Alexia (acquired dyslexia)
Encyclopedia
Alexia (Alexia from the Greek
, privative
, expressing negation, and = "word") occurs when damage to the brain
causes a patient to lose the ability to read. It is also called word blindness, text blindness or visual aphasia.
Those who suffer from "alexia" and "dyslexia" can have similar difficulties, however, "alexia" refers to an acquired reading disability, where reading ability had previously been developed, usually occurring in adulthood conditions, while "dyslexia
" refers to developmental reading disability.
which is usually the left. It can also occur with lesions to the occipital
and/or parietal lobes
, which are responsible for processing auditory, phonological and visual aspects of language. The region at the junction of occipital and temporal lobes (sometimes called the occipito-temporal junction) coordinates information that is gathered from visual and auditory processing and assigns meaning to the stimulus. Alexia can also occur following damage to the inferior frontal
. Damage to these different areas of the cortex result in somewhat different patterns of difficulty in affected individuals. In some cases, a stroke
can cause alexia.
(the inability to produce or comprehend spoken language). Alexia can also co-occur with agraphia, the specific loss of the ability to produce written language even when other manual motor abilities are intact. In other cases, damage is restricted to areas responsible for input processing. The result is known as pure alexia. In this scenario, an individual's ability to produce written language is spared even though they are unable to understand written text.
Alexia without agraphia results from a left occipital splenium of the corpus callosum
lesion.
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, privative
Privative a
In Ancient Greek grammar, privative a is the prefix a- that expresses negation or absence . It is derived from a Proto-Indo-European syllabic nasal *, the zero ablaut grade of the negation *ne, i.e. /n/ used as a vowel...
, expressing negation, and = "word") occurs when damage to the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
causes a patient to lose the ability to read. It is also called word blindness, text blindness or visual aphasia.
Those who suffer from "alexia" and "dyslexia" can have similar difficulties, however, "alexia" refers to an acquired reading disability, where reading ability had previously been developed, usually occurring in adulthood conditions, while "dyslexia
Dyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
" refers to developmental reading disability.
Classification
There are two groups of alexia.- The first or main group is "the central dyslexia" group which includes surface dyslexia, semantic dyslexiaSemantic dyslexiaSemantic dyslexia is, as the name suggests, a subtype of the group of cognitive disorders known as Alexia . Those who suffer from semantic dyslexia are unable to properly attach words to their meanings in reading and/or speech...
, phonological dyslexia, and deep dyslexiaDeep dyslexiaDeep dyslexia is a form of alexia that disrupts reading processes that were functioning normally before the individual suffered a head trauma to the dominant hemisphere...
. - The second group, "the peripheral dyslexia" group, includes neglect dyslexia, attentional dyslexia, and pure alexia which is also known as alexia without agraphia.
Causes
Alexia typically occurs following damage to the dominant hemisphere of the brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
which is usually the left. It can also occur with lesions to the occipital
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
and/or parietal lobes
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
, which are responsible for processing auditory, phonological and visual aspects of language. The region at the junction of occipital and temporal lobes (sometimes called the occipito-temporal junction) coordinates information that is gathered from visual and auditory processing and assigns meaning to the stimulus. Alexia can also occur following damage to the inferior frontal
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
. Damage to these different areas of the cortex result in somewhat different patterns of difficulty in affected individuals. In some cases, a stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
can cause alexia.
Presentation
Alexia may be accompanied by expressive and/or receptive aphasiaAphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
(the inability to produce or comprehend spoken language). Alexia can also co-occur with agraphia, the specific loss of the ability to produce written language even when other manual motor abilities are intact. In other cases, damage is restricted to areas responsible for input processing. The result is known as pure alexia. In this scenario, an individual's ability to produce written language is spared even though they are unable to understand written text.
Alexia without agraphia results from a left occipital splenium of the corpus callosum
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
lesion.
Treatment
One patient with damage to areas responsible for visual processing was able to regain the ability to read by using motor processing (tracing the shapes of letters).See also
- AphasiaAphasiaAphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
- DementiaDementiaDementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
- StrephosymboliaStrephosymboliaStrephosymbolia was first coined in 1925 by Samuel Orton as being an answer to the implications the term word blindness makes. Specifically this new word was created to make a distinction between itself and word-blindness, but no reasons are given for what these distinctions arise from, or what...
- StrokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
- SynesthesiaSynesthesiaSynesthesia , from the ancient Greek , "together," and , "sensation," is a neurologically based condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway...
- Visual agnosiaVisual agnosiaVisual agnosia is the inability of the brain to make sense of or make use of some part of otherwise normal visual stimulus and is typified by the inability to recognize familiar objects or faces...