Circadian Modulation of the Time Course of Automatic and Controlled Semantic Processing

Abstract

Background: Circadian rhythm patterns vary across individuals, producing the existence of different chronotypes. Chronotype refers to the preferences of individuals to perform their daily life activities, being classified as intermediate-types (no specific circadian preference), morning-types (preference for early morning hours) and evening-types (preference for later hours). We investigated whether chronotype and time-of-day modulate the time course of automatic and controlled semantic processing. Participants performed a category semantic priming task at either the optimal or non-optimal time-of-day. We varied the prime-target onset asynchrony (100-, 450-, 650-, and 850-ms SOAs) and kept the percentage of unrelated targets constant at 80%. Automatic processing, producing facilitatory priming, was expected with the short SOA, and controlled processing, producing inhibitory priming, was expected with longer SOAs. Results: Intermediate-types (Experiment 1) verified that our task was sensitive to capturing both types of processes. Facilitatory automatic priming was observed early in the first trials of the short 100-ms SOA, then controlled and automatic processing cancelled each other producing a lack of priming effects (2nd and 3rd subblocks of the 100-ms SOA and the 450-ms SOA). Finally, with the longer SOAs only inhibitory controlled priming was observed, which size increased with time. This time course of automatic and controlled processing in intermediate-types served as reference to assessed both types of processes in extreme chronotypes. Morning-type and evening-type participants (Experiment 2) differed in the influence of time of testing on priming effects. Morning-types applied control in all conditions, and no modulation of performance by time-of-day was observed. In contrast, evening-types were only able to suppress automatic processing when the task was performed at their optimal time of day. Also, they were considerably slower in the implementation of controlled processing as inhibitory priming occur in the longest 850-ms SOA only. Conclusions: These results suggest that extreme chronotypes are associated with different styles of cognitive control. Morning-types show a proactive control style that fosters maintenance of active response strategies to resolve conflict without producing negative effects. Evening-types show a reactive control style such that conflict resolution is influenced by task demands. This dissociation suggests a better adaptation strategy of the morning-type chronotype.