Different brain activation patterns to pain and pain-related unpleasantness during the menstrual cycle

The changes in the functional magnetic resonance imaging signal during anticipation, pain stimulation, and the poststimulation periods were investigated to determine whether changes in sex hormones affect brain activity.

Eighteen participants were examined twice, once in the follicular phase and once in the luteal phase. Half the participants were tested first during the follicular phase, and the other half were tested first in the luteal phase.

The pain and unpleasantness ratings were significantly higher in the luteal phase than in the follicular. During the anticipation of pain, the prefrontal cortices were activated during the follicular phase, whereas the parahippocampal gyrus and amygdala were activated during the luteal phase. During the pain stimulation, putamen and cerebellum and precentral gyrus involving motor preparation and defense mechanism related to antinociceptive behavior were activated during the follicular phase, whereas the thalamus was activated during the luteal phase. During the poststimulation periods, the prefrontal cortices were activated during the follicular phase, whereas parahippocampal gyrus was activated during the luteal phase. The temporal pole was activated during the anticipation, pain stimulation, and poststimulation periods of the luteal phase.

During surgical and medical procedures, requirements of anesthetic and analgesic and anxiolytic drugs may be reduced during the follicular phase and increased during the luteal phase. These results highlight the need to consider the effects of the sex hormones in women when designing clinical or neuroimaging studies or when treating patients for pain and pain-related unpleasantness.