The sense of smell is much more important than many people realize. This is evidenced by the fact that the sense of olfaction, which is the act of smelling, takes up 5% of human DNA. How do smells affect the brain? The answer to that question is a little better understood than how many aromas the nose can detect or how important olfaction is to human life.
How Do Smells Affect the Brain in Terms of Anatomy and Physiology?
What human beings perceive as smell are actually molecules shed by various objects, as well as living things. When you inhale through your nose, the particles are drawn through the nasal passages toward the back of the skull. These passages are lined with olfactory epithelium, a layer of tissue that consists of millions of sensory neurons. There are proteins called receptors at the tips of each of these neurons, and human beings are able to smell because the odor molecules bind to the receptors.
The sensory neurons connect to a structure at the base of the forebrain called the olfactory bulb. The act of an odor molecule binding to a neural receptor sends an electrical from the sensory neuron to the olfactory bulb, which relays the information to other areas of the brain for further processing.
The main part of the brain that controls the sense of smell is the limbic system. Consisting of the amygdala, the hippocampus, the thalamus, and the hypothalamus as the four main parts, the limbic system is the oldest part of the brain in evolutionary terms and is primarily responsible for emotion and memory.
What Specific Effects Do Smells Have on the Brain?
Because smell is processed in the limbic system, it primarily affects brain functions also centered there.
Most people think of taste and smell as two different senses and consider the tongue to be the primary taste organ. However, while it is true that the tongue has a role to play, most of what you taste is actually smell. The act of chewing releases molecules from the food that make their way from behind the nose into the olfactory epithelium, where they latch onto the receptors. The resulting nerve signals are relayed to the thalamus, which sends some of them to the orbitofrontal cortex in the front of the brain. There, it integrates with taste information, and that is why you can detect the different flavors of the food you eat.
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In his 1913 novel, “The Remembrance of Things Past,” French author Marcel Proust describes an uncontrollable rush of memory in response to consuming a sip of tea with a little cake. Since what human beings perceive as taste is in fact mostly smell, it was probably the aroma of the tea and cake that was responsible for this “Proustian moment” more than the taste. With years’ worth of accumulated recollections stored in the brain, some can seem so deeply buried as to be irretrievable, yet a smell associated with them can bring them right back to the surface, often accompanied by strong emotions.
The hippocampus and the amygdala are the areas of the brain responsible for processing memory and emotions. The olfactory bulb sends electrical signals related to smell directly to these areas of the brain, bypassing the areas of rational thought. This is why a smell may evoke a strong memory and emotional response before you are even consciously aware of it.
The connection between olfaction and memory may have given early humans an evolutionary advantage. If a smell reminded them of a dangerous situation that they had encountered before, the rush of memory associated with it may have helped them to avoid the new peril, thus improving the likelihood of survival.
Aromatherapy has been used for centuries to improve conditions related to both mind and body. Modern science backs up the ancient practice by demonstrating that certain scents do have a calming effect on the mind and help to relieve stress.
For example, the smell of lavender has been shown specifically to boost mood, promote relaxation, and improve sleep quality. Another study demonstrated decreased blood pressure and heart rate from the smell of roses. It is not only the smells of flowers that may have a calming effect on the brain but also the scents of certain foods, such as vanilla and coffee.
Studies show that certain smells help improve concentration and focus. Children exposed to the aroma of fresh strawberries performed better on tests, while athletes became faster and more focused after smelling peppermint. Factory workers in Japan showed improved productivity after being exposed to the smell of lavender during a tea break. The ability of lavender to elevate the mood and relieve stress may have had something to do with the improved performance.
How Can Scientists Measure How Do Smells Affect the Brain?
The effects of smells on the brain are extrapolated from more than just subjective reports or anecdotal evidence. It is possible to measure the effects with a diagnostic technique called an electroencephalogram. An EEG measures the amount of electrical activity in the brain and shows where the activity is occurring. More electrical activity means more stimulation.
Why Do People Underestimate How Smells Affect the Brain?
Perhaps part of the reason why the sense of smell in humans is underestimated is because of its inferiority to that of other animals. Dogs are renowned for having a much more sensitive olfactory sense than ours. The 200 million receptor cells in canine nasal passages dwarf the 5 million that human beings have. Nevertheless, new research suggests that the number of distinct odors that human beings can detect has been grossly underestimated. While the previous estimate was approximately 10,000 distinct odors, the real capacity may be at least 1 trillion. If that’s the case, then human beings can detect more distinct scents than auditory tones or different colors and shades.
Knowing the answer to the question “how do smells affect the brain?” helps you to appreciate more fully how they can influence your life in significant ways. With a diffuser from Whole Home Scenting, you can help ensure that the effect on your family members and guests is a positive one. Contact us for more information.