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Front Hum Neurosci. 2014 Jun 24;8:460. doi: 10.3389/fnhum.2014.00460. eCollection 2014.

Magnocellular-dorsal pathway and sub-lexical route in developmental dyslexia.

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Developmental and Cognitive Neuroscience Laboratory, Dipartimento di Psicologia Generale, Università degli Studi di Padova Padova, Italy ; Developmental Neuropsychology Unit, Istituto Scientifico "E. Medea" di Bosisio Parini Lecco, Italy.
Ophthalmological Unit, Istituto Scientifico "E. Medea" di San Vito al Tagliamento Pordenone, Italy.
Developmental Neuropsychology Unit, Istituto Scientifico "E. Medea" di Bosisio Parini Lecco, Italy.


Although developmental dyslexia (DD) is frequently associate with a phonological deficit, the underlying neurobiological cause remains undetermined. Recently, a new model, called "temporal sampling framework" (TSF), provided an innovative prospect in the DD study. TSF suggests that deficits in syllabic perception at a specific temporal frequencies are the critical basis for the poor reading performance in DD. This approach was presented as a possible neurobiological substrate of the phonological deficit of DD but the TSF can also easily be applied to the visual modality deficits. The deficit in the magnocellular-dorsal (M-D) pathway - often found in individuals with DD - fits well with a temporal oscillatory deficit specifically related to this visual pathway. This study investigated the visual M-D and parvocellular-ventral (P-V) pathways in dyslexic and in chronological age and IQ-matched normally reading children by measuring temporal (frequency doubling illusion) and static stimuli sensitivity, respectively. A specific deficit in M-D temporal oscillation was found. Importantly, the M-D deficit was selectively shown in poor phonological decoders. M-D deficit appears to be frequent because 75% of poor pseudo-word readers were at least 1 SD below the mean of the controls. Finally, a replication study by using a new group of poor phonological decoders and reading level controls suggested a crucial role of M-D deficit in DD. These results showed that a M-D deficit might impair the sub-lexical mechanisms that are critical for reading development. The possible link between these findings and TSF is discussed.


dorsal stream; phonological decoding; reading acquisition; reading disability; transient system; visual disorder

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