Atypical Reading/Laterality Profile Associated with Reversed Planum Temporale Asymmetry Christine Chiarello 1, Suzanne Welcome 1, & Christiana M. Leonard 2 University of California, Riverside 1,University of Florida, Gainesville 2 Introduction Acknowledgment This research was supported by NIDCD grant 5R01DC6957. Conclusions Method Even among college students, there is diversity in reading ability. We identified 4 reading subgroups with differing VF laterality profiles. Normal leftward planum temporale asymmetry was observed in each of these “typical” profiles. A minority of the sample could not be classified by their reading and VF lateralization performance, showing no discernable pattern of performance on measures used in the cluster analysis. These “outliers” had very good reading comprehension, but demonstrated extreme variability and slowed responses in divided visual field reading tasks. This group also failed to demonstrate typical leftward planar asymmetry, and many had reversed (rightward) asymmetry. Hence, among normal readers, reversed or absent planar asymmetry is not associated with poor reading skill, and may not be a predictor of dyslexia. However, atypical planum temporale asymmetry was associated with an atypical behavioral profile. This may reflect a less regulated pattern of neural development, in which random genetic and environmental factors influence cerebral lateralization and behavioral outcomes. We are investigating the neuroanatomical correlates of one acquired cognitive skill, reading. There is substantial individual variation in reading skill among college students, but the relationship of this to variation in cortical anatomy and lateralization is unclear. It has been speculated that poor reading skill may be associated with reduced or reversed planum temporale asymmetry, but findings have been contradictory (Leonard & Eckert, 2008). Most previous approaches to this issue investigate differences between groups defined a priori (i.e., sex, handedness, diagnostic group) (e.g., Chiarello, et al, in press). Here we explore an alternate approach, in which groups are identified in a bottom-up fashion by patterns in their behavioral data (reading subtest scores and asymmetries in divided visual field word reading tasks, see Chiarello, et al., in press). A cluster analysis of data from 200 college students revealed four groups with distinctive reading/lateralization profiles. However, 17 individuals were unclassifiable by this approach (“outliers”). In this report we focus on these latter individuals to examine whether their atypical behavioral outcomes are associated with unusual asymmetry of the planum temporale. If absent or reversed planar asymmetry is attributable to less regulated neural development, then atypical, but not necessarily deficient, behavioral profiles may occur. References Chiarello, C., Welcome, S.E., Halderman, L.K., Towler, S., Julagay, J., Otto, R., Leonard, C.M. (In press). A large-scale investigation of lateralization in cortical anatomy and word reading: Are there sex differences? Neuropsychology. Leonard, C.M., & Eckert, M.A. (2008). Asymmetry and dyslexia. Developmental Neuropsychology, 33, PARTICIPANTS: 100 male, 100 female native English speakers years of age BEHAVIORAL MEASURES: Verbal IQ estimated from Wechsler Abbreviated Scale of Intelligence (Wechsler, 1977) Reading subscales from Woodcock Reading Mastery Test - Revised (Woodcock, 1998) Word Identification (word reading) Word Attack (nonword reading) Passage Comprehension Asymmetry scores across the following divided visual field tasks calculated separately for accuracy and reaction time: Lexical Decision Masked Word Recognition (2 AFC procedure) Word Naming Nonword Naming Semantic (manmade vs natural) Decision Verb Generation Category Generation BRAIN MEASUREMENTS FROM MRI: Volumetric MRI scans (1.2 mm thick sagittal slices) on 1.5 GE scanner Surface area of the planum temporale was calculated between sagittal coordinates x = 47 and 56, a region for which asymmetry has correlated with behavior in many studies (Leonard & Eckert, 2008). Analyses and Results Outliers The 17 “outliers” showed quite variable performance on the measures used in the cluster analysis (i.e., they do not form a fifth cluster). However, they did share some characteristics that differentiated them from the rest of the sample: Very good performance on Passage Comprehension (77.2 %ile) Very slow responses on VF tasks (mean RT-zscore =.317), relative to any cluster (mean RT-zscores <.09) Extreme variability across task asymmetries - much higher average standard deviations (sd RT = 1.64, sd Acc =.51) than any cluster (sd RT <.30; sd Acc <.26) Very high percentage of consistent-handers (70.6%), relative to any cluster (38.5% - 54%) Unusual planum temporale asymmetries: Mean coeffiecient of asymmetry =.12, ns Large % of reversed (i.e., rightward) asymmetries (41%), relative to any cluster (12%-27%) The distribution of planar asymmetries for the entire sample is shown in the figure. Clusters Poorer Reader Average Reader Good Reader Good Reader Low-to-Average Large Low VF VF Asymmetries VF Asymmetry VF Asymmetry AsymmetryVary by Task (N = 61) (N = 63) (N = 26) (N = 33) Word Att%ile Word Id%ile P Comp%ile Mean VF Asym (sd)(.206)(.320)(.274)(.495) PT Asym 2.32**.30**.40**.41** 1 Asymmetry expressed as z-score; 0 = average asymmetry; negative = smaller than average asymmetry 2 Coefficient of asymmetry; positive values = leftward asymmetry; ** p <.001 The following measures, which were not strongly correlated, were used in the cluster analysis (Ward’s method): word attack; accuracy asymmetry for masked word recognition, lexical decision, and verb generation; RT asymmetry for nonword naming, masked word recognition, lexical decision and verb generation. A four-cluster solution (eigenvalue = 0.97) successfully classified all but 17 of the participants. As shown below, the clusters represented differing reading/VF asymmetry profiles. All groups showed the expected leftward planar asymmetry.