In 2 experiments, the authors examined 69 mice selectively bred for high or low levels of open-field (OF) thigmotactic behavior (high open-field thigmotaxis [HOFT] and low open-field thigmotaxis [LOFT], respectively). They found that the strains differed in defecation during the 60-min exposure to the OF. Furthermore, the strains differed with regard to their life spans: The more thigmotactic HOFT mice lived longer than the LOFT mice. The strains were not differentiated by food intake or excretion. The strain difference in thigmotaxis was not age dependent, and it persisted in the home-cage condition as well. Neither the location (center or wall) of the starting point nor the shape (circular or square) of the OF arena affected the difference in wall-seeking behavior between the two strains. The authors concluded that the difference in thigmotaxis (or emotionality) between the HOFT and LOFT mice is a stable and robust feature of these animals.
Key words: emotionality, HOFT mice, life span, LOFT mice, open field, selective breeding, thigmotaxis
THE OPEN-FIELD (OF) TEST, originally developed by Hall (Hall & Ballachey, 1932), is one of the most widely used methods in the study of emotionality in rodents. The test is conducted in an enclosed open area in which the animal is confronted with a strange and potentially threatening situation. The OF apparatus provides a number of psychological stimuli in a novel environment that evoke unconditioned fear and multiple spontaneous behavioral responses (Castanon & Mormede, 1994; Clement, Calatayud, & Belzung, 2002; Gershenfeld & Paul, 1997).
One of the most prominent fear-related OF responses is thigmotactic or wall-seeking behavior, which refers to the propensity of a rodent to stay in close contact with the OF wall because of the underlying tendency to avoid open, unknown, and potentially dangerous places (see Choleris, Thomas, Kavaliers, & Prato, 2001). Researchers have demonstrated the validity of thigmotaxis in measuring emotionality in mice (Choleris et al; Simon, Dupuis, & Costentin, 1994) as well as in rats (Treit & Fundytus, 1989; van der Staay, Kerbusch, & Raaijmakers, 1990).
In addition to thigmotaxis, researchers have used many other OF parameters to measure emotionality in rodents, with the most traditional index being defecation (Broadhurst, 1976; Gray, 1987, p. 51; Walsh & Cummins, 1976). In particular, a high level of defecation has been interpreted as an indicator of a high level of emotionality. However, some researchers have questioned the validity of this index in mice (e.g., Archer, 1973; Ramos & Mormede, 1998).
In OF research, several selection experiments have been performed on mice and rats (e.g., Broadhurst, 1975; DeFries, Gervais, & Thomas, 1978; Ewalds-Kvist, Selander, & Kvist, 1999; van Abeelen, van der Kroon, & Bekkers, 1973). However, to the best of our knowledge, we are not aware that any selection experiments based on mouse OF thigmotactic behavior have been previously conducted. Therefore, in the present study, the mice were selectively bred for high or low levels of OF thigmotactic behavior (high open-field thigmotaxis [HOFT] and low open-field thigmotaxis [LOFT], respectively).
In animal psychology, the selective-breeding method is used mainly for two purposes: (a) To study the inheritance of a certain characteristic, and (b) to reveal correlational relationships between the selection trait and other behavioral or physiological properties (Castanon, Perez-Diaz, & Mormede, 1995; Lagerspetz & Lagerspetz, 1983). In fact, it is well known that strains selected on the basis of some behavioral trait often differ in a number of other behavioral or biological characteristics as well (Boissy, 1995; Broadhurst, 1975; Castanon & Mormede, 1994). In addition, it is common knowledge that different strains of mice vary in the length of their life spans. This fact demonstrates that genetic factors play an important role in the determination of life expectancy (Russell, 1966). On the basis of these findings, one can presume that the HOFT and LOFT mice may also differ in some biological properties, such as life span or basic metabolic characteristics.
The expression of genetically mediated behavioral differences in rodents may be age dependent (van Abeelen, 1979). With regard to emotionality, researchers have hypothesized that the particular age at which the testing is conducted may affect the detection of strain differences in this characteristic (Elias, Elias, & Eleftheriou, 1975). Consequently, it is possible that the strain difference in thigmotaxis between the HOFT and LOFT mice may be expressed only at a certain age. In previous studies, researchers have established age-dependent strain differences in mice with respect to OF ambulation and defecation (Homanics, Quinlan, & Firestone, 1999). In addition, other study results have shown that age-related within-strain changes in OF ambulation, defecation, exploration, and rearing differ across mice strains (Dixon & DeFiles, 1968; Lhotellier, Perez-Diaz, & Cohen-Salmon, 1993). Furthermore, it has been suggested that animals should be tested at several different ages before one makes general conclusions about the behavior of a particular strain (Nagy & Glaser, 1970).
The terms "emotionality" and "anxiety" are commonly used as synonyms (see Ramos & Mormede, 1998). The traditional OF test is supposed to measure primarily state anxiety (provoked by an anxiogenic stimulus; Belzung & Griebel, 200l; Lister, 1990). In contrast, trait anxiety (an enduring feature of an animal; Lister) should be measured in the absence of novelty or other aversive stimuli, for example, in the animal's home cage (see Ramos & Mormede). Until now, the thigmotactic behavior of the HOFT and LOFT mice has been measured only in an anxiety-provoking, traditional OF. Therefore, in the present study, we investigated whether the mice differ in a home-cage condition as well.
Study results have shown that the location of the starting point (center vs. wall) in the OF test plays a decisive role in the thigmotactic behavior of mice. More specifically, study results have shown that wall starting increases thigmotaxis compared with center starting (Kvist & Selander, 1992). Furthermore, rats tend to occupy that side of the OF arena on which they are originally placed (Satinder, 1969). As a result, the strain difference in thigmotaxis between the HOFT and LOFT mice may be affected by the location of the starting point. In addition, the shape (circular vs. square) of the OF apparatus may have an impact on the wall-seeking behavior of these strains because mice are naturally attracted to corners (for rats, see van der Staay et al., 1990).
The aim of the present study was to answer the following questions:
1. Do the selectively bred HOFT and LOFT mice differ in OF defecation, the traditional index of emotionality?
2. Do the strains differ in the length of their life spans?
3. Do the strains differ in basic metabolic characteristics, that is, in food intake and excretion?
4. Does the strain difference in OF thigmotaxis vary as a function of age?
5. Is the strain difference in thigmotaxis also present in a home-cage condition?
6. Does the variation in the location (center or wall) of the starting point or in the shape (circular or square) of the OF arena affect the strain difference in OF thigmotaxis?
Subjects
The mice were selectively bred for high or low levels of OF thigmotactic behavior (HOFT and LOFT, respectively). The selection was based on the differences between the mice with regard to the thigmotactic ratio (Experiment 1). The HOFT and LOFT mice were derived from a Swiss albino outbred stock originating from Malmo, Sweden. They were bred, reared, and selected in the laboratory at the Department of Psychology at Abo Akademi University, Finland. The selection was made from animals that had been exposed to the OF apparatus for at least 2 min on each of 4 consecutive days and then tested on the 5th day. The selection experiment started in 1993.
Housing
All of the animals were reared on a 12:12 light:dark cycle in a noiseless room at a normal room temperature (approximately 20-23[degrees]C). They were fed standard laboratory pellets, R3 (1,260 kJ/100 g), from Lactamin, Sweden, and had free access to fresh tap water. The cage had a bedding of wood shavings, and it was changed for a clean cage weekly.
EXPERIMENT 1
In Experiment 1, the HOFT and LOFT mice were examined with respect to life span, OF thigmotaxis at seven different ages, OF defecation, home-cage thigmotaxis, and metabolism.
Method
Subjects
A total of 51 mice (28 females, 23 males) that originated from the 13th generation ([S.sub.13]) of the HOFT (n = 27; 14 females, 13 males) and LOFT (n = 24, 14 females, 10 males) strains. With the exception of the life span experiment, only the recordings from the males are reported. Of the HOFT males, 6 to 13 mice were randomly chosen for different recordings, and for the LOFT males, the number of subjects in each experiment varied from 6-10. Some of the animals were selected to continue the selection lines at the age of approximately 3.5 months, and some participated in one or two additional experiments (not presented here) during their lifetime. The measurements performed on the HOFT and LOFT males are presented in Table 1, which also shows the number of subjects in each measurement and the age at which the recordings were conducted.
Housing
The animals were weaned at 4 weeks of age, after which they were housed individually in aluminum cages measuring 14 x 14 x 12 cm until the age of approximately 3.5 months. After this, the animals were group-housed in polycarbonate cages measuring 38 x 22 x 15 cm, except for 4 days before each OF thigmotaxis measurement, when they were individually housed.
Apparatus
The open-field apparatus consisted of a circular, flat, white, wooden arena (40 cm in diameter) with a 20-cm-high wall of flat, white, metallic plate. The field was marked with thin black lines to delineate three concentric circles. The outer circle was divided into 12 partitions and the middle circle (24 cm in diameter) into 6 partitions. The center circle (8 cm in diameter) was not divided. That is, the floor of the arena was subdivided into a total of 19 partitions to aid the recording of the ambulation of the animal, thereby providing raw scores for computation. The center circle and the 6 partitions of the middle circle were defined as 7 inner units, and the 12 partitions of the peripheral circle as outer units. The floor of the arena was cleaned between successive recordings.
Procedure
Life span. The animals were inspected about three times a week during their entire life span to check whether they were dead or alive.
Open-field thigmotaxis. Thigmotaxis in the OF was recorded at seven different ages during the males' life spans (see Table 1). The parameters were: the thigmotactic ratio, inner ambulation, and outer ambulation. Before each recording, the animals were exposed to the OF apparatus for at least 2 min on each of 4 consecutive days.
The thigmotactic ratio was computed on the basis of ambulation scores. At the beginning of the test, the animal was placed in the center unit of the OE The ambulation of the animal was manually recorded when the mouse moved from one floor unit to another during a 2-min period. The thigmotactic ratio was calculated by dividing the number of inner units the mouse entered by the total sum of units it visited (McIlwain, Merriweather, Yuva-Paylor, & Paylor, 2001; Sanberg & Ossenkopp, 1977; Valle & Bols, 1976). Hence, the smaller the ratio, the more prone the mouse was to keeping close to the OF wall. The thigmotactic ratio signifies the animal's orientation toward the OF peripheral units but does not necessarily imply bodily contact with the wall. The thigmotactic ratio ranged from 0.00 to 1.00. Inner ambulation and outer ambulation were recorded by counting the number of inner units and outer units entered during a 2-min OF test.
Open-field defecation. The floor of the OF arena was covered with a 1-mm-thick white filter paper. The mouse was placed in the OF for 60 min, after which the animal's fecal boli were counted (Selander & Kvist, 1991).
Home-cage thigmotaxis. Each mouse resided undisturbed for a period of 5 days in an OF (see Apparatus) in which the floor was covered with approximately 250 g of wood shavings (Kvist & Selander, 1990). Food and water were freely available, and the mouse was prevented from leaving the OF by a wire-mesh ceiling. From days 6 to 10, the mouse was tested once a day with respect to the thigmotactic ratio, inner ambulation, and outer ambulation (see under heading, Open-field thigmotaxis), and the recordings from the 10th day were reported. Given that the floor of the OF arena (and the partitions drawn on it) was covered with wood shavings, the wire-mesh ceiling was replaced with a transparent plastic film that was divided by thin black lines into 19 partitions identical to those on the floor of the OF arena (see Apparatus), thereby providing raw scores for computation. Thus, the ambulation of the animal was recorded by monitoring the animal's movements through the plastic film.
Metabolism. In the beginning of the metabolism experiment, the animals were weighed and deprived of pellets for 12 hr, but they had free access to fresh tap water. After that, the cages were replaced with clean cages that contained preweighed bedding. The mice were then given access to preweighed food for a period of 72 hr, after which the remaining food and bedding were reweighed. The difference between the preweighed food and the remaining food was the measure of food intake (Ewalds-Kvist & Selander, 1996; Hansen & Ferreira, 1986). By comparing the weight of the bedding in the cage before and after the test period, a measure of excretion (i.e., defecation and urination) was established (Ewalds-Kvist & Selander). We derived food intake and excretion measures that were proportionate to the weight of the mouse and the duration of the experiment by dividing the original measures by mouse weight and experiment duration (72 hr = 3 days). These measures were used in the statistical analyses.
Results
Life Span
Figure 1 shows the life spans of the HOFT and LOFT mice. We used a two-way (Strain x Sex) analysis of variance (ANOVA; General Linear Model Univariate procedure in SPSS), which revealed a significant strain difference in life span. That is, the HOFT mice exhibited longer life spans (M = 691.2 days, SD = 127.2) than did the LOFT mice (M = 600.1 days, SD = 214.3), F(1, 47) = 4.71, p = .035. There was no statistically significant sex-related difference or Strain x Sex interaction.
[FIGURE 1 OMITTED]
Open-Field Thigmotaxis
We recorded OF thigmotactic behavior at seven different ages during the males' life spans (see Table 1). Given the rather small number of subjects, we analyzed the data by using both an independent-samples t test (two-tailed significance) and a Mann-Whitney U test. With the exception of the second recording at the age of approximately 95 days, the HOFT males always exhibited significantly lower thigmotactic ratios (i.e., were more thigmotactic; see Procedure) than did the LOFT males (for both t tests and Mann-Whitney U tests, ps < .05; see Figure 2). Both tests showed that the strain difference in inner ambulation was statistically significant at Recordings 1, 4, 5, and 6 (ps < .05), with the LOFT males entering more inner OF units than the HOFT males did (see Figure 3). Both tests also showed that the strains were significantly differentiated by outer ambulation, with the HOFT males entering more outer OF units than the LOFT males did, at Recordings 2, 3, and 4 (ps < .05; see Figure 4).
[FIGURES 2-4 OMITTED]
Open-Field Defecation
Table 2 shows the means of OF defecation, home-cage thigmotactic and metabolic parameters among the HOFT and LOFT males, and a summary of the statistical analyses. Both the t test and the Mann-Whitney U test showed that the HOFT males defecated more fecal boli than the LOFT males did during the 60-min exposure to the OF (ps = .008 and .011, respectively).
Home-Cage Thigmotaxis
In the home-cage condition, the t test showed that the HOFT males exhibited significantly lower thigmotactic ratios (i.e., were more thigmotactic) than did the LOFT males (p = .045; see Table 2). However, the Mann-Whitney U test narrowly failed to reach statistical significance (p = .053). In addition, both tests showed that the HOFT males entered significantly more outer OF units than the LOFT males did (ps = .008 and .012, respectively). The strain difference in inner ambulation was not statistically significant.
Metabolism
Both the t test and the Mann-Whitney U test showed that the LOFT males were significantly heavier than the HOFT males (p < .001 and p = .002, respectively; see Table 2). In contrast, the strains did not differ in food intake or excretion.
EXPERIMENT 2
In Experiment 2, the HOFT and LOFT males were examined with respect to OF thigmotaxis under four conditions with varying OF starting points (center or wall) and shapes (circular or square).
Method
Subjects
A total of 18 male mice were used in Experiment 2, originating from the 21st generation ([S.sub.21]) of the HOFT (n = 9) and LOFT (n = 9) strains. At the age of approximately 19 weeks, the mice were mated to continue the selection lines. The LOFT males were tested at the age of 5.6 months and the HOFT males at the age of 5.9 months.
Housing
The animals were weaned at 4 weeks of age, after which they were individually housed in polycarbonate cages measuring 20.5 x 10.5 x 13.0 cm until the mating at the age of approximately 19 weeks. After this, the mice were group-housed in polycarbonate cages measuring 38 x 22 x 15 cm.
Apparatus
Circular open field. The apparatus was identical to that in Experiment 1.
Square open field. The OF consisted of a flat, white, wooden arena measuring 35.5 x 35.5 cm. It was surrounded by a 23.5-cm-high wall of flat, white, wooden plate. The field was divided by thin black lines into 25 squares to aid the recording of the ambulation of the animal, thereby providing raw scores for computation. The floor of the arena was cleaned between successive recordings.
Procedure
Before the experiment started, the animals were exposed to the OF apparatus for at least 2 min on each of 4 consecutive days. On the 5th day, the mice of both strains were tested in the circular OF, and on the 6th day, they were tested in the square-shaped OF. On both days (5th and 6th), the mice were tested using the center starting point at approximately 7:00 a.m. and the wall starting point at approximately 5:00 p.m. In the center starting, the mouse was placed in the center of the field, and in the wall starting, it was placed near the wall (in the square-shaped OF, in a corner). The different testing conditions were not counterbalanced, given that we were interested only in strain differences (we expected no Strain x Time/Order of Testing interactions).
Parameters
The parameters were the thigmotactic ratio, inner ambulation, and outer ambulation. For each condition, the thigmotactic ratio was calculated by dividing the number of inner partitions entered by the total sum of units visited by the mouse (see Experiment 1). For inner and outer ambulation, see Experiment 1.
Results
Table 3 shows the means of study parameters among the HOFT and LOFT males as well as a summary of the statistical analyses. Given the rather small number of subjects, the data were analyzed by an independent-samples t test (two-tailed significance) as well as by a Mann-Whitney U test. Independently of the location (center or wall) of the starting point and the shape (circular or square) of the OF apparatus, the HOFT males always exhibited significantly lower thigmotactic ratios (i.e., they were more thigmotactic; ps [less than or equal to] .001) and entered fewer OF inner units (ps [less than or equal to] .012) than the LOFT males did. In contrast, the strain difference in outer ambulation was not statistically significant in any of the four situations.
Discussion
The results of Experiment 1 indicated that during the 60-min exposure to the OF, the HOFT males defecated more than the LOFT males did. Because defecation is the most traditional index of emotionality in rodents (Walsh & Cummins, 1976), this finding conforms to the view of the HOFT mice being more emotional than the LOFT mice. However, some researchers have proposed that defecation in male mice, in addition to measuring emotionality, may also be an indicator of odor deposition or territorial marking (Archer, 1973, 1975; Bruell, 1969). As a result, the difference in defecation between the HOFT and LOFT males may also reflect differences in these characteristics, especially because the exposure to the apparatus lasted longer than in a typical OF test. That is, as the exposure to the OF increased, the field became less frightening to the mouse, thereby decreasing emotionality and increasing other types of behaviors (see Blois-Heulin & Belzung, 1995). In a previous crossfostering study (Leppanen & Ewalds-Kvist, 2005), the strains did not differ in defecation in a 2-min OF test.
On the one hand, in the life span experiment, the more thigmotactic (i.e., the more emotional) HOFT mice exceeded the less anxious LOFT mice in longevity. This is at variance with the previous observations that strains exhibiting high levels of emotionality in a novel environment typically show a short life span (Viveros, Fernandez, Guayerbas, & De la Fuente, 2001). On the other hand, evidence for a positive correlation between emotionality and the length of the life span is provided from the senescence-accelerated mice (SAM): In novel situations (OF and plus maze), the senescence-prone mice (SAM-P/8) were less emotional than the senescence-resistant mice (SAM-R/l; Markowska, Spangler, & Ingram, 1998; Miyamoto, Kiyota, Nishiyama, & Nagaoka, 1992). This finding supports the idea that a short life span may be related to a low level of thigmotactic behavior.
On the basis of the present study, one can only speculate on the causes of the difference in the life span between the HOFT and LOFT mice. Naturally, a mouse's life span is determined by interactions among the environment and a number of genes (Russell, 1966; Yunis et al., 1984). However, some researchers have proposed that immunological processes are one of the main mediating factors in controlling longevity (Popp, 1982; Yunis et al.). In contrast to the length of the life span, the HOFT and LOFT males did not differ with regard to food intake or excretion.
Some researchers have suggested that the expression of strain differences in behavioral characteristics may be affected by the age at which testing is done (Elias et al., 1975; Homanics et al., 1999; van Abeelen, 1979). However, the strain difference in thigmotaxis between the HOFT and LOFT males was not affected by age: The HOFT males always exhibited lower thigmotactic ratios (i.e., were more thigmotactic) than did the LOFT males, with the exception that the strain difference was not statistically significant at the age of approximately 95 days. At this age, however, the strains differed with regard to outer ambulation, the HOFT mice entering more outer OF units than the LOFT mice. At each age, the two strains were statistically differentiated by the thigmotactic ratio, inner ambulation, or outer ambulation. This agrees with the suggestion by Elias et al. that, even if the strain differences in emotionality may be age dependent to a certain degree, when one compares strains that differ greatly with respect to this characteristic, one observes strain differences at all ages.
The strain difference in thigmotaxis between the two strains also persisted in the home-cage condition, in which the field was highly familiar to the animals. This means that the strain difference was not provoked only by the novelty of the field. Consequently, the HOFT and LOFT mice seem to differ with regard to trait anxiety rather than state anxiety (see Lister, 1990; Ramos & Mormede, 1998). Moreover, the interstrain difference did not vary with the characteristics of the OF testing: Neither the location of the starting point nor the shape of the OF arena affected the strain difference in thigmotaxis.
On the basis of the present findings, it seems obvious that the difference in thigmotaxis between the selectively bred HOFT and LOFT mice is a stable and robust feature of these animals.
TABLE 1. Measurements Performed on the HOFT
([S.sub.13]) and LOFT ([S.sub.13]) Males
HOFT LOFT
Age Age
Measurement n (days) n (days)
Open-field thigmotaxis
1. 13 65 10 64
2. 7 96 8 95
3. 7 126 9 133
4. 11 208 8 201
5. 13 271 8 269
6. 12 488 6 481
7. 8 541 6 534
Open-field defecation 8 303 8 296
Home-cage thigmotaxis 6 313 7 310
Metabolism 8 473 6 466
Note. HOFT = high open-field thigmotaxis;
LOFT = low open-field thigmotaxis.
TABLE 2. Recordings From the HOFT
([S.sub.13]) and LOFT ([S.sub.13]) Males
Measurement HOFT LOFT df t P U P
Open-field defecation
(number of boli) 14 3.06 .008 8.0 .011
M 14.8 11.1
SD 2.3 2.5
Home-cage thigmotaxis
Thigmotactic ratio
(inner/total ambulation) 11 2.26 .045 7.5 .053
M .16 .35
SD .16 .14
Inner ambulation
(inner units entered) 11 .62 ns 12.0 ns
M 4.7 6.1
SD 5.4 3.0
Outer ambulation
(outer units entered) 11 3.25 .008 3.5 .012
M 22.2 12.1
SD 5.5 5.6
Metabolism
Weight (g) 12 5.39 <.001 0.0 .002
M 28.9 33.6
SD 1.2 2.0
Food intake
(g/body weight/24 hr) 12 0.17 ns 22.0 ns
M 0.20 0.20
SD 0.02 0.02
Excretion
(g/body weight/24 hr) 12 0.98 ns 15.0 ns
M 0.13 0.14
SD 0.02 0.02
Note. HOFT = high open-field thigmotaxis;
LOFT = low open-field thigmotaxis.
TABLE 3. Thigmotactic Recordings From the HOFT ([S.sub.21]) and LOFT
([S.sub.21]) Males Using Different Open-Field Shapes and Starting
Points
Measurement HOFT LOFT df t P U P
Circular OF, center SP
Thigmotactic ratio 12.5 4.61 .001 4.5 .001
M .12 .43
SD .10 .18
Inner ambulation 10.1 4.36 .001 7.5 .003
M 2.0 10.4
SD 2.0 5.5
Outer ambulation 16 0.74 ns 30.0 ns
M 17.2 14.2
SD 8.2 9.0
Circular OF, wall SP
Thigmotactic ratio 16 6.03 <.001 1.0 <.001
M .07 .46
SD .13 .14
Inner ambulation 9.7 3.94 .003 3.0 .001
M 1.2 8.8
SD 1.8 5.5
Outer ambulation 12.7 0.71 n.s 34.0 n.s
M 12.1 9.9
SD 8.1 4.6
Square OF, center SP
Thigmotactic ratio 16 5.47 <.001 4.0 .001
M .12 .39
SD .11 .10
Inner ambulation 8.7 3.15 .012 10.5 .007
M 2.0 10.8
SD 1.7 8.2
Outer ambulation 16 1.12 ns 30.0 ns
M 19.8 14.4
SD 12.1 7.7
Square OF, wall SP
Thigmotactic ratio 10.7 5.99 <.001 2.0 .001
M .03 .37
SD .07 .16
Inner ambulation 8.3 4.49 .002 2.0 .001
M 0.4 8.3
SD 0.7 5.2
Outer ambulation 10.0 0.69 ns 40.0 ns
M 15.2 12.6
SD 10.9 3.9
Note: HOFT = high open-field thigmotaxis; LOFT = low open-field
thigmotaxis; OF = open field; SP = starting point.
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Manuscript received January 20, 2004
Revision accepted for publication August 31, 2004
Address correspondence to Pia Leppanen, Sauvontie 3 A 1, FI-00280 Helsinki, Finland; pkleppanen@hotmail.com (e-mail).
PIA K. LEPPANEN
S. BEATRICE M. EWALDS-KVIST
Department of Psychology
University of Turku, Finland
RITVA-KAJSA SELANDER
Department of Psychology
Abo Akademi University at Turku, Finland