Overview

Gerstmann syndrome, also known as angular gyrus syndrome, is a particularly rare neurological disorder. There is no defined age group for Gerstmann syndrome and affects infants, adolescents, adults, and the elderly. 

The left hemisphere of the brain, specifically the parietal lobe in the brain is where it is seen to primarily manifest, with symptoms that span from physical to being triggered from neurological damage.

This article will focus on the cognitive deficits of Gerstmann syndrome; in order to understand the deficits, it is helpful to also understand the neurological traces of this syndrome. A cognitive deficit is mainly a physical or mental manifestation of a neurological (brain) issue. Therefore, understanding the neurological issue that is behind this observed cognitive issue is helpful in exploring this syndrome further.

Causes and symptoms of Gerstmann syndrome 

Gerstmann syndrome can be caused by multiple different types of factors, for example: 

• Traumatic brain injury
• Neurodegeneration, usually seen as a disease such as Alzheimer's, dementia or Parkinson’s disease
• Focal lesions triggered by a stroke, tumour, aneurysm and many other neurological incidences⁴

All of these possible factors can trigger Gerstmann syndrome when the angular gyrus (in the left parietal lobe)  is damaged. The angular gyrus processes sensory information and has motor and interneural communicating nerves with the rest of the brain, when damaged, there is a tetrad of symptoms that can arise. These symptoms are known as: the tetrad of Gerstmann symptoms:

• Acalculia - difficulty in doing mathematical calculations
• Finger agnosia - difficulty identifying fingers as separate digits
• Agraphia - difficulty in writing 
• Left-right disorientation - difficulty distinguishing between left and right

The tetrad of symptoms primarily manifests as a result of the factors that cause this syndrome. These factors damage the brain causing neurological issues and changes, specifically when the cause targets the parietal lobe and particular regions in the left parietal hemisphere of the brain. The result of this trauma, cause, and symptoms seen are a plethora of cognitive and neurological deficits. Understanding the mechanism that leads to the cognitive deficits in Gerstmann syndrome starts with understanding what the normal function of the brain is, and then how Gerstmann syndrome affects it.

Neurological basis of cognitive deficits

As stated in the overview, Gerstmann syndrome affects the left side of the brain, particularly, a lobe of the brain called the parietal lobe. The parietal lobe is located in the top and centre of the brain, it is a part of the cerebral cortex (the outermost layer of the brain). 

Role of the left parietal lobe

The parietal region of the brain is important for receiving sensory information from the body, this includes the five senses, which is also known as the primary somatosensory cortex.^1,3

The left parietal lobe in particular contains many important parts of the brain, including: 

• Temporoparietal junction - this contains the Wernicke’s area (region for speaking and reading) and angular gyrus²
• Inferior parietal lobule - this is responsible for collecting information from the outside world through the senses and processing it
• Posterior parietal cortex - this is where a large section of the primary somatosensory cortex lies. It is also responsible for planning movement, attention span, and spatial awareness³
• Post central gyrus - it also makes up some of the primary somatosensory cortex, and it assists with processing sensor information and understanding the external world³

It is important to understand that no specific function is localised to a particular part of the brain. There is a delicate interplay between multiple brain regions, however, certain areas are highlighted as prominent in carrying out their function on par with other regions in order to carry out a range of processes.

By being aware of the main functions of the left parietal lobe, understanding the core cognitive deficits seen in Gerstmann syndrome will now be easier.

Core cognitive deficits

Understanding the link between the neurological damage in the left parietal lobe, core cognitive deficits, and the tetrad of symptoms is done by breaking down the symptoms and linking the observable cognitive deficit to the corresponding neurological region in the left parietal hemisphere of the brain.

Agraphia

• This is where there is a difficulty in a patient's ability to write. Not only does it affect writing, but also sometimes verbal communication, patients will find it difficult to write or speak full sentences
• This symptom could occur from neurological trauma in the Wernicke area in the left parietal lobe⁸
• The Wernicke area is a large component in motor control of communication, allowing individuals to formulate and write words, however, damage to this area and the connection between the Wernicke area and the body’s motor output is how agraphia comes about⁵

Acalculia

• This is where patients find it difficult to perform simple arithmetic operations or any numerical concepts 
• Acalculia is associated with damaged connections from the angular gyrus, which is a key player in semantic processing⁷
• Semantic processing is the brain's method of storing and accessing dynamic information (continuously changing stream of incoming information) to access and ‘update’ it⁷
• The connections from the angular gyrus are damaged hence creating difficulties in carrying out semantic processing in Gerstmann syndrome, with acalculia; seen is through difficulty in performing mathematical calculations since calculations need to access stored information and manipulate it⁶

Finger agnosia 

• This is a symptom of Gerstmann syndrome where an individual is unable to name, or differentiate fingers, as well as problems in finger naming and localization 
• This can result from trauma and damage to regions of the brain that are important in relation to body schema and spatial awareness 
• The post-central gyrus and posterior parietal cortex, are regions found to be associated with finger agnosia. The most prominent out of the 2 listed is the posterior parietal cortex as it is a ‘central hub’ for processing sensory information⁹ 

Left-right disorientation

• Difficulty distinguishing between the left and right sides of one's own body or other people's bodies can also be seen in navigational situations where left and right distinctions can not be followed due to this disorientation
• This can also extend into difficult directions or orienting oneself spatially

Additional cognitive deficits (occasional/secondary)

Language impairments

• Difficulties in language comprehension can be carried over into speaking different languages or even learning one. This affects a patient because it is difficult to state their thoughts or communicate
• There are many regions in the brain that play a role in language processing, however, the Wernicke area in the left parietal lobe is a key player and where language impairments are theorised to manifest

Visual-spatial deficits

• Difficulty in perceiving spatial cues and forming spatial relationships causes tasks using visual-motor coordination to be difficult 
• Daily tasks become difficult, for example, it is harder to: pick up objects due to poor spatial awareness, write due to visual impairments or move fingers upon command due to impaired motor skills¹¹ 
• Numerical calculations, as previously established to be affected by Gerstmann syndrome through acalculia, can worsen with visual-spatial deficits. Examples of this include: misaligned numbers on a page or the inability to identify numbers and their spatial position relative to other numbers on the page¹⁰

Daily life, management, and future therapeutic techniques

Impact of cognitive deficits on quality of life

As mentioned in previous sections of this article, the cognitive deficits from Gerstmann syndrome severely decrease the quality of the patient's life. It takes away their independence and impairs their ability to carry out tasks without assistance. 

Performing everyday tasks are difficult, hand-eye coordination tasks as simple as picking up a glass of water or writing on paper are strenuous. This is due to damage to the angular gyrus thus affecting motor coordination.¹²

Resultantly, patients require assistance provided through living with special care assistance however, they can undergo rehabilitation therapy and symptomatic treatments to become less reliant on assistance. 

Potential rehabilitation and therapies

Common therapeutic strategies that target symptoms of Gerstmann syndrome include:

• Speech therapy - assists in improving the children's ability to communicate by focusing on improving speech and language skills
• Occupational therapy - targets improving coordination, motor skills, balance, and everyday skills
• Calculators and word processors - these processors are helpful tools in helping children in speech therapy
• Finger gnosis training - assists patients in the development of nerve connections to their digits. This training should improve motor coordination, quantitative skills (when counting fingers) and movement. Ultimately allowing patients to differentiate fingers by touch whilst blindfolded
• Neuropsychological rehabilitation 
• Special education and counselling 

With Gerstmann syndrome cases in children, many symptoms diminish and become less prominent and prevalent over time, thus meaning severity decreases by adulthood, furthermore, many children learn to adapt to deficits instead of overcoming them and the therapies listed above can assist their adaptation.

Summary

The rare neurological disorder: Gerstmann syndrome, develops from the left parietal lobe of the brain and a tetrad of symptoms manifest from it: acalculia, finger agnosia, agraphia, and left-right disorientation. These symptoms are triggered by neurodegeneration or traumatic brain injury which damages the left parietal lobe, specifically the connective neurons that run in and out of the angular gyrus.

The impact of this syndrome on a patient's daily life is large and patients rely heavily on continuous care and assistance. However, despite there being no cure, management therapies such as speech therapy, occupational therapy, and finger gnosis training, help patients reduce their reliance on assistance, furthermore, symptom severity reduces over time in children and they are able to adapt to deficits over time too.