Why do people want to fall in love more in spring?

Many animals go into heat in the spring. Some animals only go into heat once a year or even several years, while some go into heat several times a year. Humans are different from animals. They can go into heat at any time. The mechanisms behind these two situations are completely different. When spring comes, the daylight hours become longer, the temperature gradually rises, all things come back to life, red flowers and green leaves compete for beauty, and insects, birds and animals also sing. These experiences come quickly and are in stark contrast to the dull motivations. This will affect the human nervous system in the following ways.

1. Seasonal neural cycles driven by daylight changes

In addition to cones and rods, the human retina has a third type of photoreceptor cells, intrinsically photosensitive retinal ganglion cells (ipRGC). ipRGC was discovered not long ago and there is currently no unified Chinese translation, so ipRGC will be used in the following text.

The ipRGC cells contain melanopsin, which produces a series of chemical reactions to light, causing the ipRGC cells to discharge under light.

The signals of ipRGC are directly transmitted to the suprachiasmatic nucleus (SCN) and other neural nuclei in the hypothalamus through the optic nerve.

The hypothalamus is a higher-level nerve center that regulates endocrine activity. It controls the secretion of various neurotransmitters through various nuclei, thereby controlling multiple functions of the body. The volume of the hypothalamus is less than 4cm^3, but there are many nuclei inside, and the relationships between them are very complex. The SCN is one of the most functionally important nuclei in the hypothalamus. It acts as a rhythm controller, regulating human circadian and seasonal cycles. The long days that come with spring drive endocrine changes in the nervous systems of animals and humans through this mechanism.

Specifically for humans, the changes are reflected in melatonin, thyroid hormone, and vitamin D, which respectively affect a person's sleep (sleeping soundly during the spring, more adequate sleep), energy (more energy), and physical sensations (better bone condition, feeling full of energy). This reminds the body that spring is a good time to eat well and find a partner as soon as possible while food is plentiful.[8] At this time, even the quality and quantity of sperm in men increases significantly, reaching the highest level of the year.

Although humans do not have an estrus period, our bodies, like those of many animals, are prepared for love in all aspects during the spring.

2. Changes in the neural environment driven by novel experiences in spring

The richness of spring’s colors, smells, and sounds frequently gives people new and surprising experiences. This changes the neuroendocrine activity of the human brain. The most important thing is that it will constantly stimulate the human brain's nervous system to secrete dopamine, giving people a sense of euphoria, which is similar to addiction.

This change in the neural environment will change our cognitive state: we will not have enough knowledge about the flaws of others, or we will unconsciously turn a blind eye to them, and our stressful experience of life and environment will be reduced. In other words, it will make us relax, let down our psychological defenses, have more sense of participation, and be more willing to contact and trust strangers and things. This experience is so good that our brains are addicted and need more dopamine. The most powerful source of dopamine is undoubtedly the experience of falling in love.

This state of addiction is what we call romance. Our brains don’t differentiate between the burst of dopamine produced by a large number of novel experiences and the burst of dopamine produced by love. This neuroendocrine mutation, driven by novel experiences in spring, is interpreted by the brain as love, which in turn drives the desire for love.

3. Actual effect

With the above 1 and 2 as the basis, let's take a look at the actual results caused by these factors:

Statistics on sexual activity show that the most sexual activity occurs in April and August, which are the beginnings of spring and autumn respectively, and are also the months when we experience the novelty of the seasons the most.

Specifically, sexual activity occurs most frequently during the week on Fridays and Saturdays - when stress is lowest - and is least frequent on Sundays - when people dread Mondays. In other words, the level of stress our bodies feel is negatively correlated with our desire for sexual behavior.

The longer daylight hours in the spring drive the seasonal rhythms of our brains and bodies, allowing us to reach our annual optimal physical and mental levels, and our brains don't distinguish between the feel-good effects of light and the feel-good effects of love.

The abundance of novel experiences in spring drives a burst of dopamine secretion in the nervous system, and our brains cannot distinguish it from the dopamine burst of love.

The good feelings of 1 and 2 caused by the spring time make our brains slightly addicted, driving us to look for things that can promote the secretion of a large amount of dopamine - love.

From the perspective of neuroscience, romance is about abundant and rich novel experiences. Therefore, creating a romantic atmosphere means creating surprises, which is the key to pursuing love.