Every sensory experience is mediated by cells. Cells accumulate defects over time, eventually slowing or ceasing their work. And so, to experience the passage of time in an animal body is to experience sensory diminishment.

2 thoughts on “Ageing

  1. shinichi Post author

    The Birds Are Singing, but Not for Me

    by David George Haskell

    Animal sounds are my connection to the changing seasons. Every week, a new voice appears or fades. Early winter arrives with the chip of juncos. The chitter of nestling bluebirds signals the onset of summer, closely followed by the first cicadas.

    This year, though, the yearly cycle was missing a voice. In that absence, I learned something about my creeping deafness and, beyond, the Faustian bargains that our ancestors struck with evolution.

    Where I live in the Southeast, late spring is marked by the songs of blackpoll warblers, tiny black-and-white birds migrating from South America to the boreal forests of Canada where they breed. They’re here for a week just as the school year ends and tomato-planting season begins, a joyful time. This year, I heard none. My partner, though, could hear their high-pitched song and pointed the birds out as they flitted in the treetops.

    The sonic erasure felt deeply unsettling. I could hear other everyday sounds — passing cars, cardinals whistling, neighborhood kids at play — but the blackpoll’s song was gone.

    Graphs from my audiologist show hearing loss across all sound frequencies, but especially for high sounds, so I was expecting this moment. Still, the loss of blackpoll warblers hit me hard. I had looked forward all winter to hearing them and then … nothing. Now, in summer, I notice other gaps in the soundscape, especially the high, raspy thrumming of the meadow katydids. This is a strange grief: The songs are there, but not for me. I miss them.

    As a biologist fascinated with sound, I’ve tried to protect my ears, using earplugs around power tools and at loud concerts. Yet my hearing loss is now worse than most of my cohort of friends in their mid-50s, a quirk of my genes. I’m not alone. The National Institutes of Health reports that approximately 15 percent of Americans over the age of 18 report some trouble hearing. Among those older than 75, nearly half do.

    We can lose hearing in many ways. Eardrums, middle ear bones and nerves can falter, as can auditory processing in the brain. For many people, loss of function in hair cells in the inner ear are to blame. These cells amplify the motions of sound waves in the inner ear, and then turn the motion into nerve impulses.

    The hair cells in our ears are descendants of the wiggly cilia hairs that animate single-celled creatures swimming around in ponds and ocean water. These cilia enable hearing throughout the animal kingdom, from vibration-sensitive organs in the skin of fish to sound detectors in the legs of insects.

    Sudden shocks like gun blasts kill inner-ear hair cells. Other losses take time, like prolonged exposure to loud noise. Some pharmaceutical drugs can kill hair cells. But much of the loss has little to do with assaults from the outside. Instead, aging undermines hair cells. Even a life spent drug-free in quiet surrounds would not protect our ears from the erosive power of passing years. Once gone, the cells never grow back or heal.

    Just by being alive, we’re locked into a process of sensory decline. Why?

    Every sensory experience is mediated by cells. Cells accumulate defects over time, eventually slowing or ceasing their work. And so, to experience the passage of time in an animal body is to experience sensory diminishment. The only animals known to have broken this deal with time are relatives of jellyfish called hydra. Their bodies are sacs topped by tentacles. Their nerves are woven into a net, with no brain or complex sense organs. This simple body lets hydra regularly purge and replace defective cells. These eternally youthful inverted jellyfish live seemingly without aging, at the cost of having rudimentary senses.

    Evolution struck a different deal for our ancestors: We live in richly sensual bodies, but are too complex to be ageless.

    We can, though, partly break the deal. Sensory experience is about attention as much as it is about the physiology of cells. The undergraduate students in my field biology class generally have ears that can pick up more frequencies than mine. Yet when we go outside, I hear more. At least at first. I invite students, regardless of hearing “ability,” into what the philosopher Simone Weil called the “rarest and purest form of generosity”: attention.

    We listen through our chests for low hums and percussive beats. We rest fingertips on twigs to perceive how wind converses with wood. We send our bodily attention outward, using ears, palms, soles, guts and muscles.

    What we find differs among us in its tones and textures. We connect to stories of the world around us, carried in sound’s many pulsations. We share these stories, listening through one another’s perceptions. We name bird, insect and frog species, and hear the diversity of human voices. We study the energies of traffic and buildings. We follow vibrations back to their sources, some beautiful and life-affirming, like the music of other species, and others broken, such as excessive and unjust noise.

    With repetition, sensory attentiveness works its way into everyday experience. I paradoxically listen more and with greater pleasure than in previous years, even as my inner ear hair cells die off. Doing so with other people helps. I find the blackpoll warbler through the ears of my companions. I share with others what my listening has taught me. Take that, hydra.

    Opening our senses to the living world does not erase the sorrows of aging. But paying attention in community can bring delight in the moment, and is a defiant and joyful answer to evolution’s bequest.

  2. shinichi Post author

    Aging changes in the senses


    As you age, the way your senses (hearing, vision, taste, smell, touch) give you information about the world changes. Your senses become less sharp, and this can make it harder for you to notice details.

    Sensory changes can affect your lifestyle. You may have problems communicating, enjoying activities, and staying involved with people. Sensory changes can lead to isolation.

    Your senses receive information from your environment. This information can be in the form of sound, light, smells, tastes, and touch. Sensory information is converted into nerve signals that are carried to the brain. There, the signals are turned into meaningful sensations.

    A certain amount of stimulation is required before you become aware of a sensation. This minimum level of sensation is called the threshold. Aging raises this threshold. You need more stimulation to be aware of the sensation.

    Aging can affect all of the senses, but usually hearing and vision are most affected. Devices such as glasses and hearing aids, or lifestyle changes can improve your ability to hear and see.


    Your ears have two jobs. One is hearing and the other is maintaining balance. Hearing occurs after sound vibrations cross the eardrum to the inner ear. The vibrations are changed into nerve signals in the inner ear and are carried to the brain by the auditory nerve.

    Balance (equilibrium) is controlled in the inner ear. Fluid and small hair in the inner ear stimulate the auditory nerve. This helps the brain maintain balance.

    As you age, structures inside the ear start to change and their functions decline. Your ability to pick up sounds decreases. You may also have problems maintaining your balance as you sit, stand, and walk.

    Age-related hearing loss is called presbycusis. It affects both ears equally. Hearing, particularly the ability to hear high-frequency sounds, may decline. You may also have trouble telling the difference between certain sounds. Or, you may have problems hearing a conversation when there is background noise. If you are having trouble hearing, discuss your symptoms with your health care provider. One way to manage hearing loss is by getting fitted with hearing aids.

    Persistent, abnormal ear noise (tinnitus) is another common problem in older adults. Causes of tinnitus may include wax buildup, medicines that damage structures inside the ear or mild hearing loss. If you have tinnitus, ask your provider how to manage the condition.

    Impacted ear wax can also cause trouble hearing and is common with age. Your provider can remove impacted ear wax.


    Vision occurs when light is processed by your eye and interpreted by your brain. Light passes through the transparent eye surface (cornea). It continues through the pupil, the opening to the inside of the eye. The pupil becomes larger or smaller to control the amount of light that enters the eye. The colored part of the eye is called the iris. It is a muscle that controls pupil size. After light passes through your pupil, it reaches the lens. The lens focuses light on your retina (the back of the eye). The retina converts light energy into a nerve signal that the optic nerve carries to the brain, where it is interpreted.

    All of the eye structures change with aging. The cornea becomes less sensitive, so you might not notice eye injuries. By the time you turn 60, your pupils may decrease to about one third of the size they were when you were 20. The pupils may react more slowly in response to darkness or bright light. The lens becomes yellowed, less flexible, and slightly cloudy leading to the development of cataracts. The fat pads supporting the eyes decrease and the eyes sink into their sockets. The eye muscles become less able to fully rotate the eye.

    As you age, the sharpness of your vision (visual acuity) gradually declines. The most common problem is difficulty focusing the eyes on close-up objects. This condition is called presbyopia. Reading glasses, bifocal glasses, or contact lenses can help correct presbyopia.

    You may be less able to tolerate glare. For example, glare from a shiny floor in a sunlit room can make it difficult to get around indoors. You may have trouble adapting to darkness or bright light. Problems with glare, brightness, and darkness may cause problems driving at night.

    As you age, it gets harder to tell blues from greens than it is to tell reds from yellows. Using warm contrasting colors (yellow, orange, and red) in your home can improve your ability to see. Keeping a red light on in darkened rooms, such as the hallway or bathroom, makes it easier to see than using a regular night light.

    With aging, the gel-like substance (vitreous) inside your eye starts to shrink. This can create small particles called floaters in your field of vision. In most cases, floaters do not reduce your vision. But if you develop floaters suddenly or have a rapid increase in the number of floaters, you should have your eyes checked by a professional, as this may indicate a retinal detachment.

    Reduced peripheral vision (side vision) is common in older people. This can limit your activity and ability to interact with others. It may be hard to communicate with people sitting next to you because you cannot see them well. Driving can become dangerous.

    Weakened eye muscles may prevent you from moving your eyes in all directions. It may be hard to look upward. The area in which objects can be seen (visual field) gets smaller.

    Aging eyes also may not produce enough tears. This leads to dry eyes which may be uncomfortable. When dry eyes are not treated, infection, inflammation, and scarring of the cornea can occur. You can relieve dry eyes by using eye drops or artificial tears.

    The upper eyelids may sag because of weakened muscular support. This may lead to visual loss if the sagging is severe.

    Common eye disorders that cause vision changes that are NOT normal include:

    • Cataracts — clouding of the lens of the eye
    • Glaucoma — rise in fluid pressure in the eye
    • Macular degeneration — disease in the macula (responsible for central vision) that causes vision loss
    • Retinopathy — disease in the retina often caused by diabetes or high blood pressure

    If you are having vision problems, discuss your symptoms with your provider.


    The senses of taste and smell work together. Most tastes are linked with odors. The sense of smell begins at the nerve endings high in the lining of the nose.

    You have about 10,000 taste buds. Your taste buds sense sweet, salty, sour, bitter, and umami flavors. Umami is a taste linked with foods that contain glutamate, such as the seasoning monosodium glutamate (MSG).

    Smell and taste play a role in food enjoyment and safety. A delicious meal or pleasant aroma can improve social interaction and enjoyment of life. Smell and taste also allow you to detect danger, such as spoiled food, gases, and smoke.

    The number of taste buds decreases as you age. Each remaining taste bud also begins to shrink. Sensitivity to the five tastes often declines after age 60. In addition, your mouth produces less saliva as you age. This can cause dry mouth, which can affect your sense of taste.

    Your sense of smell can also diminish, especially after age 70. This may be related to a loss of nerve endings and less mucus production in the nose. Mucus helps odors stay in the nose long enough to be detected by the nerve endings. It also helps clear odors from the nerve endings.

    Certain things can speed up the loss of taste and smell. These include diseases, smoking, and exposure to harmful particles in the air.

    Decreased taste and smell can lessen your interest and enjoyment in eating. You may not be able to sense certain dangers if you cannot smell odors such as natural gas or smoke from a fire.

    If your senses of taste and smell have diminished, talk to your provider. The following may help:

    • Switch to a different medicine, if the medicine you take is affecting your ability to smell and taste.
    • Use different spices or change the way you prepare food.
    • Buy safety products, such as a gas detector that sounds an alarm you can hear.


    The sense of touch makes you aware of pain, temperature, pressure, vibration, and body position. Skin, muscles, tendons, joints, and internal organs have nerve endings (receptors) that detect these sensations. Some receptors give the brain information about the position and condition of internal organs. Though you may not be aware of this information, it helps to identify changes (for example, the pain of appendicitis).

    Your brain interprets the type and amount of touch sensation. It also interprets the sensation as pleasant (such as being comfortably warm), unpleasant (such as being very hot), or neutral (such as being aware that you are touching something).

    With aging, sensations may be reduced or changed. These changes can occur because of decreased blood flow to the nerve endings or to the spinal cord or brain. The spinal cord transmits nerve signals and the brain interprets these signals.

    Health problems, such as a lack of certain nutrients, can also cause sensation changes. Brain surgery, problems in the brain, confusion, and nerve damage from injury or long-term (chronic) diseases such as diabetes can also result in sensation changes.

    Symptoms of changed sensation vary based on the cause. With decreased temperature sensitivity, it can be hard to tell the difference between cool and cold and hot and warm. This can increase the risk of injury from frostbite, hypothermia (dangerously low body temperature), and burns.

    Reduced ability to detect vibration, touch, and pressure increases the risk of injuries, including pressure ulcers (skin sores that develop when pressure cuts off blood supply to the area). After age 50, many people have reduced sensitivity to pain. Or, you may feel and recognize pain, but it does not bother you. For example, when you are injured, you may not know how severe the injury is because the pain does not trouble you.

    You may develop problems walking because of reduced ability to perceive where your body is in relation to the floor. This increases your risk of falling, a common problem for older people.

    Older people can become more sensitive to light touches because their skin is thinner.

    If you have noticed changes in touch, pain, or problems standing or walking, talk with your provider. There may be ways to manage the symptoms.

    The following measures can help you stay safe:

    • Lower the water heater temperature to no higher than 120°F (49°C) to avoid burns.
    • Check the thermometer to decide how to dress, rather than waiting until you feel overheated or chilled.
    • Inspect your skin, especially your feet, for injuries. If you find an injury, treat it. Do not assume the injury is not serious because the area is not painful.


    As you grow older, you will have other changes, including:


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