Neuronal and behavioral sensitivity to binaural time differences in the owl

We demonstrated that ongoing time disparity (OTD) was a sufficient cue for the azimuthal component of receptive fields of auditory neurons in the owl (Tyto alba) midbrain and that OTDs were sufficient to mediate meaningful behavioral responses. We devised a technique which enabled us to change easily between free field and dichotic stimuli while recording from single auditory neurons in the owl mesencephalicus lateralis pars dorsalis (MLD). MLD neurons with restricted spatial receptive fields (“space-mapped neurons”) showed marked sensitivity to specific ongoing time disparities. The magnitudes of these disparities were in the behaviorally significant range of tens of microseconds. The ongoing time disparities were correlated significantly with the azimuthal center of receptor fields. Space-mapped neurons were insensitive to transient disparities. MLD neurons which were not space- mapped, i.e., were omnidirectional, did not show any sensitivity to specific OTDs. We confirmed the behavioral relevance of OTD as a cue for localizing a sound in azimuth by presenting OTD differences to tame owls. Using head turning as an assay, we showed that OTD was a sufficient cue for the azimuth of a sound. The relationship between azimuth and OTD obtained from our neurophysiological experiments matched closely the relationship obtained from our behavioral experiments

Binaural characteristics of units in the owl's brainstem auditory pathway: precursors of restricted spatial receptive fields

The barn owl uses binaural phase and intensity differences for sound localization. These two cues also determine the receptive fields of specialized neurons in the inferior colliculus. The main aim of this study was to investigate where neuronal sensitivity to the binaural cues emerges in the brainstem auditory nuclei, and how this sensitivity reaches the neurons in the inferior colliculus. The owl's phase- sensitive neurons are selective to microsecond phase differences of high frequency signals, unlike mammalian phase-sensitive neurons which are restricted to low frequency signals. In certain nuclei virtually all of the neurons are sensitive to either phase differences or intensity differences, but not to both. These nuclei form two distinctly separate pathways that converge at the inferior colliculus where neurons selective to both phase and intensity differences occur. In contrast to the mammalian auditory system, the owl's phase- and intensity difference-sensitive pathways are not segregated into low frequency and high frequency channels

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

Fatal tumor lysis syndrome in a patient with metastatic gastric adenocarcinoma

Tumor lysis syndrome is a well-characterized and potentially deadly complication of spontaneous or treatment-related tumor destruction, and it is most commonly associated with hematologic malignancies. Our case illustrates a rare example of fatal tumor lysis syndrome in the setting of metastatic gastric adenocarcinoma treated with radiation therapy. This case highlights the critical importance of identifying patients with solid organ malignancies at risk for tumor lysis syndrome and of early recognition and treatment of this syndrome

At the Rhythm of Language: Neural Bases of Language-Related Frequency Perception in Children

Brain, Behavior, and Cognitive Scienceshttp://deepblue.lib.umich.edu/bitstream/2027.42/85306/1/biancam.pd

Variation in blood selenium and serum vitamin E in reindeer (Rangifer tarandus tarandus) described by location, husbandry, and season

Reindeer (Rangifer tarandus tarandus) are important livestock for arctic and subarctic herders, including those in North America, but as climate change affects traditional herding practices, alternative methods of rearing (such as captive rearing) will likely become common. Proper nutrition is critical in livestock production, but there is minimal information available on circulating nutrient concentrations in reindeer, who are adapted to a unique climate. This study looks at 2 important antioxidants. Blood and serum were taken from female reindeer from three herds:  a free-ranging herd from the Seward Peninsula, Alaska (AK), during the summer, and two captive herds (one in Fairbanks, AK and one in Upstate New York (NY) during the summer and winter. Selenium (Se) and vitamin E concentrations were described stratified on season (when possible), location, and management practices (captive or free range). Herd mean values across seasons for Se ranged from 2.42 to 4.88 µmol/L. Herd mean values across seasons for vitamin E ranged from 5.27 to 6.89 µmol/L.

Utility and Versatility of Extracellular Recordings from the Cockroach for Neurophysiological Instruction and Demonstration

The principles of neurophysiology continue to be challenging topics to teach in the context of undergraduate neuroscience education. Laboratory classes containing neurophysiological demonstrations and exercises are, therefore, an important and necessary complement for covering those subjects taught in lecture-based courses. We developed a number of simple yet very instructive exercises, described below, which make use of extracellular recordings from different sensory systems of the cockroach (Periplanta americana). The compendium we developed provides students with hands-on demonstrations of several commonly taught topics of neurophysiology including sensory coding by neural activity

How spiking neurons give rise to a temporal-feature map

A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cells’ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit from the nonlinearity

Decoding neural responses to temporal cues for sound localization

The activity of sensory neural populations carries information about the environment. This may be extracted from neural activity using different strategies. In the auditory brainstem, a recent theory proposes that sound location in the horizontal plane is decoded from the relative summed activity of two populations in each hemisphere, whereas earlier theories hypothesized that the location was decoded from the identity of the most active cells. We tested the performance of various decoders of neural responses in increasingly complex acoustical situations, including spectrum variations, noise, and sound diffraction. We demonstrate that there is insufficient information in the pooled activity of each hemisphere to estimate sound direction in a reliable way consistent with behavior, whereas robust estimates can be obtained from neural activity by taking into account the heterogeneous tuning of cells. These estimates can still be obtained when only contralateral neural responses are used, consistently with unilateral lesion studies. DOI: http://dx.doi.org/10.7554/eLife.01312.001

How male sound pressure level influences phonotaxis in virgin female Jamaican field crickets (Gryllus assimilis)

Understanding female mate preference is important for determining the strength and direction of sexual trait evolution. The sound pressure level (SPL) acoustic signalers use is often an important predictor of mating success because higher sound pressure levels are detectable at greater distances. If females are more attracted to signals produced at higher sound pressure levels, then the potential fitness impacts of signalling at higher sound pressure levels should be elevated beyond what would be expected from detection distance alone. Here we manipulated the sound pressure level of cricket mate attraction signals to determine how female phonotaxis was influenced. We examined female phonotaxis using two common experimental methods: spherical treadmills and open arenas. Both methods showed similar results, with females exhibiting greatest phonotaxis towards loud sound pressure levels relative to the standard signal (69 vs. 60 dB SPL) but showing reduced phonotaxis towards very loud sound pressure level signals relative to the standard (77 vs. 60 dB SPL). Reduced female phonotaxis towards supernormal stimuli may signify an acoustic startle response, an absence of other required sensory cues, or perceived increases in predation risk