links to J Neurophys article: Cortical Involvement in the Recruitment of Wrist Muscles

[Ashvin Shah]

Hello Connectionists - the following article may be of interest. I've 
included the citation and the abstract. Thank you.  

- Ashvin Shah, ash at cs.umass.edu, (413) 545-1596
  Neuroscience and Behavior Program, University of Massachusetts, Amherst 

Shah, A., Fagg, A. H., and Barto, A. G. (2004)
Cortical Involvement in the Recruitment of Wrist Muscles
Journal of Neurophysiology vol. 99(6), pages 2445 - 2456

http://www-all.cs.umass.edu/pubs/2004/shah_fb_JNP04.pdf
http://www-all.cs.umass.edu/pubs/2004/shah_fb_JNP04.ps

http://jn.physiology.org/
PMID: 14749314 [PubMed - in process]

ABSTRACT:
In executing a voluntary movement, one is faced with the problem of
translating a specification of the movement in task space (e.g., a
visual goal) into a muscle-recruitment pattern. Among many brain
regions, the primary motor cortex (MI) plays a prominent role in the
specification of movements. In what coordinate frame MI represents
movement has been a topic of considerable debate. In a two-dimensional
wrist step-tracking experiment, Kakei et al. described some MI cells
as encoding movement in a muscle-coordinate frame and other cells as
encoding movement in an extrinsic-coordinate frame. This result was
interpreted as evidence for a cascade of transformations within MI
from an extrinsic representation of movement to a muscle-like
representation. However, we present a model that demonstrates that,
given a realistic extrinsic-like representation of movement, a simple
linear network is capable of representing the transformation from an
extrinsic space to the muscle-recruitment patterns implementing the
movements on which Kakei et al. focused. This suggests that cells
exhibiting extrinsic-like qualities can be involved in the direct
recruitment of spinal motor neurons. These results call into question
models that presume a serial cascade of transformations terminating
with MI pyramidal tract neurons that vary their activation exclusively
with muscle activity. Further analysis of the model shows that the
correlation between the activity of an MI neuron and a muscle does not
predict the strength of the connection between the MI neuron and
muscle. This result cautions against the use of correlation methods as
a measure of cellular connectivity.

--