6,447 research outputs found
Periodotopy in the gerbil inferior colliculus: local clustering rather than a gradient map
Periodicities in sound waveforms are widespread, and shape important perceptual attributes of sound including rhythm and pitch. Previous studies have indicated that, in the inferior colliculus (IC), a key processing stage in the auditory midbrain, neurons tuned to different periodicities might be arranged along a periodotopic axis which runs approximately orthogonal to the tonotopic axis. Here we map out the topography of frequency and periodicity tuning in the IC of gerbils in unprecedented detail, using pure tones and different periodic sounds, including click trains, sinusoidally amplitude modulated (SAM) noise and iterated rippled noise. We found that while the tonotopic map exhibited a clear and highly reproducible gradient across all animals, periodotopic maps varied greatly across different types of periodic sound and from animal to animal. Furthermore, periodotopic gradients typically explained only about 10% of the variance in modulation tuning between recording sites. However, there was a strong local clustering of periodicity tuning at a spatial scale of ca. 0.5 mm, which also differed from animal to animal
An Overrepresentation of High Frequencies in the Mouse Inferior Colliculus Supports the Processing of Ultrasonic Vocalizations
Mice are of paramount importance in biomedical research and their vocalizations are a subject of interest for researchers across a wide range of health-related disciplines due to their increasingly important value as a phenotyping tool in models of neural, speech and language disorders. However, the mechanisms underlying the auditory processing of vocalizations in mice are not well understood. The mouse audiogram shows a peak in sensitivity at frequencies between 15-25 kHz, but weaker sensitivity for the higher ultrasonic frequencies at which they typically vocalize. To investigate the auditory processing of vocalizations in mice, we measured evoked potential, single-unit, and multi-unit responses to tones and vocalizations at three different stages along the auditory pathway: the auditory nerve and the cochlear nucleus in the periphery, and the inferior colliculus in the midbrain. Auditory brainstem response measurements suggested stronger responses in the midbrain relative to the periphery for frequencies higher than 32 kHz. This result was confirmed by single- and multi-unit recordings showing that high ultrasonic frequency tones and vocalizations elicited responses from only a small fraction of cells in the periphery, while a much larger fraction of cells responded in the inferior colliculus. These results suggest that the processing of communication calls in mice is supported by a specialization of the auditory system for high frequencies that emerges at central stations of the auditory pathway
Midbrain adaptation may set the stage for the perception of musical beat
The ability to spontaneously feel a beat in music is a phenomenon widely believed to be unique to humans. Though beat perception involves the coordinated engagement of sensory, motor and cognitive processes in humans, the contribution of low-level auditory processing to the activation of these networks in a beat-specific manner is poorly understood. Here, we present evidence from a rodent model that midbrain preprocessing of sounds may already be shaping where the beat is ultimately felt. For the tested set of musical rhythms, on-beat sounds on average evoked higher firing rates than off-beat sounds, and this difference was a defining feature of the set of beat interpretations most commonly perceived by human listeners over others. Basic firing rate adaptation provided a sufficient explanation for these results. Our findings suggest that midbrain adaptation, by encoding the temporal context of sounds, creates points of neural emphasis that may influence the perceptual emergence of a beat
A variable corona during the transition from type-C to type-B quasi-periodic oscillations in the black hole X-ray binary MAXI J1820+070
We analyze a Neutron Star Interior Composition Explorer (NICER) observation
of the black hole X-ray binary MAXI J1820+070 during a transition from type-C
to type-B quasi-periodic oscillations (QPOs). We find that below ~2 keV, for
the type-B QPOs the rms amplitude is lower and the magnitude of the phase lags
is larger than for the type-C QPOs. Above that energy, the rms and phase-lag
spectra of the type-B and type-C QPOs are consistent with being the same. We
perform a joint fit of the time-averaged spectra of the source, and the rms and
phase-lag spectra of the QPOs with the time-dependent Comptonization model
vkompth to study the geometry of the corona during the transition. We find that
the data can be well-fitted with a model consisting of a small and a large
corona that are physically connected. The sizes of the small and large coronae
increase gradually during the type-C QPO phase whereas they decrease abruptly
at the transition to type-B QPO. At the same time, the inner radius of the disc
moves inward at the QPO transition. Combined with simultaneous radio
observations showing that discrete jet ejections happen around the time of the
QPO transition, we propose that a corona that expands horizontally during the
type-C QPO phase, from ~10^{4} km (~800 Rg) to ~10^{5} km (~8000 Rg) overlying
the accretion disc, transforms into a vertical jet-like corona extending over
~10^{4} km (~800 Rg) during the type-B QPO phase.Comment: 22 pages, 16 figures, 2 tables, accepted for publication in MNRA
Solar Neutrinos Before and After KamLAND
We use the recently reported KamLAND measurements on oscillations of reactor
anti-neutrinos, together with the data of previously reported solar neutrino
experiments, to show that: (1) the total 8B neutrino flux emitted by the Sun is
1.00(1.0 \pm 0.06) of the standard solar model (BP00) predicted flux, (2) the
KamLAND measurements reduce the area of the globally allowed oscillation
regions that must be explored in model fitting by six orders of magnitude in
the Delta m^2-tan^2 theta plane, (3) LMA is now the unique oscillation solution
to a CL of 4.7sigma, (4) maximal mixing is disfavored at 3.1 sigma, (5)
active-sterile admixtures are constrained to sin^2 eta<0.13 at 1 sigma, (6) the
observed ^8B flux that is in the form of sterile neutrinos is
0.00^{+0.09}_{-0.00} (1 sigma), of the standard solar model (BP00) predicted
flux, and (7) non-standard solar models that were invented to completely avoid
solar neutrino oscillations are excluded by KamLAND plus solar at 7.9 sigma .
We also refine quantitative predictions for future 7Be and p-p solar neutrino
experiments.Comment: Published version, includes editorial improvement
BLM and RMI1 alleviate RPA inhibition of topoIIIα decatenase activity
RPA is a single-stranded DNA binding protein that physically associates with the BLM complex. RPA stimulates BLM helicase activity as well as the double Holliday junction dissolution activity of the BLM-topoisomerase IIIα complex. We investigated the effect of RPA on the ssDNA decatenase activity of topoisomerase IIIα. We found that RPA and other ssDNA binding proteins inhibit decatenation by topoisomerase IIIα. Complex formation between BLM, TopoIIIα, and RMI1 ablates inhibition of decatenation by ssDNA binding proteins. Together, these data indicate that inhibition by RPA does not involve species-specific interactions between RPA and BLM-TopoIIIα-RMI1, which contrasts with RPA modulation of double Holliday junction dissolution. We propose that topoisomerase IIIα and RPA compete to bind to single-stranded regions of catenanes. Interactions with BLM and RMI1 enhance toposiomerase IIIα activity, promoting decatenation in the presence of RPA
A ferroelectric memristor
Memristors are continuously tunable resistors that emulate synapses.
Conceptualized in the 1970s, they traditionally operate by voltage-induced
displacements of matter, but the mechanism remains controversial. Purely
electronic memristors have recently emerged based on well-established physical
phenomena with albeit modest resistance changes. Here we demonstrate that
voltage-controlled domain configurations in ferroelectric tunnel barriers yield
memristive behaviour with resistance variations exceeding two orders of
magnitude and a 10 ns operation speed. Using models of ferroelectric-domain
nucleation and growth we explain the quasi-continuous resistance variations and
derive a simple analytical expression for the memristive effect. Our results
suggest new opportunities for ferroelectrics as the hardware basis of future
neuromorphic computational architectures
Will all scientists working on snails and the diseases they transmit please stand up?
Copyright © 2012 Adema et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.No abstract available
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