In 1971, Ian Waterman suddenly collapsed due to a severe case of what appeared to be gastric flu. Although his illness subsided after a few days, a peculiar set of symptoms persisted. Despite his muscles and joints remaining healthy, Waterman found himself unable to move or feel anything from the neck down. Eventually, he was diagnosed with a rare and extreme form of deafferentation, a neurological condition where certain signals from the nervous system are interrupted or impaired.
Without his body’s constant feedback on how his limbs were moving, Waterman was unable to perform basic actions such as sitting up, standing, or walking. However, over time, he taught himself to use sight to judge the distance of his limbs from other objects. Eventually, he regained complete control of his body, as long as he could see it.
We often overlook the importance of touch in movement. However, touch is just one part of the somatosensory system, a network that oversees all the sensations arising from the surface and interior of our bodies. This system regulates touch, pain, temperature, and our awareness of our bodies in space, also known as proprioception. When something goes wrong with this system, the effects can be dramatic.
All these sensations are processed by millions of tiny receptor cells embedded in our skin, muscles, tendons, and organs. Every square centimeter of our skin is packed with hundreds of these cells, and their shape, size, and depth determine what kind of stimuli they respond to. Mechanoreceptors sense mechanical deformation of the skin, thermoreceptors respond to temperature changes, nociceptors sense pain, and proprioceptors sit deep in your muscles and tendons, continually detecting and relaying information about the position of your body.
Your brain combines this information with other sensory data to move through space without needing to see your limbs. All of these receptors work by sending electrical signals to the brain through the fibers they’re attached to. The speed of those signals varies with the fiber’s thickness. For example, some nociceptors are attached to fibers with slightly more conductive, fatty myelin than others. So when you get hurt, the electrical impulses from thicker nociceptors trigger sharp, intense pain, while thin, unmyelinated nociceptors are responsible for the dull, aching pain that follows.
If this process is disrupted—either by damage to the skin, the nerves, or the brain—the network breaks down. Since it underpins so many bodily functions, damage to the somatosensory system can manifest in a wide variety of ways. In Waterman’s case, an autoimmune reaction attacked a large swath of his nervous system, leaving him with no tactile or proprioceptive sensations from the neck down. However, deafferentation is just one of many somatosensory disorders.
Individuals can receive damage to a specific brain area or a section of skin, resulting in the loss of certain sensations in particular locations. The impact of this loss can be significant. Losing tactile sensations makes it difficult to gauge how much strength to use in a situation. Without the warning signals provided by thermal and pain stimuli, we don’t react when our bodies are damaged. Moreover, being deprived of social touch can cause a condition known as touch starvation, characterized by anxiety, depression, high blood pressure, and even a weakened immune system.
Many individuals who face these realities have found innovative ways to adapt. However, it’s undeniable that all these invisible sensations play a vital role in how we navigate the world—even if they can be difficult to put your finger on.
Create an interactive diagram of the human nervous system. Label the different types of receptor cells (mechanoreceptors, thermoreceptors, nociceptors, and proprioceptors) and explain their functions. Use this diagram to quiz yourself and classmates on the roles of each receptor type.
Conduct a series of proprioception exercises, such as balancing on one leg with your eyes closed or touching your nose with your finger while blindfolded. Record your observations and discuss how the lack of visual feedback affects your ability to perform these tasks.
Analyze the case of Ian Waterman in a group discussion. Reflect on how his condition affected his daily life and the strategies he used to overcome his challenges. Compare his experiences with other somatosensory disorders and discuss the importance of the somatosensory system.
Conduct a sensory deprivation experiment by temporarily limiting one of your senses (e.g., wearing earplugs or a blindfold). Document your experiences and how it affects your ability to perform everyday tasks. Share your findings with the class and discuss the importance of each sense.
Choose a somatosensory disorder to research in-depth. Create a presentation that includes the causes, symptoms, and treatments of the disorder. Highlight any innovative adaptations or technologies that help individuals manage their condition. Present your findings to the class.
deafferentation – the loss or interruption of sensory input to the brain – After the car accident, the patient experienced deafferentation, resulting in a loss of sensation in her left arm.
somatosensory system – the part of the nervous system responsible for processing sensory information related to the body’s position, touch, temperature, and pain – The somatosensory system allows us to feel and perceive sensations from various parts of our body.
proprioception – the sense that enables us to perceive the position, movement, and orientation of our body parts – Proprioception allows dancers to perform precise movements without constantly looking at their feet.
mechanoreceptors – sensory receptors that respond to mechanical pressure or distortion of tissues – When you press your finger against your skin, mechanoreceptors detect the pressure and send signals to your brain.
thermoreceptors – sensory receptors that respond to changes in temperature – Thermoreceptors in the skin help us sense and respond to hot and cold stimuli.
nociceptors – sensory receptors that detect and transmit signals related to pain – When you accidentally touch a hot stove, nociceptors immediately send pain signals to your brain to protect you from further harm.
myelin – a fatty substance that surrounds and insulates nerve fibers, allowing for faster transmission of electrical signals – The deterioration of myelin can result in impaired nerve function and slower signal transmission.
autoimmune reaction – an immune response in which the body’s immune system mistakenly attacks its own cells or tissues – In autoimmune diseases like multiple sclerosis, the immune system targets and damages the protective myelin sheath around nerve fibers.
touch starvation – a state of prolonged deprivation of physical touch or contact – During the COVID-19 pandemic, many people experienced touch starvation due to social distancing measures and isolation.
tactile sensations – physical sensations perceived through the sense of touch – The soft, warm fabric provided a pleasant tactile sensation when she ran her fingers over it.
