Alfalo - 2006 - Possible origins of the complex topographic organization of motor cortex ...

Citation

Aflalo TN, Graziano MS. Possible origins of the complex topographic organization of motor cortex: reduction of a multidimensional space onto a two-dimensional array. J Neurosci. 2006 Jun 7;26(23):6288-97. PUBMED - FULL TEXT

10 Word Summary

Motor cortex is organized by behavioral, spatial and anatomical "likeness".

Abstract

We propose that some of the features of the topographic organization in motor cortex emerge from a competition among several conflicting mapping requisites. These competing requisites include a somatotopic map of the body, a map of hand location in space, and a partitioning of cortex into regions that emphasize different complex, ethologically relevant movements. No one type of map fully explains the topography; instead, all three influences (and perhaps others untested here) interact to form the topography. A standard algorithm (Kohonen network) was used to generate an artificial motor cortex array that optimized local continuity for these conflicting mapping requisites. The resultant hybrid map contained many features seen in actual motor cortex, including the following: a rough, overlapping somatotopy; a posterior strip in which simpler movements were represented and more somatotopic segregation was observed, and an anterior strip in which more complex, multisegmental movements were represented and the somatotopy was less segregated; a clustering of different complex, multisegmental movements into specific subregions of cortex that resembled the arrangement of subregions found in the monkey; three hand representations arranged on the cortex in a manner similar to the primary motor, dorsal premotor, and ventral premotor hand areas in the monkey; and maps of hand location that approximately matched the maps observed in the monkey.

Notes

• Ethological - relating to the study of human behavior and social interaction
• Motor mapping competes based on at least three "requisites":
  • somatotopic map of the body
  • location of hand in space
  • behaviorally relevant movements
• Kohonen map uses training data to update the closest matching node and its surrounding nodes to better match the input.
• The SOM (self-organizing map) produced physiologically observed phenomena:
  • Simpler movements in a posterior "primary" strip
  • Cortical zones for behaviorally relevant movements
  • Three hand representations (posterior M1, ventral premotor and dorsal premotor)
  • Noisy maps of hand location in space