The Tick-Tock of Language: Is Language Processing Sensitive to Circadian Rhythmicity and Elevated Sleep Pressure?

Abstract

The master circadian pacemaker emits signals that trigger organ-specific oscillators and, therefore, constitutes a basic biological process that enables organisms to anticipate daily environmental changes by adjusting behavior, physiology, and gene regulation. Although circadian rhythms are well characterized on a physiological level, little is known about circadian modulations of higher cognitive functions. Thus, we investigated circadian repercussions on language performance at the level of minimal syntactic processing by means of German noun phrases in ten young healthy men under the unmasking conditions of a 40 h constant-routine protocol. Language performance for both congruent and incongruent noun phrases displayed a clear diurnal rhythm with a peak performance decrement during the biological night. The nadirs, however, differed such that worst syntactic processing of incongruent noun phrases occurred 3 h earlier (07:00 h) than that of congruent noun phrases (10:00 h). Our results indicate that language performance displays an internally generated circadian rhythmicity with optimal time for parsing language between 3 to 6 h after the habitual wake time, which usually corresponds to 10:00–13:00 h. These results may have important ramifications for establishing optimal times for shiftwork changes or testing linguistically impaired people.

• Syntactic processing
• Constant routine
• Language
• Circadian rhythms
• Gender-congruency effect

Acknowledgments

This research was supported by the Gottlieb Daimler- and Karl Benz-Foundations. We thank Doreen Anders, Daniel Bratzke, Serge Daan, Ingo Fietze, Simon Folkard, Silvia Frey, Johannes Gerwien, Martin Glos, Marijke Gordijn, Ingrid Häfner, Andreas Häußler, Joachim Hermsdörfer, Isabelle Jasper, Myriam Juda, Thomas Kantermann, Guido Kiecker, Kurt Kräuchi, Ildiko Meny, Martha Merrow, Thomas Penzel, Karin Reichelt, Claudia Renz, Bettina Roelke, Till Roenneberg, Juliane Schütte, Katharina Spalek, Jakub Späti, Michael Steinborn, Katja Suckow, Rolf Ulrich, Stefan Vangeel, Celine Vetter, and Anna Wirz-Justice for their support in preparing and/or their assistance in conducting this study.