"Willed action: a functional MRI study of the human prefrontal cortex during a sensorimotor task",
Fahmeed Hyder,  Elizabeth A. Phelps, Christopher J. Wiggins, Kevin S. Labar, Andrew M. Blamire, and Robert G. Shulman 

Proc. Natl. Acad. Sci. USA,  Vol. 94, pp. 6989-6994, June 1997. Neurobiology

Keywords: positron emission tomography, human brain mapping, dorsolateral prefrontal cortex, verbal fluency, Brodmann areas 6,8,9,24,32,45 and 46

URL: http://www.pnas.org/cgi/content/full/94/13/6989