Neural mechanism of reading and writing in the Japanese language

Three Japanese patients presenting with pure alexia showed agraphia for Kanji in addition. A left angular gyrus lesion caused agraphia for both Kanji and Kana, but Kanji reading was preserved. A left posterior inferior temporal (PIT) lesion resulted in alexia and agraphia for Kanji, while the Kana function was preserved. These results imply that the semantic processing of reading Kanji words depends upon the left PIT area, while the phonological reading of Kana is mediated by the left angular gyrus. The PIT area also plays an important role in writing Kanji words.     

A case of alexia with agraphia following left occipital lobe

Since Dejerine reported cases of alexia with agraphia in 1891 and of pure alexia in 1892, it is generally said that the former may occur due to the lesion of the left angular gyrus and the latter due to that of the medial inferior area of the left occipital lobe. In this article, we reported a case of alexia with agraphia who had the main lesion in the medial inferior area of the occipital lobe of the left hemisphere. A 62-year-old right-handed male showed alexia with agraphia. CT scan and single photon emission CT revealed the main lesion in the medial occipital area on the left side. Alexia with agraphia of the patient was characterized as follows: with regard to reading, though his recognition of forms as letter was nearly spared, he could neither read letters or words nor differentiate Kana- from Kanji-letters. Paralexic errors included confusion of Kana and Kanji. He manifested no kinesthetic facilitation in reading. Regarding writing, his disturbances were more severe in Kanji-writing, but there were paragraphia and difficulty of letter-form evocation even in Kana-writing. He could not write spontaneously or to dictation. His copying of letters was also disturbed. Since it is said that there is no difference between Kana- and Kanji-disturbance in Japanese pure alexics, an aspect of alexia of the patient may be common to pure alexia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dorsal type letter-by-letter reading accompanying alexia with agraphia due to a lesion of the lateral occipital gyri

ABSTRACT

We report a patient with alexia with agraphia accompanied by letter-by-letter reading after hemorrhage in the left middle and inferior occipital gyri that spared the angular gyrus and the fusiform gyrus. Kanji (Japanese morphograms) and kana (Japanese phonetic writing) reading and writing tests revealed that alexia with agraphia was characterized by kana-predominant alexia and kanji-predominant agraphia. This type of “dorsal” letter-by-letter reading is discernable from conventional ventral type letter-by-letter reading that is observed in pure alexia in that (1) kinesthetic reading is less effective, (2) kana or literal agraphia coexists, and (3) fundamental visual discrimination is nearly normal.     

Different neural substrates for Kanji and Kana writing: a PET study

To investigate the neural substrate underlying the mechanisms of Kanji and Kana writing, we conducted a PET activation study during mental writing task in eight right-handed normal Japanese subjects. During scans subjects were required to mentally write a Kanji or three Kana letters with their right hand, for each stimulant word presented auditorily. The direct comparisons between Kanji writing and Kana writing revealed that the left posterior inferior temporal gyrus was activated in Kanji writing while the left angular gyrus was activated in Kana writing. In addition, more extensive areas were activated in Kanji writing compared with Kana writing. These results suggest that different respective neural substrates are involved in Kanji and Kana writing respectively.     

Ideogram reading in alexia.

A case of alexia with agraphia in a Japanese patient is presented. Reading difficulty was severe in words composed of phonograms (Kana), while reading of words composed of Ideograms (Kanji) was better preserved. Writing was severely impaired in both types of characters. Occlusion of the angular branch of the left middle cerebral artery was demonstrated by carotid arteriography and was considered responsible for the symptoms. Two additional cases of alexia with agraphia from the Japanese literature are reviewed. Their linguistic features were similar to the present case. A hypothesis of a functional disconnexion between visual and auditory-oral systems is proposed to explain why Kana processing was more severly affected than Kanji processing.     

A case of pure agraphia due to left parietal lobe infarction]

We reported a case of an 86-year old woman with pure agraphia due to the left parietal lobe infarction. The characteristics of agraphia were as follows. Most errors in Kana and Kanji writing to dictation and copying were no response. She was able to write only numerals from 1 to 12 precisely. Most errors in numerals were substitution. One unrecognizable numeral was found. She succeeded in pointing to nine among ten single Kana letter named by the examiner with the systematic table of the Japanese syllabary, but missed in pointing to Kana words. It took more time for the patient to point to single Kana letter than the control. Magnetic resonance imaging showed a cerebral infarction in the left parietal lobe which included a part of superior parietal lobule and supramarginal gyrus. We classified pure agraphia with parietal lobe infarction into two types in our previous report. In one type (type 1), letters in writing are poorly formed, but the ability to make words with the methods other than writing are reserved. The only deficit of graphic motor pattern could cause Type 1 agraphia. In another type (type 2), letters in writing were well-formed, but spelling with anagram or typing was disturbed. The deficits of writing process other than graphic motor pattern could cause Type 2 agraphia. This typing seems to be effective not only in Kana but also in Kanji. In this report, we investigated the differences of lesion between two types out of some references. Type1 agraphia seems related to lesion of left superior parietal lobule, while Type 2 agraphia seems related to lesion of left supramarginal gyrus. This case had the features of type 2 agraphia at least, and the compatible lesions.     

Pure agraphia after infarction in the superior and middle portions of the left precentral gyrus: Dissociation between Kanji and Kana

The present study describes a Japanese patient with pure agraphia displaying differential disturbances in processing Kanji (morphogram) and Kana (syllabogram) letters after an infarction in the middle and superior portions of the left precentral gyrus. Kana errors reflected the patient’s difficulty with retrieving both motor and visual letter images, whereas Kanji errors included partial letter stroke omissions or additions. This present case suggests that differences in writing disturbances between Kana and Kanji letters are caused by a differential dependency on letter motor images.     

Cerebral localization of the center for reading and writing music

The mechanisms that underlie the ability to read and write music remain largely unclear compared to those involved in reading and writing language. We had the extremely rare opportunity to study the cerebral localization of the center for reading and writing music in the case of a professional trombonist. During rehearsal immediately before a concert, he suffered a hemorrhage that was localized to the left angular gyrus, the area that has long been known as the center for the ability to read and write. Detailed tests revealed that he showed symptoms of alexia with agraphia for both musical scores and language.     

A case of pure agraphia with a deficit of drawing]

We examined a drawing ability in a case with pure agraphia. The patient, having lesions in the left middle frontal gyrus and inferior parietal lobule, could not write in both dictation and spontaneous writing tasks, with the ability to copy letters being well spared. Correspondingly, he showed a deficit of spontaneous drawing, with the ability to copy complex figures being well spared. These findings suggest that he could have an impairment of retrieving visual image, not restricted to letter image. Although some previous cases with pure agraphia were attributed to an impairment of retrieving visual letter image, drawing ability which seemed to be related to retrieving visual image had not been investigated. In the present case, disability of both writing and drawing could be attributed to a common mechanism, that was an impairment of retrieving visual image. In addition, the patient did not show a significant difference between the performance on Kana writing and on Kanji writing. But it has been said that an impairment of retrieving visual letter image could be related to a deficit of Kanji writing more than of Kana writing. Then, it could be assumed that the mechanism of Kana writing involved not only the pathway depending on graphical motor pattern but one depending on visual image.     

Dual neural circuit model of reading and writing

In the hypothetical neural circuit model of reading and writing that was initially proposed by Dejerine and subsequently confirmed by Geschwind, the left angular gyrus was considered as a unique center for processing letters. Japanese investigators, however, have repeatedly pointed out that this angular gyrus model cannot fully explain the disturbances observed in reading and writing Kanji letters in Japanese patients with various types of alexia with or without agraphia. In 1982, I proposed a dual neural circuit model of reading and writing Japanese on the basis of neuropsychological studies on the various types of alexia with or without agraphia without aphasia. This dual neural circuit model proposes that apart from the left angular gyrus which was thought to be a node for phonological processing of letters, the left posterior inferior temporal area, also acts as a node for semantic processing of letters. Further investigations using O15-PET activation on normal subjects revealed that the left middle occipital gyrus (area 19 of Brodmann) and the posterior portion of the left inferior temporal gyrus (area 37 of Brodmann) are the cortical areas responsible for reading Japanese letters; the former serving for phonological reading and the latter for semantic reading. This duality of the neural circuit in processing letters was later applied to explain disturbances in reading English, and was finally accepted as a valid model for other alphabetic letter systems too.     

Selective Kana agraphia: a case report

We present a Japanese man with selective Kana (phonogram) agraphia as a sequela of two cerebral infarctions in a part of the left angular gyrus and its adjoining posterior superior temporal gyrus and the left corona radiata. The agraphia of this patient showed the following features: (1) His writing difficulty was greater for Kana than for Kanji (ideogram) when a word was polysyllabic. (2) Kana errors consisted of perseveration and substitution with another letter, resulting in jargon agraphia. (3) This jargon agraphia often contained a correct number of letters for a target word. Based on these findings, we speculate that the basic defect of this agraphia lies in the process of converting an acoustic word image into a Kana motor grapheme sequence.     

Alexia caused by a fusiform or posterior inferior temporal lesion

We evaluated the alexia and agraphia of three patients with different lesions using Japanese kanji (morphograms) and kana (phonograms) and made a lesion-to-symptom analysis. Patient 1 (pure alexia for both kanji and kana and minor agraphia for kanji after a fusiform lesion) made more paragraphic errors for kanji, whereas patient 2 (alexia with agraphia for kanji after a posterior inferior temporal lesion) showed severe reading and writing disturbances and more agraphic errors for kanji. Brodmann Area 37 was affected in both patients, but in patient 2 the lesion was located lateral to that in patient 1. Patient 3 showed agraphia without alexia after restricted lesion to the angular gyrus. We believe that pure alexia (patient 1) results from a disconnection between the medial fusiform gyrus and posterior inferior temporal area (the lateral fusiform and inferior temporal gyri), whereas alexia with agraphia for kanji (patient 2), corresponding to lexical agraphia in Western countries, results from damage to the posterior inferior temporal area, in which whole-word images of words are thought to be stored. Furthermore, restricted lesion in the angular gyrus (patient 3) does not produce alexia; the alexic symptom of "angular" alexia with agraphia may be the result of damage to the adjacent lateral occipital gyri.     

Rehabilitation of pure alexia: A review

Acquired reading problems caused by brain injury (alexia) are common, either as a part of an aphasic syndrome, or as an isolated symptom. In pure alexia, reading is impaired while other language functions, including writing, are spared. Being in many ways a simple syndrome, one would think that pure alexia was an easy target for rehabilitation efforts. We review the literature on rehabilitation of pure alexia from 1990 to the present, and find that patients differ widely on several dimensions, such as alexia severity and associated deficits. Many patients reported to have pure alexia in the reviewed studies, have associated deficits such as agraphia or aphasia and thus do not strictly conform to the diagnosis. Few studies report clear and generalisable effects of training, none report control data, and in many cases the reported findings are not supported by statistics. We can, however, tentatively conclude that Multiple Oral Re-reading techniques may have some effect in mild pure alexia where diminished reading speed is the main problem, while Tacile-Kinesthetic training may improve letter identification in more severe cases of alexia. There is, however, still a great need for well-designed and controlled studies of rehabilitation of pure alexia.     

Mechanisms of reading and spelling in a case of alexia without agraphia

In the clinical syndrome of alexia without agraphia, reading is greatly disturbed while writing and spelling remain relatively intact. The most commonly accepted explanation of this pattern of findings is that the center for written language interpretation remains intact, but has become inaccessible to visual input. This paper examines the nature of the intact written language center with respect to specific mechanisms of reading and spelling in a patient presenting with the major components of alexia without agraphia. It is concluded that the dissociation between reading and writing performance found in this patient reflects the existence of separate and distinct mechanisms for reading and spelling.     

A case of alexia with agraphia caused by the re-infarct in left lateral occipital gyrus]

The angular gyrus has been proposed as the key area of reading and writing function. In recent PET (positron emission topography) activation studies, role of angular gyrus in the reading and writing has been reestimated. Whether the angular gyrus is necessary for reading and writing or not is now under discussion and should be clinically revised. We experienced a case that presented classical alexia with agraphia of kana (Japanese syllabogram) caused by the re-infarct in left lateral occipital gyrus. This case showed the alexia with agraphia more apparent in Japanese kana than in kanji characters. Interestingly, no higher cortical dysfunction was revealed at the first cerebral infarction in left angular gyrus which was assumed as the key area for alexia with agraphia. This case supported the opinion which pointed out the importance of left occipital gyrus on Japanese kana reading.     

Pure alexia caused by separate lesions of the splenium and optic radiation

Pure alexia is severe difficulty in reading and understanding written language but with normal oral language and writing abilities. We report a patient with pure alexia caused by two different infarct lesions in the left lateral thalamus and the left splenium of the corpus callosum. A 56-year-old right-handed man was admitted to hospital with right homonymous hemianopia associated with pure alexia. He could write kana characters but not kanji. His cranial magnetic resonance imaging revealed two different infarct lesions in the left optic radiation and the left splenium of the corpus callosum. Magnetic resonance angiography showed mild stenosis at the origin of the right vertebral artery and stenosis of the left distal posterior cerebral artery. The mechanism of developing pure alexia can be simply explained by disconnection. We assumed that agraphia of kanji was caused by the effect of ischemia and edema following transient obstruction in branches from the distal posterior cerebral artery.     

Pure alexia in Japanese and agraphia without alexia in kanji. The ability dissociation between reading and writing in kanji vs kana

A 60-year-old right-handed Japanese man with infarction of the left occipital lobe and inferior temporal gyrus initially showed pure alexia in kana and kanji. Later, though pure alexia in kana persisted, his kanji reading improved markedly, but with little improvement of kanji writing. We speculate that different pathways are involved in kanji reading and writing. Wernicke's area and its surrounding left middle temporal lobe might play the most important role for kanji reading when visual information is transmitted by any pathway. The pathway from Wernicke's area to the left occipital lobe via the middle and inferior temporal pathway may be indispensable for kanji writing. We postulate "agraphia without alexia in kanji" due to left inferior temporal subcortical damage.     

The nature and treatment of phonological text agraphia

Phonological alexia and agraphia are written language disorders characterised by disproportionate difficulty reading and spelling nonwords in comparison to real words. In phonological alexia, it has been shown that, despite relatively accurate reading of words in isolation, text-level reading deficits are often marked and persistent. Specifically, some individuals demonstrate difficulty reading functors and affixes in sentences, a profile referred to as phonological text alexia. In this paper, we demonstrate an analogous manifestation of the phonological impairment on text-level writing and suggest the term “phonological text agraphia”. We examined four individuals with phonological alexia/agraphia who also showed disproportionate difficulty writing well-formed sentences in comparison to their grammatical competence in spoken utterances. Implementation of a phonological treatment protocol resulted in significantly improved sublexical phonology skills as well as improvements in grammatical accuracy of written narratives. These findings support the notion of a common phonological impairment underlying nonword reading/spelling deficits and sentence-level difficulties.