The Neurology of Reading Disorders
http://www.scma.org/scp/scp960506/harris.html







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Local Frontiers


The Neurology of Reading Disorders






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By Milton E. Harris, PhD

Dr. Harris is a Santa Rosa Neuropsychologist.

The Sufi teacher and folklorist Idries Shah tells a story of a man meeting a snail. The snail, never having

met a human being, is anxious to leam of the differences between humans and snails. The man explains

that people see with eyes in their heads rather than on stalks, that their legs carry them vast distances, and

that they have no need of shells.

The man continues, "And we can communicate without words, without even being together. Our method

is to take something like, say, a leaf, make a mark on it, called writing, and send it by another human

being. Now, by what is called reading, the person who receives it can know what the writer was thinking."

To which the snail replies, "The trouble with you, as with all liars, is that you go too far. I have trapped

you into overreaching by pretending to believe you. But if I further encourage you by not expressing the

disbelief natural to all rational beings, I shall be a partner in your sinful lies." [1]

Memories of Sounds

The human capacity for symbolic communication is truly miraculous. Yet, some people cannot fully

partake of this miracle. Intellectually competent people who read poorly despite adequate training and

"normal sensory functioning may be called "dyslexic." About 3 to 6 percent of the school-age children in

developed countries may suffer from dyslexia, accounting for roughly one-third of the children identified

as needing special education services. [2]

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The Neurology of Reading Disorders http://www.scma.org/scp/scp960506/harris.html
Modern neurological understanding of dyslexia began with Dejerine, who in 1892 observed alexia (with
^agraphia) in an adult following insult to the left angular gyrus, a cerebral association area where visual,
luditory and tactile-kinesthetic pathways overlap. Although blind and deaf people can leam to translate
symbols into meaning, the generally accepted theory is that normal readers must be able to use "pictures"
(letters arranged into words) to activate their memories of sounds (phonemes). These activated
sound-memories then trigger meaning.
Since most dyslexics have normal vision and are able to derive meaning from speech, dyslexia probably
involves disruption of neural pathways linking vision and audition. [3] This assumption generally has
research support, but the research is far from consistent, and many people with serious reading problems
appear to have normal brains. Although some dyslexics may have subtle neural deficits in vision, most
appear to fit the vision-hearing misconnection model.
Lasting language deficits, including dyslexia, are frequent results of serious insult to the left cerebral
hemisphere following completion of brain lateralization, in the age range of 6 to 8 years. Prior to that age,
left hemisphere injury may result in temporary aphasia followed by recovery. Because brain injury
resulting in dyslexia can occur earlier than age 6, dyslexics are slightly overrepresented among left
handers. Reading problems can also occur when an early right hemisphere injury causes a "crowding" of
functions in the left hemisphere.
Abundant Hypotheses
Several features of the neurophysiology of reading are relevant to dyslexia. First, reading is not
"hard-wired" or innate. Second, reading is complexly dependent upon both oculomuscular integrity and
— multiple neural circuits. Third, reading involves voluntary, involuntary and learned components. These
jeatures make reading an ontogenetically fragile ability.
The behavioral neurologist Norman Geschwind observed that left-handed asthmatic males were
overrepresented among classic dyslexics. He used this observation to elaborate a controversial theory of
dyslexia that integrates factors of gender, handedness, autoimmune disorder and maternal stress in
pregnancy. [4]
Other hypotheses have abounded. Early theories championed by ophthalmologists used the term
"congenital word blindness." Orton's concept of mixed cerebral dominance resulting in strephosymbolia
(twisted symbols) launched a continuing research effort.
The present understanding is that dyslexia is a complex condition, and much current research involves
defining subtypes. A distinction is made between primary dyslexia (with basis in neurological
dysfunction) and secondary dyslexia (with basis in sociocultural maladaptation). In the primary subtype,
investigators have identified both auditory and visual versions, the former being far more common.
Diagnostic Complexities
A thorough dyslexia evaluation starts with a review of history. Primary hearing or vision problems must be
excluded. Reading and spelling are examined qualitatively and quantitatively, and sight reading and
reading comprehension are compared. Verbal abilities are examined relative to nonverbal abilities, ideally
in the context of a standardized intelligence battery. Significant differences in the ability profile are
^~~ Followed up with sensori-motor measures to examine incomplete or abnormal lateralization. Comorbid or
alternative diagnoses may be addressed by measures of attention, emotional functioning and observed
behavior.
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The Neurology of Reading Disorders http://www.scma.org/scp/scp960506/harris.html
Dyslexia is often diagnosed on the basis of psychological testing. Typically, significant discrepancies are
^ found between general intelligence test scores, which may be average or better, and measures of spelling
ind reading accuracy, speed and comprehension. Misspellings and misread-ings may be dysphonetic and
bizarre. Verbal intelligence scores are frequently lower than perceptual-motor intelligence scores, and
reading and spelling scores lower than math scores.
Dyslexics have problems sounding out nonsense syllables, generating word lists and learning associations
between phonemes and letters. Complex copying tasks may reveal detail errors, with preservation of
contours. Motor and dichotic listening tasks may yield evidence for incomplete lateralization of functions
usually dominant in the left cerebral hemisphere. This relatively pure syndrome, which has a significant
genetic component, occurs more often in males than in females.
Classic, uncomplicated dyslexia, with otherwise normal cognitive functioning, occurs relatively rarely.
When it does occur, the prognosis is positive. Energetic habilitation that emphasizes phonics and the
acquisition of compensatory learning strategies can lead to excellent psycho-social adaptation. (I am aware
of a severely dyslexic physician who managed medical school by laboriously reading his texts into a tape
recorder, then repeatedly listening to the tape.)
But pure dyslexia is not typical. Reading disabilities are frequently comorbid with other problems, such as
attention deficit disorder, undifferentiated learning problems, oppositional or conduct disorder, and
depression. Differentiating primary dyslexia from secondary reading problems is complicated by the broad
spectrum of reading talent among normal readers. Both a 5-year-old child able to read the word book and
another able to read only a few letters are considered normal readers, as are pairs of 10-year-olds reading
stratagem versus bulk or 40-year-olds reading terpsichorean versus benign. [5]
Multiple Treatments
Treatment issues in dyslexia tend to be emotionally charged, reflecting the general rule that the amount of
professed "expertise" in a field varies inversely with the factual knowledge base. Although some excellent
research has examined the treatment of dyslexia, outcome studies vary in quality. The general wisdom is
that no single therapy works for all cases, and that treatment is most effective when adapted to subtype.
Four broad categories of therapy are used: developmental, remedial, compensatory and supportive. The
developmental approach views reading problems as maturational delays, providing intensified standard
instruction as treatment. This method can be particularly helpful for non-neurologic reading problems.
Remedial approaches identify cognitive or perceptual deficits and then attempt to lessen those deficits
through appropriate training. The Orton-Gillingham approach, for example, emphasizes sound blending,
whereas Fernald stresses sensory integration of lexical stimuli, and Lindamood teaches auditory
discrimination.
Subsets of the remedial approach stress visual-motor training through eye exercises or through
normalization of hypothesized vestibular dysfunction. Some of these approaches suffer from post hoc,
ergo propter hoc reasoning, mistaking phenomena associated with dyslexia with the cause of the
disability. Research generally supports the efficacy of the Orton-Gillingham, Fernald and Lindamood
procedures.
-'— A. new auditory-based procedure using video games has been explored by Tallal. [6] Observing that many
language-impaired children lack facility in distinguishing rapid phoneme blends, such as pa versus ba, she
used a computer to lengthen the blends, then shaped appropriate discrimination through reinforcement.
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The Neurology of Reading Disorders http://www.scma.org/scp/scp960506/harris.html
Preliminary findings with this method have been promising with regard to oral language skills, but the
procedure has not been studied with dyslexia.
Like remedial methods, compensatory approaches try to identify cognitive or perceptual "weak links" in
language processing. Intervention then attempts to strengthen uncompromised perceptual-cognitive
functions. The compensatory approach, most closely associated with the field ofneuropsychology, has
strong theoretical support but has been insufficiently researched.
Supportive approaches include prescription of corrective lenses and use of visual guides. Little scientific
evidence is available to demonstrate the efficacy of the tinted non-optical filters (Irlen lenses) or the
relevance of the "scotopic sensitivity syndrome" on which the supportive method is based.
Recommendations
Current therapy for reading problems generally involves intervention over a span of at least six months at a
frequency of two to five sessions per week. Many public schools have strong remedial reading programs,
sometimes obviating the need for private treatment.
Potential consumers of dyslexia therapy should be skeptical of single-method approaches and of
interventions based on cursory evaluations. Ideally, the clinician providing assessment should be
independent from the proposed therapist. Treatment progress should be continuously monitored with
standardized tests and, if the patient is in school, feedback from teachers. Appropriately trained personnel
from any number of educational, psychological or medical disciplines can administer treatment.
References
1. I. Shah, The Magic Monastery, Dutton (1972).
2. G. Hynd and M. Cohen, Dyslexia, Grune and Stratton (1983).
3. T. Kemper, "Asymmetrical Lesions in Dyslexia," in N. Geschwind and A. Galaburda, Cerebral
Dominance, Harvard (1984).
4. N. Geschwind and P. Behan, "Laterality, Hormones, and Immunity," in N. Geschwind and A.
Galaburda, Cerebral Dominance, Harvard (1984).
5. G. Wilkinson, Wide Range Achievement Test 3 Manual, Jastak (1993).
6. J. Nash, "Zooming in on Dyslexia," Time, Jan. 29:62-64 (1996).
Copyright © 1996 by the Sonoma County Medical Association
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