Agnosia: Looking to your surroundings from a different perspective
As a Neuroscience postgraduate student at King’s College London, I have always found the unknowns of the brain and the brain disorders that keep their mystery, fascinating.
I believe agnosia is one of those disorders that needs to be deciphered. Imagine not being able to successfully recognise objects, sounds, or people by utilising your senses (sight, hearing, touch, smell and taste). In this blog, I will try to provide some insight into this rare neurological disorder.
What actually is agnosia?
If you are in the field of neuroscience or have read the patient tales of Oliver Sacks in The Man Who Mistook His Wife for a Hat, you might have an idea of the term ‘agnosia’. If not, let me introduce the complex neurological disorder that leads to the inability to identify or recognise everyday objects, loved ones, or sounds through despite otherwise normally functioning senses. Imagine being able to smell, see or sense things but not being able to correctly interpret without even realising that that’s what you’re doing. Imagine having an internal model of the world where the things you perceive are interpreted differently from the real world.
Agnosia can result from a variety of things ranging from dementia, stroke, neurological disorders, brain infection, or head injury. Brain damage usually occurs in the temporal, parietal, or occipital lobes.
The temporal lobe is located close to ear level and is mainly involved in long-term and conscious memory. The parietal lobe is roughly located at the upper back area in the skull and processes sensory information it receives from the outside world, mainly relating to touch, taste and temperature. In contrast, the occipital lobe is primarily involved in interpreting visual information. These areas are vital parts of the brain that are involved in higher perceptions related to vision, hearing and sensations.
Primary Visual Agnosia: Seeing without identifying
Now, given the different functions of each of the brain lobes, it makes sense that depending on which area is affected, different symptoms or types of agnosia will result.
It is essential to mention that agnosia usually alters one sensory modality. For instance, visual agnosia refers to the inability to identify or recognise familiar people and/or objects despite having normal vision. Indeed, patients with associative agnosia cannot categorise different visual stimuli. For example, a such a patient would not associate a glove and a hand or a rectangle and a book with one another; hence, verbal identification of the object would not be possible.
On the other hand, the second main category of visual agnosia — apperceptive agnosia — refers to the inability to identify the shape of the objects. These patients can verbally interpret the objects’ colour and texture, yet, they fail to match identical objects. Therefore, as shown in the right side set in the figure below, although a circle can be identified verbally from a drawing, these patients fail to copy the image of the circle. Hard to imagine?
To further classify visual agnosia, I would like to mention one of the most interesting and challenging types of apperceptive agnosia:
Prosopagnosia — the inability to recognise familiar faces.
Take some time to imagine waking up and not being able to identify your loved ones, close friends, and family, even though you can see them. Patients with this brain disorder cannot process facial features and are usually unable to differentiate faces. However, as a remarkable fact, they can identify a person by their smell, speech or even walking style.
Glen Alperin, a prosopagnosic patient and writer, mentions that this condition affects all aspects of his life. In his blog, he describes how he can only recognise ice hockey players by their names and the numbers on the uniforms. Indeed, patients with prosopagnosia have a much harder time recognising people they do not often see; hence specific striking characteristics like hair colour or even the numbers/names on the uniforms can be the visual cues helping them identify the person they ‘see’.
Word Deafness: Hearing without awareness
One of the other forms of agnosia is auditory agnosia which refers to the inability to process sounds despite unaffected hearing and intact speaking, reading and writing abilities.
This is thought to be associated with a disconnection between the language centres and sound processing brain areas. For instance, a person with auditory agnosia can interpret the sound of a car horn as a loud sound that lasts for a short period but would not be able to recognise the car horn itself. Not being able to identify someone, a usual sound, or inability to categorise and interpret objects make agnosia a form of a communication disorder despite the preserved sensory functions. The unknowns of agnosia highlight the knowledge gaps in neuroprocessing networks and memory formation within the brain that are yet to be solved.
The Prognosis, Treatment, and the Future
Diagnosis of agnosia includes neuropsychologic testing to measure the brain’s cognitive function, neurologic examination to examine impairment of the nervous system, and brain imaging (MRI or CT scan) to characterise the lesion (the area that has been damaged).
Following diagnosis, occupational therapy and rehabilitation with speech are recommended to aid patients with their deficits. If the cause of agnosia is reversible and can be treated with surgery and/or radiation, often a recovery period of between 3 months to 1 year is needed. Although agnosia can be cured in some cases, for others, the condition can be lifelong, with those needing to adapt their lives around this condition.
While it may take us forever to understand the visual, auditory and tactile experiences of agnostic patients, the study of these patients can provide insight into this neuropsychological syndrome, as well as helping to provide further understanding of normal visual, auditory and sensory processing mechanisms. Undoubtedly, studying these rare disorders can help the addition of new ideas into the knowledge box and decipher the mysteries about our most fascinating and intricate organ — the brain.
