Presented by Dr. Giuseppe Chiarenza, MD, BCN: The study of goal directed behavior in normal and dyslexic subjects during spontaneous reading was the guiding thread of my research in the field of neuroevolutionary disorders. Reading can be defined as an active perceptual process of gathering information from the external world that involves, attention, memory, articulation, planning and intention. In this sense, reading can be considered a behavior teleologically purposive. Unfortunately, most of the experimental reading conditions have been restricted to automatic presentation of stimuli on a computer screen where the subjects had to passively look or read silently.
Furthermore, there are no studies describing the modifications of the brain electrical activity when the subjects in a self-paced condition read single letters aloud. This meant that the components related to planning and intention were not examined. For this purpose, the chronology of movement-related potentials during skilled actions will be presented which shows that dyslexia is not only a defect of the auditory and/or visual perceptual processes but may also be considered as a praxic disorder in which praxic abilities, such as motor programming, sequential and sensory-motor integration and error system analysis show reduced efficiency. Furthermore, when comparing the Reading-Related Potentials (RRPs) during passive and self-paced condition, significant differences emerge regarding the time course and spatial distribution on the scalp of these potentials. Self-paced reading aloud is characterized, by the most numerous and significant modifications of RRPs morphology in all the cerebral areas. The self-paced condition and the acquisition of extra cerebral signals, as subjects’ voice, EMG activity of forearm and of lips, allowed to identify the potentials occurring before, during and after reading and the cerebral areas mostly involved in each of these periods. The potentials belonging to the pre-lexical period are undoubtedly related to perceptual analysis of stimuli, while those occurring during the lexical and post-lexical periods likely represent reafferent activity for the control of linguistic processes.
Important and significant differences have also been described when comparing different clinical subtypes of dyslexia. This was possible thanks to the direct self-paced reading and spelling test developed by Chiarenza (2010), inspired by the reading and writing model proposed by Boder (1973). Boder described three main subtypes of dyslexia: dysphonetic dyslexia (DD), dyseidetic, mixed and besides a fourth group defined non-specific reading delay (NSRD). The subtypes are identified by an algorithm that considers the reading quotient and the % of errors in the spelling test. Thanks to this precise clinical distinction, it was possible to observe that the dysphonetic subjects compared to the subjects with nonspecific reading delay had significant higher activity in delta and theta bands in the frontal, central and parietal areas bilaterally. The hypothesis that there is a timing defect at the basis of dyslexia is confirmed by the study of the effective and directed connectivity. Two very important areas perform as hubs in the information flow: one is the left calcarine sulcus, which is more active in the DD group. The second is the left rolandic operculum, which is more active in the NSRD group. In the DD group, the calcarine sulcus is sending information to the right postcentral gyrus, the left paracentral gyrus, the right angular gyrus and the right supplementary motor area. This flow of information occurs in almost all frequency bands, including delta and theta band. Slow connections may indicate less efficient or even pathological information flow. In conclusion, dyslexia can be defined, from a psychophysiological point of view, as a cerebral disregulation in all frequency bands that affects programming, planning, fast processing and integration of sensory information. All these phenomena occur at different levels of the central nervous system and at different times.
