Integrated Calendar

Holes in elastic metamaterials, defects in 2D curved crystals, localized plastic deformations in amorphous solids and T1 transitions in epithelial tissue, are typical realizations of stress-relaxation mechanisms in different solid-like structures, interpreted as mechanical screening.
In this talk I will present a mechanical screening theory that generalizes classical theories of solids, and introduces new moduli that are missing from the classical theories. Contrary to its electrostatic analog, the screening theory in solids is richer even in the linear case, with multiple screening regimes, predicting qualitatively new mechanical responses.
The theory is tested in different physical systems, including disordered granular solids that do not have a continuous mechanical description. These materials are shown to violate energy conservation and are best described by Odd-Screening: a screening model that does not derive from an energy function. Experiments reveal a mechanical response that is strictly different from classical solid theory and is completely consistent with our mechanical-screening theory. Finally, I will discuss the relevance of this theory to 3D solids and a new Hexatic-like state in 3D matter.

How information is processed within the brain is a key question in systems neuroscience. We address the issue in spiking neuronal networks of freely moving mice. I will describe our recent findings and conclusions pertaining to three specific information processing steps: transmission, representation, and storage.
First, using feedforward optogenetic injection of white noise input to a small group of adjacent neocortical excitatory cells, we find that spike transmission to a postsynaptic cell exhibits error correction, improved precision, and temporal coding. The results are consistent with a nonlinear coincidence detection model in the postsynaptic neuron.
Second, by triggering input on animal kinematics, we create an artificial place field in an otherwise-silent pyramidal cell. In hippocampal region CA1 but not in the neocortex, artificial fields exhibit synthetic phase precession that persists for a full cycle. The local conversion of an induced rate code into an emerging phase code is compatible with a dual-oscillator interference model.
Third, by triggering input on spontaneous spiking, we impose self-terminating spike patterns in a group of presynaptic excitatory neurons and a postsynaptic cell. The precise timing of all pre- and postsynaptic spikes has a more substantial impact on long-lasting effective connectivity than that of individual cell pairs, revealing an unexpected plasticity mechanism.
We conclude that intrinsic properties of single neurons support millisecond-timescale operations, and that cortical networks are organized in functional modules which we refer to as “converging assemblies”.