Presentation on theme: "Introduction Impairments in development dyslexia are not confined to reading and literacy skills. Additional behavioural deficits include phonological."— Presentation transcript:
Introduction Impairments in development dyslexia are not confined to reading and literacy skills. Additional behavioural deficits include phonological processing, motor skills and automatic balance. These difficulties are not observed consistently and vary from individual to individual. Do some dyslexics have multiple impairments at the neurological level? Or might there be a single causal mechanism that accounts for all problems? Selected References 1] McCrory, E., Mechelli, A., Frith, U., and Price, C., (2005) More than words: A common neural basis for words and naming deficits in developmental dyslexia? Brain, 261-267. 2] Nicolson, R.I., & Fawcett, A.J., Berry, E.L., Jenkins, I.H., Dean, P., & Brooks, D.J. (1999) Association of abnormal cerebellar activation with motor learning difficulties in dyslexic adults. Lancet, 353, 1662-1667. Clare Shakeshaft, Cathy Price & HweeLing Lee Background Functional Imaging Studies Many areas of abnormal activation observed (including cerebellum), but not consistent across studies and usually confounded by task performance differences. Left occipito-temporal cortex abnormalities are observed during both reading and picture naming (McCrory et al., 2005) when task performance difficulties explicitly controlled. It is important to investigate other neural substrates that may contribute to impairments that manifest behaviourally in dyslexia, such as the cerebellum (Nicolson et al., 1999). Exp 1: Structural Scan Method Do dyslexic individuals show differences in brain structure relative to age matched controls without reading difficulties? 34 dyslexic subjects and 17 controls scanned using a whole brain unbiased objective technique, voxel based morphology (VBM). This shows a region of the cerebellum whose structure reflects spelling ability. 1a1b 2a2b 3a3b 4a4b Anchor Ship Truck Cup Axe Slide Results Conclusion Structural analyses revealed grey matter density increased with spelling ability in a region of the midline cerebellum. Fig 1. Localisation of reduced grey matter density in a midline cerebellar region when correlated with spelling (comparisons across all subjects) Exp 2: Reading, Naming & Semantic Decisions Method 1) The same midline cerebellar region was activated during reading in dyslexics and controls as reported in Exp. 1. Conclusion The deficit observed in the occipito-temporal region is not specific to phonology. Exp 3: Music Reading Task Method Subjects indicated the position of four black dots in a simple music note reading task that did not involve phonological or semantic processing. Vocal and manual responses were made with corresponding baseline conditions. Fig. 3. Reading activation in both groups at the same coordinates of the structural abnormality in the same midline cerebellar region Results Both dyslexics and controls activated the same cerebellar region found to be structurally abnormal in Exp.1. Activation in this area reflects non-verbal sensori-motor integration. This study shows structural abnormalities in a region of the cerebellum that may mediate spelling and reading ability in developmental dyslexia. Structural abnormalities in this cerebellar region are associated with sensori- motor integration. Functional abnormalities are reported in the left occipito-temporal cortex for meaningful stimuli only, therefore this region is not specific to phonology. Impaired phonological abilities in dyslexic behaviour may reflect a more general deficit in sensori-motor integration. Summary Conclusion Fig 5. Stimuli used for music reading task in activation condition (left) and baseline condition (right). Functional and structural brain abnormalities in developmental dyslexia: The role of the cerebellum and occipitotemporal lobe Are differences in brain activation are observed in the same regions that show differences in brain structure? Subjects scanned during word reading, picture naming, semantic decisions on written words or pictures of objects and perceptual decisions on meaningless non-objects or symbols. Only subjects with accuracy of 85% and over in naming condition included in analyses, resulting in 20 dyslexics and 14 controls. Results Fig. 2. Stimuli used for Exp. 2. (1a) Semantic decisions on Words (1b) Perceptual decisions on triads of meaningless symbols; (2a) Semantic decisions on Pictures; (2b) Perceptual decisions on triads of meaningless non objects; (3a) Reading aloud Words; (3b) Saying “one, two three” to triads of meaningless symbols; (4a) Naming aloud Pictures; (4b) Saying “one, two three” to triads of meaningless non objects 2) Dyslexics showed reduced activation relative to controls in the right occipito- temporal cortex during all tasks, irrespective of whether the stimuli were meaningful and meaningless. 3) Reduced activation in the dyslexic group relative to the controls in the left occipito-temporal cortex for naming and semantic tasks with meaningful stimuli only. Fig. 4. Reduced activation in dyslexics relative to the controls in right fusiform gyrus for all perceptual and semantic tasks with meaningful and meaningless stimuli (red). Reduced activation in the dyslexic group relative to controls in the left fusiform gyrus for naming and semantic tasks with meaningful stimuli only (yellow). Fig. 6. Activation in sensori-motor integration in the same region of the cerebellum (yellow) as Exp 1.