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.     

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.     

Fusiform type alexia: pure alexia for words in contrast to posterior occipital type pure alexia for letters

OBJECTIVE: To clarify the behavioral differences between patients with pure alexia from different lesions. METHODS: Two patients with pure alexia caused by damage to the fusiform or posterior occipital gyri were given reading and writing tests including kanji (Japanese morphograms) and kana (Japanese phonetic writing). RESULTS: Patient 1 (pure alexia from a fusiform gyrus lesion) had difficulty reading both kanji and kana, with kanji reading more impaired, and imageability and visual complexity effects (imageable or less complex words/characters were read better than nonimageable or more complex words/characters), whereas patient 2 (pure alexia from a posterior occipital gyri lesion) showed selective impairment of kana reading. CONCLUSION: Pure alexia for kanji (and kana; fusiform type) is characterized by impairments of both whole-word reading, as represented in kanji reading, and letter identification, and is different from pure alexia for kana (posterior occipital type) in which letter identification is primarily impaired. Thus, fusiform type pure alexia should be designated pure alexia for words, whereas posterior occipital type pure alexia should be designated pure alexia for letters.     

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.     

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.     

Temporal lobe epilepsy manifesting as alexia with agraphia for kanji

Alexia with agraphia results from lesions of the left angular gyrus or the left posteroinferior temporal lobe. In Japanese or Korean persons, lesions of the latter cause alexia with agraphia for ideograms. We describe a case of alexia with agraphia for kanji (Japanese ideograms) caused by temporal lobe epilepsy. After generalized convulsions, a 32-year-old man noticed that he had difficulty in reading and writing kanji, although he could read and write kana (Japanese syllabograms). His EEG showed frequent sharp waves on the left occipitotemporal region. MRI of the brain revealed a hyperintense lesion on the left hippocampus. Single-photon-emission computed tomography revealed marked hyperperfusion at the left hippocampus and the left posteroinferior temporal cortex. Antiepileptic drugs improved his alexia with agraphia for kanji. This is the first report describing alexia with agraphia for kanji caused by temporal lobe epilepsy.     

The Eye Movements of Japanese Pure Alexic Patients During Single Word and Nonword Reading

Abstract

Two Japanese patients with pure alexia, SH and YH, who showed right homonymous hemianopia following a left occipital lobe lesion, demonstrated letter-by-letter (LBL) reading in pronouncing Japanese kana words and nonwords. In contrast to alphabetic letters, each Japanese kana character has an invariant and identical pronunciation whether it appears in isolation or as a component of any word and nonword string. It is important to investigate the eye movements as well as reading latency and duration in Japanese-speaking LBL readers. Relative to normal controls, these patients demonstrated a more robust string-length effect, which was characterized by larger increases in reading latency and duration as well as in the number of fixations as the string length increased. We propose that in pure alexia, parallel activation of orthographic representations is abnormally delayed but not completely abolished.     

Alexia with agraphia of kanji (Japanese morphograms).

The case of the right-handed young Japanese woman with alexia with agraphia of kanji (the Japanese morphograms) due to a small circumscribed haematoma in the left posterior inferior temporal gyrus is described. Her chief complaint was the inability to read and write kanji. Detailed examination showed that her alexia with agraphia was much more predominant for kanji than kana (the Japanese syllabograms). These facts suggest that the processing of kanji and kana involves different intrahemispheric mechanisms.     

Differential Reorganization of Fusiform Gyrus in Two Types of Alexia after Stroke

Lesions affecting the left fusiform gyrus (FG) commonly result in dyslexia and recovery largely depends on efficient reorganization of the reading network. We performed a follow-up fMRI study to elucidate the reorganization patterns of the FG according to the recovery of reading ability in two patients (MH with pure alexia and KM with alexia with agraphia) after stroke involving the left FG. Initially, MH was an effortful letter-by-letter (LBL) reader, and she improved to become a proficient LBL reader. The initial fMRI results showed scattered activation on occipital and ventral temporal cortex during reading, which was localized to right FG in the follow-up study. KM's severe alexia with agraphia did not improve, even after 6 months had passed since the onset of the alexia. The initial and follow-up fMRI results showed no significant activation in the bilateral FG or central higher language areas during word reading. Our results suggest that the reorganization of the FG is different according to the type of alexia and the amount of clinical recovery in each patient. Also, the successful reorganization of the visual component of reading in the right FG is responsible for the recovery of LBL reading in pure alexia.     

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.     

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.     

Neural mechanism of reading]

We conducted positron emission tomography studies on reading and found that two distinct areas were activated, i.e. the left fusiform/inferior temporal gyri (posterior inferior temporal cortex, Area 37) by kanji words and the fusiform/inferior occipital gyri (posterior occipital gyri, Area 18/19) by kana words. Clinically, alexia and agraphia for kanji is caused by a posterior inferior temporal cortex lesion. Moreover, pure alexia more impaired for kanji results from a fusiform gyrus lesion, whereas pure alexia for kana occurs because of damage to the posterior occipital gyri. These experimental and clinical findings suggest that impaired letter identification in Area 18/ 19 causes pure alexia for kana, disrupted visual images of words in Area 37 results in alexia with agraphia for kanji, and impaired access to the visual image storage (Area 37) yields pure alexia dominantly disturbed for kanji.     

Pure alexia for kana. Characterization of alexia with lesions of the inferior occipital cortex

OBJECTIVE: To characterize reading impairments caused by lesions in the posterior occipital cortices. METHODS: We gave six patients with these lesions reading and writing tests and located a critical site for alexia using MRI and SPECT. RESULTS: The patients read three-character kana (Japanese syllabograms) nonwords, and five-character kana nonwords significantly or at a near significant level more poorly and slowly than normal subjects, whereas they read kanji (Japanese morphograms) almost correctly but more slowly. Letter-by-letter reading with a single-kana character identification impairment (in five patients), a word-length effect, kinesthetic facilitation, a lexicality effect, and minor to mild agraphia for kanji (in three patients) were observed. These deficits were characteristic of pure alexia. Alexia disappeared within a few months except in one patient who had extensive hypoperfusion in the left occipital lobe. A shared lesion was located in the left posterior fusiform/inferior occipital gyri (Area 18/19) on MRI, and there was blood flow reduction around this area on SPECT. This area coincided with the activation site for kana word covert reading in our previous study. CONCLUSIONS: These results suggest that pure alexia particularly for kana, or more generally pure alexia for letters, is caused by a lesion in the posterior inferior occipital cortex, characterized primarily by impaired kana character or letter identification, with relatively preserved kanji or word recognition.     

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.     

"Apperceptive" alexia in posterior cortical atrophy

The most common presenting complaint in posterior cortical atrophy (PCA) is reading difficulty. Although often described as an alexia without agraphia, alexia in PCA may have multiple causes, including a primary visuoperceptual etiology, attentional alexia, and central reading difficulty. This study evaluated 14 patients with early PCA and disturbances in reading ability in comparison to 14 normal controls. All 14 patients had a progressive disorder of complex visual functions and neuroimaging evidence of occipitoparietal dysfunction. They underwent a task requiring identification of single letters with and without flanking distractors. They also read single words consisting of regular English spelling or irregular grapheme-phoneme correspondence (irregular words) and pronounceable nonsense words (pseudowords). The PCA patients made errors in letter identification when letters were flanked by visually similar letters or numbers. They could read most single regular and irregular words but made visual errors and had particular trouble with pseudowords. They could not use a letter-by-letter reading strategy effectively. The PCA patients had similar difficulties on other visuoperceptual tests. These findings are consistent with an alexia manifested by perceptual and attentional difficulty on attempting serial visual processing of letters in the context of other letters. This "apperceptive alexia" results when the configuration of letters into words is impaired during letter-by-letter reading. Disproportionate difficulty reading pseudowords suggests an additional impairment in phonological processing. PCA patients have variable neuropathology and individual patients may have other contributions to their reading impairment.     

The eye movements of Japanese pure alexic patients during single word and nonword reading

Two Japanese patients with pure alexia, SH and YH, who showed right homonymous hemianopia following a left occipital lobe lesion, demonstrated letter-by-letter (LBL) reading in pronouncing Japanese kana words and nonwords. In contrast to alphabetic letters, each Japanese kana character has an invariant and identical pronunciation whether it appears in isolation or as a component of any word and nonword string. It is important to investigate the eye movements as well as reading latency and duration in Japanese-speaking LBL readers. Relative to normal controls, these patients demonstrated a more robust string-length effect, which was characterized by larger increases in reading latency and duration as well as in the number of fixations as the string length increased. We propose that in pure alexia, parallel activation of orthographic representations is abnormally delayed but not completely abolished.     

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.     

Anomic alexia of kanji in a patient with anomic aphasia

The ability to read aloud kanji (logogram) words and to comprehend their meaning was systematically examined to clarify the underlying mechanism of kanji alexia in a patient with anomic aphasia. Confrontation naming, reading aloud and reading comprehension tasks were performed using 110 words from 11 semantic categories written in kanji or kana. Performance in oral reading of kanji words was significantly worse than oral reading of the same words transcribed into kana words. In addition, for kanji words reading aloud was much worse than reading comprehension. Oral reading of kanji words had a significant correlation with naming pictures corresponding to the words, but no correlation with comprehension of kanji words. Qualitative analyses demonstrated that errors in oral reading and naming tasks had many features in common. Our results indicated that some common mechanisms underlie both naming and oral reading of kanji words. We propose calling this type of alexia "anomic alexia of kanji", which should be distinguished from kanji alexia with difficulty in both reading aloud and comprehension. Lesions in our patient were located in the middle part of the left middle temporal gyrus and its subcortical area, which could be important for access to the phonological lexicon from semantics.     

Pure alexia from a posterior occipital lesion

The authors report a patient with pure alexia (letter-by-letter reading) selectively impaired for kana (Japanese phonograms), cerebral achromatopsia, and right lower quadrantanopsia after hemorrhage in the left posterior occipital lobe, mainly under the lateral occipital gyri. The patient also could not recognize some single-character kana, nor could he discriminate between two shapes of a similar size. The authors believe that the posterior occipital lobe, including the lateral occipital gyri, is specialized to recognize kana characters in this patient.     

Pure agraphia of kanji due to thrombosis of the Labbé vein.

A case is described of a 56 year old Japanese male with pure agraphia of kanji (the Japanese morphograms) due to haemorrhagic infarction of the left temporal lobe caused by the rare condition of cortical vein thrombosis of Labbé. Writing kanji was severely impaired without disturbed consciousness, aphasia or apraxia. On the other hand, writing kana (the Japanese syllabograms), and reading kanji and kana were almost intact. This suggests that the process of writing kanji involves a different pathway from that of reading kanji in the left temporal lobe. Pure agraphia of kanji is considered to be similar to lexical agraphia in Indo-European languages, in that the writing system with a poor or irregular phoneme-grapheme transformation is impaired by the left temporal lesion. This case indicates the necessity for considering thrombosis of the Labbé vein when a subcortical haematoma is detected in a temporal lobe on computed tomography of the brain.