Neuroanatomical and Behavioral Asymmetry in an Adult Compensated Dyslexic Christine Chiarello 1, Linda Lombardino 2, Natalie Kacinik 1, Ronald Otto 3 & Christiana Leonard 2 Department of Psychology, University of California, Riverside 1, University of Florida, Gainesville 2 & Diagnostic Imaging Center, Riverside, CA 3 Introduction 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 Conclusions Method and Results 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 case’s 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. 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. 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 individual’s unusual educational background provided in a detailed interview, and a description of his unusual brain structure. References CategorySkill (Subtest) Percentile ReadingUntimed word reading (WRMT-R Word Identification) 32 Timed word reading (TOWRE Sight Words) 13 Untimed nonword reading (WRMT-R Word Attack) 29 Timed nonword reading (TOWRE Phonemic Decoding) 35 Word Comprehension (WRMT-R) 72 Passage Comprehension (WRMT-R) 95 SpellingUntimed Spelling (WRAT3) 61 GrammarGrammaticality Judgment (CASL) 30 Syntax Construction (CASL) 50 Rapid Naming Letter Naming (CTOPP) 50 Digit Naming (CTOPP) 50 Nonverbal IQ Raven’s Advanced Progressive Matrices 86 MathTimed Calculations and Solving Equations (WJ COG III Calculation) 78 Timed Arithmetic (WJ COG III Math Fluency) 39 Table 1. Percentile Scores for Standardized Tests. 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 ms in the right or left visual field. This student’s scores for each task were compared to asymmetries observed from 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). Table 2. Accuracy Asymmetry Z-score for Case and Z-score Range for Control Participants Task CaseControl Participants’ Range Word Recognition Measures Word Naming … Nonword Naming … Lexical Decision … Controlled Word Retrieval Measures Verb Generation … Category Generation … Rhyme Generation … 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. 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 Heschl’s 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)/((R+L)/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 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, Felton, R. H., Naylor, C. E., & Wood, F. B. (1990). Neuropsychological profile of adult dyslexics. Brain and Language, 39, 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, 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, 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, Witelson, S. F., Kigar, D., & Harvey, T. (1999). The exceptional brain of Albert Einstein. Lancet, 353, 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).