Planum temporale asymmetry and ear advantage in dichotic listening in developmental dyslexia and Attention-Deficit 0 Hyperactivity Disorder (ADHD) LORI M. FOSTER, 1 GEORGE W. HYND, 2 ALLISON E. MORGAN, 3 and KENNETH HUGDAHL 4 1 Virginia Beach City Public Schools, Virginia Beach City, Virginia 2 University of Georgia, Athens, Georgia 3 Baltimore Public Schools, Baltimore, Maryland 4 University of Bergen, Bergen, Norway (Received June 10, 1999; Revised July 14, 2000; Accepted October 25, 2000) Abstract The planum temporale is clearly involved in language processing, for it serves as the auditory association cortex. Research has consistently demonstrated that 60 to 70% of the population has leftward asymmetry of the planum temporale. Research has also suggested that dyslexic individuals tend to have either rightward asymmetry or symmetrical plana. Moreover, many studies have found a relationship between the presence of dyslexia and 0or language impairment and deficits in the normal right ear advantage found in dichotic listening paradigms. In this context, this study examined the relationship between planum temporale asymmetry and ear preference in dichotic listening performance in children with Developmental Dyslexia and Attention-Deficit 0 Hyperactivity Disorder (ADHD). Subjects included 19 children with dyslexia (10 of whom had a comorbid diagnosis of ADHD), 23 children with ADHD, and 12 diagnosed normal control children. Dichotic listening data were not collected for 8 of the 12 normal control children and for 3 of the 23 ADHD children. Results revealed no significant difference between ADHD and dyslexic subjects in regard to ear advantage on the free recall dichotic listening task. In addition, although the directed dichotic listening tasks were not related to degree of planum asymmetry, as predicted, results indicated that subjects who consistently displayed an atypical left ear advantage tended to have larger right bank lengths than those who consistently displayed a typical right ear advantage. These findings support the notion that some individuals with dyslexia or language deficits tend to have a larger right planum temporale and that performance on dichotic listening tasks may reflect this relatively unusual pattern. (JINS, 2002, 8, 22–36.) Keywords: Dichotic listening, Planum temporale, Dyslexia, ADHD INTRODUCTION Numerous studies have demonstrated abnormal neuroana- tomical patterns of asymmetry in individuals with dyslexia (e.g., Galaburda, 1989; Galaburda & Kemper, 1979; Gala- burda et al., 1985; Humphreys et al., 1990; Hynd et al., 1990; Larsen et al., 1990; Morgan, 1996). Moreover, many studies have found a relationship between the presence of dyslexia and 0or language impairment and deficits in the normal right ear advantage found in dichotic listening par- adigms (e.g., Hugdahl et al., 1995; Hynd & Obrzut, 1981; Hynd et al., 1979; Mercure & Warren, 1978; Sparrow & Satz, 1970; Zurif & Carson, 1970). Because of these rela- tively consistent findings, it seemed that exploration of the relationship among planum temporale morphology, planum temporale asymmetry patterns, and auditory processing, as revealed through dichotic listening performance in dys- lexia was warranted, as an improved understanding of the neurological and perceptual substrates of learning disorders may be revealed. The planum temporale is considered to be a crucial struc- ture in the language process, for it serves as the auditory association cortex and is a component of the temporal speech region of Wernicke’s area (Geschwind & Levitsky, 1968; Geschwind, 1972; Geschwind & Galaburda, 1985). More specifically, as conceptualized in the Wernicke-Geschwind model for language, Wernicke’s area, containing the pla- num, is thought to include an auditory comprehension cen- Reprint requests to: George W. Hynd, Center for Clinical and Devel- opmental Neuropsychology, GIDE Aderhold Hall, The University of Georgia, Athens, GA 30602-7101. Journal of the International Neuropsychological Society (2002), 8, 22–36. Copyright © 2002 INS. Published by Cambridge University Press. Printed in the USA. DOI: 10.1017.S1355617701020033 22