Libido, also referred to as sex drive, is a person's overall desire for sexual activity. Libido is often an important factor in the formation and maintenance of relationships, and a libido mismatch between partners can affect relationships negatively.
Why Do We Have A Sex Drive?
Libido is recognised as an important force in the Darwinian theory of natural selection. Libido’s evolutionary purpose is to get the species to procreate, therefore passing genetic material to the next generation. From an evolutionary perspective, any mechanism that can increase the frequency of sexual intercourse during fertile days of a woman’s menstrual cycle, has a selective advantage by improving the chance of conception. And that’s why women have highly fluctuating sex drives, with a high urge to engage sexually just before ovulation in each menstrual cycle. Men’s sex drives remain relatively stable.
Neurobiology Of Libido
Libido is governed primarily by activity in the mesolimbic dopamine pathway. So what is the mesolimbic pathway? The mesolimbic pathway is also referred to as the reward pathway. The pathway connects an area called the ventral tegmental area in the midbrain to another area called the ventral striatum of the basal ganglia in the forebrain. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.
For simplicity, just understand this: the release of neurochemicals through this pathway gives us pleasure, and that facilitates reinforcement; that is, any activity that gives us pleasure makes us want to keep doing it again and again. The same pathway is also involved in addiction to substances or behaviours. In this pathway, dopamine and related trace amines (primarily phenethylamine) that modulate dopamine neurotransmission play a critical role in regulating libido. Other neurotransmitters, neuropeptides, and sex hormones that affect sex drive by acting on this pathway include:
Testosterone (directly correlated)
Estrogen (directly correlated)
Oxytocin (directly correlated)
Progesterone (inversely correlated)
Serotonin (inversely correlated)
Norepinephrine (inversely correlated)
However, keep in mind that all of them affect sex drive to varying degrees; with Dopamine and Testosterone being the strongest modulators.
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Effects Of Age
The surge in testosterone hits the male at puberty resulting in a sudden and extreme sex drive which reaches its peak at age 15–16, then drops slowly over his lifetime. In contrast, a female's libido increases slowly during adolescence and peaks in her mid-thirties.
Sex Hormone Levels And The Menstrual Cycle
Testosterone levels rise gradually from about the 24th day of a woman's menstrual cycle until ovulation on about the 14th day of the next cycle, and during this period the woman's desire for sex increases consistently. The 13th day is generally the day with the highest testosterone and oestrogen levels. In the week following ovulation, the oestrogen and testosterone levels are the lowest and as a result women will experience less interest in sex. Also, during the week following ovulation, progesterone levels increase, resulting in a woman experiencing difficulty achieving orgasm.
Libido During Pregnancy And Lactation
In the first trimester of pregnancy, estrogen and progesterone levels rise. Symptoms in early pregnancy that may lower sexual desire include:
Around week 10, these increased hormone levels will drop off. At that point, fatigue and nausea decrease significantly. With the loss of those two symptoms may come an increase in sex drive, which peaks in late 1st trimester, and early 2nd trimester. Later in the third trimester, weight gain, back pain, and other symptoms again decrease sexual drive.
Also, during pregnancy a