Acalculia, or dyscalculia, is difficulty or inability in performing simple mental arithmetic. This depends on two processes, number processing and calculation; a deficit confined to the latter process is termed anarithmetia.
Acalculia may be classified as:

  • Primary:
    • A specific deficit in arithmetical tasks, more severe than any other coexisting cognitive dysfunction
  • Secondary:
    • In the context of other cognitive impairments, for example of language (aphasia, alexia, or agraphia for numbers), attention, memory, or space perception (e.g., neglect). Acalculia may occur in association with alexia, agraphia, finger agnosia, right-left disorientation, and difficulty spelling words as part of the Gerstmann syndrome with lesions of the dominant parietal lobe.

Secondary acalculia is the more common variety.
Isolated acalculia may be seen with lesions of:

  • dominant (left) parietal/temporal/occipital cortex, especially involving the angular gyrus (Brodmann areas 39 and 40)
  • medial frontal lobe (impaired problem solving ability?)
  • subcortical structures (caudate nucleus, putamen, internal capsule).

Impairments may be remarkably focal, for example one operation (e.g., subtraction) may be preserved while all others are impaired.

In patients with mild to moderate Alzheimer’s disease with dyscalculia but no attentional or language impairments, cerebral glucose metabolism was found to be impaired in the left inferior parietal lobule and inferior temporal gyrus.

Preservation of calculation skills in the face of total language dissolution (production and comprehension) has been reported with focal left temporal lobe atrophy probably due to Pick’s disease.



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Cross References

Agraphia; Alexia; Aphasia; Gerstmann syndrome; Neglect