Subcortical aphasia and the problem of attributing functional responsibility to parts of distributed brain processes.

N&C's discussion is, in places, an exemplar of the sort of rigor and attention to detail that will bring us closer to an understanding of the functional organization of the brain. Indeed, it is this level of work that pushes us to reflect on the assumptions that undergird our research efforts. Our criticisms have developed four main points. First, the level of rigor applied to the consideration of basal ganglionic aphasia should extend to each application of the CPC method (thalamic aphasia included). Second, in our haste to identify specific brain systems with distinct cognitive functions we should not neglect the more basic question of the causal mechanisms by which the brain organizes behavior. Questions of "direct" versus "indirect" involvement of a particular organ in a cognitive function are only likely to distract our attention from this more basic and less inferentially perilous issue. Third, pure cases should no longer be considered touchstones against which all behavioral disturbances are measured. Reifying such ideals is more likely to shroud than reveal the brain's true complexity. Finally, the functions that we enshrine in particular brain regions should explain the particular character of the symptoms observed when they are damaged and should admit of independent verification.