What do we know about human pheromones? Our brains are divided into specialized segments for processing the vast quantity of information perceived by our sense organs. If our eyes capture the last twinkling light of dusk, that information, in the form of light rays, is sent along the optic nerve to the optic lobe, which gives us our ability to see and tells us what it is we are looking at. If we hear a rousing symphony, our ears take in the vibrations of the music and send analogs of them to the auditory cortex, where we register the numerous instruments involved in blending the notes. When we detect the odor of chocolate cake, our olfactory cells drive nerve impulses to the olfactory bulb in the brain and then straight to the limbic system. When we are touched, those sensations move swiftly from the surface of the skin to a highly specialized sensory region of the cortex.
Although the complexity of the human brain makes it impossible for us to explain its workings in detail here, it is important to understand the delicate interplay of the six senses and the brain. The senses are our windows to the world. People place into experimental sensory deprivation, removed from the richness and color of the sensory environment, return to the re , world lugging a host of psychological problems. In the next section, we will talk brieﬂy about the senses smell because pheromonal communication and olfaction are intimately linked. The senses are our windows to the world. People place into experimental sensory deprivation, removed from the richness and color of the sensory environment, return to the re , world lugging a host of psychological problems.
In the next section, we will talk brieﬂy about the senses smell because pheromonal communication and olfaction are intimately linked.
In the physiological sense, a simple touch from a lover can speak volumes. The writer Colette said, “Massage is a woman sacred duty. Without it, how can she hope to keep a lover???” When we are touched by someone we love, our brains react by releasing the hormone oxytocin from the pituitary gland into the bloodstream. This hormonal “flood” sensitizes our bodies to pleasurable touch.” Aristotle challenged the assumption that humans have a special touch receptors that deliver messages to the brain, and our most sensitive body areas can contain thousands of these touch receptors per square millimeter of skin.
When we take in the views of our world, we do not process each image as a chunk of sensory information. Instead, everything we see is registered in the eyes as a series of light rays. Light rays hit the outer layer of the eyeball (the cornea) and then pass through the pupil, the opening in the iris that responds to fluctuations of lightness and darkness.
From there, light rays travel through the eye’s lens, which focuses the image. The image is then projected onto the retina, an area in the back of the eye that contains millions of light-detecting cells called rods and cones. When the rods and cones perceive an image, they send that image, in the form of nerve impulses, along the optic nerve, which terminates in the brain’s primary visual cortex in the optic lobe. Once there, the image registers as a whole.
The capacity of the eye to latch onto minute amounts of light is remarkable. Researchers have found that the retina can detect and process a single photon of light. (A photon is a unit of retinal illumination.) However, human sight pales in comparison to the visual acuity of certain birds of prey. For example, an eagle’s eye contains millions more densely packed rods and cones than a human eye, which allows the bird to spot animals on the ground from distances of up to three miles.
Smell and Pheromones
Marcel Proust wrote in Remembrance of Things Past, “After the people are dead, after the things are broken and scattered, taste and smell alone, more fragile but more enduring, more unsubstantial, more persistent, more faithful, remain poised for a long time, like souls, remembering, waiting, hoping, amid the ruins of all the rest.”
Proust’s eloquent rendering of the combined marvels of taste and smell is not only lovely to read, but accurate. Taste and smell are so interconnected that at times they appear to be one sense. Indeed, they are the senses that can affect us very deeply. This is because they are both connected (smell directly, taste more indirectly) to a web of neurons leading to the hippocampus, the area of the brain that houses memories and calls the forth so accurately and poignantly.
The sense of smell is triggered when the nose encounters a molecule of scent. When you dip the tip of your nose into the fragrant petals of a lilac, for example, airborne scent molecules sweep into your nostrils and gather at a thin sheet of tissue in the roof of the nasal cavity. This tissue, called the olfactory epithelium, contains millions of smell receptor cells all housed in a remarkably tiny area of about one square centimeter per nasal cavity. The epithelium contains four major types of cells: ciliated olfactory receptor cells, microvillar cells, supporting cells, and basal cells. The cells are nourished by the lamina propria, the layer of connective tissue that binds the epithelium to the bone or cartilage underneath.