Barn Owl Auditory System Research Articles

Bifurcation of learning and structure formation in neuronal maps

Most learning processes in neuronal networks happen on a much longer time scale than that of the underlying neuronal dynamics. It is therefore useful to analyze slowly varying macroscopic order parameters to explore a network's learning ability. We study the synaptic learning process giving rise to map formation in the laminar nucleus of the barn owl's auditory system. Using equation-free methods, we perform a bifurcation analysis of spatio-temporal structure formation in the associated synaptic-weight matrix. This enables us to analyze learning as a bifurcation process and follow the unstable states as well. A simple time translation of the learning window function shifts the bifurcation point of structure formation and goes along with traveling waves in the map, without changing the animal's sound localization performance.

Modeling the Nucleus Laminaris of the Barn Owl: Achieving 20 ps Resolution on a 85-MHz-Clocked Digital Device

The nucleus laminaris of the barn owl auditory system is quite impressive, since its underlying time estimation is much better than the processing speed of the involved neurons. Since precise localization is also very important in many technical applications, this paper explores to what extent the main principles of the nucleus laminaris can be implemented in digital hardware. The first prototypical implementation yields a time resolution of about 20 ps, even though the chosen standard, low-cost device is clocked at only 85 MHz, which leads to an internal duty cycle of approximately 12 ns. In addition, this paper also explores the utility of an advanced sampling scheme, known as unfolding-in-time. It turns out that with this sampling method, the prototype can easily process input signals of up to 300 MHz, which is almost four times higher than the sampling rate.

Learning Drives Differential Clustering of Axodendritic Contacts in the Barn Owl Auditory System

Computational models predict that experience-driven clustering of coactive synapses is a mechanism for information storage. This prediction has remained untested, because it is difficult to approach through time-lapse analysis. Here, we exploit a unique feature of the barn owl auditory localization pathway that permits retrospective analysis of prelearned and postlearned circuitry: owls reared wearing prismatic spectacles develop an adaptive microcircuit that coexists with the native one but can be analyzed independently based on topographic location. To visualize the clustering of axodendritic contacts (potential synapses) within these zones, coactive axons were labeled by focal injection of fluorescent tracer and their target dendrites labeled with an antibody directed against CaMKII (calcium/calmodulin-dependent protein kinase type II, alpha subunit). Using high-resolution confocal imaging, we measured the distance from each contact to its nearest neighbor on the same branch of dendrite. We found that the distribution of intercontact distances for the adaptive zone was shifted dramatically toward smaller values compared with distributions for either the maladaptive zone of the same animals or the adaptive zone of normal juveniles, which indicates that a dynamic clustering of contacts had occurred. Moreover, clustering in the normal zone was greater in normal juveniles than in prism-adapted owls, indicative of declustering. These data demonstrate that clustering is bidirectionally adjustable and tuned by behaviorally relevant experience. The microanatomical configurations in all zones of both experimental groups matched the functional circuit strengths that were assessed by in vivo electrophysiological mapping. Thus, the observed changes in clustering are appropriately positioned to contribute to the adaptive strengthening and weakening of auditory-driven responses.

Analysis of spectral shape in the barn owl auditory system

In a behavioral experiment, we investigated how efficiently barn owls (Tyto alba) could detect changes in the spectral profile of multi-component auditory signals with stochastic envelope patterns. Signals consisted of one or five bands of noise (bandwidth 4, 16, or 64 Hz each; center frequencies 1.02, 1.43, 2.0, 2.8, 3.92 kHz). We determined increment thresholds for the 2 kHz component for three conditions: single-band condition (only the 2 kHz component), all five noise bands with the envelope fluctuations of the bands being either correlated or uncorrelated. Noise bandwidth had no significant effect on increment detection. Increment thresholds for the different conditions, however, differed significantly. Thresholds in correlated conditions were generally the lowest of all conditions, whereas, thresholds in uncorrelated conditions mostly resulted in the highest thresholds. This can be interpreted as evidence for comodulation masking release in barn owls. If the increment in the 2 kHz component is balanced by decrementing the four flanking bands in amplitude, increment detection thresholds are not affected. The data suggest that the barn owls used information from simultaneous spectral comparison across different frequency channels to detect spectral changes in multi-component noise signals rather than sequential comparison of overall stimulus levels.

A Candidate Pathway for a Visual Instructional Signal to the Barn Owl's Auditory System

Many organisms use multimodal maps to generate coherent neuronal representations that allow adequate responses to stimuli that excite several sensory modalities. During ontogeny of these maps, one modality typically acts as the dominant system the other modalities are aligned to. A well studied model for the alignment of sensory maps is the calibration of the auditory space map by the visual system in the optic tectum of the barn owl. However, a projection from the optic tectum to the site of plasticity in the auditory pathway that could deliver an instructive signal has not been found so far. We have analyzed the development of the connectivity between the bimodal (visual and auditory) map of space in the barn owl's optic tectum and the auditory space map in the inferior colliculus with tracing methods and intracellular fills. Neurons in the tectal stratum griseum centrale were found to be suited to deliver an alignment signal from the visual midbrain to the auditory pathway. These neurons are presumably part of the efferent tectal projection pathway that mediates head saccades. The implications of a sensory alignment signal possibly being delivered by a (pre)motor command pathway are discussed.

Neuroethological studies of cognitive and perceptual processes

* Introduction: Neuroethology, Perception, and Cognition Sara J. Shettleworth. Specializations In Learning * Specializations in Honey Bee Learning James L. Gould. * Detecting Associations in Pavlovian Conditioning and Instrumental Learning in Invertebrates and in Vertebrates Ruth M. Colwill. * Neuroethological Studies on How Birds Discriminate Song Jeffrey Cynx. * Ecological Specialization in the Avian Brain Susan D. Healy. Specializations For Perception Of Biologically Relevant Stimuli * The Perceptual Foundations of Adult Vocal Learning in Budgerigars Robert J. Dooling, Susan D. Brown, Kazuchika Manabe, and Elizabeth F. Powell. * How Birds Use Frequency to Recognize Their Songs Daniel M. Weary. * Development of Perceptual Mechanisms in Birds: Predispositions and Imprinting Johan J. Bolhuis. * Neural Codes for Pitch Processing in a Unique Vertebrate Auditory System Andrea M. Simmons and Rebecca C. Buxbaum. * Recognition of Visual Signals: Eyes Specialize Russell D. Fernald. Specializations For Spatial Perception And Orientation * Perception Along the Axis of Target Range in the Echolocating Bat Cynthia F. Moss and James A. Simmons. * Converging Approaches to Determining Sound Localization Mechanisms in the Big Brown Bat, Eptesicus fuscus Tim Haresign, Janine M. Wotton, Michael Ferragamo, and J. A. Simmons. * Sound Localization from Binaural Cues by the Barn Owl Auditory System Andrew Moiseff, T. Haresign, and Jianxin Wang.

Representation of interaural level difference in the VLVp, the first site of binaural comparison in the barn owl's auditory system

In the avian auditory system, the posterior division of the ventral nucleus of the lateral lemniscus (VLVp) is the first site where the levels of sound arriving at the two ears are compared. VLVp units are excited by sound at the contralateral ear and are inhibited by sound at the ipsilateral ear, and, as a result, are sensitive to interaural level differences (ILD). In this study, we investigate the functional properties of VLVp units and describe the topography of ILD sensitivity along the dorsoventral dimension of this nucleus. The responses of VLVp units were tested with monaural and binaural noise delivered through earphones. Excitatory and inhibitory responsiveness was quantified using several measures that assessed the effect of contra-ear stimulation and the effect of ipsi-ear stimulation on the contra-ear response. On the basis of these measures, we characterize the map of ILD sensitivity in the VLVp. The temporal pattern of unit responses were also analyzed. The discharges of VLVp units were regular and time-locked to the onset of a stimulus, a pattern of discharge reminiscent of the ‘chopper pattern’ observed in the lateral superior olive (LSO) of mammals. The temporal discharge patterns of a single VLVp neuron often distinguished between equivalent ILDs, resulting from different combinations of contra- and ipsi-ear levels, that were not distinguished by spike count alone. However, the temporal response pattern did not distinguish between all such combinations of contra- and ipsi-ear levels. The additional information was encoded by the pattern of activity across the entire population of VLVp neurons. This study describes similarities in the functional properties of VLVp and LSO units that suggest similar physiological mechanisms in avians and mammals for encoding similar acoustic information.

Early Growth and Development of the Common Barn-Owl's Facial Ruff

Abstract The ability of the Common Barn-Owl (Tyto alba) to localize sounds produced by potential prey can be explained on the basis of sensitivity to differences in interaural time and intensity. The size of the owl's head is a prime determinant of interaural time differences, whereas the facial ruff is the prime determinant of interaural intensity differences. During the 60 days following hatching, the physical structures that establish these binaural cues undergo massive growth. Barn-owl chicks are altricial and scantily feathered when they hatch. Growth of the head and ruff feathers occur at separate times during early maturation. Between 11 and 30 days after hatching, the diameter of the head approximately doubles. Between 35 and 60 days, facial ruff feathers emerge and grow to nearly adult length (ca. 20 mm). During the first 60 days of life, the barn-owl auditory system would be subject to widely varying binaural cues which eventually stabilize.

Time and intensity cues are processed independently in the auditory system of the owl

Space-specific neurons, found in the barn owl's inferior colliculus, respond selectively to a narrow range of interaural time and intensity differences. We show that injecting a local anesthetic into one cochlear nucleus, nucleus magnocellularis, alters the space-specific cell's selectivity for interaural time difference, leaving its selectivity for interaural intensity difference intact. Anesthetizing the other cochlear nucleus, nucleus angularis, has the converse effects. We show also that the space-specific neuron's selectivity for one interaural cue is the same for all effective values of the other cue. We conclude that time and intensity cues are processed in separate neural channels of the barn owl's auditory system and that the two cues operate independently.