Corpus callosum: musician and gender e¡ects Dennis J. Lee, 1,2 Yi Chen 1 and Gottfried Schlaug 1,CA 1 DepartmentofNeurology,BethIsraelDeaconessMedicalCenterandHarvardMedicalSchool,330BrooklineAve,Boston,MA02215; 2 FacultyofArtsandSciences,HarvardCollege,HarvardUniversity,Cambridge,MA02138,USA CA CorrespondingAuthor:gschlaug@caregroup.harvard.edu Received5September2002; accepted11December2002 DOI:10.1097/01.wnr.0000053761.76853.41 Previously we found that musicians have signi¢cantly larger ante- riorcorpuscallosum(CC).Inthecurrentstudy,weintendedtore- plicate and extend our previous results using a new and larger sample of gender-matched subjects (56 right-handed professional musicians and 56 age- and handedness-matched controls). We found a signi¢cantgender  musicianship interaction for anterior and posterior CC size; male musicians had a larger anterior CC thannon-musicians,whilefemalesdidnotshowasigni¢cante¡ect of musicianship.The lack of a signi¢cant e¡ect in females may be due to a tendency for a more symmetric brain organization and a disproportionately high representation of absolutepitch (AP) mu- sicians among females. Although a direct causal e¡ect between musicianship and alterations in the midsagittal CC size cannot be established, itis likely that the earlycommencement and continu- ouspracticeofbimanualmotor trainingservesasanexternaltrig- ger that can in£uence midsagittal CC size through changes in the actualcallosal¢bercompositionandinthedegreeofmyelinization, which will have implications for interhemispheric connectivity. NeuroReport 14:205^209  c 2003LippincottWilliams&Wilkins. Key words: Absolutepitch;Corpuscallosum;Gender;Laterality;Magneticresonanceimaging;Motor skills;Music;Plasticity INTRODUCTION The corpus callosum (CC), the main band of interhemi- spheric axonal fibers in the human brain, performs a key role in the transferal and integration of information between the two hemispheres. Group differences in midsagittal callosal area are generally regarded as neuroanatomic correlates for large-scale differences in interhemispheric connectivity and brain asymmetry [1–3]. It has been shown that midsagittal callosal size correlates with the number of fibers passing through the CC [4], and that the corpus callosum is one of the last main fiber tracts to mature in humans [5]. Increases in CC size have been observed through in vivo imaging until at least the third decade of human life, with maximal growth in the first decade [6,7]. As this period of presumed callosal maturation coincides with childhood increases in synaptic density and fine tuning of the neural organization [8,9], it has been proposed that environmental stimuli, especially early in life, might affect callosal development [10]. Animal experiments have provided evidence that differential rearing affects CC size [11]. Extensive musical training, commencing at an early age and continued through life, provides exactly such extra- ordinary environmental stimuli. Professional musicians, defined as those who are performers, music teachers, or conservatory-level music students, often begin training at an early age, and practice their instruments daily, sometimes up to several hours a day, from childhood throughout their adult lives. In a previous study, we demonstrated group differences between musicians and non-musicians in the anterior CC, with early-beginning musicians displaying a significantly larger midsagittal anterior CC area [10]. We hypothesized that the increased midsagittal CC size in musicians might be evidence for externally triggered changes in the anatomical composition of the CC. These results were astonishing considering that only a few human studies have found structural brain differences between two groups of subjects as a function of certain skills or intense practice [12]. Animal experiments have provided a wealth of data that structural changes as a function of motor training can be seen [13]. In this study, we intended to replicate our previous results using a new, larger, and gender-balanced sample in order to examine possible differences in the CC size between musicians and non-musicians and to determine whether an interaction exist between musicianship and gender as has been found in other studies. MATERIALS AND METHODS Subjects: Our group of subjects consisted of 56 healthy musicians (28 males, 28 females) and 56 healthy non- musician controls matched for age. Due to the possible effect of handedness on midsagittal CC size [2,3], we selected only right-handed subjects. Our subjects were retrospectively selected from a prospective database of high-resolution anatomical MR scans of musicians and non-musicians. Subjects participated in various research protocols, which 0959-4965  c LippincottWilliams&Wilkins Vol 14 No 2 10 February 2003 205 MOTORSYSTEMS NEUROREPORT Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.