The enigma of Bálint's syndrome: neural substrates and cognitive deficits

Dyslexia: Causes and Concomitant Impairments

In recent decades, theories have been presented to explain the nature of dyslexia, but the causes of dyslexia remained unclear. Although the investigation of the causes of dyslexia presupposes a clear understanding of the concept of cause, such an understanding is missing. The present paper proposes the absence of at least one necessary condition or the absence of all sufficient conditions as causes for impaired reading. The causes of impaired reading include: an incorrect fixation location, too short a fixation time, the attempt to recognize too many letters simultaneously, too large saccade amplitudes, and too short verbal reaction times. It is assumed that a longer required fixation time in dyslexic readers results from a functional impairment of areas V1, V2, and V3 that require more time to complete temporal summation. These areas and areas that receive input from them, such as the fusiform gyrus, are assumed to be impaired in their ability to simultaneously process a string of letters. When these impairments are compensated by a new reading strategy, reading ability improves immediately.

Partial Balint's syndrome and left homonymous hemianopsia presenting after resection of a right occipito-parietal glioblastoma

A 66-year-old left-handed male was admitted to our acute inpatient rehabilitation (AIR) unit following a resection of the right occipito-parietal glioblastoma. He presented with symptoms of horizontal oculomotor apraxia, contralateral optic ataxia and left homonymous hemianopsia. We diagnosed this patient with partial Bálint's syndrome (BS)- oculomotor apraxia, optic ataxia but not simultanagnosia. BS is typically caused by bilateral posterior parietal lesions, but we here describe a unique case due toresection of a right intracranial tumor. A short AIR stay allowed our patient to learn how to compensate for visuomotor and visuospatial deficits, and improved his quality of life significantly.

Is Developmental Dyslexia Due to a Visual and Not a Phonological Impairment?

It is a widely held belief that developmental dyslexia (DD) is a phonological disorder in which readers have difficulty associating graphemes with their corresponding phonemes. In contrast, the magnocellular theory of dyslexia assumes that DD is a visual disorder caused by dysfunctional magnocellular neural pathways. The review explores arguments for and against these theories. Recent results have shown that DD is caused by (1) a reduced ability to simultaneously recognize sequences of letters that make up words, (2) longer fixation times required to simultaneously recognize strings of letters, and (3) amplitudes of saccades that do not match the number of simultaneously recognized letters. It was shown that pseudowords that could not be recognized simultaneously were recognized almost without errors when the fixation time was extended. However, there is an individual maximum number of letters that each reader with DD can recognize simultaneously. Findings on the neurobiological basis of temporal summation have shown that a necessary prolongation of fixation times is due to impaired processing mechanisms of the visual system, presumably involving magnocells and parvocells. An area in the mid-fusiform gyrus also appears to play a significant role in the ability to simultaneously recognize words and pseudowords. The results also contradict the assumption that DD is due to a lack of eye movement control. The present research does not support the assumption that DD is caused by a phonological disorder but shows that DD is due to a visual processing dysfunction.

Structure learning and the posterior parietal cortex

We propose a theory of structure learning in the primate brain. We argue that the parietal cortex is critical for learning about relations among the objects and categories that populate a visual scene. We suggest that current deep learning models exhibit poor global scene understanding because they fail to perform the relational inferences that occur in the primate dorsal stream. We review studies of neural coding in primate posterior parietal cortex (PPC), drawing the conclusion that neurons in this brain area represent potentially high-dimensional inputs on a low-dimensional manifold that encodes the relative position of objects or features in physical space, and relations among entities in abstract conceptual space. We argue that this low-dimensional code supports generalisation of relational information, even in nonspatial domains. Finally, we propose that structure learning is grounded in the actions that primates take when they reach for objects or fixate them with their eyes. We sketch a model of how this might occur in neural circuits.

Prevalence of Mathematical and Visuospatial Learning Disabilities in Patients With Posterior Cortical Atrophy

Importance

Increased prevalence of language-based learning disabilities (LDs) has been previously reported in patients with primary progressive aphasia (PPA). This study hypothesized that patients with focal neurodegenerative syndromes outside the language network, such as posterior cortical atrophy (PCA), would have a higher rate of nonlanguage LDs, congruent with their mainly visuospatial presentation.

Objective

To investigate the prevalence and type of LD (language and/or mathematical and visuospatial) in a large cohort of patients with PCA compared with patients with logopenic variant PPA (lvPPA) and amnestic Alzheimer disease (AD).

Design, Setting, and Participants

This case-control study reviewed 279 medical records from a university-based clinic and research center for patients with neurodegenerative diseases for LD history, including patients with PCA (n = 95), patients with lvPPA (n = 84), and a matched cohort with amnestic AD (n = 100). No records were excluded. The study compared cognitive and neuroimaging features of patients with PCA with and without LDs. A review of the records of patients presenting from March 1, 1999, to August 31, 2014, revealed 95 PCA cases and 84 lvPPA cases. Then 100 patients with amnestic AD from this same period were chosen for comparison, matching against the groups for age, sex, and disease severity. Data analysis was performed from September 8, 2013, to November 6, 2017.

Main Outcomes and Measures

Prevalence of total LD history and prevalence of language and mathematical or visuospatial LD history across all cohorts.

Results

A total of 179 atypical AD cases (95 with PCA and 84 with lvPPA) and 100 disease control cases (amnestic AD) were included in the study. The groups were not statistically different for mean (SD) age at first visit (PCA, 61.9 [7.0] years; lvPPA, 65.1 [8.7] years; amnestic AD, 64.0 [12.6] years; P = .08), mean (SD) age at first symptom (PCA, 57.5 [7.0] years; lvPPA, 61.1 [9.0] years; amnestic AD, 59.6 [13.7] years; P = .06), or sex (PCA, 66.3% female; lvPPA, 56.0% female; amnestic AD, 57.0% female; P = .30) but differed on non-right-hand preference (PCA, 18.3%; lvPPA, 20.2%; amnestic AD, 7.7%; P = .04), race/ethnicity (PCA, 88.3% white; lvPPA, 99.0% white; amnestic AD, 80.0% white; P < .001), and mean (SD) educational level (PCA, 15.7 [3.2] years; lvPPA, 16.2 [3.3] years; amnestic AD, 14.8 [3.5] years; P = .02). A total of 18 of the 95 patients with PCA (18.9%) reported a history of LD, which is greater than the 3 of 100 patients (3.0%) in the amnestic AD cohort (P < .001) and the 10.0% expected rate in the general population (P = .007). In the PCA cohort, 13 of 95 patients (13.7%) had a nonlanguage mathematical and/or visuospatial LD; this rate was greater than that in the amnestic AD (1 of 100 [1.0%]; P < .001) and lvPPA (2 of 84 [2.4%]; P = .006) cohorts and greater than the 6.0% expected general population rate of mathematical LD (P = .003). Compared with the patients with PCA without LDs, the group with LDs had greater preservation of global cognition and a more right-lateralized pattern of atrophy.

Conclusions and Relevance

Nonlanguage mathematical and visuospatial LDs were associated with focal, visuospatial predominant neurodegenerative clinical syndromes. This finding supports the hypothesis that neurodevelopmental differences in specific brain networks are associated with phenotypic manifestation of later-life neurodegenerative disease.

['Stroke chameleons']

The diagnosis of acute stroke should be correct and early that allows physician planning the most effective treatment strategies (reperfusion therapy, undifferentiated (basic) treatment, early secondary prevention). However, stroke symptoms can be atypical and similar to some other (non-vascular) event. It can significantly complicate the clinical diagnosis of stroke and decrease the patient's chances for effective treatment. A stroke should be suspected in every patient with acute onset of neurological symptoms, especially when the patient has the 'vascular' risk factors. Furthermore it is important to remember that negative CT-scan data and/or MRI data do not exclude the presence of not only ischemic stroke but also hemorrhagic stroke. The article describes the main variants of strokes with atypical symptoms (strokes-chameleons), emphasizes the importance of careful clinical examination, provides supportive differential diagnostic criteria and discusses limitations of neuroimaging methods.

Balint syndrome (chronic visual-spatial disorder) presenting without known cause

Balint's syndrome is a rare disorder characterized by a triad of simultanagnosia, optic apraxia, and ocular apraxia. The syndrome manifests when there is an injury to the posterior parietal and occipital lobes and is often bilateral. Several causes of this syndrome were published in the literature, such as trauma, infarctions, infections, tumors, and pre-eclampsia. It can also be the presenting feature of several neurodegenerative disorders, such as atypical Alzheimer's disease. We report a case of a 62-year-old lady who presented with simultanagnosia, optic apraxia, and ocular ataxia which are the typical signs and symptoms of this syndrome. Neuropsychological evaluation revealed severe affection of the visual-spatial function with intact memory, language, and cognition. Brain imaging confirmed atrophy and decreased perfusion in the posterior parietal and occipital lobes. No underlying cause could be identified to explain the brain parenchymal atrophy. The follow-up neuropsychological assessment and brain imaging did not show any progression confirming the static course of the disease.

Posterior cortical atrophy: a single case cognitive and radiological follow-up

Posterior cortical atrophy (PCA) is a rare neurodegenerative syndrome characterized by initial predominant visuoperceptual deficits followed by a progressive decline in other cognitive functions. This syndrome has not been as thoroughly described as other dementias, particularly from a neuropsychological evolution perspective with only a few studies describing the evolution of its cognitive progression. In this investigation we review the literature on this rare condition and we perform a 7-year neuropsychological and neuroradiological follow-up of a 64-year-old man with PCA. The subject's deficits initially appeared in his visuoperceptual skills with later affectation appearing in language and other cognitive functions, this being coherent with the patient's parieto-temporal atrophy evolution.

Rubiano A. Post-Traumatic Balint's Syndrome: A Case Report and Review of the Literature

Balint’s syndrome is a rare neurological disorder associated with bilateral parieto-occipital damage which was described by Rezsö Bálint in 1909.The syndrome is manifested clinically by the presence of a hemispatial negligence. The lesion is usually inside parietooccipital region bilaterally in most cases but may also be compromised angular convolutions, the dorsolateral area of the occipital lobe as the superior parietal lobule. We herein report a 61-year-old man with traumatic brain injury who was diagnosed to have right parieto-occipital contusion in radiologic evaluation. Physical examination was consistent with Balint's syndrome. The patient was followed for 12 months post-injury and received 4-months of outpatient rehabilitation. Patient showed improvement of Balint’s syndrome 8 months after the starts of symptoms.

The visual pathway--functional anatomy and pathology

Visual failure of any kind is a common clinical presentation and indication for neuroimaging. Monocular deficits should concentrate the search to the anterior (prechiasmatic) visual pathway. Bitemporal hemianopia suggests a chiasmatic cause, whereas retrochiasmatic lesions characteristically cause homonymous hemianopic defects. Quadrantanopias usually arise from lesions in the optic radiations. Disorders of visual perception can be broadly divided into "where" and "what" problems caused by lesions in the parietal and temporal lobes, respectively, and their associated white matter tracts. Visualization of the retrochiasmatic visual and visual association pathways is aided by diffusion tensor imaging.