Acalculia: an explainer

Acalculia: an explainer

What is acalculia?

Acalculia is a neurological condition that causes an inability to process numbers or perform mathematical calculations. It comes from the Greek (‘a’, meaning ‘not’), and the Latin (‘calculare’, meaning ‘to count’).

It was first described in 1920, by neurologist Salomon Henschen, who discovered that impairment across multiple areas of the brain correlates with calculation deficits. Acalculia primarily affects an area of the brain’s frontal lobes that deals with mathematical reasoning.

Acalculia is one of the symptoms of Gerstmann syndrome, alongside finger agnosia, agraphia and left-right disorientation. Gerstmann syndrome is a very rare condition caused by specific brain lesions of the left parietal lobe, or cortex, of the angular gyrus in the dominant hemisphere; typically, it results from a left hemisphere disorder, however the right hemisphere has also been associated with certain components of the syndrome. However, clinical neuropsychological research suggests that acalculia may, in fact, extend beyond our notion of its being linked with Gerstmann syndrome (Cohen, Wilson, Izard and Dehaene, 2007).

What causes acalculia?

Acalculia is an acquired condition, meaning that a person is not born with it – it can occur at any time.

It’s caused by traumatic brain injury or brain damage that causes neurological disruption. For example, common causes include strokes, brain tumours, physical blows to the head and other brain injuries. Neuroscience professionals also indicate the prevalence of acalculia in individuals suffering with dementia, with many in clinical neurology deeming it a criterion for diagnosing the condition.

What is the difference between acalculia and dyscalculia?

Both acalculia and dyscalculia are disorders that affect mathematical ability.

They are distinct in that acalculia is an acquired condition, whereas dyscalculia is a developmental disorder. Developmental dyscalculia presents during the initial stages of early mathematical knowledge acquisition, whereas someone with acalculia may have previously had mathematical abilities.

Different intervention strategies are required for each of the conditions.

What are the symptoms of acalculia?

According to experts, as acalculia is not routinely screened for, there exists a lack of understanding about the nature, prevalence and impact of the condition.

The condition may be present when an individual who has previously been able to understand and complete basic mathematical problems experiences loss of the ability to do so.

There are a number of common difficulties and dissociations related to the symptoms of acalculia to look out for:

  • counting backwards and forwards
  • reading and writing numbers
  • transcribing between numbers written in word and numerical form
  • comparing numbers and determining which is smaller or larger
  • performing mathematical operations, such as adding and subtracting
  • interpreting mathematical symbols
  • aligning numbers in columns
  • lack of basic numerical knowledge – for example, the number of days or weeks in a year.

In addition to testing number processing and completion of mathematical problems, screening tests may also cover similar skills that impact mathematical ability, such as verbal skills and spatial reasoning.

How much an individual experiences these impairments to their cognitive functions, and to what degree, can vary. It can affect many practical, day-to-day tasks, such as managing money, using timetables, making appointments, managing medication, and organising employment and social activities.

Are there different types of acalculia?

Ardila and Rosselli proposed a classification of acalculias: primary acalculia (also known as anarithmetia) and secondary acalculia. However, they note there is a certain degree of overlap between them.

While both relate to cognitive impairment affecting numerical processing, there are three main differences between primary and secondary acalculia including the:

  1. skills affected
  2. brain injury location
  3. degree to which the injury affects the skills.

Primary acalculia presents a loss of concepts related to numeracy that are observed in both oral and written calculations. In contrast, according to an article published in MedLink Neurology, ‘secondary acalculia refers to calculation defects resulting from a different cognitive deficit: memory disorders, attention impairments, language defects, spatial defects, etc.’ Secondary acalculia is commonly associated with other disorders, such as aphasia, alexia, apraxia, agraphia, visuospatial issues, and executive function disorders.

How do you treat acalculia?

As there is no cure for acalculia – or Gerstmann’s syndrome – treatment and recovery generally focuses on occupational therapy and supportive care. Recovery is variable, and depends on a range of different factors, including the extent and etiology of the brain pathology. Some individuals may find they spontaneously recover from acalculia, others may experience a diminishing of symptoms over time, and others will struggle with the condition for the rest of their lives.

For primary acalculia, recovery is largely aimed at managing symptoms. As the brain is unable to recover lost nerve tissue, long-term rehabilitation interventions are based on the teaching and learning of new strategies based on neuroplasticity. For example, an individual may begin with more simple activities, such as counting objects, before progressing to more complex tasks, such as using arithmetical operations. The use of technologies, such as calculators, word-processing software and apps for specific functions, can help to bridge gaps in ability and alleviate the burden of the condition.

What more could be done to support people living with acalculia? Professionals indicate there are a number of measures that could help, including:

  • increasing awareness among patients and professionals, encouraging people to seek help and push for new diagnostic tools and interventions
  • developing and integrating acalculia assessment into patient care pathways
  • investing in research into the effectiveness of interventions.

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