through auditory fear conditioning or when the cortical electric stimulation is paired with an electric stimulation of the cholinergic basal forebrain, the cortical plastic changes become larger and long-term, whereas the subcortical changes stay short-term, although they also become larger. Acetylcholine plays an essential role in augmenting the plastic changes and in producing long-term cortical changes. The corticofugal system has multiple functions. One of the most important functions is the improvement and adjustment (reorganization) of subcortical auditory signal processing for cortical signal processing.^ URL: http://www.springerlink.com/content/t5232183717608m3/ For reprints please contact Nobuo Suga (Email: [EMAIL PROTECTED]) Kind regards Sonja Amoser
