Our daily life is organized by three different clocks: a solar clock, providing light and warmer temperatures during the day, a social clock, which we see or hear first thing on a working day, and a biological clock which we sense most vividly when jet-lagged, during shift work, or when adjusting to daylight savings time. When shielded from the other clocks (constant external conditions), the biological clock "runs free" with its own timing. In real life, circadian clocks are usually synchronized (entrained) to the 24 h day. The major entraining signal (zeitgeber) is light which, in mammals including humans, can only act through the eyes. The circadian clock controls our bodily functions at many levels, from gene expression to complex behaviours, such as sleep and performance. The control of the circadian clock is profound. At specific times of day, many different genes are switched on or off in all organs and tissues. These systematic changes of the cells’ biochemistry form the basis for a temporal program that concerns every aspect of life. This circadian program has a strong genetic basis. As with other genetic traits, individual differences in circadian properties depend on variations of specific genes (so-called “alleles” of “clock genes”). In a given population including human populations, freerunning periods are distributed around a species-specific mean. These genetic differences can also be seen when the clock is entrained because the position of the internal clock in relation to the external clock (e.g., sleep in relation to dawn) depends on the individual’s free-running period. Thus, human preferences in the timing of sleep and wake (called "chronotypes", such as "larks" and "owls") are, at least partly, based on genetics. The relationship off chronotype and shift-work tolerance and preferences are questions dealt with, in detail, in project 1 but, in general, also in all other projects.(Please see also Individual Projects pages)

These insights into the bio-medical aspects of daily life have changed the way we look at social temporal structures in modern society. The circadian clock of shift workers, for example, is rarely appropriately adjusted to the enforced social schedules, which has severe consequences on performance, quality of life, sleep quality, and general health.These consequences are central to several chronobiological studies and are the central question of project I. It is, however, important to link the insights of chronobiology with many different, equally important aspects of daily life. Only if many different aspects of daily life are investigated in a coordinated and interactive way, it will be possible to devise strategies to optimise the structure of daily work. We, therefore, propose ClockWORK, a network of specialists that combines circadian research with research into cognitive and socio-psychological aspects of work and free time. The first two projects represent the chronobiological bases for daily structure. They specialise in the formal basis of the biological clock, epidemiological and genetic as well as field studies (project I) and measurements of sleep quality and clinical parameters under controlled conditions (constant routines, project II).

The variables in these projects are individual circadian differences in conjunction with light-exposure, age, temperature, and diet. Projects I and II will also be responsible for circadian know-how and methodology in all other projects. In daily life and work, people have to frequently switch between different tasks. Cognitive and experimental psychologists have investigated the specific mental work load of task switching. In this context, task switching refers to switches on lower levels of tasks (switching between reading and writing, between counting and sorting, between pipetting different volumes, etc) rather than switching between entirely different tasks (e.g., switching between manual work at the bench to writing a protocol or report). This low level task switching is a main source of mistakes and is, therefore, important for costs and quality standards. It has been shown, that task switching demands a reconfiguration of cognitive processes before one can proceed to the new task. This mental reconfiguration is effortful, requires time, and is subject to more errors than continuously and repeatedly performing the same task. Several factors contribute to such switch costs, e.g., memory processes necessary to retrieve the corresponding task set. The efficiency of memory retrieval processes is impaired by many different variables, including time-of-day, sleep dept or fatigue. The circadian and sleep-related variables of task switching costs will be investigated in detail and will be related to individual preferences in structuring the 24-h-day (project III).

Language is a species-specific faculties of man and is central to any kind of work but especially within a team. Producing a sentence means transforming an idea into structured strings of sound or graphic symbols. Listening means analysing physical inputs (sound, symbol), extracting the content and understanding the message or idea. It allows verbal (oral and/or written) communication and is the most important instrument for information exchange. Language communication is the prototypical activity for coordinating tasks. Speaking, listening, reading and writing either face to face or electronically mediated, man/machine interaction, job training and continuous education form a crucial component of the daily structure of work. The core activity of communication is language processing, a special case of cognitive information processing. Quality and speed of language processing depend largely on a person's capacity to concentrate and focus his attention on the involved mental activities. There are convincing theoretical reasons for the assumption that the communicative performance is affected by vigilance and sleepiness, respectively and that these qualities vary over the course of the day with individual characteristics that are related to chronotype. A detailed investigation of the daily variation in language processing will be instrumental in optimising the daily structure of work and team efforts (project IV).

 Practically all aspects of work demand the fast and precise execution of psychomotor processes. Especially skilled and dextrous manual manipulations constitute an inherent feature of every day life (eating, toileting, dressing, handwriting, etc.) and are indispensable in any skilled activity. The neuronal system controlling dexterous hand function in primates, including man, is uniquely characterized by a specific organization, the direct cortico-motoneural connection. A number of outstanding studies have demonstrated the high precision and effectiveness of the system coordinating dexterous hand function by measuring movement parameters such as forces produced by the fingers during manipulation of objects. As any other system, dexterous hand function is vulnerable to specific disturbances. After section of the pyramidal tract (in monkeys), for example, most motor deficits disappear after a while, but independent finger movements remain permanently impaired. Apart from structural lesions in the nervous system, many other factors affect fine motor control. Among these are perturbations of environmental conditions, drug consumption, fatigue, distractors etc. Given this evidence it seems obvious that structural and temporal aspects of work affect fine motor control. A detailed analysis of the variance during daily work and under different shifts of flexible work schedules is, therefore, of high importance (project V).