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  • Updated 03.11.2023
  • Released 06.14.1999
  • Expires For CME 03.11.2026




Brain pathology is frequently associated with disturbance in reading ability (alexia). Since the 19th century, two major types of alexias have been recognized: alexia with and without a preserved ability to write. In the mid-20th century, two additional types of alexias were proposed: alexia due to spatial disturbances and alexia associated with frontal pathology. During the 1970s and 1980s, a new approach to the analysis of alexia was developed. This new approach (psycholinguistic or cognitive perspective) shifted the focus from the anatomical correlates of acquired reading disturbances to the functional mechanisms underlying alexias. Some special types of alexias, such as alexia for Braille reading, have also been reported. Contemporary neuroimaging studies have significantly contributed to a better understanding of the brain organization of reading processes and reading disturbances.

Key points

• Two major types of alexias were described during the late nineteenth century: alexia without agraphia and alexia with agraphia.

• During the mid-twentieth century two additional types of alexia were proposed: spatial alexia and frontal alexia.

• Psycholinguistic models of alexia distinguish between central and peripheral alexias.

• Excepting spatial alexia, acquired reading disturbances are associated with left hemisphere pathology – usually strokes, tumors, or traumas.

• Alexia rehabilitation is usually carried out simultaneously with aphasia rehabilitation.

Historical note and terminology

Alexia (or acquired dyslexia) refers to an acquired disorder in reading caused by brain pathology (22; 116). Alexia has been recognized for over a millennium, but only in the twentieth century did literacy become sufficiently widespread that alexia represented a significant medical problem. Two case reports published by Dejerine in 1891 and 1892 represent important milestones in the study of alexia (36; 35). In the 1891 paper, he described a patient who suffered a cerebrovascular accident that produced some degree of right-sided visual field defect and mild difficulty in naming and in understanding spoken language together with a complete loss of the ability to read. The patient could write nothing but his signature. Spoken language improved, but the alexia and agraphia remained basically unchanged until his death. Postmortem examination showed an old infarct in the left parietal lobe involving three quarters of the angular gyrus and extending deep to the lateral ventricle (36). One year later, Dejerine reported a second patient who noted an inability to read, but no other language disturbances. The only neurologic finding was a right hemianopia. Unlike the former case, this patient, although unable to read except for a few individual letters, could write adequately. Four years later, a second vascular accident led him to death. Postmortem examination revealed two different infarcts: one infarct was a large softening that involved the left angular gyrus and was obviously of recent origin, and the other infarct was an old gliotic infarct that involved the medial and inferior aspects of the left occipital lobe and the splenium of the corpus callosum. The old infarct was the source of the alexia without agraphia (35).

Alexia without agraphia (also known as occipital alexia or pure alexia) and alexia with agraphia (parietal-temporal alexia or central alexia) were extensively corroborated during the following years. They represent the classic alexic syndromes. A third clinically distinct alexia syndrome, frontal alexia, which is associated with pathology in the frontal language areas, was later proposed (20). A fourth form of alexia, spatial alexia, has been associated primarily with right-hemisphere damage (53; 07). However, spatial alexia involving right neglect can also occur after left-hemisphere damage (108).

These four types of alexias (without agraphia, with agraphia, frontal, and spatial) represent the neurologic, classic, or neuroanatomically based classification of alexias. Significant variability, however, in the pattern of disturbances is observed particularly in parietal-temporal alexia (with agraphia). During the 1970s and 1980s, a new approach to the analysis of alexia was developed (78; 27). This approach to alexias is usually known as the psycholinguistic or cognitive perspective of alexias. Interest shifted from the anatomical correlates of acquired reading disturbances to the functional mechanisms underlying alexias. It should be noted that, in the psycholinguistic or cognitive interpretation of alexias, the name "acquired dyslexia" is preferred, rather than "alexia."

The linguistic and cognitive approaches to alexia required the development of models for normal reading. Several partially coincidental cognitive models of normal reading have been proposed (31; 27). In general, most of these models propose that after the initial letter identification, reading proceeds along two linguistically different routes: (1) the direct route, wherein the written word is associated with a visual word in the lexicon memory; and (2) the indirect route, wherein the written word is transformed in a spoken word following a graphophonemic set of rules, and the meaning of the word is attained through its phonological mediation. If one or the other of these reading systems is altered, different error patterns can be observed. In some cases, both systems can be disrupted simultaneously.

Psycholinguistic models of alexias usually introduce a major distinction between central and peripheral alexias (122). In central alexias, the patient can perceive a word correctly but has difficulties recognizing it with either semantic or phonological processing. Three different types of central alexias are distinguished: (1) phonological, (2) surface, and (3) deep. Each features a specific pattern of reading errors (paralexias). In the peripheral alexias, the reading impairment corresponds more exactly to a perceptual disturbance. The patient has difficulty attaining satisfactory visual word processing (89). Usually, three different types of peripheral alexias are recognized: (1) letter-by-letter reading, (2) neglect alexia, and (3) attentional alexia.

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