Explicit and implicit processing of words and pseudowords by adult developmental dyslexics - A search for Wernicke's Wortschatz?

Two groups of male university students who had been diagnosed as dyslexic w hen younger, and two groups of control subjects of similar age and IQ to th e dyslexics, were scanned whilst reading aloud and during a task where read ing was implicit, The dyslexics performed less well than their peers on a r ange of literacy tasks and were strikingly impaired on phonological tasks, In the reading aloud experiment, simple words and pseudowords were presente d at a slow pace so that reading accuracy was equal for dyslexics and contr ols, Relative to rest, both normal and dyslexic groups activated the same p eri- and extra-sylvian regions of the left hemisphere that are known to be involved in reading, However, the dyslexic readers showed less activation t han controls in the left posterior inferior temporal cortex [Brodmann area (BA) 37, or Wernicke's Wortschatz], left cerebellum, left thalamus and medi al extrastriate cortex, In the implicit reading experiment, word and pseudo word processing was contrasted to visually matched false fonts while subjec ts performed a feature detection paradigm, The dyslexic readers showed redu ced activation in BA 37 relative to normals suggesting that this group diff erence, seen in both experiments, resides in highly automated aspects of th e reading process, Since BA 37 has been implicated previously in modality-i ndependent naming, the reduced activation may indicate a specific impairmen t in lexical retrieval, Interestingly, during the reading aloud experiment only, there was increased activation for the dyslexics relative to the cont rols in a pre-motor region of Broca's area (BA 6/44). We attribute this res ult to the enforced use of an effortful compensatory strategy involving sub lexical assembly of articulatory routines. The results confirm previous fin dings that dyslexic readers process written stimuli atypically, based on ab normal functioning of the left hemisphere reading system, More specifically , we localize this deficit to the neural system underlying lexical retrieva l.