Hemodynamic signals correlate tightly with synchronized gamma oscillations

Functional imaging methods monitor neural activity by measuring hemodynamic signals. These are more closely related to local field potentials (LFPs) than to action potentials. We simultaneously recorded electrical and hemodynamic responses in the cat visual cortex. Increasing stimulus strength enhanced spiking activity, high-frequency LFP oscillations, and hemodynamic responses. With constant stimulus intensity, the hemodynamic response fluctuated; these fluctuations were only loosely related to action potential frequency but tightly correlated to the power of LFP oscillations in the gamma range. These oscillations increase with the synchrony of synaptic events, which suggests a close correlation between hemodynamic responses and neuronal synchronization.     

A 5-micron-bright spot on Titan: evidence for surface diversity

Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80 degrees W and 20 degrees S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot, reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena.     

Abiotic forcing of plankton evolution in the Cenozoic

We characterize the evolutionary radiation of planktic foraminifera by the test size distributions of entire assemblages in more than 500 Cenozoic marine sediment samples, including more than 1 million tests. Calibration of Holocene size patterns with environmental parameters and comparisons with Cenozoic paleoproxy data show a consistently positive correlation between test size and surface-water stratification intensity. We infer that the observed macroevolutionary increase in test size of planktic foraminifera through the Cenozoic was an adaptive response to intensifying surface-water stratification in low latitudes, which was driven by polar cooling.