WASHINGTON - A woman's hormones affect specific parts of the brain called the reward pathway, researchers said on Monday in a finding that could offer insight into treating drug abuse and mood disorders.

A study of women playing an imaginary slot machine game showed their brain responses changed in anticipation of a payout depending on the phases of their menstrual cycles.

This might help explain other studies that show women get a bigger kick from cocaine and amphetamines during one phase of the fertility cycle -- and perhaps why women are less vulnerable to schizophrenia than men are, the researchers said.

"This demonstrates for the first time that female ... hormones affect the reward system in very specific ways during particular parts of the cycle," said Dr. Karen Berman of the U.S. National Institute of Mental Health, who worked on the study published in the Proceedings of the National Academy of Sciences.

"It is interesting to speculate that this may have evolutionary advantages and may affect behaviors that have been shown in other studies to also be affected by cycles."

For instance, not only are women more susceptible to drug abuse at certain points, but they may also find testosterone-type facial traits in men more appealing at certain times in their cycles, Berman said.

What this does not mean is that women are somehow more emotional or vulnerable to hormones than men are, she stressed.

"I think it is important to keep in mind that this isn't the only thing that is going on in women's brains," she said in a telephone interview.

"We have very important regulatory areas and homeostatic mechanisms that keep us in line, keep us functioning, keep us focused, keep us productive," she added.

"I would really hate for this work to be interpreted in a way to make us seem that we are at the call of our hormones because I don't think that is the case."

Berman, working with Dr. Jean-Claude Dreher of France's national scientific research center CNRS and colleagues, used functional magnetic resonance imaging or fMRI to get real-time images of the brain activity of 15 women.

The women played a hypothetical slot machine game, with payouts of $10 or $20.

Different areas of the brain lit up in anticipation of a payout -- a reward -- depending on the menstrual cycle phase. For instance, during the midfollicular phase, which comes four to eight days after menstrual bleeding starts, the orbitofrontal cortex and amygdala of the brain were more active.

At this phase, estrogen is produced but progesterone levels are low.

Berman said it is too soon to connect any of the findings with specific behaviors.