Integrated Calendar

Slow waves and sleep spindles are the two fundamental brain oscillations of NREM sleep, yet they have been mostly studied in vitro, under anesthesia, within few brain regions or with scalp EEG recordings. We examined intracranial depth EEG and single-unit activity recorded simultaneously in up to 12 brain regions in neurosurgical patients to better characterize regional diversity in these sleep oscillations. First, we found changes in spindle occurrence, frequency, and timing between regions and across sleep, reflecting anatomical projections and thalamocortical hyperpolarization levels that change with sleep depth. We further show that both slow waves (and the underlying active and silent neuronal states) and sleep spindles occur mostly locally, thereby showing that constrained intracerebral communication is an important feature of sleep. Next, we confirmed that in freely behaving rats, slow waves and silent periods in sleep likewise occur predominantly locally. Moreover, after a long period of being awake, while both EEG and behavior indicate wakefulness, local populations of neurons go offline, exhibiting "local sleep". We are now exploring whether such local sleep may lead to cognitive consequences, such as lapses of attention, in awake people who are sleep deprived
Another line of research focuses on disconnection from the external environment - conditions in which sensory stimuli fail to be incorporated into our perceptual stream. To this end, we are examining neuronal responses to sounds in rats across spontaneous vigilance states with an emphasis on comparing wakefulness with REM sleep. Responses of individual neurons in primary auditory cortex are comparable in wake and sleep, calling into question the proposal that the thalamus does not relay peripheral signals effectively to the cortex in sleep. Important differences between waking and sleep may lie in how signals propagate across cortical regions and layers.

Every chemist and every scientist in the neighbouring fields is familiar with those little curved arrows in Lewis structures of reactants of pericyclic reactions - they represent the net electron transfers or fluxes of valence electrons during the reactions in the electronic ground state, and they allow to predict which chemical bonds are broken, which are formed, etc. But in spite of many empirical successes and also many theoretical investigations e.g. concerning the Woodward-Hoffmann rules for pericyclic reactions, those electron fluxes have never been observed or evaluated, during 84 years after the discovery of the Schrödinger equation. On the experimental side, the first real-time observation of valence electron motion in atoms is a break-through which should pave the way to monitoring electron motions during reactions [1]. On the theoretical side, the fundamental obstacle has been the Born Oppenheimer approximation: On one hand it is the doorway to all successful quantum chemistry calculations of molecular properties. But on the other hand it is a disaster because it predicts zero (0 !) electron flux densities. We overcome this problem by means of the continuity equation and Gauss' theorem. The result is - for the first time! - the quantum quantification of those little arrows in Lewis structures, i.e. we are able to answer question such as: in which directions do the electrons really flow during the pericyclic reaction? How many electrons are really transferred? Do they flow synchronously? On which time scale? The electron fluxes are visualized by movies for simple model systems.

The results have been achieved in wonderful cooperation with PhD students Timm Bredtmann, Falko Marquardt, Axel Schild, with post-docs and visiting scientists Dirk Andrae, Ingo Barth, Anatole Kenfack and Gennadii K. Paramonov, with my colleagues, Hans-Christian Hege and Beate Paulus, and with invaluable advice from several colleagues from organic and theoretical chemistry. Our work is supported, by Deutsche Forschungsgemeinschaft, and by Fonds der Chemischen Industrie.

[1] E. Goulielmakis et al.: Real-time observation of valence electron motion, Nature, 466, 739-744 (2010)

In animals, all microRNAs have potentially hundreds of targets, yet in all studied cases the phenotype associated with a particular miRNA is due to very few of its targets. In this talk I'll discuss this apparent contradiction and the approaches we take to resolve it.