A deficit in the ability to recognize objects by touch is called astereognosis. It often happens after you've had a brain tumor or stroke that causes damage to your brain.
What Is Stereognosis?
Stereognosis is the ability to recognize objects by touch without seeing them. It’s also known as haptic perception. Normally, your brain stores information about items you see and use and you draw on this stored memory to recognize items with other senses, such as touch. For example, if you put your hand in a pocket full of coins, paperclips, and a key, you can feel around, recognize your house key in the mix, and pull it out without seeing it.
There are two different types of stereognosis: manual stereognosis and oral stereognosis.
Manual stereognosis. This type of stereognosis is the ability to recognize objects with your hands. You use your sense of touch to feel your way around and recognize items without relying on your sight. Some examples of this are:
- Finding the armhole in your sweater
- Getting your keys from the bottom of your bag
- Buttoning your collar behind your neck
Oral stereognosis. This type of stereognosis is the ability to recognize objects and their shape inside your mouth with no visual help. You mainly use this ability to help with chewing and swallowing. For example, stereognosis helps you recognize when a lump of chewed food in your mouth is small enough to swallow safely.
What Is Astereognosis?
Astereognosis is a recognition problem that causes you to have trouble identifying objects by handling them with your eyes closed or without seeing them. It’s sometimes also called tactile agnosia or somatosensory agnosia. There are two main types of astereognosis:
Primary astereognosis. The primary type of astereognosis is when you can’t recognize the physical features of an object, such as its shape, texture, or size.
Secondary astereognosis. In this type, your sense of touch might function well, so you can feel how big an object is or whether it’s rough or smooth. But you can’t recognize what the object is. You can feel the dimensions and texture of the shape, but you can’t match the information stored in your brain to the object.
What Is the Cause of Astereognosis?
Astereognosis happens when you have damage or a breakdown in your nervous system and brain. Normally, your body processes and interprets touch through two key steps. First, your nerves and sensory pathways send information about touch from your body to your brain. Then, your parietal lobe combines and interprets the information and names the object.
Many parts of your brain and nervous system are involved in your sense of touch. This means astereognosis can happen if you have damage to any of the following:
- Parietal lobe
- Spinal cord
- Brain stem
Damage to these parts of your body often happens because of a tumor or a loss of blood supply that causes damage, breakdown of brain tissue, or injury. Conditions that cause astereognosis include:
- Blood clots that affect the parietal lobe or brainstem
- Brainstem tumors
- Multiple sclerosis, where your immune system attacks your nerves and causes problems with messages sent between your brain and body
- Cerebral palsy, where your brain can’t send messages to your muscles
- Head injuries, like a depressed skull fracture that causes a sunken skull
- Alzheimer’s disease
How Do You Test for Astereognosis?
In most cases, your doctor will test for astereognosis after you have an injury to your brain. It might be part of a series of tests that helps your doctor understand exactly how the damage is affecting your skills.
Tactile object recognition. The most common test is called the tactile object recognition test, or TOR. During this test, you close your eyes, and your doctor puts random objects like a pen or a paperclip in your hand for 30 seconds. They ask you to identify the object and then repeat the process a few times. Then, they rate your response as 2 for normal, 1 for some impairment, or 0 for total loss.
Nottingham sensory assessment. Your doctor might do the TOR test as part of a Nottingham sensory assessment. During this assessment, your doctor presses objects against your body to see if you can feel light touch, pinpricks, and pressure. They’ll also move some of your limbs around to see if you can sense the movement.
Together, these tests tell your doctor whether you can sense touch and interpret it and recognize objects and shapes.
Imaging scans. You might also have a computed tomography (CT) scan or magnetic resonance imaging (MRI). Your doctor might order these tests early on to help find and diagnose the underlying problem. Once they know what’s happening, your doctor can use imaging scans to find exactly where the damage is so they can plan your recovery.
How to Treat Astereognosis
The treatment for astereognosis involves treating the underlying cause first. If you had a stroke, your doctor might give you blood pressure medication and blood thinners or remove a blood clot from your arteries. If you have a tumor, they might use chemotherapy, surgery, or radiation.
Once they treat the underlying cause, you’ll also go through rehabilitation to help you regain your sensory skills. This therapy can include exploring and re-learning different textures, shapes, sizes, weights, and objects. You usually need to practice some of these exercises at home to help you learn.
What Are the Risks of Astereognosis?
Losing your ability to recognize objects can affect your daily life. You use these skills for many tasks, which can make everyday activities hard. You might be clumsy or have trouble with movement while holding objects. For example, you might know an object is in your hand, but you might have trouble knowing what it is, which can disturb the movements of your hand.
Numb and clumsy hands are common with astereognosis. People who have Alzheimer’s disease and astereognosis also have worsening problems with memory and thinking.
Astereognosis is common after a stroke, brain tumor, or brain injury, and it takes time to recover. It can take days or months, depending on the seriousness of the injury. The main treatment is to focus on the underlying cause, but therapy to explore and re-learn shapes, sizes, and objects can help. If you think you have astereognosis, talk to your doctor.