Timing (Not Just Amount) of Sleep Makes the Difference for Learning in Class: Event-related Potential Correlates of Delayed Phase Preference in Adolescent Students

Timing (Not Just Amount) of Sleep Makes the Difference: Event-related Potential Correlates of Delayed Sleep Phase in Adolescent Female Students Matthew Kirby (mfk13@hotmail.com) Department of Psychology, 1125 Colonel By Drive Ottawa, ON, K1S 5B6, Canada Amedeo D’Angiulli (amedeo_dangiulli@carleton.ca) Department of Psychology, 1125 Colonel By Drive Ottawa, ON, K1S 5B6, Canada Abstract Adolescents tend to experience alterations in their sleep cycles inducing them to go to sleep and wake up at later times than they typically would at younger age (Delayed Sleep Phase, DSP). We asked a relatively homogeneous sample (N = 22) of female high-school students to maintain an exhaustive sleep log during two weeks. Within this period, we randomly assigned each participant to a morning or afternoon testing condition (morning vs. afternoon group), in which we measured performance data along with ERPs during a standard Stroop task. The sleep log data confirmed a two-hour DSP in both groups. Participants in the afternoon group performed significantly better (less Stroop interference) than those in the morning group and showed a differential ERP pattern to incongruent and congruent stimuli, not shown by the morning group. We conclude that DSP can be associated with an attentional impairment in the morning. Keywords: Delayed Phase Preference; Sleep & Circadian Rhythms; Attention; Stroop; Adolescence. As children transition to adolescence, they tend to experience alterations in their sleep cycles (Delayed Sleep Phase, DSP) which may induce them to go to sleep and wake up at a later time than they typically would (Crowley, Acebo, & Carskadon, 2007; Fischer, Radosevic-Vidacek, Koscec, Teixeira, Moreno, & Lowden, 2008; Mitru, Millrood, & Mateika, 2002). We investigated the influence of sleep cycles on the performance of adolescent females during mornings and afternoons of ordinary school days by examining neural correlates of cognitive performance using Event-Related Potentials (ERPs), along with behavioral data. Our results support previous research which has found that early school start times, which do not accommodate the DSP observed in adolescents, result in poor academic performance (Epstein, Chillag, & Lavie, 1998; Fischer, Radosevic-Vidacek, Koscec, Teixeira, Moreno, & Lowden, 2008; Hansen et al., 2005; Walhstrom, Wrobel, & Kubow, 1998). The findings of our study show that adolescents tested in the morning are cognitively performing at a low level in comparison to their counterparts tested in the afternoon. Furthermore, the poor cognitive performance observed in the morning was associated with significantly different ERP patterns which appear to be evidence of a deficit in attentional resources and an impeded ability to respond when competing stimuli are present. Method Participants Twenty two female adolescents, ranging in age from 16 to 18, were recruited from grades 11 and 12 psychology classes at a high school in Central Southern, British Columbia. Participants took part in the study for course credit in their psychology class. Measures Stroop Task. A standard version of the Stroop Colour-Word Task, selected from STIM (Neuroscan, Compumedics Ltd.). Stimulus duration was set at 200 ms with an inter-trial interval of 1000 ms. Participants’ response time and accuracy were measure through a hand- held response pad. To counterbalance any possible novelty effects incongruent stimuli were presented at a higher frequency than congruent stimuli (Macloed, 1991) at a ratio of approximately 3:1, 224 trials and 76 trials respectively, for a total of 300 trials. Event-Related Potentials (ERPs). EEG was recorded concurrently with the Stroop task. Electrodes were placed at: Pz, P3, P4, Cz, C3, C4, Fz, F3, and F4 (International System) with reference electrode at nose tip. An electro-oculogram (EOG) was vertically placed above and below. Using the standard eye movement reduction algorithm devised by Semlitsch, Anderer, Schuster and Presslich (1986), the EOG was used to filter out artifacts due to eye movement from the relevant EEG signal. Impedance was kept below 5Ω. High and low pass filters were set at 0.5Hz and 30Hz respectively. Time locking was implemented through an internal serial port trigger synchronized with stimulus presentation. 2-week sleep-log questionnaire. The sleep log questionnaire was adapted from the Thompson Rivers University Respiratory Therapy Program Sleep Questionnaire. The questionnaire was used to assess the sleeping schedules of participants over a two week period including weekends. Pre- and Post-Stroop affective questionnaires. Before and after the Stroop task, participants completed a 5- point rating scale measuring affective states, adapted from an affective questionnaire (Usala & Hertzog, 1989), and a task appraisal questionnaire (Tomaka et al., 1999). Procedure The participants began recording their sleeping schedule over a two week period beginning on the Thursday