Visual stimulation of saccades in magnetically tethered Drosophila

Flying fruit flies, Drosophila melanogaster, perform `body saccades', in which they change heading by about 90° in roughly 70 ms. In free flight, visual expansion can evoke saccades, and saccade-like turns are triggered by similar stimuli in tethered flies. However, because the fictive turns in rigidly tethered flies follow a much longer time course, the extent to which these two behaviors share a common neural basis is unknown. A key difference between tethered and free flight conditions is the presence of additional sensory cues in the latter, which might serve to modify the time course of the saccade motor program. To study the role of sensory feedback in saccades, we have developed a new preparation in which a fly is tethered to a fine steel pin that is aligned within a vertically oriented magnetic field, allowing it to rotate freely around its yaw axis. In this experimental paradigm, flies perform rapid turns averaging 35° in 80 ms, similar to the kinematics of free flight saccades. Our results indicate that tethered and free flight saccades share a common neural basis, but that the lack of appropriate feedback signals distorts the behavior performed by rigidly fixed flies. Using our new paradigm, we also investigated the features of visual stimuli that elicit saccades. Our data suggest that saccades are triggered when expanding objects reach a critical threshold size, but that their timing depends little on the precise time course of expansion. These results are consistent with expansion detection circuits studied in other insects, but do not exclude other models based on the integration of local movement detectors

Symmetries and reversing symmetries of polynomial automorphisms of the plane

The polynomial automorphisms of the affine plane over a field K form a group which has the structure of an amalgamated free product. This well-known algebraic structure can be used to determine some key results about the symmetry and reversing symmetry groups of a given polynomial automorphism.Comment: 27 pages, AMS-Late

The structure of reversing symmetry groups

We present some of the group theoretic properties of reversing symmetry groups, and classify their structure in simple cases that occur frequently in several well-known groups of dynamical systems.Comment: 12 page

Do Professional Traders Exhibit Myopic Loss Aversion? An Experimental Analysis

Two behavioral concepts, loss aversion and mental accounting, have been combined to provide a theoretical explanation of the equity premium puzzle. Recent experimental evidence supports the theory, as students-behavior has been found to be consistent with myopic loss aversion (MLA). Yet, much like certain anomalies in the realm of riskless decision-making, these behavioral tendencies may be attenuated among professionals. Using traders recruited from the CBOT, we do indeed find behavioral differences between professionals and students, but rather than discovering that the anomaly is muted, we find that traders exhibit behavior consistent with MLA to a greater extent than students.

A simple test of expected utility theory using professional traders

We compare behavior across students and professional traders from the Chicago Board of Trade in a classic Allais paradox experiment. Our experiment tests whether independence, a necessary condition in expected utility theory, is systematically violated. We find that both students and professionals exhibit some behavior consistent with the Allais paradox, but the data pattern does suggest that the trader population falls prey to the Allais paradox less frequently than the student population.Allais paradox, experiments, futures traders

The durability of oral diabetic medications: Time to A1c baseline and a review of common oral medications used by the primary care provider.

Introduction:Cost of generic medications has risen more in the past few years than any other time in history. While medical insurance covers much of these costs, health care professionals can better provide medications that have the longest duration of action when compared to placebo-treated controls. This will save health care costs and improve prescribing accuracy. Methods:Papers in PubMed were identified with keywords placebo. The study must be at least 2 years in length to evaluate the change in A1c over time. The primary endpoint was time to A1c neutrality (return of A1c to baseline at a maximum dose of single oral agent). A medication would be considered at neutrality if the 95% CI crossed baseline. Time to neutrality was averaged for each medication within the class and each summarized for class effect. Results:Effective therapy for the DPP-4 and sulfonylurea classes of medications are 3-4 years as compared to a 5-year time to A1c neutrality for metformin usage. In comparison, the projected time to A1c neutrality was approximately 6-8 years for rosiglitazone and pioglitazone. While only a few studies have been published in the SGLT-2 class of medication, the time to A1c neutrality was also 6-8 years with Canagliflozin and full dosage of Empagliflozin. Conclusion:Metformin appears to have a 5-year duration of effect before the A1c returns to baseline. The sulfonylureas and DPP-4 inhibitors class of medications have one of the shortest durability which ranges between 3.3 to 4.4 years. In contrast, the SGLT-2 class of medication and the TZD class of medications has a projected time to A1c neutrality from 6-8 years. Diabetic duration of therapy as compared to placebo should be listed with those medications tested so the provider can choose wisely

Social capital and coping with economic shocks

"South African households live in an environment characterized by risks, and many face a significant probability of experiencing economic losses that threaten their daily subsistence. Using household panel data that include directly solicited information on economic shocks and employing household fixed-effects estimation, we explore how well households cope with shocks by examining the effects of shocks on child nutritional status. Unlike in the idealized village community, some households appear unable to insure against risk, particularly when others in their communities simultaneously suffer large losses. Households in communities with more social capital, however, seem better able to weather shocks." from Authors' Abstract