Amygdala reactivity to negative stimuli is influenced by oral contraceptive use

Abstract

The amygdala is a highly interconnected region of the brain that is critically important to emotional processing and affective networks. Previous studies have shown that the response of the amygdala to emotionally arousing stimuli can be modulated by sex hormones. Because oral contraceptive pills dramatically lower circulating sex hormone levels with potent analogs of those hormones, we performed a functional magnetic resonance imaging experiment to measure amygdala reactivity in response to emotional stimuli in women using oral contraceptives, and compared their amygdala reactivity with that of naturally cycling women. Here, we show that women who use oral contraceptive pills have significantly decreased bilateral amygdala reactivity in response to negatively valenced, emotionally arousing stimuli compared with naturally cycling women. We suggest that by modulating amygdala reactivity, oral contraceptive pills may influence behaviors that have previously been shown to be amygdala dependent-in particular, emotional memory.

Keywords: amygdala; emotional memory; fMRI; menstrual phase; oral contraceptive pills.

Fig. 1

The final ROIs comprised areas of functional activity within anatomically defined amygdala masks. This figure shows the left amygdala ROI in pale blue and the right amygdala ROI in dark blue.

Fig. 2

Mean estradiol levels did not differ between groups.

Fig. 3

The luteal group had significantly higher baseline progesterone levels than either OC group (**P < 0.01). The follicular group had significantly higher baseline progesterone than the inactive OC group (*P < 0.05).

Fig. 4

(a) The contrast between activity associated with emotional stimuli vs that associated with neutral activity in the amygdala was significantly greater in NC women compared with OC users (P < 0.05). No effect of hemisphere was found, nor was an interaction between contraceptive use and hemisphere present. (b) Within the naturally cycling women, a significant interaction was found between hemisphere and menstrual cycle phase. (c) No interaction between pill phase and hemisphere was observed in the OC users.