Two different areas within the primary motor cortex of man

• Published in: Nature (London) Vol. 382; no. 6594; pp. 805 - 807
• Main Authors: Geyer, Stefan, Ledberg, Anders, Schleicher, Axel, Kinomura, Shigeo, Schormann, Thorsten, Bürgel, Uli, Klingberg, Torkel, Larsson, Jonas, Zilles, Karl, Roland, Per E
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 29.08.1996; Nature Publishing Group
• Subjects: Anatomy; Anatomy & physiology; Autoradiography; Biological and medical sciences; Brain Mapping; Fingers - innervation; Fundamental and applied biological sciences. Psychology; Humans; Macaca; Mammals; Medicin och hälsovetenskap; Motor Activity - physiology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Motor Cortex - anatomy & histology; Motor Cortex - metabolism; Motor Cortex - physiology; Neurology; Neurotransmitter Agents - metabolism; Reaction Time; Thumb - innervation; Tomography; Tomography, Emission-Computed; Touch - physiology; Vertebrates: nervous system and sense organs; Human; Motor pathway; Motor cortex; Central nervous system; Neurotransmitter; Binding site; Anatomy; Brain (vertebrata)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/382805a0

The primary motor area (M1) of mammals has long been considered to be structurally and functionally homogeneous. This area corresponds to Brodmann's cytoarchitectural area 4. A few reports showing that arm and hand are doubly represented in M1 of macaque monkeys and perhaps man, and that each subarea has separate connections from somatosensory areas, have, with a few exceptions, gone largely unnoticed. Here we show that area 4 in man can be subdivided into areas '4 anterior' (4a) and '4 posterior' (4p) on the basis of both quantitative cytoarchitecture and quantitative distributions of transmitter-binding sites. We also show by positron emission tomography that two representations of the fingers exist, one in area 4a and one in area 4p. Roughness discrimination activated area 4p significantly more than a control condition of self-generated movements. We therefore suggest that the primary motor area is subdivided on the basis of anatomy, neurochemistry and function.