Arch Hellen Med, 17(5), September-October 2000, 506-517
The pathogenesis of learning disorders
Child and Adolescent Unit, Community Mental Health Center of Byron-Kesariani,
Department of Psychiatry, University of Athens, Greece
Scientific interest concerning children with learning difficulties started in the 19th century along with the obligatory enforcement of primary education. The causes of specific developmental learning disorders are still vague. Given the significant heterogeneity of children with learning difficulty, it is possible that more than one mechanism is responsible and even at a clearly descriptive level there are no common features. Many factors are implicated in the predisposition to learning disorders, including low birth weight, premature birth, maternal alcoholism and smoking, cerebral palsy, inadequate development of brain lateralisation, early and protracted poor nutrition, and even thyroid disorders. Studies have shown that the effect of learning disorders is higher in identical than in fraternal twins and large family studies have confirmed both the familial nature and the heterogeneity of learning disorders. It is believed that more children with learning difficulty are left-handed, although left-handedness per se is not sufficient to cause learning disorders. Findings from electrophysiological studies and descriptive methods confirm that there are qualitative differences in neurophysiological activity in children with learning difficulties. It is believed that developmental reading disorder has its roots in word recognition disorder and recent studies have shown deficiencies in (a) the phonological process or the system of sound comprehension, (b) grammar or syntax, (c) vocabulary or word semantics, and (d) communication strategy. Phonological processing presupposes that the child has developed three skills: (a) phonological awareness, (b) phonological recoding in verbal access, and (c) phonetic recoding in short term memory. Of these three processes, phonological awareness is believed to play the most important role in difficulty in the comprehension of reading. It is acknowledged that learning is a product of a complex process related to various influences, personal, environmental, genetic and neurophysiological, as well as cognitive factors.
Key words: Cognitive factors, Learning disorder, Neurobiological factors, Pathogenesis, Phonological awareness, Predisposing factors.