These are the regions of the brain that light up while reading. Dyslexics simply use a different pathway to process language.
With Orton Gillingham, new neurological pathways can form in the brain that are similar to the typical pathways. This creates greater fluency and automaticity for readers and increases their reading grade level.
What is dyslexia?
Dyslexia is a reading difference that affects 10-20% of the population. According to the International Dyslexia Association, "Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge." This has nothing to do with intelligence but does create difficulties for students when reading and spelling.
Common issues besides reading and spelling problems
Oftentimes, students with dyslexia struggle with working memory, poor writing skills, and decreased rapid word recognition. When speaking about a topic, a dyslexic usually has extensive knowledge about the subject matter, but their writing skills indicate a much lower level and falsely represent a lack of knowledge. Furthermore, dyslexics often have reduced rapid word recognition. They may say "continent" for "consonant" because of the same amount of syllables and the similarity of the words.
By using methods such as Orton Gillingham, the neurological structure of the brain that processes language can be reinforced and actually new neurological connections can be made to enhance reading fluency and increase grade level reading. You can read more about this at dyslexia.yale.edu.