Intern. J. Neuroscience, 1996, Vol. 86, pp. 211-224 Reprints available directly from the publisher Photocopying permitted by license only 0 1996 OPA (OverseasPublishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science Publishers SA Printed in Malaysia MORPHOLOGICAL ASYMMETRIES OF MOTONEURONS INNERVATING UPPER EXTREMITIES: CLUES TO THE ANATOMICAL FOUNDATIONS OF HANDEDNESS? GUDRUN MELSBACH Allgemeine Psychologie, Sozialwissenschafliche Fakultat, Universitat Konstanz, 78434 Konstanz, Germany ANDREAS WOHLSCHLAGER Max-Planck Institut f ir psychologische Forschung, kopoldstr. 24,80802 Munchen, Germany MARTIN SPIEB Wirtsc~fswissensc~~liche Fakultdt, Universitat Regensburg, 93040 Regensburg, Germany ONUR GUNTURKUN AE Biopsychologie, Fakultat fur Psychologie, Ruhr- Universitat Bochum, 44780 Bochum, Germany (Received March 24, 1996) Handedness is one of the main issues in laterality research and is known to he related to a large number of mor- phological asymmetries of the central nervous system. However, the main focus of previous studies were cere- bral structures, which ignored the spinal cord as the most distal neural entity innervating the muscles of the extremities. We analyzed morphometrically motoneurons from segments innervating the arms and hands and compared them with motoneurons of segments that innervated the upper trunk. We found an asymmetry with larger motoneuron perikaryas on the right side of the spinal cord in segments innervating the upper limbs. To our knowledge this is the first time a morphological asymmetry on single-cell-level was shown in the spinal cord of man. The possible relation of this cellular asymmetry to the origins of handedness is discussed. Keywords: Spinal cord, lateralization, morphometry, prenatal reflexes, handedness The search for the biological foundations of handedness has been a predominant issue since the beginning of laterality research. Older theories of the 19th and the beginning of the 20th century proposed that nonneural asymmetries of e.g., blood supply to the extrem- Correspondence to: Onur Guntiirkiin, AE Biopsychologie, Fakultat fur Psychologie, Ruhr-Universitat Bochum, 44780 Bochum, Germany We are grateful to the staff of the pathological institute of the Krankenanstalten Konstanz for providing us samples of spinal cords. Supported by grant Gu 227/4 of the Deutsche Forschungsgemeinschaft and a grant from the Alfried Krupp-Stiftung. 217 Int J Neurosci Downloaded from informahealthcare.com by UB Bochum on 03/26/14 For personal use only.