doi: 10.1111/j.1365-2869.2009.00811.x Performance monitoring during sleep inertia after a 1-h daytime nap SHOICHI ASAOKA 1,2,3 , HIROAKI MASAKI 1 , KEIKO OGAWA 1 , TIMOTHY I. MURPHY 4 , KAZUHIKO FUKUDA 3 and KATUO YAMAZAKI 1 1 Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan, 2 Department of Somnology, Tokyo Medical University, Tokyo, Japan, 3 Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, Japan and 4 Department of Psychology, Brock University, St Catharines, ON, Canada Accepted in revised form 12 October 2009; received 29 July 2009 SUMMARY Performance monitoring is an essential function involved in the correction of errors. Deterioration of this function may result in serious accidents. This function is reflected in two event-related potential (ERP) components that occur after erroneous responses, specifically the error-related negativity ⁄ error negativity (ERN ⁄ Ne) and error positivity (Pe). The ERN ⁄ Ne is thought to be associated with error detection, while the Pe is thought to reflect motivational significance or recognition of errors. Using these ERP components, some studies have shown that sleepiness resulting from extended wakefulness may cause a decline in error-monitoring function. However, the effects of sleep inertia have not yet been explored. In this study, we examined the effects of sleep inertia immediately after a 1-h daytime nap on error-monitoring function as expressed through the ERN ⁄ Ne and Pe. Nine healthy young adults participated in two different experimental conditions (nap and rest). Participants performed the arrow- orientation task before and immediately after a 1-h nap or rest period. Immediately after the nap, participants reported an increased effort to perform the task and tended to estimate their performance as better, despite no objective difference in actual performance between the two conditions. ERN ⁄ Ne amplitude showed no difference between the conditions; however, the amplitude of the Pe was reduced following the nap. These results suggest that individuals can detect their own error responses, but the motivational significance ascribed to these errors might be diminished during the sleep inertia experienced after a 1-h nap. This decline might lead to overestimation of their performance. keywords daytime nap, error monitoring, error negativity/error-related negativity, error positivity, sleep inertia INTRODUCTION Accidents and sleepiness are closely related. Approximately 9–20% of vehicle accidents are thought to be sleep related (Horne and Reyner, 1995; Maycock, 1996). The relative frequency of these accidents peaks in early morning and mid afternoon, which are synchronized to points in the circadian cycle associated with sleepiness (e.g. Garbarino et al., 2001; Horne and Reyner, 1995; Maycock, 1996). This phenomenon is also observed in the patterns of errors made by individuals reading gas meters (Mitler and Miller, 1996). To date, many laboratory-based studies have demonstrated that sleepiness resulting from acute or cumulative sleep deprivation is associated with impairments across a wide variety of cognitive functions (see Durmer and Dinges, 2005 for review). Recently, not only simple cognitive performance, but also higher Correspondence: Shoichi Asaoka, Department of Somnology, Tokyo Medical University 6-7-1, Nishishinjuku, Shinjuku-ku, Tokyo 160- 0023, Japan. Tel.: +81 3 3342 6111 (ext 5757); fax: +81 3 3342 7083; e-mail: asaoka@gmail.com J. Sleep Res. (2010) 19, 436–443 Sleep inertia 436 Ó 2010 European Sleep Research Society