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.     

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.     

Naming difficulties seen in a case of alexia with agraphia caused by a left postero-inferior temporal lesion]

A 71-year-old right-handed man presented writing and reading difficulties as well as naming difficulties. Neuropsychological examinations revealed mild fluent type aphasia accompanied by alexia and agraphia predominantly affecting kanji and also severe naming difficulties. Brain MRI showed cerebral subcortical hemorrhage extending from the anterior one-third of the left temporal lobe to the temporo-occipital junction involving the fusiform gyrus. The analysis of the several reported cases with severe alexia with agraphia for kanji including ours revealed a close correlation between the severity of kanji writing disturbances and that of naming difficulties. It was also shown that cases with severe naming difficulties had lesion extending anteriorly to the anterior middle temporal gyrus or medially to the parahippocampal gyrus, suggesting that the disconnection between the parahippocampal gyrus and other cortices including the temporal lobe was essential for production of naming difficulties.     

Disorders of Visuo-spatial Cognition

Posterior fusiform gyrus (BA 37) is responsible for Hanja (ideogram) alexia in stroke patients. Patients with semantic dementia (SD) have lesions in the basal temporal area. The close proximity in these two lesions and the fact that reading ideograms requires holistic processing as is necessary in recognition of objects, suggests a possibility that ideogram alexia/agraphia may occur in patients with SD. We established and carried out Hanja and Hangul (phonogram) reading/writing tasks on six SD patients and nine Alzheimer's disease (AD) patients as control to see if these two patient groups show dissociation in the two sets of tests. SPM analysis was performed on the SD patients' PET images to look for any dysfunctions in the posterior fusiform gyrus. The SD patients manifested Hanja alexia/agraphia whereas Hangul reading/writing ability was relatively preserved. There were group differences between SD and AD in the Hanja tasks but not in the Hangul tasks. The SPM analysis revealed no hypometabolism in the posterior fusiform gyrus, but only in the middle and the anterior part of the temporal gyrus. Dysfunction in the middle temporal gyrus (BA 21) may have disrupted the temporal lobe connections preventing the function of the posterior fusiform gyrus.     

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.     

Temporal lobe gray matter in schizophrenia spectrum: a volumetric MRI study of the fusiform gyrus, parahippocampal gyrus, and middle and inferior temporal gyri

Although several brain morphologic studies have suggested abnormalities in the temporal regions to be a common indicator of vulnerability for the schizophrenia spectrum, less attention has been paid to temporal lobe structures other than the superior temporal gyrus or the medial temporal region. In this study, we investigated the volume of gray matter in the fusiform gyrus, the parahippocampal gyrus, the middle temporal gyrus, and the inferior temporal gyrus using magnetic resonance imaging in 39 schizotypal disorder patients, 65 schizophrenia patients, and 72 age and gender matched healthy control subjects. The anterior fusiform gyrus was significantly smaller in the schizophrenia patients than the control subjects but not in the schizotypal disorder patients, while the volume reduction of the posterior fusiform gyrus was common to both disorders. Volumes for the middle and inferior temporal gyri or the parahippocampal gyrus did not differ between groups. These findings suggest that abnormalities in the posterior region of the fusiform gyrus are, as have been suggested for the superior temporal gyrus or the amygdala/hippocampus, prominent among the temporal lobe structures as a common morphologic substrate for the schizophrenia spectrum, whereas more widespread alterations involving the anterior region might be associated with the development of full-blown schizophrenia.     

Basal temporal language area demonstrated by electrical stimulation

We report on a 38-year-old patient with intractable complex partial seizures originating in the dominant left medial temporal region. In the work-up for seizure surgery, arrays of subdural electrodes were placed, and electrical stimulation revealed marked language interference in a 2 X 2-cm area in the left basal temporal fusiform gyrus (3.5 to 5.5 cm posterior to the temporal tip). Complete receptive and expressive aphasia, inability to repeat, agraphia, and alexia were elicited, but visual memory was preserved, and no constructional apraxia was noted. Stimulation of the basal temporal gyrus at lower stimulus intensities produced a relatively selective and severe anomia.     

Brain activity related to integrative processes in visual object recognition: bottom-up integration and the modulatory influence of stored knowledge

We report evidence from a PET activation study that the inferior occipital gyri (likely to include area V2) and the posterior parts of the fusiform and inferior temporal gyri are involved in the integration of visual elements into perceptual wholes (single objects). Of these areas, the fusiform and inferior temporal gyri were more activated by tasks with recognizable stimuli than by tasks with unrecognizable stimuli. We propose that the posterior parts of the fusiform and inferior temporal gyri, compared with the inferior occipital gyri, are involved in higher level integration, due to the involvement of re-entrant activation from stored structural knowledge. Evidence in favor of this interpretation comes from the additional finding that activation of the anterior part of the left fusiform gyrus and a more anterior part of the right inferior temporal gyrus, areas previously associated with access to stored structural knowledge, was found with recognizable stimuli, but not with unrecognizable stimuli. This latter finding also indicates: (i) that subjects may not refrain from (automatically) identifying objects even if they only have to attend to the objects' global shape, and (ii) that perceptual and memorial processes can be dissociated on both functional and anatomical grounds. No evidence was obtained for the involvement of the parietal lobes in the integration of single objects.     

Patterns of temporal lobe atrophy in semantic dementia and Alzheimer's disease

Volumetric magnetic resonance imaging analyses of 30 subjects were undertaken to quantify the global and temporal lobe atrophy in semantic dementia and Alzheimer's disease. Three groups of 10 subjects were studied: semantic dementia patients, Alzheimer's disease patients, and control subjects. The temporal lobe structures measured were the amygdala, hippocampus, entorhinal cortex, parahippocampal gyrus, fusiform gyrus, and superior, middle, and inferior temporal gyri. Semantic dementia and Alzheimer's disease groups did not differ significantly on global atrophy measures. In semantic dementia, there was asymmetrical temporal lobe atrophy, with greater left-sided damage. There was an anteroposterior gradient in the distribution of temporal lobe atrophy, with more marked atrophy anteriorly. All left anterior temporal lobe structures were affected in semantic dementia, with the entorhinal cortex, amygdala, middle and inferior temporal gyri, and fusiform gyrus the most severely damaged. Asymmetrical, predominantly anterior hippocampal atrophy was also present. In Alzheimer's disease, there was symmetrical atrophy of the entorhinal cortex, hippocampus, and amygdala, with no evidence of an anteroposterior gradient in the distribution of temporal lobe or hippocampal atrophy. These data demonstrate that there is a marked difference in the distribution of temporal lobe atrophy in semantic dementia and Alzheimer's disease. In addition, the pattern of atrophy in semantic dementia suggests that semantic memory is subserved by anterior temporal lobe structures, within which the middle and inferior temporal gyri may play a key role.     

Recovery from alexia without agraphia: report of an autopsy.

The patient is a 58-year-old Japanese teacher of German literature who suffered twice from cerebrovascular accidents, showing alexia without agraphia. Pathological examination showed an old infarct in the posterior two-thirds of the fusiform and almost the whole lingual gyrus, involving the posterior border of the parahippocampal gyrus in the left hemisphere. The left cuneus and the calcarine cortex were preserved. There was degeneration of the lower third of the splenium of the corpus callosum, extending to its occipital radiation and tapetum on both sides. Comparing clinico-pathological findings of the 31 known autopsy cases, it was proposed that the lesion of the left spleno-lingual system produces alexia without agraphia but it may ameliorate. In addition, when spleno-cuneate system is also involved alexia becomes persistent and it may accompany object agnosia or optic aphasia.     

Anatomic Distribution of Cortical Language Sites in the Basal Temporal Language Area in Patients with Left Temporal Lobe Epilepsy

Summary: In evaluation for surgical treatment of intractable psychomotor seizures originating in the language-dominant left mesiotemporal region, subdural grid electrodes were placed in 29 patients over the temporoparietal cortex and over the basotemporal region. In 13 patients, cortical stimulation of the basotemporal region showed interference with language processing. The most anterior border of the basotemporal language area began 1.1 cm posterior to the anterotemporal tip, and the most posterior margin of the language region was located 6.1 cm posteriorto the temporal tip. The most lateral and the most mesial border were located 1.4 and 5.9 cm, respectively, from the lateral edge of the temporal lobe. The region in which language disturbance could be elicited included the inferior temporal gyrus, the fusiform (lateral and medial occipitotemporal) gyrus, and the parahippocampal gyrus. The basotemporal area most consistently involved with language function was the fusiform gyrus (60% of affected electrodes), followed by the inferotem-poral (30%), and the parahippocampal (10%) gyri.     

Misidentification syndromes related to face specific area in the fusiform gyrus

The "delusional misidentification syndromes" are a group of uncommon and varied disorders in which, in typical form, the patient thinks that a particular familiar person is someone else or a certain familiar place is a duplicate. Although first identified and considered a memory disorder by Pick, evidence in support of this has been difficult to identify. They have been most often seen in various psychotic and organic brain diseases but lesions have been generally diffuse although the right temporal lobe has been implicated. A patient was investigated who abruptly developed a disorder wherein she misidentified her husband as her deceased sister and claimed that her home was a duplicate of her real home that were typical of Frégoli syndrome and Pick's reduplicative paramnesia, respectively. A discrete area of brain damage, probably ischaemic, in this patient was seen on MRI in the anterior part of the right fusiform gyrus and a smaller area in the nearby anterior middle and inferior temporal gyri with associated parahippocampal and hippocampal atrophy. A high order nervous system function that is devoted to the identification of faces is located in the adjacent midportion of the fusiform gyrus and a similar locus for environmental scenes, termed the parahippocampal place area, is present in the bordering parahippocampal gyrus. The misidentification phenomena in this case can be explained by disruption of the connections of these highly specialised areas with the most anterior inferior and medial part of the right temporal lobe where long term memory and mechanisms for the retrieval of information that are required for the visual recognition of faces and scenes are stored.     

Object identification and lexical/semantic access in children: a functional magnetic resonance imaging study of word-picture matching

Theoretical models for lexical access to visual objects have been based mainly on adult data. To investigate the developmental aspects of object recognition and lexical access in children, a large-scale functional MRI (fMRI) study was performed in 283 normal children ages 5-18 using a word-picture matching paradigm in which children would match an aurally presented noun to one of two pictures (line drawings). Using group Independent Component Analysis (ICA), six task-related components were detected, including (a) the posterior superior temporal gyrus bilaterally; (b) the fusiform, inferior temporal, and middle occipital gyri bilaterally; (c) the dorsal aspect of the inferior frontal gyrus bilaterally, the left precuneus, the left superior/middle temporal gyrus, and the anterior cingulate; (d) the right medial fusiform gyrus; (e) a left-lateralized component including the inferior/middle frontal, middle temporal, medial frontal, and angular gyri, as well as the thalamus and the posterior cingulate; and (f) the ventral/anterior aspect of the inferior frontal gyrus bilaterally. Increased activation associated with age was seen in the components (b) and (d) (ventral visual pathway) for object recognition, and (c) and (f) likely associated with semantic maintenance and response selection. Increased activation associated with task performance was seen in components (b) and (d) (ventral visual pathway) while decreased activation associated with task performance was seen in component (f) (ventral/anterior inferior frontal gyrus). The results corroborate the continued development of the ventral visual pathway throughout the developmental period.     

Fields of origin and pathways of the interhemispheric commissures in the temporal lobe of macaques

The interhemispheric connections of the cortical areas of the temporal lobe and some neighboring regions were investigated in monkeys (Macaca mulatta and Macaca fascicularis) by anterograde autoradiographic tracing, following injection of radioactively labeled amino acids. The results revealed that the interhemispheric projections of the temporal lobe course through three interhemispheric commissures on their way to the opposite hemisphere. The anterior commissure receives fibers from virtually the entire temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. Moreover, area 13 of the orbitofrontal cortex, the frontal and temporal subdivisions of the prepiriform cortex, and the cortical and deep nuclei of the amygdala also contribute fibers to the anterior commissure. The heaviest projections arise in the rostral third of the temporal isocortex. These projections become progressively lighter from more caudal regions. By contrast, the corpus callosum receives fibers from the caudal two-thirds of the temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. The heaviest projections arise in the caudal third of the temporal lobe and cross primarily in the caudal third of the corpus callosum, including the splenium. Progressively lighter projections arise more rostrally. Fibers from proisocortical and isocortical areas of the posterior parahippocampal gyrus cross in the ventralmost part of the splenium (inferior forceps), whereas cortical areas lateral to the occipitotemporal sulcus give rise to fibers that cross in the caudal part of the body of the corpus callosum and dorsal splenium. The dorsal hippocampal commissure receives fibers exclusively from the parahippocampal gyrus. The fibers of the corpus callosum, hippocampal commissure, and, to a lesser extent, the anterior commissure are intimately associated with the ventricular system as they course through the white matter of the temporal lobe. The fields of origin of the anterior commissure and corpus callosum overlap extensively over the caudal two-thirds of the temporal lobe. The posterior parahippocampal gyrus is unique in that it gives rise to fibers that cross in all three commissures.     

Differing patterns of temporal atrophy in Alzheimer's disease and semantic dementia

OBJECTIVE: To characterize and quantify the patterns of temporal lobe atrophy in AD vs semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia), clinical studies suggest polar and inferolateral temporal atrophy with hippocampal sparing, but quantification is largely lacking. METHODS: A volumetric method for quantifying multiple temporal structures was applied to 26 patients with probable AD, 18 patients with semantic dementia, and 21 matched control subjects. RESULTS: The authors confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, patients with semantic dementia had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the semantic dementia group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, whereas naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures. CONCLUSIONS: Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.     

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.     

Pure topographical disorientation--the anatomical basis of landmark agnosia

We used MRI studies of four patients to investigate the lesions responsible for landmark agnosia. A detailed investigation of the relationship between the symptoms and the lesions suggests that the right posterior part of the parahippocampal gyrus is critical for the acquisition of novel information about buildings and landscapes, and that the same region plus the anterior half of the lingual gyrus and the adjacent fusiform gyrus play an important role in the identification of familiar buildings and landscapes. Furthermore, the lesion responsible for prosopagnosia, which frequently occurs with landmark agnosia, seems to involve the posterior half of the lingual and fusiform gyri. This suggests that the lesions responsible for landmark agnosia and prosopagnosia are close to each other, but distinct.     

Specialization of phonological and semantic processing in Chinese word reading

The purpose of this study was to examine the neurocognitive network for processing visual word forms in native Chinese speakers using functional magnetic resonance imaging (fMRI). In order to compare the processing of phonological and semantic representations, we developed parallel rhyming and meaning association judgment tasks that required explicit access and manipulation of these representations. Subjects showed activation in left inferior/middle frontal gyri, bilateral medial frontal gyri, bilateral middle occipital/fusiform gyri, and bilateral cerebella for both the rhyming and meaning tasks. A direct comparison of the tasks revealed that the rhyming task showed more activation in the posterior dorsal region of the inferior/middle frontal gyrus (BA 9/44) and in the inferior parietal lobule (BA 40). The meaning task showed more activation in the anterior ventral region of the inferior/middle frontal gyrus (BA 47) and in the superior/middle temporal gyrus (BA 22,21). These findings are consistent with previous studies in English that suggest specialization of inferior frontal regions for the access and manipulation of phonological vs. semantic representations, but also suggest that this specialization extends to the middle frontal gyrus for Chinese. These findings are also consistent with the suggestion that the left middle temporal gyrus is involved in representing semantic information and the left inferior parietal lobule is involved in mapping between orthographic and phonological representations.     

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.     

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.