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Werth R. Revealing the Causes of Dyslexia through a Differential Diagnosis, a Short-Term Effective Treatment and an Appropriate Conceptual Framework. Diagnostics (Basel) 2024; 14:1965. [PMID: 39272749 PMCID: PMC11393927 DOI: 10.3390/diagnostics14171965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2024] [Revised: 08/27/2024] [Accepted: 09/02/2024] [Indexed: 09/15/2024] Open
Abstract
Various different impairments and their interactions can cause reading problems referred to as "dyslexia". Since reading requires the interaction of many abilities, the impairment of each of these abilities can result in dyslexia. Therefore, the diagnosis must differentiate various kinds of dyslexia. The diagnosis of a certain kind of dyslexia cannot be delimited to the investigation and description of symptoms but must also include the investigation of the causes of each kind of dyslexia. For this purpose, a scientifically unequivocal concept of causation and appropriate methods are needed to distinguish them from co-existing impairments that have no causal influence on reading performance. The results of applying these methods cannot be adequately accounted for by a non-scientific, intuitive understanding of necessary and sufficient conditions and causation. The methods suitable for revealing the causes of dyslexia are described in detail, and the results of applying these methods in experiments, in which 356 children with developmental dyslexia participated, are reviewed. Since the concepts of "necessary" and "sufficient" conditions and "causation" proposed in the philosophy of science are not suitable for describing causes of dyslexia and their interaction, they are replaced by a more detailed, experimentally based conceptual framework that provides an accurate description of the conditions required for correct reading and the causes of dyslexia.
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Affiliation(s)
- Reinhard Werth
- Institute for Social Pediatrics and Adolescent Medicine, Ludwig-Maximilians-University of Munich, Haydnstr. 5, D-80336 Munich, Germany
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Aydoğan Avşar P, Kara T, Kocaman O, Akkuş M. The relationship between digit ratio (2D:4D) and intelligence levels in specific learning disorders. Early Hum Dev 2024; 196:106085. [PMID: 39084185 DOI: 10.1016/j.earlhumdev.2024.106085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 07/25/2024] [Accepted: 07/26/2024] [Indexed: 08/02/2024]
Abstract
BACKGROUND Higher prenatal testosterone exposure regulates brain development and affects learning and intelligence directly. The digit ratio (2D:4D) is regarded as an indicator of prenatal testosterone exposure. This study aims to investigate the 2D:4D ratios and intelligence levels in individuals with specific learning disorders (SLD) and compare the ratios with healthy subjects. METHODS The study included a total of 117 patients diagnosed with SLD and 67 healthy controls. We measured the 2D:4D ratios and administered the Wechsler-Intelligence Scale for Children-Revised to assess intelligence quotient (IQ) scores in the SLD group. Sociodemographic data was obtained for both patients and healthy subjects and compared in both groups, as well as 2D:4D ratios. RESULTS Compared to healthy controls, both-hand 2D:4D ratios were found to be lower in the SLD group. In addition, male and female participants with SLD showed lower 2D:4D ratios in both hands than controls. The total scores on the WISC-R were found to decrease as the right-hand 2D:4D ratios and the age increased in the SLD group. CONCLUSION Our findings add to the literature examining the influence of prenatal testosterone exposure on learning and intelligence in the SLD sample. Further research in this domain may yield valuable insights into the underlying mechanisms and potential clinical implications for the management of SLDs examining additional variables that could potentially impact alongside the impact of sex hormones on brain development.
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Affiliation(s)
- Pınar Aydoğan Avşar
- Department of Child and Adolescent Psychiatry, Alanya Education and Research Hospital, Antalya 07425, Turkey.
| | - Tayfun Kara
- Department of Child and Adolescent Psychiatry, Alanya Alaaddin Keykubat University Faculty of Medicine, Antalya 07425, Turkey
| | - Orhan Kocaman
- Department of Child and Adolescent Psychiatry, Alanya Alaaddin Keykubat University Faculty of Medicine, Antalya 07425, Turkey
| | - Merve Akkuş
- Department of Psychiatry, Faculty of Medicine, Kütahya Health Sciences University, Kütahya 43100, Turkey
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Wang A, Yan X, Feng G, Cao F. Shared and task-specific brain functional differences across multiple tasks in children with developmental dyslexia. Neuropsychologia 2024; 201:108935. [PMID: 38848989 DOI: 10.1016/j.neuropsychologia.2024.108935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Revised: 06/04/2024] [Accepted: 06/05/2024] [Indexed: 06/09/2024]
Abstract
Different tasks have been used in examining the neural functional differences associated with developmental dyslexia (DD), and consequently, different findings have been reported. However, very few studies have systematically compared multiple tasks in understanding what specific task differences each brain region is associated with. In this study, we employed an auditory rhyming task, a visual rhyming task, and a visual spelling task, in order to investigate shared and task-specific neural differences in Chinese children with DD. First, we found that children with DD had reduced activation in the opercular part of the left inferior frontal gyrus (IFG) only in the two rhyming tasks, suggesting impaired phonological analysis. Children with DD showed functional differences in the right lingual gyrus/inferior occipital gyrus only in the two visual tasks, suggesting deficiency in their visuo-orthographic processing. Moreover, children with DD showed reduced activation in the left dorsal inferior frontal gyrus and increased activation in the right precentral gyrus across all of the three tasks, suggesting neural signatures of DD in Chinese. In summary, our study successfully separated brain regions associated with differences in orthographic processing, phonological processing, and general lexical processing in DD. It advances our understanding about the neural mechanisms of DD.
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Affiliation(s)
- Anqi Wang
- Department of Psychology, Sun Yat-Sen University, China
| | - Xiaohui Yan
- Department of Psychology, the University of Hong Kong, China; State Key Lab of Brain and Cognitive Sciences, the University of Hong Kong, China
| | - Guoyan Feng
- Department of Psychology, Sun Yat-Sen University, China; School of Management, Guangzhou Xinhua University, China
| | - Fan Cao
- Department of Psychology, the University of Hong Kong, China; State Key Lab of Brain and Cognitive Sciences, the University of Hong Kong, China.
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Werth R. Dyslexia Due to Visual Impairments. Biomedicines 2023; 11:2559. [PMID: 37760998 PMCID: PMC10526907 DOI: 10.3390/biomedicines11092559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 08/28/2023] [Accepted: 09/01/2023] [Indexed: 09/29/2023] Open
Abstract
Reading involves many different abilities that are necessary or sufficient conditions for fluent and flawless reading. The absence of one necessary or of all sufficient conditions is a cause of dyslexia. The present study investigates whether too short fixation times and an impaired ability to recognize a string of letters simultaneously are causes of dyslexia. The frequency and types of reading mistakes were investigated in a tachistoscopic pseudoword experiment with 100 children with dyslexia to test the impact of too short fixation times and the attempts of children with dyslexia to recognize more letters simultaneously than they can when reading pseudowords. The experiment demonstrates that all types of reading mistakes disappear when the fixation time increases and/or the number of letters that the children try to recognize simultaneously is reduced. The results cannot be interpreted as being due to altered visual crowding, impaired attention, or impaired phonological awareness, but can be regarded as an effect of impaired temporal summation and a dysfunction in the ventral stream of the visual system.
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Affiliation(s)
- Reinhard Werth
- Institute for Social Pediatrics and Adolescent Medicine, Ludwig-Maximilians-University of Munich, Haydnstr. 5, D-80336 München, Germany
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Garcia-Medina JJ, Bascuñana-Mas N, Sobrado-Calvo P, Gomez-Molina C, Rubio-Velazquez E, De-Paco-Matallana M, Zanon-Moreno V, Pinazo-Duran MD, Del-Rio-Vellosillo M. Macular Anatomy Differs in Dyslexic Subjects. J Clin Med 2023; 12:jcm12062356. [PMID: 36983356 PMCID: PMC10057708 DOI: 10.3390/jcm12062356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2023] [Revised: 03/13/2023] [Accepted: 03/16/2023] [Indexed: 03/30/2023] Open
Abstract
The macula, as the central part of the retina, plays an important role in the reading process. However, its morphology has not been previously studied in the context of dyslexia. In this research, we compared the thickness of the fovea, parafovea and perifovea between dyslexic subjects and normal controls, in 11 retinal segmentations obtained by optical coherence tomography (OCT). With this aim, we considered the nine sectors of the Early Treatment Diabetic Retinopathy Study (ETDRS) grid and also summarized data from sectors into inner ring subfield (parafovea) and outer ring subfield (perifovea). The thickness in all the four parafoveal sectors was significantly thicker in the complete retina, inner retina and middle retina of both eyes in the dyslexic group, as well as other macular sectors (fovea and perifovea) in the inner nuclear layer (INL), inner plexiform layer (IPL), IPL + INL and outer plexiform layer + outer nuclear layer (OPL + ONL). Additionally, the inner ring subfield (parafovea), but not the outer ring subfield (perifovea), was thicker in the complete retina, inner retina, middle retina (INL + OPL + ONL), OPL + ONL, IPL + INL and INL in the dyslexic group for both eyes. In contrast, no differences were found between the groups in any of the sectors or subfields of the outer retina, retinal nerve fiber layer, ganglion cell layer or ganglion cell complex in any eye. Thus, we conclude from this exploratory research that the macular morphology differs between dyslexic and normal control subjects, as measured by OCT, especially in the parafovea at middle retinal segmentations.
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Affiliation(s)
- Jose Javier Garcia-Medina
- Department of Ophthalmology, Optometry, Otolaryngology and Pathology, University of Murcia, 30100 Murcia, Spain
- General University Hospital Reina Sofia, 30003 Murcia, Spain
- General University Hospital Morales Meseguer, 30008 Murcia, Spain
- Ophthalmic Research Unit "Santiago Grisolia", 46017 Valencia, Spain
- Spanish Net of Ophthalmic Pathology OFTARED RD16/0008/0022, Institute of Health Carlos III, 28029 Madrid, Spain
- Spanish Net of Inflammatory Diseases RICORS, Institute of Health Carlos III, 28029 Madrid, Spain
| | | | - Paloma Sobrado-Calvo
- Department of Ophthalmology, Optometry, Otolaryngology and Pathology, University of Murcia, 30100 Murcia, Spain
- General University Hospital Reina Sofia, 30003 Murcia, Spain
- Spanish Net of Ophthalmic Pathology OFTARED RD16/0008/0022, Institute of Health Carlos III, 28029 Madrid, Spain
- Spanish Net of Inflammatory Diseases RICORS, Institute of Health Carlos III, 28029 Madrid, Spain
| | - Celia Gomez-Molina
- General University Hospital Reina Sofia, 30003 Murcia, Spain
- General University Hospital Morales Meseguer, 30008 Murcia, Spain
| | | | | | - Vicente Zanon-Moreno
- Ophthalmic Research Unit "Santiago Grisolia", 46017 Valencia, Spain
- Spanish Net of Ophthalmic Pathology OFTARED RD16/0008/0022, Institute of Health Carlos III, 28029 Madrid, Spain
- Spanish Net of Inflammatory Diseases RICORS, Institute of Health Carlos III, 28029 Madrid, Spain
- Faculty of Health Sciences, International University of Valencia, 46002 Valencia, Spain
| | - Maria Dolores Pinazo-Duran
- Ophthalmic Research Unit "Santiago Grisolia", 46017 Valencia, Spain
- Spanish Net of Ophthalmic Pathology OFTARED RD16/0008/0022, Institute of Health Carlos III, 28029 Madrid, Spain
- Spanish Net of Inflammatory Diseases RICORS, Institute of Health Carlos III, 28029 Madrid, Spain
- Cellular and Molecular Ophthalmobiology Group, Surgery Department, Faculty of Medicine and Odontology, University of Valencia, 46010 Valencia, Spain
| | - Monica Del-Rio-Vellosillo
- University Hospital Virgen de la Arrixaca, 30120 Murcia, Spain
- Department of Surgery, Obstetrics and Gynecology and Pediatrics, University of Murcia, 30100 Murcia, Spain
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Dadario NB, Tanglay O, Stafford JF, Davis EJ, Young IM, Fonseka RD, Briggs RG, Yeung JT, Teo C, Sughrue ME. Topology of the lateral visual system: The fundus of the superior temporal sulcus and parietal area H connect nonvisual cerebrum to the lateral occipital lobe. Brain Behav 2023; 13:e2945. [PMID: 36912573 PMCID: PMC10097165 DOI: 10.1002/brb3.2945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Revised: 02/13/2023] [Accepted: 02/17/2023] [Indexed: 03/14/2023] Open
Abstract
BACKGROUND AND PURPOSE Mapping the topology of the visual system is critical for understanding how complex cognitive processes like reading can occur. We aim to describe the connectivity of the visual system to understand how the cerebrum accesses visual information in the lateral occipital lobe. METHODS Using meta-analytic software focused on task-based functional MRI studies, an activation likelihood estimation (ALE) of the visual network was created. Regions of interest corresponding to the cortical parcellation scheme previously published under the Human Connectome Project were co-registered onto the ALE to identify the hub-like regions of the visual network. Diffusion Spectrum Imaging-based fiber tractography was performed to determine the structural connectivity of these regions with extraoccipital cortices. RESULTS The fundus of the superior temporal sulcus (FST) and parietal area H (PH) were identified as hub-like regions for the visual network. FST and PH demonstrated several areas of coactivation beyond the occipital lobe and visual network. Furthermore, these parcellations were highly interconnected with other cortical regions throughout extraoccipital cortices related to their nonvisual functional roles. A cortical model demonstrating connections to these hub-like areas was created. CONCLUSIONS FST and PH are two hub-like areas that demonstrate extensive functional coactivation and structural connections to nonvisual cerebrum. Their structural interconnectedness with language cortices along with the abnormal activation of areas commonly located in the temporo-occipital region in dyslexic individuals suggests possible important roles of FST and PH in the integration of information related to language and reading. Future studies should refine our model by examining the functional roles of these hub areas and their clinical significance.
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Affiliation(s)
- Nicholas B Dadario
- Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, USA
| | - Onur Tanglay
- Omniscient Neurotechnology, Sydney, New South Wales, Australia
| | - Jordan F Stafford
- Department of Neurosurgery, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | | | | | - R Dineth Fonseka
- Centre for Minimally Invasive Neurosurgery, Prince of Wales Private Hospital, Sydney, New South Wales, Australia
| | - Robert G Briggs
- Department of Neurosurgery, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | | | - Charles Teo
- Cingulum Health, Sydney, New South Wales, Australia
| | - Michael E Sughrue
- Omniscient Neurotechnology, Sydney, New South Wales, Australia.,Cingulum Health, Sydney, New South Wales, Australia.,Centre for Minimally Invasive Neurosurgery, Prince of Wales Private Hospital, Sydney, New South Wales, Australia
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Werth R. Dyslexia: Causes and Concomitant Impairments. Brain Sci 2023; 13:brainsci13030472. [PMID: 36979282 PMCID: PMC10046374 DOI: 10.3390/brainsci13030472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 02/07/2023] [Accepted: 03/06/2023] [Indexed: 03/12/2023] Open
Abstract
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.
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Affiliation(s)
- Reinhard Werth
- Institute for Social Pediatrics and Adolescent Medicine, Ludwig-Maximilians-University of Munich, Haydnstr. 5, D-80336 München, Germany
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Stein J. Theories about Developmental Dyslexia. Brain Sci 2023; 13:208. [PMID: 36831750 PMCID: PMC9954267 DOI: 10.3390/brainsci13020208] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Revised: 01/22/2023] [Accepted: 01/23/2023] [Indexed: 01/28/2023] Open
Abstract
Despite proving its usefulness for over a century, the concept of developmental dyslexia (DD) is currently in severe disarray because of the recent introduction of the phonological theory of its causation. Since mastering the phonological principle is essential for all reading, failure to do so cannot be used to distinguish DD from the many other causes of such failure. To overcome this problem, many new psychological, signal detection, and neurological theories have been introduced recently. All these new theories converge on the idea that DD is fundamentally caused by impaired signalling of the timing of the visual and auditory cues that are essential for reading. These are provided by large 'magnocellular' neurones which respond rapidly to sensory transients. The evidence for this conclusion is overwhelming. Especially convincing are intervention studies that have shown that improving magnocellular function improves dyslexic children's reading, together with cohort studies that have demonstrated that the magnocellular timing deficit is present in infants who later become dyslexic, long before they begin learning to read. The converse of the magnocellular deficit in dyslexics may be that they gain parvocellular abundance. This may often impart the exceptional 'holistic' talents that have been ascribed to them and that society needs to nurture.
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Affiliation(s)
- John Stein
- Department of Physiology, Anatomy & Genetics, Oxford University, Oxford OX1 3PT, UK
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Ligges C, Lehmann T. Multiple Case Studies in German Children with Dyslexia: Characterization of Phonological, Auditory, Visual, and Cerebellar Processing on the Group and Individual Levels. Brain Sci 2022; 12:1292. [PMID: 36291226 PMCID: PMC9599942 DOI: 10.3390/brainsci12101292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 09/20/2022] [Accepted: 09/21/2022] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND The underlying mechanisms of dyslexia are still debated. The question remains as to whether there is evidence of a predominant type of deficit or whether it is a multideficit disorder with individual profiles. The assumptions of which mechanism causes the disorder influences the selection of the training approach. METHODS A sample of German neurotypical reading children (NT) and children with dyslexia (DYSL) was investigated with a comprehensive behavioral test battery assessing phonological, auditory, visual, and cerebellar performance, thus addressing performance described in three major theories in dyslexia. RESULTS In the present sample using the test battery of the present study, DYSL had the strongest impairment in phonological and auditory processing, accompanied by individual processing deficits in cerebellar performance, but only a few in the investigated visual domains. Phonological awareness and auditory performance were the only significant predictors for reading ability. CONCLUSION These findings point out that those reading difficulties were associated with phonological as well as auditory processing deficits in the present sample. Future research should investigate individual deficit profiles longitudinally, with studies starting before literacy acquisition at as many processing domains as possible. These individual deficit profiles should then be used to select appropriate interventions to promote reading and spelling.
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Affiliation(s)
- Carolin Ligges
- Department of Child and Adolescent Psychiatry, Psychosomatic Medicine and Psychotherapy, Jena University Hospital, Friedrich Schiller University Jena, 07743 Jena, Germany
| | - Thomas Lehmann
- Institute of Medical Statistics, Computer and Data Sciences, Jena University Hospital, Friedrich Schiller University Jena, 07743 Jena, Germany
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