Latitude effect on bipolar temperaments.

BACKGROUND: Growing evidence points to an association of daily light exposure and both mood and mood disorders. In recent studies, we demonstrated that higher illuminance of daytime may be positively associated with hyperthymic temperament while lower illuminance of daytime may be positively associated with cyclothymic temperament. However, it is not possible to determine whether hyperthymic or cyclothymic temperament induces higher or lower illuminance via heliotropism or non-heliotropism or whether higher or lower illuminance induces hyperthymic or cyclothymic temperament via light effects. METHODS: In order to elucidate these questions, we sought to compare bipolar temperaments between residents who live in regions with varying levels of sunshine. Japan has 4 large islands -Hokkaido, Honshu, Shikoku, and Kyushu. Sapporo in Hokkaido and Oita in Kyushu located at 43° and 33° of latitude differ significantly in mean yearly sunshine. We investigated the data of 189 subjects (94 from Sapporo and 95 from Oita) including their data of Temperament Evaluation of Memphis, Pisa, Paris and San Diego-auto questionnaire version (TEMPS-A). RESULTS: Multiple regression analyses revealed that latitude (Sapporo or Oita) effect predicted significant variance of hyperthymic temperament, but not of the other temperaments. LIMITATIONS: The limitation of the present study was that there was a small but significant difference in age between the subjects of Sapporo and those of Oita. Therefore, we included age in the multiple regression analysis. Second, there were several climate factors other than sunshine which were significantly different between Sapporo and Oita. We cannot exclude these effects completely. Finally, we did not consider other factors such as psychosocial factors which might have affected bipolar temperaments. CONCLUSIONS: The present findings suggest that relatively lower latitude (potentially via more sunshine) may induce hyperthymic temperament.

Bright light during nighttime: effects on the circadian regulation of alertness and performance.

The present studies evaluated to what extent duration (all-night or 4-hour exposures) and timing of nocturnal bright light (BL) (beginning or end of the night) modulate effects on vigilance. The results showed that all-night BL exposure is able to alleviate the nocturnal decrements in alertness and performance. However, under certain circumstances, this continuous BL exposure may induce adverse effects on mood and finally reveal to be counterproductive. Shorter BL exposure (4 h) during nighttime helps improve mood and performance, although the effects of short BL pulses were less efficacious than all-night BL exposure. The latter part of the night appears the best time for using the alerting effect of BL. The immediate alerting effect of BL seems to be mediated by a global activation of the central nervous system.

Behavioral effects of long-term exposure to magnetic fields in rats.

Male rats and pregnant and nonpregnant female rats of the Wistar strain were sham-exposed or exposed to static (0.49 T) or to extremely low frequency (50 Hz) magnetic fields (0.018 T) 2 h per day for 20 consecutive days. Measures of irritability, exploratory activity, and locomotion were made in that order before and after the 4th, 10th, and 17th 2-h exposures. A reliable decrease in the irritability of rats after repeated exposure to a static or undulating field was found. No significant effects of treatment conditions on open-field behavior and locomotor activity were observed. Pregnancy had no influence on the behavioral end points. These results indicate that irritability of rats may be used as a simple behavioral indicant of mammalian sensitivity to magnetic fields.