Mapping of the preferred direction in the motor cortex

doi:10.1073/pnas.0611597104

Mapping of the preferred direction in the motor cortex

Apostolos P. Georgopoulos*,^†,^‡,^§,^¶,^‖,**,
Hugo Merchant*,^†,^††,
Thomas Naselaris*,^†, and
Bagrat Amirikian*,^†,^¶

*Brain Sciences Center, Veterans Affairs Medical Center, Minneapolis, MN 55417;
Departments of ^†Neuroscience,
^‡Neurology, and
^§Psychiatry, University of Minnesota Medical School, Minneapolis, MN 55455;
^¶Graduate Program in Neuroscience and
^‖Center for Cognitive Sciences, University of Minnesota, Minneapolis, MN 55455; and
^††Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus Juriquilla, Queretaro, 76028, México

Edited by Charles F. Stevens, The Salk Institute for Biological Studies, La Jolla, CA, and approved May 3, 2007 (received for review December 27, 2006)

Abstract

Directional tuning is a basic functional property of cell activity in the motor cortex. Previous work has indicated that cells with similar preferred directions are organized in columns perpendicular to the cortical surface. Here we show that these columns are organized in an orderly fashion in the tangential dimension on the cortical surface. Based on a large number of microelectrode penetrations and systematic exploration of the proximal arm area of the motor cortex while monkeys made free reaching 3D movements, it was estimated that (i) directional minicolumns are ≈30 μm in width, (ii) minicolumns with similar preferred directions tend to occur in doublets or triplets, and (iii) such minicolumns tend to repeat every ≈240 μm (estimated width of a column), with intermediate preferred directions represented in a gradient. These findings provide evidence for an orderly mapping of the preferred direction in the motor cortex.

Footnotes

**To whom correspondence should be addressed. E-mail: omega{at}umn.edu
Author contributions: A.P.G. and H.M. designed research; H.M. and T.N. performed research; A.P.G., H.M., T.N., and B.A. analyzed data; and A.P.G. and B.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

CS,

central sulcus;

PD,

preferred direction;

SUA,

single-unit activity.