לוח שנה משולב

Computational and experimental studies of learning and memory have traditionally focused on the role of cognitive brain areas such as the cortex and hippocampus. This work has provided invaluable insights in the ways items are learned, stored and consolidated using a variety of neural mechanisms from molecular to network levels. Relatively little has however been done on understanding how and why some items are selected to be memorized while others are not. I will present a set of experimental results in the rodent showing that the dopaminergic neurons of the rodent ventral tegmental area are actively involved in the acquisition and consolidation of positively and negatively valued memories. The experiments will include optimal spatial navigation, memory reactivation and a rodent model of post-traumatic stress disorder. This ongoing work suggests that neuromodulatory centers may have a much more active and selective role in learning and memory than previously thought.

Cells use genetic switches to shift between alternate gene expression states, e.g. to adapt to new environments or to follow a developmental
pathway. Here, we study the dynamics of switching in a generic-feedback
on/off switch. Unlike protein-only models, we explicitly account for stochastic fluctuations of mRNA, which have a dramatic impact on switch dynamics. Employing a semi-classical theory to treat the underlying chemical master equations, we obtain accurate results for the quasi-stationary distributions of mRNA and protein copy numbers and for the mean switching time, starting from either state. Our analytical results agree well with extensive Monte Carlo simulations. Importantly, one can use the approach to study the effect of varying biological parameters on the switch stability.

This research is aimed to understanding plastic deformation mechanisms through the systematic analysis of the microstructure and dislocation patterns in deformed metals, mainly by electron microscopy techniques. Dislocation dynamics and microstructural evolution under applied stresses by means of in-situ experiments in the transmission electron microscope was performed in order to explore the mechanism of dislocation pattern formation.
The combined effect of strain and temperature on the microstructural evolution of plastically deformed fcc metals (Aluminum, Copper, Nickel and Gold) was examined systematically. In particular, the detailed nano-scale, internal structure of dislocation boundaries was determined. In all the metals studied, dislocations within the boundaries tend to rearrange themselves sequentially with increasing strain from tangles into dislocation cells with tangled boundaries, followed by the formation of dislocation boundaries consisting of wavy, parallel dislocations and finally into arrays of parallel dislocations. The results were represented by strain-temperature microstructural maps. The topology of the microstructural maps was found to be similar for all metals studied, suggesting a universal strain- temperature dependence in deformed fcc metals.
The experimental strain-temperature maps of dislocation structures at the nano-scale for the studied fcc metals are scaled by the cross-slip activation energy, calculated using an atomistic based elastic model, to form a single universal strain - temperature map. Such a map unifies many observations obtained by different groups over the years and serves to direct further investigations in this fundamental area. These implications for dislocation rearrangement mechanisms are discussed.