Abstract:

Premenstrual syndrome (PMS) refers to a series of physical, emotional, and behavioral symptoms that occur periodically in women during the late luteal phase of the menstrual cycle. It peaks within a week before menses and improves or disappears after the onset of menses. PMS occurs in 30%~40% of females at reproductive-age and can have deleterious effects on the social functioning and interpersonal relationships for those with PMS during the late luteal phase. Therefore, the potential causes and mechanisms of PMS have attracted researchers' attention. Affect balance is an important basis for maintaining mental health and the imbalance of positive and negative affect might be one of the causes of PMS. However, previous studies on the mechanism of PMS mostly focused on the increase of negative affect. Only limited studies explored the decrease of positive affect. Built upon the strong link between positive affect and reward processing, the present study aims to explore the causes of positive affect deficiencies tied to the dysfunctional reward processing during PMS.

Despite the lack of consensus on the diagnostic criteria of PMS, one of the most widely used diagnostic criteria for PMS are from John Bancroft's recommendations, which have been translated into the PMS Scale in Chinese. Of the 259 women who were asked to self-assess using this scale, 45 right-handed females (23 with PMS and 22 without PMS) with regular menstrual cycle voluntarily participated in this study. After completing a series of questionnaires, a simple gambling task was used to elicit reward positivity (RewP, 250~350 ms), an event-related potential (ERP) component elicited by feedback indicating gain versus loss. All participants completed this task twice, once in the late luteal and the other in the early follicular phase, respectively. In addition to ERP analysis, we also conducted time-frequency analysis to examine the neural oscillations underlying the reward processing.

Questionnaire results showed that women with PMS reported lower levels of happiness and calmness than healthy women, and their affect balance was also lower than that of healthy women, independent of menstrual cycle. Electrophysiological results suggested that in the late luteal phase, compared with healthy women, women with PMS were characterized by reduced RewP responses towards monetary gains, but not towards monetary losses. Further correlational analysis showed that the amplitude of RewP to gain feedback and difference wave amplitude in women with PMS was related to the affect balance in the late luteal phase. Time-frequency analysis showed that the theta-band (4~7 Hz, 250~4000 ms) power to gain feedback in PMS group was lower than that of healthy group in the late luteal phase.

Taken together, the amplitude of RewP and the theta-band power are related to reward processing. Results showed that in the late luteal phase, the amplitude of RewP and the theta-band power in women with PMS were lower than that in healthy women, and the amplitude of RewP was related to affect balance for women with PMS. These results suggest that the altered neurophysiological response in reward processing of women with PMS may be one of the causes of their low positive affect and affect imbalance in the late luteal phase. Our findings provide a basis for PMS intervention from the perspective of increasing positive affect, which supplements and enriches previous interventions mostly based on reducing negative affect.

Key words: premenstrual syndrome, menstrual cycle, late luteal phase, positive affect, reward processing, reward positivity, theta-band, time-frequency analysis