Neuropsychologia Vol 33 No 8 pp 1047 1055 1995 Copyright 1995ElsevierScienceLtd Printedm GreatBritain All rightsreserved 0028 3932 95 9 50 0 00 Pergamon 0028 3932 95 00045 3 INCREASED CORPUS CALLOSUM SIZE IN MUSICIANS GOTTFRIED SCHLAUG fLUTZ J ANCKE YANXIONGHUANG t JOCHEN F STAIGERI and HELMUTH STEINMETZ1 1 Department of Neurology Heinrich Heine University P O Box 101007 D 40001 Diisseldorf Germany Received 20 June 1994 accepted 27 February 1995 Al tract Using in vivo magnetic resonance morphometry it was investigated wbetheT the midsagittal area of the corpus callosum CC would differ between 30 professional musicians and 30 age sex and handedness matched controls Our analyses revealed that the anterior half of the CC was significantly larger in musicians This difference was due to the larger anterior CC in the subgroup of musicians who had begun musical training before the age of 7 Since anatomic studies have provided evidence for a positive correlation between midsagittal callosal size and the number of fibers crossing through the CC these data indicate a difference in interhemispheric communication and possibly in hemispheric a symmetry of sensorimotor areas Our results are also compatible with plastic changes of components of the CC during a maturation period within the first decade of human life similar to those observed in animal studies Key Words corpus callosum laterality magnetic resonance imaging motor cortex motor skills music neuronal plasticity INTRODUCTION The corpus callosum CC as the main interhemispheric fibertract plays an important role in interhemispheric integration and communication Gender and handedness differences in the anatomy of the CC have been a matter of long standing dispute A lesser degree of functional lateralization i e increased ambilaterality as found in left handers and in subjects with fight hemisphere language dominance has been associated with a larger midsagittal callosal area 14 31 42 43 although this may still be disputable 26 40 Nevertheless group differences in callosal size or shape observed in morphometric studies were generally regarded as a neuroanatomical substrate of differences in cerebral asymmetry and interhemispheric connectivity 10 11 14 31 40 42 43 Theories to explain these differences in CC morphology include naturally occurring regressive events such as death of neurons and elimination of axon collaterals 8 28 44 However this axonal elimination occurs supposedly prior to most environmental influences Alternatively it has been proposed that functional maturation of the CC extends into late childhood and adolescence and coincides with the termination of its myelination cycle According to Rakic and Yakovlev 34 and Yakovlev and Lecours 41 the CC is one of the latest fiber tracts in the central nervous system to be myelinated Furthermore in vivo imaging has revealed that increases of callosal size can be seen at Address for correspondence Dr Gottfried Schlaug Dept of Neurology Beth Israel Hospital 330 Brookline Avenue Boston MA 02215 U S A or Dr Helmuth Steinmetz at the above address 1047 1048 G SCHLAUGet al least up to the middle o f the third decade with a m a x i m u m during the first decade o f h u m a n life 2 9 33 This presumed progression in m a t u r a t i o n o f the C C m a y also correspond to a period o f cortical plasticity since continuing changes in cortical synaptic density occur t h r o u g h o u t childhood 20 27 There is also a general consensus that m o v e m e n t control and m o t o r coordination as well as intermanual transfer o f s e n s o r i m o t o r information i m p r o v e gradually from ages 4 to 11 years an age span coinciding with callosal m a t u r a t i o n 12 17 25 29 30 Although previous reports already suggested that a larger caUosal area m a y indicate a higher capacity for interhemispheric transfer 10 40 42 43 a positive correlation between midsagittal C C area and the n u m b e r of fibers crossing through was only established recently 1 F o r studying possible differences in callosal m o r p h o l o g y in h u m a n s with p r e s u m e d differences in interhemispheric communication the midsagittal C C area and its subdivisions were measured in musicians and controls using high resolution in vivo magnetic resonance M R imaging Recent functional imaging studies already suggested that certain abilities unique to musicians relied on specialized cortical representations in b o t h hemispheres and a m o r e distributed network than similar nonmusical operations 37 F u r t h e r m o r e certain cortical areas such as the p r e m o t o r cortex and the s u p p l e m e n t a r y m o t o r area play a particular role in the t e m p o r a l control o f sequential m o t o r tasks and the integration o f bilateral m o t o r behavior 13 15 Both aspects o f m o t o r control are especially i m p o r t a n t for performing musicians In the current study we tested the hypothesis that early and intensive training in key and string players m a y facilitate increased and faster interhemispheric transfer in order to p e r f o r m complex sequential b i m a n u a l m o t o r sequences F u r t h e r m o r e the recall o f stored m o t o r p r o g r a m s could require m o r e and faster interhemispheric exchange than in those not routinely p e r f o r m i n g b i m a n u a l interactions of similarly complex m o t o r sequences In a m o r e general sense we also speculated that due to their intense and early exposure to extraordinary stimuli musicians m a y form a particularly promising group to disclose relationships between brain structure and behavior MATERIALS AND METHODS Subjects We examined 30 professional classical musicians keyboard or string instrument players or both who described themselves as right handers All of them were students or had just finished training at a music school As a control group we included 30 subjects matched for sex age and handedness They were taken from our database of more than 100 healthy young adults studied with high resolution MR morphometry who have been described elsewhere 23 39 40 Most of them were medical students or young faculty members in university hospitals without any musical training All subjects gave informed consent To further investigate the proposed hypothesis the musicians were divided in subgroups with or without commencement of musical training before the age of 7 Gender age and body height distributions for the …