1. Discriminating left from right with a Likert rating scale: Sylvian fissure asymmetry in healthy adults Christiana M. Leonard, Ph.D. 1, Stephen Towler 1, Dawn Joseph 1, Suzanne Welcome 2, Laura Halderman 2, Ron Otto 3 and Christine Chiarello 2 1 University of Florida, McKnight Brain Institute, 2 University of California, Riverside, Department of Psychology, 3 Riverside Imaging, Riverside CA 343 Introduction Method References PARTICIPANTS: 100 male, 100 female native English speakers 18-34 years of age 28 (14%) are not right-handed PROCEDURE: Volumetric MRI scans (1.2 mm thick sagittal images) on 1.5 GE Scanner Brain tissue extracted, reoriented, and segmented into isometric 1 mm voxels with FSL software http://www.fmrib.ox.ac.ukhttp://www.fmrib.ox.ac.uk After paging through sagittal images of each hemisphere, two raters, blind to hemisphere and individual characteristics, used a 5 pt Likert scale to rate (1) the probability that there was an extra or missing gyrus in the parietal operculum and (2) the ratio between the PT and the parietal operculum (PP) on an image 51 mm lateral to the midline. As at least 86% of the two ratings were within 1 point of each other, the two ratings were averaged. For some analyses adjacent ratings were collapsed to produce a three point scale on each dimension. Results Chiarello C, Kacinik N, Manowitz B, Otto R, Leonard C. Cerebral asymmetries for language: evidence for structural-behavioral correlations. Neuropsychology 2004; 18: 219-31 Chiarello C, Lombardino LJ, Kacinik MA, Otto R, Leonard CM. Neuroanatomical and behavioral asymmetry in an adult compensated dyslexic. Brain Lang 2006; 98: 169-81. Dorsaint-Pierre, R., Penhune, V. B., Watkins, K. E., Neelin, P., Lerch, J. P., Bouffard, M., et al. (2006). Asymmetries of the planum temporale and Heschl's gyrus: relationship to language lateralization. Brain, 129, 1164-1176. Eckert, M. A., Leonard, C. M., Possing, E. T., & Binder, J. R. (2006). Uncoupled leftward asymmetries for planum morphology and functional language processing. Brain and Language, 98, 102-111. Eckert MA, Galaburda AM, Karchemskiy A, Liang A, Thompson P, Dutton RA, et al. Anomalous sylvian fissure morphology in Williams syndrome. Neuroimage 2006; 33: 39- 45. Steinmetz H, Ebeling U, Huang Y, Kahn T. Sulcus topography of the parietal opercular region: An anatomic and MR study. Brain Lang 1990; 38: 515-33. Witelson SF, Kigar D. Sylvian fissure morphology and asymmetry in men and women: bilateral differences in relation to handedness in men. J Comp Neurol 1992; 323: 326- 40. Witelson SF, Kigar D, Harvey T. The exceptional brain of Albert Einstein. Lancet 1999; 353: 2149-53. This research was supported by NIDCD R01 006957 and the McKnight Brain Institute. In 1968, Geschwind and Levitsky reported that the post mortem analysis of 100 human brains of unknown sex and hand preference demonstrated unequivocal evidence of structural asymmetry in the superior surface of the temporal lobe.. The planum temporale (PT) was six times as likely to be larger on the left as the right. They speculated that this structural asymmetry provided a biological basis for the localization of language function to the left hemisphere. As this interpretation has not been confirmed in two recent fMRI studies (Eckert et al., 2006; Doursaint-Pierre et al., 2006) the functional significance of this highly reliable and replicated population asymmetry remains mysterious. In a small sample, we found that PT asymmetry was associated with asymmetry in the speed and accuracy of word processing presented to the left and right visual field (Chiarello et al., 2004). We are now attempting to confirm this relationship in a sample of 200 healthy adults. As part of this study we have developed a reliable way to capture asymmetries in (1) parietal operculum morphology (Steinmetz et al. 1990) and (2) the ratio between PT and the parietal planum (PP) (Witelson & Kigar (1991). Fig. 3. Five point scale. Treating the upper and lower banks of the Sylvian fissure as two independent dimensions demonstrates a dramatic degree of asymmetry between the two hemispheres. The left and right parietal opercula were characterized by highly significant differences in PT/PP ratio (top) and gyral number (bottom). The left hemisphere distribution of ratios and gyral number was skewed towards longer PT and extra gyri. A discriminant analysis with these two ratings successfully classified 72% of the left hemispheres and 71% of the right hemispheres (F[2,397] = 64.4, p <.0001). The Steinmetz and Witelson/Kigar Categories Type HV/1: Horizontal (PT) and vertical (PP) rami; Vertical ramus enters supramarginal gyrus (SMG) Type H/2: No vertical ramus/PP Type 3: Vertical ramus/PP rises posterior to SMG Type V: No horizontal ramus (PT) Type 4: Vertical ramus joins postcentral sulcus or rises in sensory strip Fig. 1 (Adapted from Chiarello et al., 2006) Types 1-4 from Steinmetz et al., 1990; Types HV, H & V from Witelson and Kigar (1992). Steinmetz et al. collapsed types 2 and 3 together because many 2’s are also 3’s. There have been relatively few publications reporting use of the Steinmetz and Witelson systems. We have found it difficult to achieve reliability on the classifications due to the existence of intermediate forms. Fig 2. Extreme examples of types 3 and 4 in a severely affected dyslexic but successful builder. A type 4 fissure was also seen in another compensated dyslexic (Chiarello et al., 2006). The second individual was highly inaccurate and slow in naming words presented to his left but not his right visual field/right hemisphere. He failed English in secondary school and never learned his times tables, but had a superior ability to visualize complex mathematical equations which led to professional success. We speculated that superior visualization ability is associated with a type 4 fissure because of the the enlargement of the posterior parietal lobe. Einstein reportedly had this formation bilaterally (Witelson, et al., 1999). The table to the left compares the proportions of fissure types in the Steinmetz, Witelson/Kigar and present hybrid system. As can be seen, type 4 and V are much more common in the right hemisphere, while type 2_3 and H are much more common in the left hemisphere. There were no effects of sex, hand preference, or IQ on the distribution of fissure types. It is intriguing to speculate on the genetic and neurobiological mechanisms underlying these robust structural differences. Fig. 4. Combinations of characters collapsed to a three point scale. Chi squares = 20.0, p <.0001. Yellow columns show the proportions of type 3 fissures. Most type 3 fissures have very high PT/P ratios. Blue columns show the proportion of hemispheres with type 4 fissures. Most type 4 fissures are also type V. No V4 fissures were found in the left hemisphere. The individuals with this feature combination did not have unusual visual field asymmetries, behavioral profiles or reading histories. We are currently using Freesurfer http://surfer.nmr.mgh.harvard.edu/ to compare the brain morphology of individuals with and without unusual asymmetries. http://surfer.nmr.mgh.harvard.edu/ 2_3 1 4V 1 V 1 1 V 4NV 4NV 22 22