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PubMed2004

From orthography to phonetics: ERP measures of grapheme-to-phoneme conversion mechanisms in reading.

Neuroimaging has provided evidence that the first stages of visual word recognition activate a visual word-form center localized in the left extrastriate cortex (fusiform gyrus). Accordingly, neurological cases of patients suffering from pure alexia reported the left posterior occipital lobe as the possible locus of orthographic analysis. There is less agreement in the literature about which brain structures are involved in the subsequent stages of word processing and, in particular, their time course of activation. Functional magnetic resonance imaging and magnetic source imaging studies recently reported data that could indicate a dual route model of reading. These findings are particularly relevant to studies on the functional deficits associated with phonological and surface dyslexia. There is evidence for the existence of two different brain mechanisms supporting phonological processing in visual word recognition: one mechanism subserving "assembled phonology" for reading letter strings and another one subserving "addressed phonology" for reading meaningful words. However, available knowledge on the time course and neural locus of grapheme-to-phoneme conversion mechanisms in reading is still inadequate. In this study, we compared processing of meaningful and meaningless Italian words in a task requiring a phonemic/phonetic decision task. Stimuli were 1152 different orthographic stimuli presented in the central visual field. Half the stimuli were Italian words (with a high or low frequency of occurrence), the other half were meaningless strings of letters (legal pseudowords and letter strings). Event-related potentials were recorded from 28 scalp sites in 10 Italian university students. The task consisted of deciding about the presence/absence of a given "phone" in the hypothetical enunciation of word read: for example, "Is there a /k/ in cheese?". Results showed that lexical frequency and orthographical regularity affected linguistic processing within 150 msec poststimulus. Indeed, the amplitude of a centroparietal P150 varied as a function of stimulus type, being larger in response to high-frequency words than to low-frequency ones and to words and pseudowords than to letter strings. This component might index visual categorization processes and recognition of familiar objects, being highly sensitive to orthographic regularity and "ill-formedness" of words. The amplitude of the P150 was the same in response to well-formed meaningless and to meaningful words, when these latter had a low lexical frequency. This might indicate that highly familiar words are recognized as meaningful unitary visual objects at very early stages of processing, through a visual route to an orthographic input lexicon. Moreover, the amplitude of the negativity recorded between 250 and 350 msec showed an anteroposterior topographic dissociation for access to the phonemic representation of well- or ill-formed strings of characters. Brain responses were larger over the left occipito-temporal regions during reading of words and pseudowords and over the left frontal regions during reading of letter strings.

Adult↗
PubMedDate not supplied

Dissociation of reading strategies: letter-by-letter reading in the native language and normal reading in the learned language. A case study.

In letter-by-letter reading, which is typically observed in Dejerine's (1892) "pure alexia," oral reading seems to be mediated by the naming of the constituent letters of the printed sequence: reading time rises abnormally as a function of the number of letters of the target item. We describe a patient with fluent aphasia who showed the unusual pattern of letter-by-letter reading together with surface dyslexia in her native language (French) and apparently normal reading in the second, learned language (English). Thus, letter-by-letter reading should be considered as a description of a symptom rather than the consequence of a unique type of functional impairment.

Brain Injuries↗
PubMed2006

[Callosal disconnection syndrome due to acute disseminated enchephalomyelitis].

We have reported a very rare case of a patient with callosal disconnection syndrome due to acute disseminated enchephalomyelitis (ADEM). A 54-year-old right-handed woman developed sudden consciousness disturbance and fever after 2 weeks when she had common cold. She did not have a history of stuttering. On admission, the neurological finding showed consciousness disturbance, and exaggerated muscle stretch reflex in four extremities without meningeal irritation. The cerebrospinal fluid examination revealed the cell counts of 273/mm3, the protein of 348 mg/dl and the myelin basic protein 18.3 pg/ml. The brain MRI demonstrated a focal high signal intensity in the right cerebellar peduncle, right temporal lobe, left occipital lobe and corpus callosum on the T2-weighted and FLAIR images. The lesion of corpus callosum was the trunk and splenium, sparing the dorsal side of splenium. Her diagnosis was ADEM. The steroid pulse therapy (metylpredinisolone 1 g/day for 3 days) improved the consciousness disturbance. After 6 weeks from the onset, the neuropsycological examination was performed. The remarkable findings included pure alexia without color naming defects, the acquired stuttering and one-way disturbance of somesthetic transfer from the left hand to the right. This patient may contribute to the study of functional localization of the corpus callosum.

Apraxias↗
PubMedDate not supplied

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.

Aged↗
PubMedDate not supplied

MRI of callosal disconnection due to cerebral infarction.

Magnetic resonance imaging (MRI) was performed to study two cases of callosal disconnection due to cerebral infarction. Both cases had pure alexia and right homonymous hemianopsia. Midsagittal inversion recovery (IR) images demonstrated that the corpus callosum was completely intact, and coronal IR images revealed involvement of the lingual gyrus, fusiform gyrus, forceps major, inferior longitudinal fascicle, and optic radiation in the dominant cerebral hemisphere in both cases. Midline sagittal images provided direct visualization of the corpus callosum but did not provide sufficient information for the study of callosal disconnection syndromes. Coronal reconstructions aided in visualizing the relationship of lesions to the adjacent structures of cerebral white and gray matter. MRI may be one of the most useful tools for understanding the process of interhemispheric transference of information.

Aged↗
PubMed1981

[Confabulatory anomia from visual and tactile agnosia in a case of multi-infarct dementia. Neuropsychological study (author's transl)].

Observation of a patient suffering from a double softening of the brain (inner side of right temporal lobe, left occipital lobe). Clinically, Korsakoff's syndrome, right quadranopsia, pure alexia, tactile and visual agnosia concerning objects, colors and faces. Relative integrity of elementary perceptions (matching tests), impairments of stimulus identification (Lissauer's associative agnosia). Phenomena of sensoriphasic interactions are reported: normal speech in conversation, contrasting with confabulant anomia when naming or describing visual or tactile stimuli: then, escaping the control of sight, a relative "autonomy" of speech appears, with word perseverations and semantic "slipping" and filiations. Discussion of optical aphasia.

Agnosia↗
PubMed1994

[A study of 82 cerebral infarctions in the area of posterior cerebral arteries].

Of 598 consecutive non-selected cases of cerebral infarction included in a stroke registry, 82 cases (54 men and 28 women, mean age 66 +/- 14 years) of spontaneous and isolated posterior cerebral artery (PCA) territory infarction (right PCA in 36, left PCA in 35 and both in 11) were identified on the basis of CT combined with MRI in 51 cases. Infarction was superficial in 25 (group A), combined deep-superficial in 23 (group B) and deep in 34 (group C). Of 48 superficial lesions, 29 were massive while 19 were restricted to the territory of one branch. Of 57 deep lesions, 21 were located in the inferolateral thalamic territory, 10 in the paramedian thalamic territory, 12 in other midbrain or thalamic territories, and 14 in a combination of various midbrain and/or thalamic territories. Of 41 patients with unilateral superficial involvement, 39 had homonymous visual field defect. Unawareness of the visual defect and visual release hallucinations were observed with the same frequency in right and left lesions. Of 7 patients with bilateral superficial involvement, only 5 had bilateral visual field defect including incomplete cortical blindness in 3. The frequency of confusional state (n = 24) did not differ significantly in left versus right sided lesions while it was significantly higher in superficial or combined versus deep lesions (p = 0.05). Of 18 clinically evaluable patients with left PCA territory infarct, 14 had speech disorders including pure alexia in only one case. Of 15 patients with right territory infarction, 10 had spatial judgement disorders.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1998

[A patient with amnesic syndrome with defective route finding due to left posterior cerebral artery territory infarction].

We report a right-handed 67-year-old woman with an infarction in the left posterior cerebral artery territory presenting amnesic syndrome, right homonymous hemianopsia, pure alexia, color anomia, and defective route finding. The patient often walked in wrong directions out of her hospital room as well as in her home. She was able to recognize her own house and nearby streets by looking at them. Prosopagnosia and constructional impairment was not observed. Wechsler memory scale revised (WMS-R) revealed that she had marked disturbance in both visual and verbal recent memory. Brain MRI revealed an infarction involving the left medial inferior temporal and left medial occipital lobe, the left splenium of corpus callosum, and the left retrosplenial region. SPECT indicated a defect in the left medial occipital lobe and hypoperfusion in the left medial temporal lobe. Cerebral angiography demonstrated stenosis of the left medial occipital artery and occlusion of the left dorsal corpus callosal branches and the left calcarine artery. We conclude that left hippocampus, left parahippocampal gyrus and the left retrosplenial region may cause memory disturbance in our case. The lesion in the left retrosplenial region may have contributed to the occurrence of defective route finding. The relation between defective route finding and the retrosplenial amnesia is discussed.

Aged↗
PubMed1997

[Visual agnosia induced by cerebrovascular disease].

Visual objects can be classified into some categories such as faces, landscapes, objects and letters. Visual agnosia specific to one of these categories can occur. This type of visual agnosia occurs at the occipitotemporal lobe lesion where the visual cognitive center exists, and is often induced by vascular disease of the posterior cerebral artery. In this study we categorized the symptoms of visual agnosia and presented the natures of these symptoms of patients, and then investigated the lesions responsible for the symptoms. In addition, we clarified the current most important issue for each symptom. Based on our results, we discussed the visual cognitive functions of the occipitotemporal lobe. The results indicate that visual cognitive dysfunction with respect to faces, landscapes, objects and letters corresponds to prosopagnosia, agnosia for streets, associative object agnosia and pure alexia, respectively. Investigation of the relationship between the symptoms of the above conditions and the responsible regions shows that the right medial-posterior region, right medial-anterior region, both lateral regions (left side is superior) and the left medial region are important in the visual cognition of faces, landscapes, objects and letters, respectively. Thus, it is speculated that the visual cognitive functions occur independently at different regions of the occipitotemporal lobe for each visual category.

Agnosia↗
PubMed2002

Visually- and motor-based knowledge of letters: evidence from a pure alexic patient.

We describe a patient, VSB, whose reading was impaired as a consequence of a left temporal-parietal lesion, whereas writing was relatively preserved. At variance with other pure alexic patients described in the literature, VSB claimed to have become unable to mentally visualise letters and words. Indeed, his performance on a series of tests tapping visual mental imagery for orthographic material was severely impaired. However, performance on the same tests was dramatically ameliorated by allowing VSB to trace each item with his finger. Visual mental imagery for non-orthographic items was comparatively spared. The pattern of dissociation shown by VSB between impaired visual mental imagery and relatively preserved motor-based knowledge for orthographic material lends support to the view that separate codes, respectively based on visual appearance and on motor engrams, may be used to access knowledge of the visual form of letters and words.

Alexia, Pure↗
PubMed2005

Improvement in Tc-99m HMPAO brain SPECT findings during donepezil therapy in a patient with pure akinesia.

A 58-year-old man presented with a history of disturbance in initiating gait. His history revealed meningoencephalitis five years prior to admission. Neurological examination included gait disturbance as difficulty in initiation and a hesitating speech with many freezing episodes and micrographia Magnetic resonance imaging (MRI) showed diffuse hyperintensity of frontal subcortical white matter on T2 weighted images. He was diagnosed with PA. L-Dopa up to the dosages of 1000 mg/ day and selegiline 10 mg/day were given. First brain SPECT using technetium-99m labeled D,L-hexamethylpropylene amine oxime (Tc-99m HMPAO) was performed when he was taking L-dopa and selegiline. In visual evaluation, hypoperfusion in bilateral frontoparietal cortex was seen (Fig. 2). Treatment with L-dopa and selegiline produced no benefit. Donepezil 10 mg/day was begun. This therapy regimen resulted in dramatic clinical improvement within several days that was confirmed by blinded raters who watched the patient's video recordings. During this response second brain perfusion SPECT study was repeated during donepezil therapy. Markedly increased perfusion in bilateral frontoparietal cortex was observed. This is the first case of PA to develop possibly after an episode of bacterial pneumococcal meningoencephalitis and who responded to donepezil as documented by changes in clinical findings and Tc-99m HMPAO brain SPECT studies.

Alexia, Pure↗
PubMed2005

The rises and falls of disconnection syndromes.

In a brain composed of localized but connected specialized areas, disconnection leads to dysfunction. This simple formulation underlay a range of 19th century neurological disorders, referred to collectively as disconnection syndromes. Although disconnectionism fell out of favour with the move against localized brain theories in the early 20th century, in 1965, an American neurologist brought disconnection to the fore once more in a paper entitled, 'Disconnexion syndromes in animals and man'. In what was to become the manifesto of behavioural neurology, Norman Geschwind outlined a pure disconnectionist framework which revolutionized both clinical neurology and the neurosciences in general. For him, disconnection syndromes were higher function deficits that resulted from white matter lesions or lesions of the association cortices, the latter acting as relay stations between primary motor, sensory and limbic areas. From a clinical perspective, the work reawakened interest in single case studies by providing a useful framework for correlating lesion locations with clinical deficits. In the neurosciences, it helped develop contemporary distributed network and connectionist theories of brain function. Geschwind's general disconnectionist paradigm ruled clinical neurology for 20 years but in the late 1980s, with the re-emergence of specialized functional roles for association cortex, the orbit of its remit began to diminish and it became incorporated into more general models of higher dysfunction. By the 1990s, textbooks of neurology were devoting only a few pages to classical disconnection theory. Today, new techniques to study connections in the living human brain allow us, for the first time, to test the classical formulation directly and broaden it beyond disconnections to include disorders of hyperconnectivity. In this review, on the 40th anniversary of Geschwind's publication, we describe the changing fortunes of disconnection theory and adapt the general framework that evolved from it to encompass the entire spectrum of higher function disorders in neurology and psychiatry.

Agnosia↗