Neural mechanism of experience-dependent sensory gain control in C. elegans

Animals' sensory systems adjust their responsiveness to environmental stimuli that vary greatly in their intensity. Here we report the neural mechanism of experience-dependent sensory adjustment, especially gain control, in the ASH nociceptive neurons in Caenorhabditis elegans. Using calcium imaging under gradual changes in stimulus intensity, we find that the ASH neurons of naive animals respond to concentration increases in a repulsive odor 2-nonanone regardless of the magnitude of the concentration increase. However, after preexposure to the odor, the ASH neurons exhibit significantly weak responses to a small gradual increase in odor concentration while their responses to a large gradual increase remain strong. Thus, preexposure changes the slope of stimulus-response relationships (i.e., gain control). Behavioral analysis suggests that this gain control contributes to the preexposure-dependent enhancement of odor avoidance behavior. Mathematical analysis reveals that the ASH response consists of fast and slow components, and that the fast component is specifically suppressed by preexposure. In addition, genetic analysis suggests that G protein signaling is required for the fast component. Thus, our integrative study demonstrates how prior experience dynamically modulates stimulus-response relationships in sensory neurons, eventually leading to adaptive modulation of behavior.

Orientation of broadband seismographs in the Kashmir Himalaya: Effect on vector-based studies

<p>We used regional as well as global Rayleigh wave signals (source-receiver distance: 5°-175°; M≥ 6, Depth ≤ 150 km) recorded at 12 broadband seismic stations in northwestern Himalaya to compute arrival angles of surface waves at each station, assuming orthogonality of the horizontal components, and error-free levelling of the instrument. The average of all measurements at a station with cross-correlation values > 0.8, between Hilbert transformed vertical and radial components, was interpreted as the degree of misalignment of the horizontal components in a geographic frame of reference.</p><p>Out of the 12 station data used in this analysis, 3 were found to have instrument misorientation errors between 5° and 10° w.r.t geographic north, 2 between 10° and 15° and the remaining 7 < 5°. The number of measurements at each of these stations ranged from 75 to 331, with 11 stations having more than 90 measurements, assuring high reliability. We also analysed data from two nearby broadband instruments located in Ladakh Himalaya. One of these (LEH) with 46 measurements showed a misorientation error of 14.87°±4.87° and the other (HNL) with 48 showed an error of 0.75°±3.48°. Since misorientation errors based on less than 90 data elements are considered to be unstable, these were not used for further analysis.</p><p>We evaluated the effect of seismograph misorientations on the inverted solutions for P-wave receiver functions (RFs) and core-refracted shear waves (SKS). The errors in Moho depths and those of other intra-crustal features were within ±2 km for instrument misorientations of up to ~15°, that is close to the resolution errors. But, the SKS results, notably the azimuths of the fast component, were, found to be quite sensitive to instrument misalignment. For example, a ~14° error in orientation was found to cause a shift of up to 20° in the calculated azimuth of the fast component. Corrections of misorientation errors in both cases showed reduction of variance in the inverted solutions.</p>

Disentangling nonlinear geomagnetic variability during magnetic storms and quiescence by timescale dependent recurrence properties

Understanding the complex behavior of the near-Earth electromagnetic environment is one of the main challenges of Space Weather studies. This includes both the correct characterization of the different physical mechanisms responsible for its configuration and dynamics as well as the efforts which are needed for a correct forecasting of several phenomena. By using a nonlinear multi-scale dynamical systems approach, we provide here new insights into the scale-to-scale dynamical behavior of both quiet and disturbed periods of geomagnetic activity. The results show that a scale-dependent dynamical transition occurs when moving from short to long timescales, i.e., from fast to slow dynamical processes, the latter being characterized by a more regular behavior, while more dynamical anomalies are found in the behavior of the fast component. This suggests that different physical processes are typical for both dynamical regimes: the fast component, being characterized by a more chaotic and less predictable behavior, can be related to the internal dynamical state of the near-Earth electromagnetic environment, while the slow component seems to be less chaotic and associated with the directly driven processes related to the interplanetary medium variability. Moreover, a clear difference has been found between quiet and disturbed periods, the former being more complex than the latter. These findings support the view that, for a correct forecasting in the framework of Space Weather studies, more attention needs to be devoted to the identification of proxies describing the internal dynamical state of the near-Earth electromagnetic environment.