Dissociative methods in the study of frontal lobe function

In principle, the specialization of function within prefrontal cortex can be shown by double dissociation using any of a variety of neuroscientific methods, including functional imaging, comparison of lesion groups, and single-cell electrophysiology. In practice, full dissociation designs are rarely used, and when they are, clear dissociations are hard to obtain. Taken together, neuroimaging, lesion, and electrophysiological results suggest that well-defined regions of frontal cortex - middorsolateral, midventrolateral, and dorsal anterior cingulate - have somewhat dynamic functions, adapting themselves to solution of a broad range of cognitive problems. In neuroimaging, for example, these regions are activated by many different increases in cognitive demand, including response conflict, task novelty, working-memory load, and even perceptual difficulty. At the same time, these regions can be distinguished from much of medial and orbital frontal cortex, perhaps more concerned with affective and motivational processes. We suggest that refinement of this rather coarse subdivision of frontal functions will require a substantial strengthening of commitment to full-scale double-dissociation methodology.