Paralysis is defined as a loss of muscle function or movement, but the ability to feel sensation is a separate process. The question of whether a person experiencing paralysis can still feel touch involves the complex wiring of the human nervous system. The answer is not a simple yes or no, but rather depends entirely on the specific nature and severity of the underlying injury.
Separating Motor and Sensory Pathways
The nervous system uses distinct communication lines to manage movement and feeling. Motor commands, which control voluntary muscle movement, travel down the spinal cord through descending tracts, such as the corticospinal tract. Sensory information, which includes touch, pain, temperature, and joint position, travels up the spinal cord through ascending tracts, like the dorsal column and spinothalamic pathways, to the brain.
These two types of signals are segregated into different parts of the spinal cord. Sensory nerve fibers enter the spinal cord through the dorsal roots, while motor nerve fibers exit through the ventral roots. This anatomical separation means an injury can preferentially damage one pathway while sparing the other. This can lead to paralysis (loss of movement) with some preservation of sensation, or vice versa.
Sensory Impact of Complete Versus Incomplete Paralysis
The ability to feel touch after paralysis relates directly to whether the spinal cord injury is classified as complete or incomplete. A complete spinal cord injury results in a total lack of both motor and sensory function below the level of the injury. This means no voluntary movement and no feeling of touch, pain, or temperature can be detected in the affected body regions.
An incomplete spinal cord injury, which is more common, involves only a partial disruption of the neural pathways. Some nerve fibers remain intact, allowing for the partial preservation of motor function, sensory function, or both. Therefore, a person might retain some level of sensation, such as light touch or pressure, even if they cannot move their limbs.
Clinicians use the American Spinal Injury Association Impairment Scale (AIS) to grade this function. For instance, an AIS Grade B indicates a loss of all motor function but preserved sensory function below the level of injury. This means a person with an incomplete injury may feel touch, even if it is diminished, patchy, or only present in certain areas.
Understanding Altered Sensations and Phantom Pain
When sensation is retained after injury, it is not always perceived as normal touch, pressure, or temperature. Damage to the nerve pathways can cause signals to become disorganized or misinterpreted by the brain, leading to altered feelings. These abnormal sensations fall into distinct categories.
Paresthesia and Dysesthesia
Paresthesia describes a largely painless abnormal sensation often felt as tingling, prickling, or “pins and needles.” This occurs because damaged nerves are misfiring or being irritated, sending distorted signals to the central nervous system. Dysesthesia, in contrast, is an unpleasant or painful altered sensation, frequently described as burning, stabbing, or an electrical shock.
Phantom Pain
Phantom pain is a distinct phenomenon where a person experiences pain in a body part that has lost sensation due to injury or amputation. This pain is not caused by external touch but by the central nervous system’s attempt to reorganize and compensate for the lost input. These altered sensory experiences show that the sensory pathways are not entirely silent, but are transmitting corrupted or painful information.
How Doctors Test for Touch Sensation
To accurately determine the extent of sensory function, doctors use a standardized neurological examination that tests different types of sensation. This examination helps map the areas where the sensory pathways are still transmitting information to the brain. These tests allow clinicians to determine the precise neurological level of injury and accurately grade the completeness of the sensory loss, which is crucial for prognosis and treatment planning.
The examination includes several key tests:
- The Light Touch Test uses a cotton wisp gently stroked across the skin to assess the ability to perceive light pressure and map areas where sensory pathways are still transmitting information.
- The Pinprick Test evaluates the perception of pain and sharpness by asking the patient to distinguish between “sharp” and “dull” stimuli.
- Proprioception is tested to assess the sense of joint position.
- The ability to feel vibration is tested, often using a tuning fork placed on a bony prominence.