Graphesthesia, also called graphagnosia, is the ability to recognize symbols when they’re traced on the skin. “Graph” means writing and “esthesia” means sensing.

This ability is a measure of cortical function. Specifically, it requires a normal cortical sensory system, which includes the primary somatosensory cortex and its connections. This part of the brain makes you aware of various sensations, including:

  • touch
  • pressure
  • temperature
  • pain
  • position of your extremities

This includes the sensation of a number or letter being traced on your skin. A normal primary somatosensory cortex lets you interpret the sensation and identify the symbol.

However, if there’s a problem with this part of the brain, you won’t be able to detect the character. This indicates you have agraphesthesia, which is the opposite of graphesthesia. It’s the inability to sense symbols drawn on the skin.

If you don’t have graphesthesia, it means something isn’t right in your somatosensory cortex. Let’s look at possible causes, along with how it’s diagnosed by a doctor.

A loss of graphesthesia is a sign of a neurological disorder or damage. It could be a complication of several conditions, such as:

  • Multiple sclerosis. Multiple sclerosis is a chronic autoimmune disease that affects the central nervous system. It disrupts sensory function and causes tissue atrophy in the brain, which may result in graphesthesia loss.
  • Brain tumor. A tumor in the brain can affect the somatosensory cortex, leading to a decline in graphesthesia.
  • Brain or spinal cold injury. If a brain injury damages the somatosensory cortex, loss of graphesthesia may occur. Spinal cord injuries might also decrease sensory function, including graphesthesia.
  • Peripheral neuropathy. Graphesthesia loss might indicate peripheral neuropathy. This occurs when nerves outside the brain and spinal cord are damaged.
  • Stroke. A stroke is an interruption of blood flow to the brain. This can cause brain damage and reduce graphesthesia.
  • Dementia. Dementia is the decline of cognitive function due to nerve cell damage or loss. In dementias like Alzheimer’s disease, the damage might involve the part of the brain responsible for graphesthesia.
  • Corticobasal degeneration. In this rare neurological disorder, cell degeneration occurs in certain parts of the brain. This can lead to graphesthesia loss as well as apraxia, or the inability to do voluntary movements.

Graphesthesia is one of the most sensitive measurements of cortical sensory function. Therefore, it has become a standard neurological test when diagnosing the conditions above.

A graphesthesia test is done during a neurological exam. It’s usually performed by a neurologist. Here’s what the process typically involves:

  1. Your doctor will have you close your eyes.
  2. With the back of a pen or applicator stick, they’ll trace a letter or number on the palm of your hand.
  3. Your doctor will ask you to identify the character.
  4. They’ll repeat the procedure on your other hand with a different symbol.

This test demonstrates the ability of your somatosensory cortex to recognize, analyze, and interpret the sensations on your skin.

During the neurological exam, your doctor may also test other sensory functions such as pain, vibration, and position.

Your somatosensory cortex is also responsible for stereognosis, or the ability to identify an item by touch. It involves recognizing the shape, form, and size of the object without looking at it. “Stereo” means solid and “gnosis” means recognition.

While both abilities are related to touch, graphesthesia and stereognosis are not the same. Graphesthesia is the recognition of movements drawn on the skin, while stereognosis is the recognition of solid objects through touch.

Loss of stereognosis also indicates a problem with the somatosensory cortex. It’s known as astereognosis and can be diagnosed during a neurological exam.

To test for loss of stereognosis, your doctor will have you close your eyes. They’ll put a familiar item, like a key or pen, in your hand. If you can’t recognize the object, you don’t have stereognosis.

Graphesthesia is regulated by the primary somatosensory cortex in your brain. It lets you recognize letters or numbers when they’re traced on your skin. If you don’t have graphesthesia, it could indicate a neurological disorder or injury.

A doctor can test for graphesthesia loss by drawing a symbol in the palm of your hand. If you have the ability, you’ll be able to identify the character solely based on sensation.