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Diurnal Variation in Energetic Arousal, Tense Arousal, and Hedonic Tone in Extreme Morning and Evening Types Konrad S. Jankowski a; Wanda Ciarkowska a a Faculty of Psychology, University of Warsaw, Warsaw, Poland Online Publication Date: 01 July 2008

To cite this Article Jankowski, Konrad S. and Ciarkowska, Wanda(2008)'Diurnal Variation in Energetic Arousal, Tense Arousal, and

Hedonic Tone in Extreme Morning and Evening Types',Chronobiology International,25:4,577 — 595 To link to this Article: DOI: 10.1080/07420520802261770 URL: http://dx.doi.org/10.1080/07420520802261770

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Chronobiology International, 25(4): 577–595, (2008) Copyright # Informa Healthcare ISSN 0742-0528 print/1525-6073 online DOI: 10.1080/07420520802261770

DIURNAL VARIATION IN ENERGETIC AROUSAL, TENSE AROUSAL, AND HEDONIC TONE IN EXTREME MORNING AND EVENING TYPES

Konrad S. Jankowski and Wanda Ciarkowska Faculty of Psychology, University of Warsaw, Warsaw, Poland Downloaded By: [POLAND TRIAL] At: 14:25 3 November 2008

The aim of the present study was to examine levels of energetic arousal (EA), tense arousal (TA), and hedonic tone (HT) in individuals with different circadian preferences. Subjects were males with extreme either morning (M-type) or evening (E-type) preferences (N ¼ 31), selected using the Morningness-Eveningness Questionnaire cutoff points derived from the Polish population norms. They completed the UWIST Mood Adjective Check List every 1.5 h between 08:00 to 20:00 h in laboratory conditions. The obtained data showed higher levels of TA and lower levels of HT in E-types over the whole day as compared to M-types. As for EA, M-types showed higher levels than E-types between 08:00 to 17:00 h, but the two groups showed no differences during the later hours of the day. Both groups were found to exhibit similar diurnal patterns in TA and HT, and dissimilarity between M-types and E-types appeared in the daily course of EA. The results show the three-dimensional model of mood is more advantageous in M-types than in E-types during the hours of typical human activity. (Author correspondence: [email protected] edu.pl) Keywords Chronotype, MEQ, Diurnal rhythm, Mood

INTRODUCTION Interest in diurnal mood variations, both in healthy individuals and in various disorders, has grown over the past decades. This is due to the fact that circadian rhythm abnormalities are involved in many psychopathological conditions where mood disorders constitute the most definite and distressing symptom. The conditions include, among others, unipolar depression, bipolar depression, seasonal affective disorder (SAD) (Kupfer, 2007), chronic fatigue syndrome (CHS) (Jerjes et al., 2006), and delayed sleep phase syndrome (DSPS) (Murray et al., 2003). For Submitted September 17, 2007, Returned for revision November 5, 2007, Accepted February 21, 2008 Address correspondence to Konrad S. Jankowski, Faculty of Psychology, University of Warsaw, Stawki 5/7, 00-183 Warsaw, Poland. E-mail: [email protected]

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example, in persons suffering from unipolar affective disorder, circadian rhythm disturbances are manifested by depressed mood during the day, with particularly low mood levels in the morning hours (Morris et al., 2007; Murray, 2007) and atypically increased activity of physiological processes in the evening (Young et al., 1994). The role of chronotype in these disorders is interesting from a clinical perspective, as relationships between eveningness and depressiveness (Chelminski et al., 1999), depression (Drennan et al., 1991), and SAD (Murray et al., 2003) have been reported. Moreover, an intuitive supposition that DSPS is a pathological form of eveningness seems to be corroborated by recent studies on clock genes, suggesting that per3 polymorphism is associated both with DSPS and eveningness (Pereira et al., 2005), while per2 polymorphism is associated with advanced sleep phase syndrome (ASPS) and morningness (Carpen et al., 2005). Interestingly, the association of ASPS with affective disorders is not as strong (Reid et al., 2001) as that of DSPS; 75% of DSPS patients are diagnosed with co-morbid depression (Regestein & Monk, 1995). Therefore, it seems worthwhile to investigate diurnal mood variations in individuals with extreme circadian preferences. This paper addresses diurnal variation in mood in extreme morning and evening types. Mood is a crucial psychological function that determines life satisfaction and ability to meet environmental requirements (Larsen, 2000). It is inner-directed, and, in contradistinction to emotions, it is generally unrelated to any specific external stimulus. There is a consensual view that the substrate of mood is a neurophysiological state (Watson, 2000), sometimes termed “core affect” (Russell, 2003) or “activation” (Thayer, 1978). Mood is also commonly considered to be a state lasting longer than emotions, accessible to consciousness, and associated with experiencing pleasure and with activation processes. However, different mood structures are proposed by various conceptions that also construe the role of activation processes and pleasant feelings in different ways. Various self-report scales are generally used in mood research. They most often refer to two-dimensional concepts, in which either positive vs. negative affect (Clark et al., 1989; Watson, 2000), or energetic vs. tense arousal (Thayer, 1978), are distinguished. The dimension of energetic arousal to some extent overlaps with that of positive affect (PA), while the tense arousal dimension to some extent overlaps with that of negative affect (NA). High levels of PA are associated with terms such as enthusiasm, energy, alertness, interest, and pleasure. On the other hand, low levels are associated with states such as lethargy, tiredness, or weariness. It should be noted that PA is a wide-ranging dimension that not only includes affective aspects (e.g., enthusiastic, happy), but also physical (strong, active), and cognitive factors (alert, interested). On the other hand, high levels of NA

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are related to such states as fear, nervousness, and anger, while low levels are related to such states as calmness and relaxation. In studies investigating circadian rhythms of mood in terms of the twodimensional model, the positive component of mood was found to exhibit diurnal variation. More precisely, PA, which is initially low in the morning, increases during the day, attaining its peak around midday, and decreases in the evening (e.g., Clark et al., 1989; Thayer et al., 1988; Watson, 2000). The data reported in the literature for NA suggest that its level is stable over the day (e.g., Clark et al., 1989) or achieves its peak in the morning (Boivin et al., 1997; Ciarkowska, 2001). However, the three-dimensional model of mood seems to be the most relevant (Schimack & Grob, 2000). The one developed by Matthews et al. (1990) in a sense reduces the denotation of PA. Using factor analysis, the authors distinguished a third mood dimension within the two dimensions proposed by Thayer (1978). Namely, besides the dimensions of energetic arousal (EA) (energetic– tired) and tense arousal (TA) (nervous–relaxed), a new factor called hedonic tone (HT) (pleasant – unpleasant) was introduced. Two studies on diurnal variation of mood based on the threedimensional model have been published so far. The first one, analyzing the morningness-eveningness factor, permits no conclusion to be made about the main effect of time of day (Matthews, 1988). The other by Adan and Guardia (1993) shows that both EA and HT decrease over the day between 09:00 and 21:00 h, while TA displays an opposite trend. Chronotype, also termed the morningness-eveningness dimension ¨ stberg, 1976), a variable belonging to individual differences, (Horne & O describes individual preferences regarding optimal functioning at various times of the day. People can be categorized into three main chronotypes: morning (M-type), evening (E-type), and neither (N-type), with the last predominating in the population. Individuals differing in chronotype evidence differing circadian phasing of many physiological and psychological circadian rhythms as well as some psychological traits. The shifting of diurnal variation stages in individuals with different chronotypes can be seen not only in the sleep-vigilance rhythm (the easiest to observe), but also in the rhythms of core body temperature, cortisol secretion (Bailey ¨ stberg, 1976), and task performance & Heitkemper, 2001; Horne & O involving perception and attention (Horne et al., 1980). A number of regularities and differences have been found in the diurnal variation of mood in persons with different chronotypes. Daytime levels of NA do not differentiate between M-types and E-types (Clark et al., 1989). The level of PA is generally low in the morning, irrespective of the individual chronotype. However, while in M-types the level of PA rapidly rises to a peak before noon or early afternoon, in E-types the peak is delayed to the late afternoon or evening. Moreover, the level of PA is higher over the day in M-types than E-types, and it is

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only in the evening or at night that the difference disappears (Ciarkowska, 2001; Clark et al., 1989). In terms of the three-dimensional model by Matthews et al. (1990) , the following regularities can be seen in diurnal mood variation. The peak in EA occurs earlier in M-types than in E-types (Adan & Guardia, 1993). Moreover, while the EA level in M-types was found to be higher than that in E-types in the morning, the chronotypes did not differ in the evening at 19:30 h (Matthews, 1988). Discrepant findings are reported for TA. Irrespective of chronotype, TA levels have been reported to be higher either in the morning (Matthews, 1988) or in the evening hours (Adan & Guardia, 1993). However, the effect of chronotype was only found to be of importance in one study; in the evening, E-types displayed higher TA than M-types (Matthews, 1988). HT was reported to be higher in M-types than in E-types (Matthews, 1988). Moreover, in the former study (Adan & Guardia, 1993), the peak of HT occurred earlier in the day in M-types than in E-types, and it was concluded that the effect of chronotype and time of day on the HT level was similar to that on EA level. In summary, the three-dimensional model of mood enables a more precise analysis of affective functioning. Namely, the dimension of HT, as distinguished in the model, allows one to investigate a separate dimension of satisfaction, irrespective of these describing energy level and affective tension. The possibility of analyzing the separate factor of experienced satisfaction seems to be most important in the context of studies on individuals differing in circadian rhythm preferences, as it can be shown how synchronization/desynchronization of chronotype with the individual’s functioning at a particular time of day is related to his/her wellbeing. Such a precise distinction is not possible in the framework of the traditional, two-factor conceptions of mood, where the satisfaction scale is not distinguished. Subjective satisfaction in the PA-NA concept is associated mostly with PA, while in the concept proposed by Thayer (1978), it is associated only partly with EA and TA. The aims of the present study were to elucidate the ambiguity concerning the role of chronotype on diurnal variations in mood, as well as to determine how wide a range of diurnal fluctuation in mood is associated with the morningness-eveningness continuum. Moreover, an answer was sought to the question of whether or not individuals with an extreme evening chronotype (E-types), definitely desynchronized from social time, display a less advantageous mood profile than extreme M-types, whose synchronization with the social order is much better. The following hypotheses were posed on the grounds of the findings reported by Matthews (1988) and Adan and Guardia (1993) in the only studies conducted so far concerning diurnal variations of three-factor mood in M-types and E-types:

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. Energetic arousal (EA) should be higher in M-types than in E-types from the morning to the afternoon hours, while there should be no difference between the two groups in the evening (Matthews, 1988). Moreover, the peak in EA should appear earlier in M-types than in E-types (Adan & Guardia, 1993). . Tense arousal (TA) levels should decrease over the day in all subjects (Matthews, 1988) and increase in the evening hours (Adan & Guardia, 1993). . Hedonic tone (HT) should attain its peak earlier in M-types than in E-types. The HT level should be higher in M-types than in E-types (Matthews, 1988).

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METHODS The study was conducted as a part of a larger project researching diurnal variation in psychophysiological rhythms in extreme M-types and E-types. The description of the methods here is restricted only to the part concerning mood measurement. The study meets the ethical standards of University of Warsaw and Chronobiology International (Touitou et al., 2006).

Design A repeated-measures experimental design was used, and the Extreme Groups Approach was applied (Alf & Abrahams, 1975). The manipulated independent variable was time of day, broken down into nine levels (i.e., 08:00, 09:30, 11:00, 12:30, 14:00, 15:30, 17:00, 18:30, 20:00 h). The categorical independent variable was chronotype, broken down into two levels (i.e., morningness and eveningness). A very strict method of categorizing subjects into M-type and E-type groups was used. The criterion for M-types was a score within the range 9– 10 on the sten scale (see below) based on Polish norms, while the criterion for E-type inclusion was a score within the range 1– 2 on the sten scale. It should be noted that in most studies where morning and evening types were compared, group assignment was usually based on central tendency measures of the sample (e.g., Matthews, 1988; Nebel et al., 1996; Waterhouse et al., 2001), or on some other parameters of the sample studied (e.g., M-types and E-types: above and below one standard deviation, respectively; Ciarkowska, 1997). Moreover, selection in the present study was based on the full MEQ scale, while other investigators used either a shortened MEQ version (e.g., Adan & Guardia, 1993) or simply asked their subjects for self-appraisal as a morning, evening, or neither type (Clark et al., 1989).

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The dependent variable was the level of each of the three mood dimensions.

Materials

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Group assignment was made using the Polish adaptation (Ciarkowska, in press) of the Morningness-Eveningness Questionnaire (MEQ) of Horne & ¨ stberg (1976). The Polish adaptation of the MEQ has 21 items constitutO ing the morningness-eveningness continuum. In the process of MEQ adaptation, the original item 18 was excluded due to its low discriminating power, and the following three new items, characterized by a high content validity and a high discriminating power in the Polish population, were added: . “Getting up in the morning on an ordinary day is for you [very difficult, rather difficult, rather easy, very easy]”; . “Getting up in the morning in winter is for you [as easy/difficult as in summer, somewhat more difficult than in summer, much more difficult than in summer, definitely more difficult than in summer]”; . “By how many hours would you like to extend your sleeping time? [by 1 hr., by 2 hrs, by 3 hrs., you would not like to have any additional hours for sleep]”. Normalization of the Polish adaptation of the MEQ was conducted on a sample of 9,226 respondents 16 – 74 yrs of age. The norms were expressed in the form of a sten scale for the following four age groups: 16 – 25, 26– 40, 41 – 60, and 61 – 74 yrs. The sten scale (Canfield, 1951) is a standard scale referring to the normal distribution characteristics. The scale has 10 units, ranging from 1 to 10, with a mean of 5.5 (between the 5th and 6th sten scores) and a standard deviation of 2. Age groups were distinguished as there is a tendency for morningness to be more marked in older people. Because women 26 – 60 yrs of age were characterized by a more pronounced eveningness, separate norms were developed for men and women in this age range. The Cronbach alpha for the Polish adaptation of the MEQ was 0.825, while the test-retest stability was r ¼ 0.793 at a six-month interval and r ¼ 0.838 at three months. Mood was assessed using the UWIST Mood Adjective Check List ´ ska (UMACL) of Matthews et al. (1990) , in the Polish adaptation by Goryn (2005). The scale has 29 items divided into three subscales measuring: EA, 10 items; TA, 9 items; and HT, 10 items. In the group of men 16– 44 yrs of age, the Cronbach alphas for EA, TA, and HT were 0.75, 0.88, and 0.83, respectively. The Polish adaptation of the UMACL was normalized on a national representative sample (N ¼ 1196), and the norms were expressed

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in the sten scale. Sex was taken into account, as in the Polish version of the UMACL, women manifested higher TA levels than men. Separate norms were developed for various age groups, as in men over 69 yrs of age, the TA level tended to increase, while in women it tended to decreased with age, and in those aged over 44 yrs of age, increasing TA levels were accompanied by a HT decline.

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Subjects Only males were enrolled in the study so as to avoid any effects of sex, oral contraceptives use, or menstrual cycle phase on the subjects’ mood. The participants were selected from a cohort of 483 Warsaw college students, between 18 and 30 yrs of age (a majority of college students in Poland are in the 19–24 age range), on the basis of their morningnesseveningness scores (MEQ). The selection criteria were MEQ cutoff points derived from the Polish population norms. M-types were those who scored from z  1.5, while E-types were those who scored z  21.5, as compared to the score distribution in the Polish normalization group. Sixteen subjects were categorized into the M-type group (mean age ¼ 23.4 + SD ¼ 2.48 yrs), and 15 into the E-type group (mean age ¼ 22.3 + SD ¼ 1.89 yrs). Procedure The study consisted of two stages: screening (selection of subjects of different chronotypes to form the two groups) followed by the experiment (mood measurement). In stage 1, MEQ forms were distributed among young men who had been informed about the possibility of their participation in the planned experiment; they were asked to note down their telephone number on the response sheet. The screening was done in Warsaw in the vicinity (cafeterias, student hostels) of colleges and universities. Respondents who met the selection criteria (i.e., had appropriate MEQ scores) were then contacted by telephone and an appointment date fixed. In stage 2, each participant was asked to come to the same room nine times a day to fill out the Mood Adjective Check List (UMACL). Each subject was examined within a single day and received remuneration. Statistical Analyses EA, TA, and HT variations were analyzed in the same way; two-way ANOVA with repeated measures was used, with time of day (nine levels) as the within-subjects factor and chronotype (two levels, M-type/E-type) as the between-subjects factor. The assumption of normality was verified by the Kolmogorov-Smirnov test. Huynh-Feldt corrections were applied

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where appropriate to adjust for degrees of freedom. Moreover, polynomial contrast analyses were performed for the within-subjects factor, and a series of one-way ANOVAs was performed for simple effects of the between-subjects factor. SPSS 14.0 was used for the analyses.

RESULTS

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Energetic Arousal (EA) Two main effects—of chronotype (F(1, 29) ¼ 23.234; p , 0.001) and of time of day (F(3.7, 107.3) ¼ 4.474; p , 0.005)—plus a significant chronotype  time-of-day interaction (F(3.7, 107.3) ¼ 6.941; p , 0.001) were found (see Figure 1). For chronotype, one-way ANOVAs revealed significant intergroup differences at the time points from 08:00 to 17:00 h, a trend at 18:30 h, and no between-subjects effect at 20:00 h (see Table 1). The EA mean scores plotted in Figure 1 show higher EA levels in M-types than in E-types between 08:00 to 18:30 h. For the timeof-day effect, polynomial contrast analysis showed the best fit for a quadratic trend in M-types (F(1, 15) ¼ 10.66, p , 0.01). EA level increased from 08:00 h and attained peak level between 11:00 and 12:30 h; thereafter, it slowly decreased with a trough at 20:00 h. In E-types, on the other

FIGURE 1 Averaged EA (energetic arousal) and polynomial trends fitted to the EA data across the day in M-types and E-types.

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TABLE 1 ANOVA Results Showing the Effect of Chronotype on EA (Energetic Arousal) Level at Each Time Point Clock hour (h)

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08.00 09.30 11.00 12.30 14.00 15.30 17.00 18.30 20.00

Chronotype F(1, 29) ( p ,) 45.97 (0.001) 21.70 (0.001) 22.65 (0.001) 18.58 (0.001) 7.20 (0.05) 7.63 (0.01) 5.70 (0.05) 4.03 (¼0.054) 0.46 (n.s.)

hand, a increasing linear trend between the lowest EA level at 08:00 h and peak level at 20:00 h was seen (F(1, 14) ¼ 8.90, p , 0.01). In summary, “a crossover effect” was partially attained (i.e., the EA level decreased from 12:30 h in M-types, and increased over the day in E-types); furthermore, the former as compared to the latter systematically revealed higher EA levels until 18:30 h, and the difference disappeared only at 20:00 h. Tense Arousal (TA) Main effects of morningness-eveningness (F(1, 29) ¼ 4.47, p , 0.05) and time of day (F(3.7, 108.6) ¼ 10.332, p , 0.001) were found (see Figure 2). TA levels were significantly lower over the day in M-types than in E-types (mean raw scores of 12.32 vs. 14.19). The two groups did not differ significantly with respect to the effect of time of day on TA level. In both groups, the peak occurred in the morning at 08:00 h, and thereafter the TA level decreased sharply to a dip at 11:00 h, rising slowly afterward until 20:00 h (see Figure 2.) Polynomial contrast analysis revealed the main effect of the time of day was best represented by a quadratic trend (F(1, 29) ¼ 24.89, p , 0.001). Hedonic Tone (HT) Main effects of both morningness-eveningness (F(1, 29) ¼ 10.349, p , 0.01) and time of day (F(4.8, 139.7) ¼ 4.302, p , 0.01) were found (see Figure 3). HT levels were higher in M-types than in E-types (raw mean scores of 35.58 vs. 32.04). Polynomial contrast analysis indicated the best fit of the main effect of time of day for HT data was a cubic trend (F(1, 29) ¼ 87.67, p , 0.05). Mean HT scores presented in Figure 3 show the lowest level of HT at 08:00 h and highest level at 20:00 h, with the second peak at 14:00 h and second dip during the day at 17:00 h.

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FIGURE 2 Averaged TA (tense arousal) and polynomial trends fitted to the TA data across the day in M-types and E-types.

FIGURE 3 Averaged HT (hedonic tone) and polynomial trends fitted to the HT data across the day in M-types and E-types.

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DISCUSSION Results of the performed analyses indicate that levels of all three mood dimensions were significantly affected both by chronotype and time of testing. EA in M-types increased in the morning, attaining its peak between 11:00 and 12:30 h, and then decreased to the lowest level at 20:00 h. In E-types, on the other hand, EA was lowest at 08:00 h and increased over the day reaching its peak at 20:00 h. Moreover, between 08:00 and 17:00 h, EA was higher in M-types than in E-types, but this betweengroup difference disappeared between 18:30 and 20:00 h. The peak in TA was noted in all subjects at the first checkpoint of the day, decreasing rapidly afterward to a trough 11:00 h. Then, the TA level rose slowly again until the evening hours. Moreover, E-types showed higher TA than M-types all day. The lowest HT value occurred in all subjects at 08:00 h and thereafter increased until 14:00 h. The HT level decreased again until 17:00 h, and then it rose afterward to peak at 20:00 h. Moreover, M-types as compared to E-types displayed higher HT levels all day. Thus, the hypothesis about the course of the EA variation over the day was confirmed by the findings. Furthermore, the hypothesis about the TA pattern was corroborated. Additionally, an effect of morningness-eveningness was found. The hypothesized effect of chronotype on HT was confirmed, but the shape of the diurnal fluctuations in HT was somewhat different from that hypothesized. In the following discussion, the study results are discussed and referred to previously reported research findings. In the study by Adan and Guardia (1993), which is the most similar in design as our study and also uses the UMACL, subjects’ mood was registered four times during the day (i.e., 09:00, 13:00, 17:00, and 21:00 h), and chronotype was taken into account. As with the present study, mood variation over the day was affected by the factor of time of day. The EA profiles obtained in the present study were identical to these reported by the two authors. In both studies, the levels of EA during the day were significantly higher in M-types than in E-types until evening, when a crossover of the two curves was noted. The present results, as well as the data reported in the literature (cf. Ciarkowska, 2001), lead to a rather clear conclusion that the peak time for EA, or more generally of positive affect, occurs earlier in M-types than in E-types. Discrepancies in the research findings concerning the time of the occurrence of the peak in PA or EA can probably be ascribed to different methods of the subjects’ categorization into groups of different chronotypes. It seems that the more marked the subject’s morningness, the earlier his/her EA peak time, and conversely, the more marked the eveningness the individual, the later his/her EA peak

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time. In summary, the consistency of research findings regarding diurnal variation of EA should be emphasized. The shape of the M-type and E-type diurnal EA profiles, and particularly their crossover, suggests an analogy with the time course of the circadian temperature rhythm in persons of these two chronotypes. Generally, in pure M-types, body temperature rises in the morning hours and attains its acrophase (peak time) at about 15:00 h (Neubauer, 1992) before falling. In contrast, pure E-types’ body temperature keeps rising until 21:00 h, achieving the M-type level not earlier than about 17:00 h (i.e., at the time when the body temperature of the latter begins to decline). The similarity between the diurnal course of EA and body temperature rhythms suggests an endogenous character of variation of this mood component. This likeness also confirms that EA is justifiably identified with the dimension of positive affect (e.g., Adan & Guardia, 1993). It seems noteworthy that the latter is of endogenous character, as PA variations parallel the circadian rhythm of core body temperature (Murray et al., 2002). This is one more argument for the analogy between EA and PA, besides the fact that of all the UMACL scales, EA was found to yield the highest correlation ´ ska, 2005). with PA as a state (Goryn Regarding TA, an opposite trend was found to that reported by Adan and Guardia (1993). In the present study, we found a morning peak in TA, while the referenced study found the reverse (i.e., lowest TA level was in the morning and peak level in the evening). However, our finding is concordant with data obtained by others, such as Matthews (1988) and Boivin et al. (1997). The discrepancy in research results is probably due to the nature of this mood dimension. TA can be identified to some extent with negative affect, which is regarded as a reactive system (Watson, 2000). This means that negative affect is mostly released in response to unpredicted, threatening external stimuli. Thus, it is probable that the differences in the reported research findings were due to differences in the study procedure used in the various investigations. Although the UMACL scales are considered to be insensitive to the order of measurement (Matthews, 1988), it is nevertheless conceivable that such an effect did occur in the study. All subjects were examined in the same order, so it seems natural that a particular TA state appeared in the first series and rapidly decreased afterwards. An interesting result that has not been reported in the literature is the fact that TA was higher over the day in E-types than in M-types. This effect seems to be due to the very strict criteria of selection to the subjects for the two chronotype groups. The studied M-types and E-types were the extreme cases on the morningness-eveningness continuum, and each of the two groups constituted about 7% as compared to the Polish population norms. This means that the groups compared were probably the most extreme M-types and E-types ever investigated for diurnal mood

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variations. In other words, we feel that the conclusion that the mean level of TA during the daytime is higher in E-types than in M-types is valid only if the compared individuals represent the opposite poles of the morningness-eveningness continuum. Our result is not surprising, as TA is considered to be an anxiogenic component of mood (Ne ˛cka, 2000), and E-types are characterized by higher anxiety levels (Matthews, 1988). Regarding HT, the study by Adan and Guardia (1993) found the diurnal variation of this mood dimension parallelled that of EA. In contrast, the present study found no difference between M-types and E-types in the shape of the diurnal HT profile. The finding of higher HT levels over the day in M-types, as well as of the lowest HT level in the morning and peak level in the evening in all subjects, seems consistent with the results obtained by Matthews (1988). This discrepancy may be due to differences in the design (measurement in ambulatory and laboratory settings, respectively). This suggests the hypothesis that EA leads to pleasure-seeking activities, which is possible in the natural environment (ambulatory setting) but rather difficult in a laboratory study setting. The hypothesis might account for the unexpected HT rise at 20:00 h in E-types, which may be interpreted as indicative of the subjects’ satisfaction that the day of their participation in the experiment has ended. Moreover, it suggests a rather exogenous nature of this mood component. Because the correlations between HT with EA were positive and the correlations ´ ska, 2005), it seems worth considerbetween HT with TA negative (Goryn ing whether HT level is perhaps a resultant measure of these two elements of arousal. Assuming that variations of EA are of endogenous nature while these of TA are of exogenous nature, HT can be hypothesized to be somewhere in between, especially as the HT level is sensitive to external factors. In general, the finding that HT levels are higher in M-types than in E-types is concordant with studies reporting an association between morningness and happiness or life satisfaction (Randler, 2008). The results of the present study point to the necessity of controlling the time of day in mood assessment when using the UMACL. This seems to be most important, both in scientific research and in psychological practice. More precisely, time of day should be controlled when either TA or HT is the focus of interest. If EA is being measured, not only should time of day be controlled, but also the subject’s chronotype. If these variables are left uncontrolled, the effect of any investigated variable on mood can be confounded or enhanced. If the hour of testing is not taken into account in the individual assessment of mood using the UMACL, there is a risk of inaccurate mood assessment. This is illustrated by the following comparison. ´ ska, 2005), When compared with the Polish population norms (Goryn the peak and trough EA levels noted during the day in M-types were within the range of 4– 7 on the sten scale, while those of E-types ranged

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between 1 and 5. As for TA, its trough and peak noted during the day in M-types fell within the range of 3– 7 on the sten scale, while those of E-types ranged from 4 to 6. When compared with the norms, the trough and peak HT levels noted during the day in M-types oscillated around 7 on the sten scale, while these of E-types ranged between 4 and 7. Of course, the comparison pertains to group means with standard error not taken into account, but it shows the magnitude of possible errors in any assessment when time of day is not controlled. Because an interactive effect of chronotype and time of day on EA was found in the study, it seems necessary to include also N-type subjects in future research. No such interaction was observed in HT and TA; therefore, we speculate that in N-type persons, the diurnal profiles of HT and TA should be similar to those obtained in the study. Furthermore, we speculate that HT levels should be higher in N-types than in E-types, but lower than in M-types (assuming that there is a monotonical relationship between chronotype and HT). In a comparison of M-types with E-types, a phase difference was observed only in EA, while no such difference was found in HT. Thus, chronotype may be supposed to reflect not so much the time of day when highest satisfaction occurs (there was no phase difference in TH), but rather the time of day when energy level is highest. There is a discrepancy between the conclusion that chronotype reflects diurnal variation in energy level and the definition of chronotype as a preference for functioning at the time of day when one is feeling best. No such conclusion could be drawn within the framework of two-factor mood concepts. As evidenced by the EA data, E-types have a low energy level during the day. In terms of the Polish norms, their mean EA scores at 08:00 h fall within the range of 1 on the sten scale, and they attain the typical level of functioning (i.e., sten scores 5, as in the normalization sample) not earlier than 20:00 h. It is of interest that other studies (Adan, 1994; Wittmann et al., 2006) have found that E-types consume more psychostimulants than other chronotypes, but it is difficult to clearly explain the mechanism underlying this observation. A question arises then whether psychostimulants are used only by those E-types who want to increase their low energy level when they have to function during typical working hours. On the other hand, perhaps no stimulants are needed and used by E-types if they have flexible working hours and can adjust the time of their activity to their chronotype. This problem is worth investigating. In light of the discussion concerning social jetlag (Wittman et al., 2006), a supposition can be made that the desynchronization of E-types from the social rhythm (i.e., with the preferred morning and early afternoon activity) may lead not only to their using psychostimulants, but also to experiencing adverse effects of the longterm substance use, and to a generally poorer state of health. Results

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of the present study suggest that EA level is of crucial importance in social jetlag. During typical working hours, the EA level in extreme E-types is very low compared to that of extreme M-types and to the Polish population norms. Again, a question should be considered here of whether the individual’s diurnal preferences for working or study hours should not be taken into account. The phenomenon of adolescent phase delay is welldocumented in the literature (Carskadon et al., 1997). Namely, 14– 16yr-old adolescents were found to show a clear shift in diurnal preferences toward eveningness. Therefore, the beginning of classes in the morning hours is definitely discordant with the chronotype of a majority of senior high school students. This fact has begun to be taken into consideration in the United States, where later study hours have been officially introduced by some high schools (Abbot, 2003). Significant benefits, such as less student-reported depression, have been reported in connection with later high school start time (Wahlstrom, 2002). Regarding the choice of optimal working hours, in the case of E-types, it would be important to determine the time of day (or night) when high levels of EA occur. This is why mood level at later hours than these assessed in the present study become important and worth investigating in future research. Generally, a comparison of mood component levels in extreme E-types and extreme M-types turns out to be favorable to the latter, as they are most likely to be characterized by less tiredness and tension and have more pleasant feelings. It should be remembered though that this conclusion is limited to the three-factor mood concept. A likeness between evening types and patients with depression, as well as between morning types and individuals without depression, can be seen in the diurnal pattern of mood. Namely, E-types showed greater TA than did M-types, and depressed individuals have been found to show higher levels of negative affect than healthy controls (Peeters et al., 2006). Moreover, E-types exhibited a diurnal pattern of EA similar to that of positive affect found in patients with depression (for the record, EA can be identified as positive affect and TA as negative affect). On the other hand, M-types showed much the same pattern in EA variability during the course of the day as did the healthy controls with respect to positive affect (Peeters et al., 2006). The latter results, as well as the findings that patients diagnosed with depression reported greater eveningness (Drennan et al., 1991) and that depressiveness is associated with the E-type (Chelminski et al., 1999), suggest the hypothesis that depressiveness is a resultant effect of the circadian mood profile. If the hypothesis proves valid, it will have important implications both for the therapy and prevention of depression. Although chronotype is considered to be a temperamental trait, circadian preferences are entrained to environmental cues; thus, altering persons with this chronotype toward morningness would decrease depressiveness.

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The differences between M-types and E-types in respect to diurnal mood variations were maximized by the procedure used in this study. Extreme groups were investigated, and the confounding effect of sex was eliminated. The main advantage of this approach seems to be the fact that it allowed us to show how wide was the range of diurnal mood variations associated with individual differences in chronotype. In other words, it revealed the maximum effect of chronotype. However, due to the procedure used, the possibility of generalizing the study findings is limited. The first limitation of this study is associated with the selection of persons with extreme M and E chronotype. It should be noted that they represent jointly only about 14% of the population (7% of those manifesting extreme morningness and 7% extreme eveningness). Thus, caution should be exercised in drawing conclusions about individuals situated between the two extremes studied, who represent the remaining 86% of the population. Nonetheless, generalization of our findings to the population of intermediate chronotypes seems to be justified to some extent by the following relationships. The morningness/eveningness dimension was found to be a continuum (Natale & Cicogna, 2002) spreading from extreme morningness to extreme eveningness and reflecting the times when acrophases (peak times) of many variables occur. This means that the stronger the individual’s eveningness, the later the occurrence of the acrophases of his/her rhythms; conversely, the stronger the individual’s morningness, the earlier the occurrence his/her acrophases. This regularity is well-illustrated by the study of Baehr et al. (2000), showing that core body temperature acrophases in individuals representing various levels of morningness and eveningness occur at different times of the day. Such differences between M-types and E-types have been noted in many variables (Kerkhof, 1985), including mood (e.g., Adan & Guardia, 1993; Natale & Cicogna, 2002). Another limitation of this study results from the exclusion of women from the sample. Sex is known to affect mood and probably chronotype as well. However, in the Polish population, no sex differences in morningness/eveningness were noted in the 16 – 25 age group (in the present study 28 of the 31 subjects were under 25 yrs of age), and it is only in older age groups that women turned out to represent stronger eveningness (Ciarkowska, in press). Similar results (i.e., stronger eveningness in women or girls) were reported also by Steele et al. (1997) and Gaina et al. (2006), although in a majority of studies, either no relationship between sex and chronotype was found, or the level of eveningness turned out to be higher in men than women (Randler, 2007). Regarding the UMACL scale, in a Polish normalization sample, women showed higher scores on ´ ska, 2005). It would be of interest the TA dimension then did men (Goryn to determine if such an effect extends also to diurnal mood variation. Sex

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differences in mood during the course of the day were reported in a Spanish sample (Adan & Sanchez-Turet, 2001). The pattern of mood variations in women was similar to that of M-types, while in men it was similar to that of E-types. Moreover, a conclusion was drawn that in women the diurnal variation in mood is superimposed on the menstrual cycle, resulting in a wider range of mood fluctuations. A question then arises as to what extent sex differences in diurnal mood variation are associated with sex differences in the morningness/eveningness dimension, and whether the effect would remain significant if chronotype was controlled for. Another interesting question is to what extent sex differences in diurnal mood variation are due to the presence of the menstrual cycle in female subjects. These questions should be explored in future research. In studies conducted thus far on diurnal variation of EA, TA, and HT in individuals with different chronotypes, where both sexes were represented but the female menstrual cycle was not controlled for, a number of regularities were found. In a Spanish sample, where the ratio of female to male subjects was about 3/1, no sex differences were noted in the diurnal patterns of EA, TA, and HT (Adan & Guardia, 1993). On the other hand, in a British sample, where the number of men and women was equal, the HT level turned out to be higher in women than men (Matthews, 1988). The present study shows that through using the three-factor model of mood, additional data concerning diurnal mood variation can be obtained, and also that these changes are strongly associated with chronotype. However, generalization of the obtained findings would require the inclusion of women and control for the phase of their menstrual cycle in future research.

ACKNOWLEDGMENTS Preparation of the paper was financed from grant BW 1770/14 from the Faculty of Psychology, University of Warsaw.

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