Procedural learning difficulties: reuniting the developmental disorders?

During the past 30 years, research into developmental disorders has fragmented, emphasizing differences rather than commonalities. We propose that reunification might be achieved by using a "neural-systems" approach. Deficits in dyslexia are attributed to an intact declarative learning system combined with an impaired procedural learning system--a network that includes prefrontal language systems and basal ganglia, parietal and cerebellar structures. A typology is provided for other prevalent learning disabilities; this framework focuses on different learning skills in the understanding of learning disabilities and emphasizes the diagnostic significance of "secondary" symptoms. This approach highlights the need for development of "neurocognitive" tests to probe the function of components of each neural system and improve strategies for explanation, diagnosis and support of developmental disorders.