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.     

Mechanisms of writing]

Writing impairments are caused by various different mechanisms and lesions. The left posterior inferior temporal lobe plays the important role in retrieving the morphograms of the characters. Therefore the lesions involving this region have more effect on Kanji (Japanese morphogram) than on Kana (Japanese phonogram). The angular gyrus is considered to maintain the retrieved letter/character information and convert the naive information into writing performance. Sometimes Kana dominant impairment is detected due to this lesion because in some persons may have the direct route from phonemic presentation into writing execution process without definite retrieval of its form or morphology. The left superior parietal lobule is associated to the writing execution, thus, the lesion in this region induces the impairment of writing stroke and ill-shaped characters. The posterior part of the left middle frontal gyrus is related to select and arrange the letters to make a word, so the lesion in this area will develop paragraphia, in particular replacement of the letters within a word. Recently, the typing of the keyboard is becoming more popular in our everyday life. Reflecting this phenomenon, specific typing impairment called dystypia is reported. It is supposed that there is the impairment between linguistic process and typing execution.     

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.     

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.     

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.     

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)     

Neural substrates for writing impairments in Japanese patients with mild Alzheimer's disease: a SPECT study

Language is fairly well preserved in most patients with mild Alzheimer's disease, but writing ability seems to be impaired even in the early stages of the disease. To investigate the neural bases of writing impairments in Alzheimer's disease (AD), we examined the correlation between writing ability and regional cerebral blood flow (rCBF) in 52 Japanese patients with mild AD compared to 22 controls, using single photon emission computed tomography (SPECT). We found that, compared with control subjects, Kana writing to dictation and copying Kanji words were preserved in AD patients, but writing to dictating Kanji words was impaired. We classified the errors in the Kanji dictation task into four types to investigate the correlation between rCBF and the error type, as follows: non-response errors, phonologically plausible errors, non-phonologically plausible errors, and peripheral errors. Non-response errors, which indicated difficulty with retrieving Kanji graphic images, were the most frequent. When controlled for confounding factors, the number of non-response errors negatively correlated with rCBF in the left inferior parietal lobule, the posterior middle and inferior temporal gyri, and the posterior middle frontal gyrus. Thus, the impaired recall of Kanji in early Alzheimer's disease is related to dysfunctional cortical activity, which appears to be predominant in the left frontal, parietal, and temporal regions.     

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.     

Reading and writing Japanese: Kanji versus Kana]

In my talk, I reviewed studies on the neural substrates of Kanji vs. Kana, two types of Japanese characters, written since the 1980s. More Specifically, I reviewed the development of the studies on (1) Kanji and Kana in pure alexia/agraphia, (2) alexia with agraphia of Kanji and (3) 'musical letters' vs. 'literary letters', and reported new findings from those studies. In the 1980s, we frequently studied patients with partial callosal lesions and those with pure alexia, and many of the studies were on the neural substrates of Kanji vs. Kana. Later, we discovered cases of alexia with agraphia of Kanji caused by lesions in the posterior part of the left inferior temporal gyrus, leading us to understand the neural substrates of Kanji and Kana in more detail. In addition to the reading and writing of 'literary letters', we studied the neural mechanisms of the reading and writing of 'musical letters', i.e. musical scores. Our study showed that the neural mechanisms of reading and writing musical scores were similar to those of reading and writing 'literary letters' in professional musicians, although those neural mechanisms varied slightly.     

Kanji-predominant alexia with agraphia in opticospinal multiple sclerosis]

Alexia with agraphia is very rare symptom in multiple sclerosis. We present a patient of opticospinal multiple sclerosis with kanji-predominant alexia with agraphia. A 55-year-old, right-handed man was admitted to our hospital because of difficulty in reading and writing in August 2001. The patient had been diagnosed as having relapsing-remitting opticospinal multiple sclerosis eight years prior to admission. Language examination showed alexia with agraphia predominantly affecting kanji and also mild naming difficulties, but a good comprehension and a normal repetition. T2-weighted MRI demonstrated hyperintensity area in the left temporo-parietal lobe, involving the white matter beneath the postero-inferior temporal lobe and inferior parietal lobule. On brain SPECT, low blood perfusion was observed in the left temporo-parietal regions. Although agraphia for kana and alexia for both kana and kanji improved after steroid therapy, agraphia for kanji did not improve. After the treatment, high intensity area of inferior parietal lobule was disappeared on MRI, and the hypoperfusion of inferior parietal lobule on brain SPECT was also improved, but the lesion of left postero-inferior temporal lobe did not show any remarkable changes. We considered that the kanji-predominant alexia with agraphia was due to the lesions of left inferior parietal lobule and postero-inferior temporal lobe, and agraphia for kanji was due to the lesion of left postero-inferior temporal lobe.     

Right hand agraphia and left hand apraxia following callosal damage in a right-hander

A right-handed Japanese man showed agraphia more marked with the right hand, apraxia confined to the left hand, and right ear extinction on dichotic listening, following damage to the anterior two-thirds of the corpus callosum, the rostral and lower parts of the right medial frontal lobe and a small portion of the left medial frontal lobe. The symptoms were attributed to hemispheric disconnection, on the assumption that the right hemisphere was dominant for language and the left for limb praxis. This case provides good evidence for dissociated lateralization of language and limb praxis in some right-handed individuals. The study of writing performance suggested the following hypotheses: (1) motor engrams for limb praxis and writing may be dissociated, and (2) motor engrams for writing Kana (phonogram) and Kanji (ideogram) letters are represented on both hemispheres, although the hemisphere nondominant for language seems unable to combine graphemes into a correct meaningful sequence.     

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.     

Alexia and agraphia with lesions of the angular and supramarginal gyri: Evidence for the disruption of sequential processing

ObjectiveTo determine the features of alexia or agraphia with a left angular or supramarginal gyrus lesion.MethodsWe assessed the reading and writing abilities of three patients using kanji (Japanese morphograms) and kana (Japanese syllabograms).ResultsPatient 1 showed kana alexia and kanji agraphia following a hemorrhage in the left angular gyrus and the adjacent lateral occipital gyri. Patient 2 presented with minimal pure agraphia for both kanji and kana after an infarction in the left angular gyrus involving part of the supramarginal gyrus. Patient 3 also showed moderate pure agraphia for both kanji and kana after an infarction in the left supramarginal and postcentral gyri. All three patients made transposition errors (changing of sequential order of kana characters) in reading. Patient 1 showed letter-by-letter reading and a word-length effect and made substitution errors (changing hiragana [one form of kana] characters in a word to katakana [another form of kana] characters and vice versa) in writing.ConclusionAlexia occurs as “angular” alexia only when the lesion involves the adjacent lateral occipital gyri. Transposition errors suggest disrupted sequential phonological processing from the angular and lateral occipital gyri to the supramarginal gyrus. Substitution errors suggest impaired allographic conversion between hiragana and katakana attributable to a dysfunction in the angular/lateral occipital gyri.     

Pure agraphia. Apropos of 2 cases

Pure agraphia is a disorder of written language without aphasia, alexia or apraxia. Its existence has long been disputed. We report 2 cases due to a left parietal hematoma. In the first patient, with a deep precuneate lesion, agraphia included disorders in handwriting and orthographic problems in copying or writing from dictation with the two hands. The second patient, with a lesion of the postero-inferior part of the left angular gyrus, made errors in choice and combination of letters during dictation, whereas these same letters were well-written and copying was normal. The first cases of pure agraphia were ascribed to frontal lesions and then confusional states. Current opinion tends to implicate parietal lesions of various types: superior or inferior, internal or external. Findings in the present 2 cases and those reported indicate that pure parietal agraphia is heterogeneous.     

Tachistoscopic recognition of normal and mirror images of Kana and Kanji characters

Accuracy of recognition was investigated for normal and mirror images of Kana (syllabic symbols) and Kanji (ideographic symbols) characters tachistoscopically presented in the left and right visual fields in normal right-handed Japanese subjects. A significant right field superiority was obtained for the recognition of each type of normal letter. In the case of mirrored letters, Kanji characters were better recognized in the right field while no lateral asymmetry for the recognition of Kana characters was shown. The results indicated that Kanji processing is somewhat different from the processing of Kana characters.     

Tachistoscopic Recognition of Normal and Mirror Images of Kana and Kanji Characters

Abstract: Accuracy of recognition was investigated for normal and mirror images of Kana (syllabic symbols) and Kanji (ideographic symbols) characters tachistoscopically presented in the left and right visual fields in normal right-handed Japanese subjects. A significant right field superiority was obtained for the recognition of each type of normal letter. In the case of mirrored letters, Kanji characters were better recognized in the right field while no lateral asymmetry for the recognition of Kana characters was shown. The results indicated that Kanji processing is somewhat different from the processing of Kana characters.     

Pure "aphasic" agraphia due to damage of the left superior parietal lobule

A case of pure agraphia, due to an ischaemic lesion of the left superior parietal lobule, is reported. The neuropsychological analysis of writing performances suggests an aphasic nature of this patient's pure agraphia. The authors discuss the role played by diffuse and/or localized brain lesions in writing function, emphasizing that the left superior parietal lobule in man may be crucial for the sensorimotor linguistic integration needed for writing.     

Pure “aphasic” agraphia due to damage of the left superior parietal lobule

A case of pure agraphia, due to an ischaemic lesion of the left superior parietal lobule, is reported. The neuropsychological analysis of writing performances suggests an aphasic nature of this patient's pure agraphia. The authors discuss the role played by diffuse and/or localized brain lesions in writing function, emphasizing that the left superior parietal lobule in man may be crucial for the sensorimotor linguistic integration needed for writing.     

Isolated thalamic agraphia with impaired grapheme formation and micrographia

Two patients with isolated thalamic agraphia are described. Both showed kanji (Japanese morphograms) agraphia due to impaired character recall, grapheme deformity and micrographia (progressive reduction in character size during writing) after a lesion that involved the ventral lateral and ventroposterolateral nuclei. Single photon emission computed tomography with a ^99mTc-ethylcysteinate dimer revealed hypoperfusion in the left precentral gyrus (Brodmann Area 6) and anterior supramarginal gyrus in both. Six months later, the extent of blood flow reduction decreased in the supramarginal gyrus in both patients and the precentral gyrus in patient 1. By this time, the writing impairment improved to nearly the normal range. Our study suggests that kanji agraphia (corresponding to lexical agraphia in Western countries) with poor grapheme formation and micrographia arises from a lesion in the ventral lateral and ventroposterolateral nuclei in the left thalamus. The accompaniment of poor grapheme formation and micrographia may reflect disruption of the cortico-subcortical motor circuit involving the putamen, thalamus, premotor cortex and sensorimotor cortex. It is also suggested that multiple cortical sites can be a target for secondary dysfunction that yields agraphia in a thalamic lesion, and that the recovery of reduced cortical blood flow does not always proceed in parallel with that of agraphia.     

Functional dissociation between Kana and Kanji: agraphia following a thalamic hemorrhage

We report the case of a 61-year-old woman with a left thalamic hemorrhage causing agraphia of Kanji (morphograms). Single-photon emission computed tomography (SPECT) showed a decrease in the blood flow in the left thalamus from the superior temporal convolution to the parietal lobe, as well as in the frontal lobe while computed tomography showed no remarkable lesions in the cortex. The agraphia in this case may be due to the thalamic lesion itself, but the SPECT findings strongly suggest that a secondary cortical lesion may be involved in producing the higher cognitive disorder.