Impairment of all four of these functions in an otherwise intact patient is referred to as Gerstmann's syndrome. Since Gerstmann's syndrome is caused by lesions in the dominant parietal lobe, aphasia is often (but not always) present as well, which can make the diagnosis difficult or impossible. Each of the individual components of Gerstmann's syndrome is poorly localizing on its own, but they are worth documenting as part of the assessment of overall cognitive function:
Calculations. Can the patient do simple addition, subtraction, and so on?
Right–left confusion. Can the patient identify right and left body parts?
Finger agnosia. Can the patient name and identify each digit?
Agraphia. Can the patient write their name and a sentence?
These functions are often tested as part of language (discussed earlier). Right–left confusion and finger agnosia can both be quickly screened for with the classic command, "Touch your right ear with your left thumb."
As we have noted, abnormality of all four of these functions that is out of proportion to other cognitive deficits is strongly localizing to the dominant (usually left) parietal lobe. Otherwise, each of the individual abnormalities can be seen in many different lesions and may be present in individuals with impaired attention, language, praxis (see the next section), constructions, logic and abstraction, and so on.