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Brain Imaging in Developmental Dyslexia

Objective

To explore the cognitive and biological basis of developmental dyslexia using cognitive and functional imaging techniques.
To explore the impact of orthographic consistency on normal and dyslexic brains.
To test the hypothesis that developmental dyslexia results from a disconnection between brain areas devoted to language function.

The aim of this study is to explore systematically the nature of developmental dyslexia in three different cultural settings. On the basis of recent brain imaging studies using PET with English subjects, a new hypothesis is proposed for the cognitive and biological cause of dyslexia, the "disconnection" hypothesis. This hypothesis is independent of orthographic consistency and suggests that developmental dyslexia may result from loose connectivity within language areas. Neuronal activity during critical tasks, which dyslexics are known to find difficult, will be measured by state of the art PET activation techniques.
In order to implement these aims the following 3 PET-activation experiments will be carried out with normal and dyslexic volunteers in three languages with different orthographic consistency (Italian, French, English). Experiment 1 (reading of words and nonwords) capitalises on the classic observation that, while normal subjects can read both types of stimuli with ease, the reading of nonwords is particularly troublesome for dyslexics. This experiment should demonstrate dysfunctional anatomy in dyslexics while reading. Experiment 2 (repeating words and nonwords) focuses on speech in order to test the hypothesis that the underlying problem in dyslexia has its roots in language processing. Experiment 3 (involuntary reading) concerns visual language processing and is based on the finding that normal readers cannot refrain from reading words when extracting purely visual information, i.e. the presence of an ascender in a word (ham vs. man). This observation has been confirmed by functional imaging studies in normals which show activation of language areas during this task. In dyslexics a pattern consistent with the disconnection hypothesis would be expected, e.g. a reduced involvement of language areas.

Coordinator

Medical Research Council
Address
4,Taviton Street
WC1H OBT London
United Kingdom

Participants (6)

FONDAZIONE CENTRO SAN RAFFAELE DEL MONTE TABOR - ISTITUTO DI RICOVERO E CURA A CARATTERE SCIENTIFICO
Italy
Address
Via Olgettina 60
20132 Milano
Institut National de la Santé et de la Recherche Médicale
France
Address
C.h.u. Purpan - Service De Neurologie
31059 Toulouse
Institute of Neurology
United Kingdom
Address
Queen Street
WC1N 3BG London
Istituto di Ricovero e Cura a Carattere Scientifico Eugenio Medea
Italy
Address
Via Don Luigi Monza 20
22040 Bosisio Parini Como
Università degli Studi di Brescia
Italy
Address
Piazzale Ospedale 1
25125 Brescia
Università degli Studi di Parma
Italy
Address
Via Gramsci 14
43100 Parma