Integrated Calendar

Iron-based pnictide superconductors display the phenomenon of electronic nematicity - the electronic transport displays an anisotropic behavior that breaks the rotational symmetry of the lattice. This nematic behavior is observed across many compounds and over a large part of the phase diagram of the material. What is this nematicity? Does it have any relationship to superconductivity in the material? In this talk I will attempt to answer these questions by providing a microscopic view of one of the pnictide compounds NaFeAs obtained using atomic-resolution scanning tunneling microscopy and spectroscopy.

Drosophila melanogaster flies show complex behaviors like associative learning. Combining the available genetic tools with behavioral measures allows us to study the specific neuronal circuits of learning and memory.
Using olfactory conditioning, I directly compared the neuronal circuit of memories with different punishment paradigms: the widely used electric-shock and the newly established elevated temperature. I identified the neural pathway selectively required for olfactory-temperature conditioning, from the sensory input to the central neurons signaling reinforcement. I found that temperature and electric-shock punishments—despite being perceived by distinct sensors—eventually converge to the same neuronal network: the dopamine pathway. Thus the role of dopamine is general—attaching a motivational value to an environmental stimulus. This finding is especially significant in context of recent findings in mammalian systems, namely that in addition to their well-established role in signaling positive reinforcement, dopaminergic populations in the mammalian brain were also shown to represent aversive reinforcement.

Cortical and hippocampal oscillations play a crucial role in the encoding, consolidation and retrieval of memory. Fast oscillations (sharp-wave ripples) have been shown to be necessary for the consolidation of memory. During consolidation, information is transferred from the hippocampus to the neocortex. One of the structures at the interface between hippocampus and neocortex is the subiculum. It is therefore well suited to mediate transfer and distribution of information from the hippocampus to other areas. By juxtacellular and whole-cell recordings in awake mice we show that in the subiculum a subset of pyramidal cells is activated whereas another subset is inhibited during fast oscillations. We demonstrate that these functionally different subgroups are predetermined by their cell type. Bursting cells are selectively employed to transmit information during fast oscillations, whereas regular firing cells are silenced. With multiple recordings in vitro we show that the cell-type specific differences extend into the local network architecture. This is reflected in an asymmetric wiring scheme where bursting cells and regular firing cells are recurrently connected among themselves but connections between cell types exclusively exist from regular to bursting cells. The total excitation onto bursting cells within the local network is therefore larger than onto regular-firing cells. We conclude that information transmitted during sharp-wave ripples is preferentially routed to target regions of burst firing cells.