לוח שנה משולב

The proton electric and magnetic form factors are basic characteristics of the proton, and can be associated with the Fourier transforms of the charge and magnetic current densities in the nonrelativistic limit.
Although QCD can make rigorous predictions when the four-momentum transfer squared, Q2, is very large, in the non-perturbative regime this task is too difficult, and several phenomenological models attempt to make predictions in this domain. Measurements of the proton form factors were traditionally based on cross section measurements using the Rosenbluth separation method to extract the electric and magnetic form factors. In this method, the magnetic form factor is suppressed as Q2 decreases, and precise data at very low Q2 is not available. During the last two decades, scattering experiments with polarized beams and targets have been used for precise measurements of the proton form factors at much lower Q2 . The second part of experiment E08-007 was dedicated to measure the ratio between the proton form factors at 0.01 <
Q2 < 0.08 GeV2, lower than ever achieved, by using the double-spin asymmetry technique. The experiment was conducted during the spring of
2012 at Hall A of the Thomas Jefferson National Accelerator Facility, using a 1-2 GeV polarized electron beam, scattering off a polarized solid ammonia target. Data analysis is currently in final stages.
Recently, inconsistencies between different measurements of the proton radius have prompted intense theoretical and experimental activities to resolve the discrepancy. This experiment might improve our understanding of this problem. In this talk, I will describe the experimental system, the main challenges in the data analysis, and present preliminary results for the asymmetries and their uncertainties.

Striatal disinhibition leads to spontaneous abnormal action release manifesting as motor tics, resembling those expressed in Tourette syndrome patients. We utilized microstimulation within the motor cortex of freely-behaving rats before and after striatal disinhibition to study the spatial and temporal properties of tic expression. The spatial properties of these tics were dependent on the striatal organization while the temporal properties were dependent on the cortico-striatal activity. A data-driven computational model of cortico-striatal function closely replicated the temporal properties of abnormal action release. These converging experimental and computational findings suggest a clear functional dichotomy within the cortico-striatal network, pointing to disparate temporal (cortical) vs. spatial (striatal) encoding of action release.

Learning lays the foundation for motivated behavior, enabling us to recognize and respond appropriately to salient events. However, to function adaptively in a dynamic environment, we must be able to flexibly alter learned behavioral responses in accordance with our ongoing experience. In this talk, I will present studies examining at the cognitive, neural, and computational levels how the learning processes that support adaptive behavioral flexibility change over the course of development from childhood to adulthood. I will show that development confers marked changes in the cognitive representations engaged during learning and I will propose that learning about the degree of instrumental agency afforded by the environment may be a critical factor that shapes an individual’s behavioral repertoire.

Sexually reproducing animals display sex-specific behaviors wired onto dimorphic connectivity patterns in the nervous system. The mechanisms underlying the development of sexually dimorphic nervous systems that consists mainly of shared neuronal types remain largely unknown. Within the nervous system, males and females display a number of anatomical sexual dimorphisms often in the form of neurons that are present exclusively in one, but not the other sex. In this talk I will focus on sex-specific wiring of neurons that are present in both sexes, and demonstrate the sex-specific functions of sex-shared neurons in C. elegans. The key finding that I will present is that sex-specific wiring patterns are the result of sex-specific synaptic pruning events. I will show that many neurons initially form synapses in a non-discriminatory manner in both the male and hermaphrodite pattern before sexual maturation, but sex-specific pruning events result in the sex-specific maintenance of subsets of the connections. I will describe the behavioral tests taken to show that rewiring is indicative of repurposing of the function of sensory and interneuron. I will present the conserved genes I uncovered that function to determine sex-specific connectivity patterns. To summarize I will discuss how the sexual identity of individual neurons, by initiating selective synapse loss, refines the circuitry and defines sex-specific synaptic targets. This allows for diversification of behavioral outputs with a limited set of shared neurons.