The work that resulted in this thesis would not have been possible without the support of many people.

I am very greatful to my advisor Prof. Steinberg for all his support, the instructive and motivating discussions, his readiness to help all times, and for never loosing his confidence in me.

I would like to thank my teacher in chronobiology, PD Dr. Siegmund for helping me with all her expertise and enthusiasmus in this field and for directing my interest into rhythmical processes of life.

I am very grateful to Prof. Kirschbaum, who encouraged and supported my work with many helpful discussions and with his kind readiness to help me all the time.

I am also grateful to Dr. Georg Staaks, who helped me profoundly in many ways such as many fruitful scientific discussions and practical advice for establishing the video based analysis method at the IGB. Thanks also for his friendship.

I want to thank PD Dr. Stephan Pflugmacher for his scientific advice and the critical review of publications.

For the supporting of practical work in the laboratory I would like to thank Gabi Finke, Katja Schmidt, Liane Wieczorek and Henrik Zwadlo.

Many thanks to Maaike Binner and Jan Ohlberger for the good working atmosphere in our office.

And last but not least I am grateful to Gösta for his invaluable encouragement in many ways.