Main description:

The brain of an echo locating bat is devoted, in large part, to analyzing sound and conducting behavior in a world of sounds and echoes. This monograph is about analysis of sound in the brainstem of echolocating bats and concerns the relationship between brain structure and brain function. Echolocating bats are unique subjects for the study of such relationships. Like man, echolocating bats emit sounds just for the purpose of listening to them. Simply by observing the bat's echolocation sounds, we know what the bat listens to in nature. We therefore have a good idea what the bat's auditory brain is designed to do. But this alone does not make the bat unique. The brain of the bat is, by mammalian standards, rather primitive. The unique aspect is the combination of primitive characteristics and complex auditory processing. Within this small brain the auditory structures are hypertrophied and have an elegance of organization not seen in other mammals. It is as if the auditory pathways had evolved while the rest of the brain remained evolutionary quiescent.

Contents:

1. Biological Sonar and the World of Bats.- 1.1 Purpose of the Monograph.- 1.2 Historical Review.- 1.3 The Orientation Calls of Bats.- 1.4 Nomenclature Used to Refer to Bats Throughout the Monograph.- 1.5 How Bats Manipulate Their Signals During Echolocation.- 1.6 Echolocation Signals Are Tailored to the Habitat in Which the Bat Hunts.- 1.7 What Information Do Bats Extract from their Biosonar Signals?.- 1.8 Cues Bats Use to Extract Information from Biosonar Signals.- 1.8.1 Recognition of Targets.- 1.8.2 Localization of Targets in Space.- 1.9 Biosonar Signals and the Phylogeny of Bats.- 2. Tonotopic Organization.- 2.1 Introduction.- 2.2 The Cochlea and Auditory Nerve.- 2.3 Cochlear Nucleus.- 2.4 Superior Olivary Complex.- 2.5 Nuclei of the Lateral Lemniscus.- 2.6 Central Nucleus of the Inferior Colliculus.- 3. Anatomy of the Auditory Brainstem.- 3.1 Introduction.- 3.2 Three Divisions of the Cochlear Nucleus and the Origins of Parallel Auditory Pathways.- 3.3 Binaural and Monaural Pathways of the AVCN System.- 3.3.1 Binaural Pathways and the Localization of Echoes.- 3.3.2 Functional Considerations of LSO and MSO Pathways.- 3.3.3 Do All Bats Have an MSO?.- 3.3.4 Monaural Pathways.- 3.4 Convergence and Integration at the Inferior Colliculus.- 3.4.1 Intrinsic Organization of the Inferior Colliculus.- 3.4.2 Convergence and Divergence of Pathways at the Inferior Colliculus.- 3.4.3 Pathways to the Dorsoposterior Division of the Inferior Colliculus in the Mustache Bat.- 3.4.4 Spatial Topography of Inputs to Other Isofrequency Contours.- 3.5 Pathways to the Inferior Colliculus: Conclusions.- 3.6 The Central Acoustic Tract and the Superior Colliculus: Some Speculations on Structures for Spatial Orientation.- 3.6.1 The Central Acoustic Tract.- 3.6.2 Superior Colliculus.- 3.6.3 Connections of Frontal Cortex.- 3.6.4 Does the Frontal Cortex Play a Role in Spatial Memory?.- 4. Physiological Properties of Auditory Neurons.- 4.1 Introduction.- 4.2 Auditory Nerve.- 4.3 Anteroventral Cochlear Nucleus.- 4.4 Medial Superior Olive.- 4.5 Lateral Superior Olive.- 4.6 How Do Time-Sensitive E-I Units Code for Azimuth?.- 4.7 Inferior Colliculus.- 4.7.1 Temporal and Spectral Coding Evoked by FM Signals Related to Target Ranging.- 4.7.2 Further Coding of Target Range.- 4.7.3 Spectral Coding for Target Attributes.- 4.7.4 Temporal Coding Evoked by Sinusoidally Modulated Signals Related to Target Recognition.- 4.8 The Relevance of Doppler-Shift Compensation.- 4.9 Organizational Features Related to Convergence of Inputs at the Inferior Colliculus.- 4.9.1 Inhibitory Thresholds of E-I Neurons Are Topographically Organized Within the Dorsoposterior Division.- 4.9.2 Spatially Selective Properties of 60-kHz E-I Neurons.- 4.9.3 E-I Neurons Create a Representation of Azimuth.- 4.9.4 One Group of E-E Neurons Code for Elevation Along the Midline.- 4.9.5 Spatial Properties of Neurons Tuned to Other Frequencies.- 4.9.6 The Representation of Auditory Space in the Mustache Bat's Inferior Colliculus.- 5. Processing of Acoustic Information During Echolocation.- 5.1 Introduction.- 5.2 Pulse Beaming and the Action of the Middle Ear Muscles.- 5.3 Central Mechanisms for Attenuating Responses to Emitted Sounds.- 5.4 Neuronal Response Properties Can Be Modified During Echolocation.- 5.5 Conclusions.- 6. Summary and Conclusions.- 6.1 Specializations of Mustache Bats Reveal Details About the Modular Organization of the Auditory System.- 6.2 Processing of Frequency and Time in the AVCN System.- 6.3 Functional Significance of Monaural and Binaural AVCN Pathways.- 6.4 Convergence of Pathways at the Inferior Colliculus.- References.