The Generation of Direction Selectivity in the Auditory System

Both human speech and animal vocal signals contain frequency-modulated (FM) sounds. Although central auditory neurons that selectively respond to the direction of frequency modulation are known, the synaptic mechanisms underlying the generation of direction selectivity (DS) remain elusive. Here we show the emergence of DS neurons in the inferior colliculus by mapping the three major subcortical auditory nuclei. Cell-attached recordings reveal a highly reliable and precise firing of DS neurons to FM sweeps in a preferred direction. By using in vivo whole-cell current-clamp and voltage-clamp recordings, we found that the synaptic inputs to DS neurons are not direction selective, but temporally reversed excitatory and inhibitory synaptic inputs are evoked in response to opposing directions of FM sweeps. The construction of such temporal asymmetry, resulting DS, and its topography can be attributed to the spectral disparity of the excitatory and the inhibitory synaptic tonal receptive fields

Colective Effects from Induced Behaviour

We present a solvable model for describing quantitatively situations where the individual behaviour of agents in a group "percolates" to collective behaviour of the group as a whole as a result of mutual influence between the agents.Comment: 6 pages, 6 figures, EPJ macro

Comparison of mixed quantum states

In this article, we study the problem of comparing mixed quantum states: given $n$ unknown mixed quantum states, can one determine whether they are identical or not with an unambiguous quantum measurement? We first study universal comparison of mixed quantum states, and prove that this task is generally impossible to accomplish. Then, we focus on unambiguous comparison of $n$ mixed quantum states arbitrarily chosen from a set of $k$ mixed quantum states. The condition for the existence of an unambiguous measurement operator which can produce a conclusive result when the unknown states are actually the same and the condition for the existence of an unambiguous measurement operator when the unknown states are actually different are studied independently. We derive a necessary and sufficient condition for the existence of the first measurement operator, and a necessary condition and two sufficient conditions for the second. Furthermore, we find that the sufficiency of the necessary condition for the second measurement operator has simple and interesting dependence on $n$ and $k$. At the end, a unified condition is obtained for the simultaneous existence of these two unambiguous measurement operators.Comment: 9 page

Activation of phospholipase C beta4 by heterotrimeric GTP-binding proteins

Transient transfection assays were used to determine how the activity of phospholipase C beta 4, which is preferentially expressed in retina, was regulated. An expression vector carrying the full-length cDNA corresponding to phospholipase C beta 4 was constructed and co- transfected into COS-7 cells together with cDNA encoding the alpha subunits of the Gq class and various beta and gamma subunits corresponding to the heterotrimeric GTP-binding proteins. We found that all the alpha subunits of the Gq class, including G alpha q, G alpha 11, G alpha 14, G alpha 15, and G alpha 16 could activate PLC beta 4 and that none of the G beta gamma subunits that we tested including G beta 1 gamma 1, G beta 1 gamma 2, G beta 1 gamma 3, or G beta 2 gamma 2 activated phospholipase C beta 4. In control experiments, cotransfection with cDNA encoding the alpha subunit of transducin or Gi2 gave no activation of PLC beta 4. These results indicate that phospholipase C beta 4 is activated by G alpha subunits that are members of the Gq class, and, like the phospholipase C beta 1 isoform, it is refractory to activation in the transfection assay by many of the combinations of beta and gamma subunits found in the heterotrimeric G- proteins

Activation of phospholipase C beta 2 by the alpha and beta gamma subunits of trimeric GTP-binding protein

Cotransfection assays were used to show that the members of the GTP-binding protein Gq class of alpha subunits could activate phospholipase C (PLC) beta 2. Similar experiments also demonstrated that G beta 1 gamma 1, G beta 1 gamma 5, and G beta 2 gamma 5 could activate the beta 2 isoform of PLC but not the beta 1 isoform, while G beta 2 gamma 1 did not activate PLC beta 2. To determine which portions of PLC beta 2 are required for activation by G beta gamma or G alpha, a number of PLC beta 2 deletion mutants and chimeras composed of various portions of PLC beta 1 and PLC beta 2 were prepared. We identified the N-terminal segment of PLC beta 2 with amino acid sequence extending to the end of the Y box as the region required for activation by G beta gamma and the C-terminal region as the segment containing amino acid sequences required for activation by G alpha. Furthermore, we found that coexpression of G alpha 16 and G beta 1 gamma 1 but not G beta 1 gamma 5 in COS-7 cells was able to synergistically activate recombinant PLC beta 2. We suggest that G alpha 16 may act together with free G beta 1 gamma 1 to activate PLC beta 2, while G alpha 16 may form heterotrimeric complexes with G beta 1 gamma 5 and be stabilized in an inactive form. We conclude that the regions of PLC beta 2 required for activation by G beta gamma and G alpha are physically separate and that the nature of the G beta subunit may play a role in determining the relative specificity of the G beta gamma complex for effector activation while the nature of the G gamma subunit isoform may be important for determining the affinity of the G beta gamma complex for specific G alpha proteins

Differentiability of the volume of a region enclosed by level sets

The level of a function f on an n-dimensional space encloses a region. The volume of a region between two such levels depends on both levels. Fixing one of them the volume becomes a function of the remaining level. We show that if the function f is smooth, the volume function is again smooth for regular values of f. For critical values of f the volume function is only finitely differentiable. The initial motivation for this study comes from Radiotherapy, where such volume functions are used in an optimization process. Thus their differentiability properties become important.Comment: 11 pages, 1 figur

Formation of the Leonid meteor stream and storm

It is well known that some meteor showers display a very high level of activity at certain times, the most famous being the Leonid shower with very spectacular displays at roughly 33 year intervals. This period being also the period of the parent comet of the stream, Comet Tempel-Tuttle. An investigation of the geometry of the comet and the Earth at the time of each high activity occurrence by Yeomans suggests that most of the meteoroids are found outside the cometary orbit and lagging the comet. The formation process of such a stream by numerically integrating the orbits of dust particles ejected from the comet and moving under the influence of gravity and radiation pressure are simulated. The intersection of these dust particles with the Earth is also considered and it is concluded that about 12 percent of the ejected particles may be observed and that of those observable, 63 percent will be outside the cometary orbit and behind the comet