The heat of a new relationship is a chemical reaction, and it can fade with time. That is, unless you employ these seven incendiary strategies to keep the sparks flying.
Play Games with Her
Boosting her dopamine levels outside of the bedroom can help you connect between the sheets. "Your brain can't differentiate between the external anxiety caused by a novel situation and the internal anxiety caused by being attracted to someone," says Dr Victoria Zdrok, a clinical psychologist (and former Playboy playmate). "A boost outside of the bedroom can carry over for when it matters most."
The best way to increase her anxiety, sans cardiac arrest? Competition, says Zdrok, which also helps release sex-drive-boosting testosterone. Sign up for a couples adventure race or just belly up at the local pub's trivia night; by competing on the same team, you'll also improve communication and cooperation, the two behavioural foundations of sexual success.
Revisiting that bed-and-breakfast romp of three months ago isn't just an exercise in nostalgia. Recalling the relationship's formative moments can stir up the hormone norepinephrine, which helps the brain shine an emotional spotlight on memories. "You'll unlock her passion," says sex therapist Dr Laura Berman, "and intensify the new memories you're making too."
The brain's internal archivist responds best to strong contextual cues – smells, environments, music, textures, even certain foods – so orient her mental rearview mirror by concocting a smorgasbord of evocative sights and sounds.
Lie Down on the Job
The monogamous prairie vole might not be your sexual role model, but researchers found that the creatures are literally addicted to their mates, thanks to their receptivity to oxytocin. That hormone battles stress and increases arousal (it's released by orgasm, after all), so the lesson here is clear: up her dosage and she'll be hooked on you.
Physical contact (cuddling!) and muscle massage both unleash the chemical, so give her this sensual massage in the postcoital glow: ask her to lie facedown and, straddling the backs of her upper thighs, apply rotating thumb pressure to either side of her lower spine, says Dr Linda Banner, author of Advanced Sexual Techniques. By the time you reach her shoulders and neck, the oxytocin jets should be firing full force.
Let Her Lead You
It pays to be her willing sex toy every now and then. A study at the University of Michigan found that female rats receive a dopamine boost (there it is again – the euphoria-inducing neurotransmitter) only when they control sex. But don't just offer her the blow-up valve. "Make sure she's not just hearing 'Do me the way I want to be done'," says sex therapist Dr Gloria Brame, author of Come Hither.
Instead, Brame suggests role-playing a scenario (76 per cent of women surveyed by Men's Health said they'd be game for a little playacting) in which she's in a position of authority and you're the sexual novice. The fantasies women said they liked most: professor/student and nurse/patient.
Become a Stranger
Reinvent yourself outside the bedroom and you could help refresh her passion inside it. According to researchers at the Massachusetts Institute of Technology, we keep a sort of neural dossier on a person tucked away in our brain, just above the temples. This case file is overhauled when we meet their friends or develop deeper relationships with those we've already met, says Dr William Pollack, a professor of psychiatry at Harvard Medical School.
"She'll see you through their eyes, and it will bring out different aspects of your own personality," says Pollack, "stimulating love and lust neurotransmitters." So introduce her to Jack and Sally from your cycling group at a dinner party: it could encourage her to see your body anew.
Learn New Moves
Trying new sex positions isn't just a new way to fit the key into the lock. "Anything novel or exciting is likely to drive up the levels of dopamine in her brain," says anthropologist Dr Helen Fisher, author of Why We Love. Magnetic resonance imaging scans at Oxford University found that learning a new motor skill – whether it's fingering bar chords on your guitar or plucking a new sexual harmonic in bed – sets off a flurry of activity in many of the same brain regions activated during orgasm.
Send your sex life back to square one. "If you've learned how to pleasure her, it's too easy to forget about foreplay and all the other things that keep sex fresh," says Dr Debbie Herbenick, a sexual health educator at the Kinsey Institute.
Start with a three-day sex break to build anticipation, pooling dopamine behind her sexual Snowy Mountains Dam. Then spend a night necking like teenagers, clothes on. Wait two days and spend another one touching each other sensually – everywhere but the genitals.
Take two more days off and then use your lips instead of your fingertips to do the same. By this time, your dopamine will be redlining and both of you will have a surplus of arousal-boosting testosterone. Bonus: the heightened physical sensitivity can unearth long-neglected erogenous zones when – finally – at the two-week mark, you blow the dam.