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Alexia (from Greek ἀ- (a-) 'absence of, without', and λέξις (lexis) 'word') is a brain disorder in which a person is unable to understand written words. Sometimes also called acquired dyslexia, it differs from developmental dyslexia and refers specifically to the loss, usually in adulthood, of a previous ability to read. There are four sub-classifications of alexia. These include pure alexia, surface alexia, phonological alexia, and deep alexia. All of these sub-categories can involve fluent aphasia, nonfluent aphasia, or agraphia.

Alexia is most often caused by damage to the cortex in the temporal lobe, parietal lobe or occipital lobe by a stroke or other brain injuries.There are various treatment methods including the Lindamood Phoneme Sequencing program (LiPS) and Multiple Oral Re-reading (MOR).

Joseph Jules Dejerine discovered alexia in 1892 by studying a French merchant who was no longer able to read after experiencing a stroke.

Classifications

There are four sub-classifications of alexia. These include pure alexia, surface alexia, phonological alexia, and deep alexia. All of these sub-categories can involve fluent aphasia, nonfluent aphasia, or agraphia.

File:Visual Word Form Area.png

Visual Word Form Area

Pure Alexia

Pure alexia, also known as alexia without agraphia, is when patients experience low efficiency in identifying strings of letters and more complicated words. This does not include speech, hand writing style, language, or comprehension impairments.

Surface Alexia

In surface alexia, patients often assign seemingly “appropriate” meanings to unfamiliar words. One relies on pronunciation of specific words. Words with pronunciations that are 'regular' (highly consistent with their spelling e.g. mint) are read more accurately read than words with irregular pronunciation, such as colonel. Surface alexia is usually accompanied by agraphia and fluent aphasia.

Phonological Alexia

In phonological alexia, one cannot use the “spelling to sounds” route for reading. In this type of alexia, the letter sound converter does not function, therefore the ability to sound out words is absent. Instead patients with phonological alexia only recognize whole, previously known, words .

Deep Alexia

In deep alexia one experiences semantic paralexia. This is when one reads a word and says a related meaning instead of the denoted meaning . Deep alexia is more recently seen as a severe version of phonological alexia.

Causes

Pure Alexia

Pure alexia is caused by lesions on the visual word form area (VWFA). The VWFA is composed of the left lateral occipital sulcus and is activated during reading. A lesion in the VWFA stops transmission between the visual cortex and the left angular gyrus. It can also be caused by a lesion involving the left occipital lobe and the splenium of the corpus callosum. It is usually accompanied by a homonymous hemianopsia in the right side of the visual field.

Surface Alexia

Surface alexia is caused by lesion in temporoparietal region of the left hemisphere. The posterior superior and middle temporal gyri of the left hemisphere are key regions where surface alexia stems from. Some research shows that most dramatic cases of surface alexia are caused by lesions in the inferolateral left temporal regions which are considered to involve semantic processing .

Phonological Alexia

Phonological alexia is caused by lesions in varied locations within the left cerebral artery. The superior temporal lobe is often also involved. Research has pointed towards the theory that phonological alexia is a development of deep alexia .

Deep Alexia

Deep alexia is caused by lesions that are often widespread and include much of the left frontal lobe. Research suggests that damage to the left perisylvian region of the frontal lobe causes deep alexia, as both the phonological and lexical routes of language are impaired.

Treatment Techniques

Surface Alexia Treatment

Although no particular treatment approach is deemed most effective, one of the most popular treatments is the Lindamood Phoneme Sequencing Program (LiPS). LiPS is based on a three way sensory feedback process. One uses auditory, visual, and oral skills to learn to recognize words and word patterns. This is considered letter-by-letter reading using a bottom-up processing technique. Bottom-up processing is when individuals attempt to understand smaller parts of something bigger. In this case learning how to pronounce each letter leads to learning how to read whole words.

The Lindamood Phoneme Sequencing Program and variations on the phoneme technique have been used in a number of empirical studies on phonological alexia. In these studies, participants significantly improved in spelling and reading ability. There have also been studies conducted on patients with surface alexia and deep alexia and while, generally, all participants experienced improvements from this method, patients with surface alexia seemed to improve the most.

There have been no significant findings regarding the treatment of phonological alexia.

Pure Alexia Treatment

Though not thoroughly studied, tactile/kinesthetic reading techniques have been used particularly to treat patients with pure alexia. In this technique, patients physically trace letter forms in order to replace or supplement visual letter form information. In addition to tactile and kinesthetic reading techniques, other therapies that are aimed at improving letter-level reading include timed semantic and lexical association tasks and limited-time single word identification.

Differing from letter-level reading therapies, multiple oral re-reading (MOR) is designed to improve full text reading. MOR is considered a top-down processing technique. Top-down processing is different from bottom-up processing because patients attempt to grasp a basic understanding of a bigger thing, in this case a word, and later learn about the small parts that make up the big thing, in this case letters. In MOR, patients read and re-read texts a predetermined number of times or until reading speed and/or accuracy improves a predetermined amount. The idea behind MOR is to learn how to use context, syntax, and semantics of the text to process written information rather than using bottom-up processing techniques in which letter by letter (LBL) reading is necessary.

The theory that the MOR technique only uses top-down processing has been questioned and some studies have shown that in fact, bottom-up processing is in part responsible for reading improvement. This has been proven by reading tests that are engineered to use as few of the same words as possible that are used in training texts during MOR treatment. In these studies, patients did not significantly improve in reading speed or accuracy when reading untrained passages. Untrained passages are defined by having differing vocabulary from the texts used in reading practice. This supports the findings that MOR also has bottom-up processing components.

History of Discovery

In 1892 Joseph Jules Dejerine discovered alexia after studying the case of Oscar C., an educated French merchant who lost the ability to understand written words after suffering a stroke . Oscar C. suddenly couldn’t interpret letters or words and saw them as obscure symbols which were devoid of meaning. According to Dejerine, the white matter of Oscar C.’s lesion had severed the connection between his interpretation of visual words and his visual cortices. The patient could therefore no longer access the stored orthography of words from vision, while his spelling capacities (from non-visual memory) had not been damaged . Dejerine also observed that Oscar C.’s ability to understand numbers had remained intact, although the ophthalmologist who examined the patient before turning him over to Dejerine had found that Oscar C.’s numeral reading was very slow and fraught with error .

Notable cases

Canadian novelist Howard Engel suffered from alexia (sine agraphia) following a stroke in 2000. In this case, however, he did not suffer from agraphia, and kept his ability to write. His case was subsequently publicised by neurologist Oliver Sacks.

See also

• Agnosia
• Apraxia of speech
• Auditory agnosia
• Dementia
• Dual-route hypothesis to reading aloud
• Dyslexia

• Primary progressive aphasia
• Strephosymbolia
• Stroke
• Synesthesia
• Visual agnosia

Further reading

• Henry ML, Beeson PM, Alexander GE, Rapcsak SZ (2012). "Written language impairments in primary progressive aphasia: a reflection of damage to central semantic and phonological processes". J Cogn Neurosci. 24 (2): 261–75. doi:10.1162/jocn_a_00153. PMC 3307525. PMID 22004048. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Kim ES, Rapcsak SZ, Andersen S, Beeson PM (2011). "Multimodal alexia: neuropsychological mechanisms and implications for treatment". Neuropsychologia. 49 (13): 3551–62. doi:10.1016/j.neuropsychologia.2011.09.007. PMC 3221964. PMID 21952194. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Seghier ML, Neufeld NH, Zeidman P; et al. (2012). "Reading without the left ventral occipito-temporal cortex". Neuropsychologia. 50 (14): 3621–35. doi:10.1016/j.neuropsychologia.2012.09.030. PMC 3524457. PMID 23017598. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

External links

Category:Aphasias Category:Dyslexia Category:Learning disabilities Category:Agnosia