Pure alexia

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Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, is one form of alexia which makes up "the peripheral dyslexia" group. [1] Individuals who have pure alexia have severe reading problems while other language-related skills such as naming, oral repetition, auditory comprehension or writing are typically intact. [2]

Contents

Pure alexia is also known as: "alexia without agraphia", [1] "letter-by-letter dyslexia", [3] "spelling dyslexia", [4] or "word-form dyslexia". [5] Another name for it is "Dejerine syndrome", after Joseph Jules Dejerine, who described it in 1892; [6] however, when using this name, it should not be confused with medial medullary syndrome which shares the same eponym.

Classification

Pure alexia results from cerebral lesions in circumscribed brain regions and therefore belongs to the group of acquired reading disorders, alexia, [1] as opposed to developmental dyslexia found in children who have difficulties in learning to read. [7]

Causes

Pure alexia almost always involves an infarct to the left posterior cerebral artery (which perfuses the splenium of the corpus callosum and left visual cortex, among other things). The resulting deficit will be pure alexia – i.e., the patient can write but cannot read (even what they have just written). However, because pure alexia affects visual input, not auditory input, patients with pure alexia can recognize words that are spelled out loud to them. [8] This is because the left visual cortex has been damaged, leaving only the right visual cortex (occipital lobe) able to process visual information, but it is unable to send this information to the language areas (Broca's area, Wernicke's area, etc.) in the left brain because of the damage to the splenium of the corpus callosum. Patients with this deficit mostly do have a stroke to the posterior cerebral artery. But they may be susceptible to pure alexia as a consequence of other traumatic brain injuries (TBIs) as well. Anything that stops proper blood flow to the area necessary for normal reading abilities will cause a form of alexia. [9] The posterior cerebral artery is a main locale for the cause of this deficit because this artery is not just responsible for itself. It also supplies the anterior temporal branches, the posterior temporal branches, the calcarine branch, and the parieto-occipital branch. [10] What is important about these arteries is their location. All of them supply blood to the back outer parts of the brain. [11] This part of the brain is also referred to as the posterior lateral part of the brain. In cases of pure alexia, locations are found in the section of the brain, specifically the temporo-occipital area. [10] This is the area that is activated when people without any sort of alexia receive activation when undergoing orthographic processing. This area is known as the visual word form area due to this pattern of activation. [9]

[12] [13] The patient can still write because the pathways connecting the left-sided language areas to the motor areas are intact. [14] However, many people with pure alexia are able to identify and name individual letters over time as well as recognize sequences of letters as words. These people typically adapt to their disability and are able to use a style of compensatory reading known as letter-by-letter reading. [15] This style of reading takes longer than the conventional style of reading does. As the number of letters in a word increases, the amount of time it takes for the person with pure alexia increases. For each letter that is added, a patient may take up to an additional three seconds to read the word. [16]

Studies have shown that pure alexia may be a result of a disconnection syndrome. Analysis of diffusion images showed that the visual word form area (VWFA) is connected to the occipital lobe via the inferior longitudinal fasciculus (ILF), a projection that runs between the temporal and occipital lobe. functional magnetic resonance imaging (fMRI) and Diffusion Tensor Imaging (DTI) showed that two weeks after surgery in the ILF, the VWFA-Occipital Lobe tract was severely degenerated. The results came from an epileptic patient who showed symptoms of pure alexia after his surgery. Thus, the proposed pathophysiological mechanism is that the ILF lesion interferes with transmission of visual information to the VWFA. [17] There is, however, an alternative view that suggests the "VWFA" is devoted to processing of high acuity foveal input, which is particularly salient for complex visual stimuli like letter strings. Studies have highlighted disrupted processing of non-linguistic visual stimuli after damage to the left pFG, both for familiar and unfamiliar objects [18] [19]

Pure alexia exhibits some unexpected residual abilities despite the inability to read words. For instance, one patient had preserved calculation capabilities such as deciding which number was greater, and whether a number was odd or even with greater than chance probability. The study showed that the patient was also able to calculate simple arithmetic tasks such as addition, subtraction, and division, but not multiplication, even though the patient could not read the numbers. For example, the patient would be presented with "8 – 6", and he or she would read it as "five minus four", but still come up with the correct answer "two" with greater than chance accuracy. [20] Pure alexia patients also seem to retain some residual semantic processing. They are able to perform better than chance when forced to make a lexical decision or make a semantic-categorisation decision. [21] These subjects also performed better with nouns than functors, better with words that had high rather than low imageability, and performed poorly with suffixes. However, this may be due to right hemisphere input or residual left hemisphere input. [22]

Research

In patients, a common symptom is letter-by-letter reading or LBL. This action is a compensatory strategy which these patients use in order to come up with a semblance of reading. [9] It is essentially looking at the consonants and vowels of the word and sounding them out as they sound. However, this method does not always work, especially for words like 'phone' where the ph sounds like an f, but if sounded out, does not sound like an f. Also, by reading words in the fashion, the rate at which patients read words is much slower compared to people who do not have this disability. Petersen et al. proved that the issue of reading time had more to do with the length of the words than reading ability. The team had 4 patients with right hemisphere damage and 4 patients with left hemisphere damage in the temporo-occipital lobes as well as 26 controls were shown one word at a time on a screen. They were exposed to 20 words of 3 and 5 letters, 12 words of 7 letters. The subjects were asked to read the words as quickly and as accurately as possible. The patients with left hemisphere lesions consistently read the longer words slower than the controls despite the difficulty of the word. [10] It is thought that as the word gets longer, the letters on the outsides of the word go into peripheral vision, making the patient shift their attention thus making the patient take longer to read.[ citation needed ]

Rehabilitation

Though there have been ample attempts to rehabilitate patients with pure alexia, few have proven to be effective on a large scale. Most rehabilitation practices have been specialized to a single patient or small patient group. At the simplest level, patients seeking rehabilitation are asked to practice reading words aloud repeatedly. This is meant to stimulate the damaged system of the brain. This is known as multiple oral re-reading (MOR) treatment. This is a text-based approach that is implemented in order to prevent patients from LBL reading. MOR works by reading aloud the same text repeatedly until certain criteria are reached. [9] The most important criteria for a pure alexic patient is reading at an improved rate. The treatment aims to shift patients away from the LBL reading strategy by strengthening links between visual input and the associated orthographic representations. This repetition supports the idea of using top-down processing initially minimize the effects peripheral processing which were demonstrated in the study above. [9] [11] From here, the goal is to increase bottom-up processing. This will hopefully aid in word recognition and promote interactive processing of all available information to support reading. 'The supported reading stimulation from MOR has a rehabilitative effect so that reading rate and accuracy are better for untrained text, and word-form recognition improves as evidenced by a reduced word-length effect.' [10] These tactics have seen quite good success. Another tactic that has been employed is the use of cross modal therapy. In this therapy, patients are asked to trace the words in which they are trying to read aloud. There has been success using cross modal therapy such as kinaesthetic or motor-cross cuing therapy, but tends to be a more feasible approach for those on the slower reading end of the spectrum. [23]

Related Research Articles

<span class="mw-page-title-main">Agnosia</span> Inability to process sensory information

Agnosia is a neurological disorder characterized by an inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality, such as vision or hearing. More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.

Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neurological disorders; disorders appearing commonly with agraphia are alexia, aphasia, dysarthria, agnosia, acalculia and apraxia. The study of individuals with agraphia may provide more information about the pathways involved in writing, both language related and motoric. Agraphia cannot be directly treated, but individuals can learn techniques to help regain and rehabilitate some of their previous writing abilities. These techniques differ depending on the type of agraphia.

<span class="mw-page-title-main">Anomic aphasia</span> Medical condition

Anomic aphasia is a mild, fluent type of aphasia where individuals have word retrieval failures and cannot express the words they want to say. By contrast, anomia is a deficit of expressive language, and a symptom of all forms of aphasia, but patients whose primary deficit is word retrieval are diagnosed with anomic aphasia. Individuals with aphasia who display anomia can often describe an object in detail and maybe even use hand gestures to demonstrate how the object is used, but cannot find the appropriate word to name the object. Patients with anomic aphasia have relatively preserved speech fluency, repetition, comprehension, and grammatical speech.

<span class="mw-page-title-main">Parietal lobe</span> Part of the brain responsible for sensory input and some language processing

The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.

<span class="mw-page-title-main">Occipital lobe</span> Part of the brain at the back of the head

The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ob, 'behind', and caput, 'head'.

<span class="mw-page-title-main">Visual memory</span> Ability to process visual and spatial information

Visual memory describes the relationship between perceptual processing and the encoding, storage and retrieval of the resulting neural representations. Visual memory occurs over a broad time range spanning from eye movements to years in order to visually navigate to a previously visited location. Visual memory is a form of memory which preserves some characteristics of our senses pertaining to visual experience. We are able to place in memory visual information which resembles objects, places, animals or people in a mental image. The experience of visual memory is also referred to as the mind's eye through which we can retrieve from our memory a mental image of original objects, places, animals or people. Visual memory is one of several cognitive systems, which are all interconnected parts that combine to form the human memory. Types of palinopsia, the persistence or recurrence of a visual image after the stimulus has been removed, is a dysfunction of visual memory.

<span class="mw-page-title-main">Angular gyrus</span> Gyrus of the parietal lobe of the brain

The angular gyrus is a region of the brain lying mainly in the posteroinferior region of the parietal lobe, occupying the posterior part of the inferior parietal lobule. It represents the Brodmann area 39.

Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. Cortical blindness can be acquired or congenital, and may also be transient in certain instances. Acquired cortical blindness is most often caused by loss of blood flow to the occipital cortex from either unilateral or bilateral posterior cerebral artery blockage and by cardiac surgery. In most cases, the complete loss of vision is not permanent and the patient may recover some of their vision. Congenital cortical blindness is most often caused by perinatal ischemic stroke, encephalitis, and meningitis. Rarely, a patient with acquired cortical blindness may have little or no insight that they have lost vision, a phenomenon known as Anton–Babinski syndrome.

<span class="mw-page-title-main">Posterior cerebral artery</span> Artery which supplies blood to the occipital lobe of the brain

The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifurcates into the left and right posterior cerebral arteries. These anastomose with the middle cerebral arteries and internal carotid arteries via the posterior communicating arteries.

<span class="mw-page-title-main">Commissural fiber</span> Axons that connect the two hemispheres of the brain

The commissural fibers or transverse fibers are axons that connect the two hemispheres of the brain. In contrast to commissural fibers, association fibers connect regions within the same hemisphere of the brain, and projection fibers connect each region to other parts of the brain or to the spinal cord.

<span class="mw-page-title-main">Homonymous hemianopsia</span> Visual field loss on the left or right side of the vertical midline

Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes.

<span class="mw-page-title-main">Posterior cerebral artery syndrome</span> Medical condition

Posterior cerebral artery syndrome is a condition whereby the blood supply from the posterior cerebral artery (PCA) is restricted, leading to a reduction of the function of the portions of the brain supplied by that vessel: the occipital lobe, the inferomedial temporal lobe, a large portion of the thalamus, and the upper brainstem and midbrain.

Deep dyslexia is a form of dyslexia that disrupts reading processes. Deep dyslexia may occur as a result of a head injury, stroke, disease, or operation. This injury results in the occurrence of semantic errors during reading and the impairment of nonword reading.

Auditory agnosia is a form of agnosia that manifests itself primarily in the inability to recognize or differentiate between sounds. It is not a defect of the ear or "hearing", but rather a neurological inability of the brain to process sound meaning. While auditory agnosia impairs the understanding of sounds, other abilities such as reading, writing, and speaking are not hindered. It is caused by bilateral damage to the anterior superior temporal gyrus, which is part of the auditory pathway responsible for sound recognition, the auditory "what" pathway.

The history of dyslexia research spans from the late 1800s to the present.

Phonological dyslexia is a reading disability that is a form of alexia, resulting from brain injury, stroke, or progressive illness and that affects previously acquired reading abilities. The major distinguishing symptom of acquired phonological dyslexia is that a selective impairment of the ability to read pronounceable non-words occurs although the ability to read familiar words is not affected. It has also been found that the ability to read non-words can be improved if the non-words belong to a family of pseudohomophones.

<span class="mw-page-title-main">Visual word form area</span> Region of the brain

The visual word form area (VWFA) is a functional region of the left fusiform gyrus and surrounding cortex that is hypothesized to be involved in identifying words and letters from lower-level shape images, prior to association with phonology or semantics. Because the alphabet is relatively new in human evolution, it is unlikely that this region developed as a result of selection pressures related to word recognition per se; however, this region may be highly specialized for certain types of shapes that occur naturally in the environment and are therefore likely to surface within written language.

<span class="mw-page-title-main">Neuronal recycling hypothesis</span>

The neuronal recycling hypothesis was proposed by Stanislas Dehaene in the field of cognitive neuroscience in an attempt to explain the underlying neural processes which allow humans to acquire recently invented cognitive capacities. This hypothesis was formulated in response to the 'reading paradox', which states that these cognitive processes are cultural inventions too modern to be the products of evolution. The paradox lies within the fact that cross-cultural evidence suggests specific brain areas are associated with these functions. The concept of neuronal recycling resolves this paradox by suggesting that novel functions actually utilize and 'recycle' existing brain circuitry. Once these cognitive functions find a cortical area devoted to a similar purpose, they can invade the existing circuit. Through plasticity, the cortex can adapt in order to accommodate for these novel functions.

<span class="mw-page-title-main">Disconnection syndrome</span> Collection of neurological symptoms

Disconnection syndrome is a general term for a collection of neurological symptoms caused – via lesions to associational or commissural nerve fibres – by damage to the white matter axons of communication pathways in the cerebrum, independent of any lesions to the cortex. The behavioral effects of such disconnections are relatively predictable in adults. Disconnection syndromes usually reflect circumstances where regions A and B still have their functional specializations except in domains that depend on the interconnections between the two regions.

The occipital face area (OFA) is a region of the human cerebral cortex which is specialised for face perception. The OFA is located on the lateral surface of the occipital lobe adjacent to the inferior occipital gyrus. The OFA comprises a network of brain regions including the fusiform face area (FFA) and posterior superior temporal sulcus (STS) which support facial processing.

References

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  2. ↑ Behrmann M, Shomstein SS, Black SE, Barton JJ (2001). "The eye movements of pure alexic patients during reading and nonreading tasks". Neuropsychologia. 39 (9): 983–1002. doi:10.1016/S0028-3932(01)00021-5. PMID   11516450. S2CID   9526540.
  3. ↑ Fiset D, Arguin M, Bub D, Humphreys GW, Riddoch MJ (July 2005). "How to make the word-length effect disappear in letter-by-letter dyslexia: implications for an account of the disorder". Psychol Sci. 16 (7): 535–41. doi:10.1111/j.0956-7976.2005.01571.x. PMID   16008786. S2CID   34286805.
  4. ↑ Warrington EK, Langdon D (February 1994). "Spelling dyslexia: a deficit of the visual word-form". J. Neurol. Neurosurg. Psychiatry. 57 (2): 211–6. doi:10.1136/jnnp.57.2.211. PMC   1072453 . PMID   8126508.
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  6. ↑ Imtiaz KE, Nirodi G, Khaleeli AA (2001). "Alexia without agraphia: a century later". Int. J. Clin. Pract. 55 (3): 225–6. doi:10.1111/j.1742-1241.2001.tb11019.x. PMID   11351780. S2CID   39921061.
  7. ↑ Temple CM (August 2006). "Developmental and acquired dyslexias". Cortex. 42 (6): 898–910. doi:10.1016/S0010-9452(08)70434-9. PMID   17131596. S2CID   4490916.
  8. ↑ Carlson, Neil R. (2013). Physiology of behavior (11th ed.). Boston: Pearson. p. 501. ISBN   978-0-205-23939-9.
  9. 1 2 3 4 5 Kim, E. S., Rising, K., Rapcsak, S. Z., & Beeson, P. M. (2015). "Treatment for Alexia With Agraphia Following Left Ventral Occipito-Temporal Damage: Strengthening Orthographic Representations Common to Reading and Spelling". Journal of Speech, Language, and Hearing Research. 58 (5): 1521–1537. doi:10.1044/2015_JSLHR-L-14-0286. PMC   4686312 . PMID   26110814.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. 1 2 3 4 Petersen, A.; Vangkilde, S.; Fabricius, C.; Iversen, H. K.; Delfi, T. S.; Starrfelt, R. (2016). "Visual attention in posterior stroke and relations to alexia". Neuropsychologia. 92: 79–89. doi:10.1016/j.neuropsychologia.2016.02.029. PMID   26970141. S2CID   8938987.
  11. 1 2 "Imaging". 30 March 2015.
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  13. ↑ "Baylor Neurology Case of the Month". Archived from the original on 2007-05-10. Retrieved 2007-06-07.
  14. ↑ Nolte, John (2009). The human brain: an introduction to its functional anatomy. St. Louis, Mo: Mosby/Elsevier. p. 571. ISBN   978-0-323-04131-7. OCLC   181903953.
  15. ↑ "Alexia". Cognitive Neuropsychology Laboratory. Center for Aphasia Research and Rehabilitation. Retrieved 30 March 2015.
  16. ↑ Montant, Marie; Behrmann, Marlene (2000). "Pure Alexia" (PDF). Neurocase. 6 (4): 265–294. doi:10.1080/13554790008402777. S2CID   220357240 . Retrieved 30 March 2015.
  17. ↑ Epelbaum, S. (2008). "Pure alexia as a disconnection syndrome: New diffusion imaging evidence for an old concept". Cortex. 44 (8): 962–974. doi:10.1016/j.cortex.2008.05.003. PMID   18586235. S2CID   14956468.
  18. ↑ Roberts, DJ; Woollams, AM; Kim, E; Beeson, PM; Rapcsak, SZ; Lambon Ralph, MA (24 August 2012). "Efficient Visual Object and Word Recognition Relies on High Spatial Frequency Coding in the Left Posterior Fusiform Gyrus: Evidence from a Case-Series of Patients with Ventral Occipito-Temporal Cortex Damage". Cerebral Cortex. 23 (11): 2568–2580. doi:10.1093/cercor/bhs224. PMC   3792736 . PMID   22923086.
  19. ↑ Roberts, DJ; Lambon Ralph, MA; Kim, ES; Tainturier, MJ; Beeson, PM; Rapcsak, SZ; Woollams, AM (November 2015). "Processing deficits for familiar and novel faces in patients with left posterior fusiform lesions". Cortex. 72: 79–96. doi:10.1016/j.cortex.2015.02.003. PMC   4643682 . PMID   25837867.
  20. ↑ Cohen, L. (2000). "Calculating Without Reading: Unsuspected Residual Abilities In Pure Alexia". Cognitive Neuropsychology. 17 (6): 563–583. doi:10.1080/02643290050110656. PMID   20945195. S2CID   926892.
  21. ↑ Roberts, DJ; Lambon Ralph, MA; Woollams, AM (July 2010). "When does less yield more? The impact of severity upon implicit recognition in pure alexia". Neuropsychologia. 48 (9): 2437–2446. doi:10.1016/j.neuropsychologia.2010.04.002. PMID   20406652. S2CID   29783028.
  22. ↑ Coslett, H.B. (1989). "Evidence For Preserved Reading In 'Pure Alexia'". Brain. 112 (2): 327–359. doi:10.1093/brain/112.2.327. PMID   2706436.
  23. ↑ Leff, Alexander P.; Schofield, T. M. "Rehabilitation of acquired alexia". International Encyclopedia of Rehabilitation. Center for International Rehabilitation Research Information and Exchange. Retrieved 30 March 2015.


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