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Large-Scale Organization of Preferred Directions in the Motor Cortex. II. Analysis of Local Distributions

¹Brain Sciences Center, Veterans Affairs Medical Center; ²Department of Neuroscience, ³Department of Neurology, and ⁴Department of Psychiatry, University of Minnesota Medical School; ⁵Cognitive Sciences Center, University of Minnesota, Minneapolis, Minnesota; and ⁶Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico

Submitted 8 May 2006; accepted in final form 6 September 2006

The spatial arrangement of preferred directions (PDs) in the primary motor cortex has revealed evidence for columnar organization and short-range order. We investigated the large-scale properties of this arrangement. We recorded neural activity at sites on a grid covering a large region of the arm area of the motor cortex while monkeys performed a 3D reaching task. Sites were projected to the cortical surface along anatomically defined cortical columns and a PD was extracted from each site with directionally tuned activity. We analyzed the resulting 2D surface map of PDs. Consistent with previous studies, we found that any particular reaching direction was rerepresented at many points across the recorded area. In particular, we determined that the median radius of a cortical region required to represent the full complement of reaching directions is at most 1 mm. We also found that for the majority of regions of this size, the distribution of PDs within them exhibits an enrichment for the representation of forward and backward reaching directions (see companion paper). Finally, we found that the error of a population vector estimate of reaching direction constructed from neural activity within these regions is small on average, but varies significantly across different sections of the motor cortex, with the highest levels of error sustained near the fundus of the central sulcus and lowest levels achieved near the crown. We interpret these findings in the context of two well-known features of motor cortex, that is, its highly distributed anatomical organization and its behaviorally dependent plasticity.

This article has been cited by other articles:

				A. P. Georgopoulos, H. Merchant, T. Naselaris, and B. Amirikian Mapping of the preferred direction in the motor cortex PNAS, June 26, 2007; 104(26): 11068 - 11072. [Abstract] [Full Text] [PDF]