Neuroanatomical and Behavioral Asymmetry in an Adult Compensated Dyslexic Christine Chiarello1, Linda Lombardino2, Natalie Kacinik1, Ronald Otto3

1
Neuroanatomical and Behavioral Asymmetry in an
Adult Compensated DyslexicChristine Chiarello1,
Linda Lombardino2, Natalie Kacinik1, Ronald Otto3
Christiana Leonard2 Department of Psychology,
University of California, Riverside1, University
of Florida, Gainesville2 Diagnostic Imaging
Center, Riverside, CA3
Introduction
Conclusions
Divided Visual Field Tests   This individual took
part in several divided visual field (DVF)
experiments which measured various aspects of
visual word recognition and controlled retrieval.
In each experiment, 3-6 letter concrete nouns
were presented for 120-150 ms in the right or
left visual field. This students scores for
each task were compared to asymmetries observed
from 14-19 male student controls. VF accuracy
for each task was converted to a standard
laterality index (RVF-LVF)/(RVF LVF), and, to
permit comparison across tasks, z-scores were
computed for the laterality index by task. A
z-score of zero indicates the typical VF
asymmetry for that task (e.g., a moderate RVF/LH
advantage).
Although the individual we studied had never
been diagnosed with dyslexia, his extremely poor
word decoding skills, calculation and grammatical
deficits, and his weak academic performance prior
to college, are consistent with the profile
reported for phonological dyslexics (Felton, et
al., 1990). Nevertheless, his reading
comprehension was excellent and he eventually
reached a high level of academic achievement,
particularly in more advanced levels of
mathematics that involve visuospatial abilities.
In both the verbal and mathematics domains, he
was able to successfully compensate for his
deficiencies in lower level skills. Indices of
brain lateralization in this person were notable.
On DVF tasks of word decoding and basic word
recognition, his LVF/RH performance was extremely
poor, producing exaggerated LH advantages
relative to controls. However, on more
reflective lexical tasks that require controlled
word retrieval his overall performance and
asymmetries were well within the control range.
This suggests that he can rely on top-down
strategies to compensate for poor bottom-up
skills, and it is interesting that abnormal
behavioral asymmetries were observed only in
tasks that require bottom-up word decoding
skills. The exaggerated planum temporale
asymmetry evidenced in this case is similar to
that reported in a study investigating adult
recovered dyslexics (Leonard, et al., 1993,
2001). We suggest that right, as well as left,
hemisphere language substrates may be important
for mastery of the word decoding skills needed to
acquire reading normally. Interestingly, a
recent PET study of compensated dyslexics
indicated reduced activation in several RH
regions, compared to controls, during a word
reading task (Ingvar, et al., 2002). The sylvian
fissure morphology (type 4 fissure) in the RH in
this case results in greater parietal cortex at
the expense of superior temporal cortex, and was
previously reported in Einstein's brain
(Witelson, et al., 1999), as well and one
individual with language and reading disorders
(Leonard, et al., 1993). One can speculate that
this parietal shift may enhance some
visuospatial skills, as evidenced by our cases
well-developed spatial mathematical skills. The
link between anatomy and behavior requires more
research, as Steinmetz originally reported that
this formation was present in 15 of 58 right
hemispheres presumed to be normal. In
conclusion, we suggest that the particular
profile of neuroanatomical and behavioral
asymmetry described here may characterize some
high functioning dyslexics with special talents,
and may differ from the brain organization in
poor readers who cannot compensate for deficient
word decoding skills.
Individual differences in cortical anatomy are
readily observable, but their functional
significance is not well-understood (Chiarello,
et al., 2004). For example, 25-30 of
individuals do not show the typical leftward
asymmetry of the planum temporale, and the degree
of the leftward asymmetry, when present, can vary
substantially from person to person. Here we
report a case of an individual with unusually
large asymmetries on several divided visual field
lexical tasks, who also evidenced an extreme
leftward asymmetry of the planum temporale and an
unusual form of Sylvian fissure morphology
(Steinmetz type 4, Steinmetz, et al. 1990). We
report data from psychometric testing, several
divided visual field tasks including measures of
basic word recognition (word naming, nonword
naming, lexical decision) and tasks requiring
more controlled word retrieval (verb, category,
and rhyme generation), information about the
individuals unusual educational background
provided in a detailed interview, and a
description of his unusual brain structure.
Method and Results
Biographical Data At the time of testing, the
participant was a 28-year-old male Ph.D.
candidate in a social science field. He was
strongly right-handed (1.00) based on a
five-item hand preference measure (Bryden, 1982).
His GREs, taken 4 years earlier, were 440
(verbal), 750 (quantitative), 690 (analytical).
He had several first-authored publications, and
successfully completed his Ph.D. work the
following year. His research involved
2-dimensional (geometrical) modeling of human
data. He is currently has a University position
as a tenure-track Assistant Professor. The
participant stated that he had never been
diagnosed with any reading or learning
disability, although he reported long-standing
problems with letter reversals. His kindergarten
teacher suspected mental retardation, but a
psychological evaluation at that time showed no
unusual features, except for color blindness. He
was a very poor student, did not read for
pleasure, and barely graduated high school. He
reported difficulties performing simple
calculations, and took the lowest levels of math
in high school. He also found writing and
grammar to be difficult. He attended a community
college, and was initially attracted to his field
because he thought it involved little math. He
became intrigued by his field, transferred to a
4-year institution, and taught himself study
skills, trigonometry, and geometry, and earned
straight As in his major. In graduate school, he
specialized in data analyses that depended on
abstract mathematical principles and the
visualization of mathematic relationships. Yet
he reported embarrassment about his poor ability
to perform simple calculations when teaching
statistics. Psychometric Tests The data
(Table 1) suggest that this individual may be a
compensated phonological dyslexic. His reading
comprehension and nonverbal IQ were well into the
high normal range, yet, given his level of
educational attainment, his basic word decoding
skills (word and nonword pronunciation), grammar,
syntax, rapid naming, and arithmetic scores were
all low. This pattern of skills and deficits is
characteristic of high functioning adult
compensated dyslexics (Felton, et al., 1990).
References
As indicated in Table 2, his accuracy
asymmetries were quite atypical for all of the
word recognition tasks, falling outside of the
range of scores obtained from the control
participants. His data indicated an exaggerated
RVF/LH advantage, due to extremely low accuracies
for stimuli presented to the LVF/RH (23-38
correct). In contrast, his asymmetries for the
tasks involving more controlled word retrieval
were within the control range, with typical
accuracies for both visual fields.
Bryden, M.P. (1982). Laterality Functional
asymmetry in the normal brain. New York
Academic Press. Chiarello, C., Kacinik, N.,
Manowitz, B., Otto, R., Leonard, C. (2004).
Cerebral asymmetries for language Evidence for
structural-behavioral correlations.
Neuropsychology, 18, 219-231. Felton, R. H.,
Naylor, C. E., Wood, F. B. (1990).
Neuropsychological profile of adult dyslexics.
Brain and Language, 39, 485-497. Ingvar, M., af
Trampe, P., Greitz, T., Eriksson, L.,
Stone-Elander, S., von Euler, C. (2002).
Residual differences in language processing in
compensated dyslexics revealed in simple word
reading tasks. Brain and Language, 83,
249-267. Leonard, C. M., Eckert, M. A.,
Lombardino, L. J., Oakland, T., Kranzler, J.,
Mohr, C. M., et al. (2001). Anatomical risk
factors for phonological dyslexia. Cerebral
Cortex, 11, 148-157. Leonard, C.M., Voeller,
K.K.S., Lombardino, L.J., Morris, M.K., Hynd,
G.W., Alexander, A.W., Andersen, H.G.,
Garofalakis, M., Honeyman, J.C., Mao, J., Agee,
O.F., Staab, E.V. (1993). Anomalous cerebral
structure in dyslexia revealed with magnetic
resonance imaging. Archives of Neurology, 50,
461-469. Witelson, S. F., Kigar, D., Harvey, T.
(1999). The exceptional brain of Albert Einstein.
Lancet, 353, 2149-2153.
Figure 1. Top Typical right and left sylvian
fissures. Bottom Type 4 fissure in right
hemisphere of present case. Planum parietale
(purple) rises posterior to the central sulcus in
the postcentral gyrus rather than the
supramarginal gyrus. Normally, the planum
parietale (purple) rises posterior to postcentral
sulcus (black). In a type 4 fissure, there is a
large parietal lobe posterior to the sylvian
fissure.
Neuroanatomy   A volumetric MRI with 1.2 mm thick
sagittal images was acquired in a 1.5T GE
scanner. Visual inspection of the images
indicated a relatively uncommon form of sylvian
fissure morphology (Steinmetz type 4) previously
reported in Einstein's brain (Witelson, et al.,
1999). In a type 4 fissure, the planum parietale
ascends directly posterior to Heschls gyrus and
enters the postcentral gyrus, rather than the
supramarginal, gyrus (Fig 1 bottom left). We
have previously seen Type 4 fissures coupled with
extreme planar asymmetry in a severely dyslexic
individual with a history similar to the present
case (Leonard, Alexander, unpublished data), and
in one identical twin diagnosed with a word
finding difficulty (Lombardino, unpublished
data). In individuals with type 4 fissures, the
coefficient of asymmetry (R-L)/((RL)/2) for
the planum temporale is very large. In this case,
it was 1.67, more than 2 standard deviations
larger than the mean for control participants.
His other brain measurements were unremarkable.
Arrowheads Borders of planum temporale Purple
Planum parietale Black Postcentral sulcus Blue
Central sulcus
Acknowledgment The individual described in this
case was enthusiastic about participating in our
study and signed an informed consent form
approved by both institutions The research was
supported by NSF grant BCS-0079456.