Photo: Markus Scholz for the Leopoldina
In 2019, the Leopoldina is dedicating its Annual Assembly to the topic of “Time in Nature and Culture”. From 20–21 September, scientists will come together in Halle (Saale) to discuss technological developments and societal changes. The four main topics on Saturday, 21 September 2019, are philosophy and psychology, chronological developing processes, chronobiology and chronomedicine and time in life. In each scientific session, there will be several lectures by members of the Leopoldina and non-members.
Speaker: David Poeppel, Frankfurt am Main, Germany
Speaker: Norman Sieroka, Bremen, Germany
Time is a fundamental dimension for humans, independently of whether they are considered primarily as biological-physical or as mindful beings. Accordingly, a broad range of academic disciplines investigates questions about time in its different manifestations: as physical time, as geologic or deep time, as individually experienced or psychological time, as socio-intersubjective time, as historical time, etc. However, the commonalities, differences, and connections between these manifestations are rarely discussed. At this point, philosophy can take on an important coordination task; and this is exactly what the present lecture is meant to illustrate. Starting from a few conceptual distinctions – most importantly that between different basic types of time order – individual aspects from some of the other lectures will be revisited and related to each other. This also provides insights into the relationship between questions of a more scientific and theoretical nature, such as the directedness of physical time or questions of chronobiology, and questions of social and ethical concern, such as transitional justice or specific forms of chronopolitics. It turns out that significant differences in attitudes and over disciplines often go hand in hand with a difference in how one thinks about the existence of the three different modalities of time – that is, whether or to what extent one assumes that the past and the future exist alongside the present.
Speaker: Martin Grötschel, Berlin, Germany
In 1908 Hermann Minkowski, introducing his lecture “Space and Time” on the revolutionary concept of spacetime, formed one of the most poetic sentences, which can be found in mathematical and natural-science literature:
Henceforth, space by itself, and time for itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.
Today, the approach is more sober – time is simply regarded as a variable, which has to be taken into account in the mathematical modelling of processes in nature, technology, or society. Mathematics and computer science do not ask what time actually is. The focus is pragmatic and lies on the interdependency between time and other variables. Whether time is considered continuous or discrete, depends on the respective application. Today, the issue “runtime” (of computer algorithms) plays an increasingly important role, especially in computer science. Terms such as online algorithms and real time have meanwhile found their way into everyday language. In my lecture I will look into the aspects of time indicated above in a generally understandable manner.
Speaker: Eckehard Schöll, Berlin, Germany
Rhythms influence our life in various ways, e.g., through heart beat and respiration, oscillating brain currents, life cycles and seasons, clocks and metronomes, pulsating lasers, transmission of data packets, and many others. The physics of complex nonlinear systems has developed methods to describe and analyze periodic oscillations and their synchronization in complex networks, which are composed of many components. Synchronized oscillations as well as completely asynchronous chaotic oscillations play a major role in many networks in nature and technology. For instance, the synchronous firing of all neurons in the brain represents a pathological state, like in epilepsy or Parkinson's disease, and should be suppressed, as well as the synchronous mechanical vibration of bridges. On the other hand, synchronization is desirable for the stable operation of power grids or in encrypted communication with chaotic signals. In networks composed of identical components, intriguing hybrid states ("chimeras") may form spontaneously, which consist of spatially coexisting synchronized and desynchronized domains, i.e., seemingly incongruous parts. This might be of relevance in inducing and terminating epileptic seizures, or in unihemispheric sleep which is found in certain migratory birds and mammals, or in cascading failures of the power grid.
Speaker: Steve A. Kay, Los Angeles, USA
Our laboratory studies the composition and architecture of circadian networks in plants and animals. These networks provide adaptive advantages to organisms, and are now known to be pervasive in their integration with many other regulatory modules in multiple cell types. We employ high throughput genomic and chemical biology pipelines to identify network components and apply mechanistic approaches to understand their detailed function and interactions. In both plant and animal systems we have found that circadian networks are hierarchical and composed of regulatory layers that act at the transcriptional and post-transcriptional levels. Increasingly we are finding that circadian regulation is tightly integrated with metabolic networks and operate with reciprocal regulatory interactions.
Now that we have a reasonably robust knowledge base at hand, we can exploit our understanding of the composition and dynamics of clock proteins for specific translational use in agricultural biotechnology in crop species and drug discovery in humans. Specific examples of such knowledge translation will be presented.
Speaker: Russell G. Foster, London, UK
By studying how circadian rhythms and sleep are regulated (entrained) by the dawn/dusk cycle we demonstrated the existence of a “3rd class” of photoreceptor within the eye and showed that these new photoreceptors comprise a small number of photosensitive retinal ganglion cells (pRGCs) that utilise the blue light sensitive photopigment melanopsin (OPN4). Whilst there has been remarkable progress in understanding the complex intracellular mechanisms that generate circadian rhythms, the molecular pathways whereby the pRGCs entrain circadian biology has remained poorly understood.
The suprachiasmatic nuclei (SCN) are the site of the primary circadian pacemakers within the mammalian brain, and until recently, the model for entrainment involved a simple linear pathway whereby glutamate release from the pRGCs resulted in Ca2+ influx and raised intracellular cAMP in SCN neurones. This in-turn resulted in CREB phosphorylation leading to increased transcription of two key clock genes, Per1 and Per2, which either advanced or delayed the molecular clockwork. However, an important feature of entrainment is that circadian responses to light are limited – as typified by jet lag. Full recovery from jet lag requires a day for every time-zone crossed. We addressed this issue and have identified and characterized a key role for Salt Inducible Kinase 1 (SIK1) and the CREB-regulated transcription co-activator 1 (CRTC1) in clock re-setting. In addition, our more recent and unpublished findings have shown that light entrainment also involves the parallel activation of a Ca2+-ERK1/2-AP-1 signalling pathway. Thus, both CRE and AP-1 regulatory elements drive light-induced clock gene expression.
These findings then led to a new understanding of how sleep/wake behaviour modulates the effects of light upon the molecular clockwork. Adenosine builds within the brain during wake and dissipates during sleep, effectively encoding sleep/wake history. Pharmacological and genetic approaches demonstrated that adenosine also acts upon the circadian clockwork via A1/A2A signalling through the activation of the Ca2+-ERK1/2-AP1 and CREB/CRTC1-CRE signalling pathways to regulate the clock genes Per1 and Per2. We show that these signalling pathways converge upon and effectively inhibit the same pathways activated by light. Thus, the resulting phase shift of the circadian clock is the integrated product of sleep/wake history (via adenosine) and light.
Finally, the presentation will explore how such signalling mechanisms provide a potentially new and exciting target for the regulation of circadian rhythms and the “pharmacological” replacement of light for sleep/wake re-setting in individuals lacking eyes or in individuals with severe circadian rhythm disruption as seen in schizophrenia and dementia.
Speaker: Jan Assmann, Heidelberg
Speaker: Daniel Hamermesh, Austin (Texas), USA
Economists have done immense amounts of research on work time; but they have done very little research on how time is spent outside of paid work. With non-work time accounting for 20 hours each day for the average adult in Western economies, this neglect is remarkable. Using data from the US, France, Germany and the UK, this lecture examines how time is divided among various activities, including sleep and television-watching, the first and third most important uses of time. It shows how all of these uses differ among demographic groups and studies the effects of economic incentives--income and wage rates--on them. It examines how time zones affect our spending of time; it demonstrates how the stress that people feel about time is affected by their economic circumstances. It concludes by considering how changes in economic policy can lead people to alter their activities in order to generate a less stressful life in which time is balanced more evenly over their lives.
Speaker: Gabriele Doblhammer, Rostock
Health and mortality are determined by the interplay between nature and nurture. During the last 150 years this interplay has resulted in an ever increasing life expectancy and more active years in good health. How can this interplay be imagined? Seasonal variations influence not only the number of births, but also health from birth on, as well as the timing of death. The number of births differs by seasons, albeit in Germany the seasonal pattern has changed over the last decades. To what extent cultural patterns and/or biological factors are responsible is still lively debated. The risk of suffering from diabetes, chronic cardio-vascular diseases, and dementias depends on the month of birth, which is also true for life expectancy at old age. The pattern differs between the northern and the southern hemisphere and is still present among centenarians. Seasonal patterns in infections and diet are discussed as possible causes. Mortality depends on ambient air temperature, and extreme weather constellations result in mortality peaks. Improvements in public health, medical care, care provision, and a healthy life style can modify and counterbalance external influences by “nature”. Still they have the capacity to affect our health and life expectancy.