Abstract

Kanaan and McGuire elegantly describe three challenges facing the use of fMRI to uncover cognitive mechanisms. They shows how these challenges ramify in the case of identifying the mechanisms responsible for psychiatric disorders. In this commentary, I would like to raise another difficulty for fMRI that also appears to ramify in similar cases. This is that there are good reasons for doubting one of the assumptions on which many fMRI studies are based: that neural mechanisms are always and everywhere sufficient for cognition. I suggest that in the case of the mechanisms underlying psychiatric disorders, this assumption should be doubted. I do not dispute that a malfunctioning neural mechanism is likely to be a necessary component of a psychiatric disorder—as Kanaan and McGuire say, the experimental evidence from cognitive neuropsychiatry gives us excellent reasons to think that this is so. My question is whether a story only in terms of these neural mechanisms is sufficient to explain the mechanism of a psychiatric disorder. Is the reduction, projected by cognitive neuropsychiatry, of psychiatric disorders to disorders in neural functioning even in principle possible? Drawing on recent concerns about the location of mental states, I argue that such a reduction is likely to fail. Even if the considerable problems raised by Kanaan and McGuire for fMRI could be addressed, we have no reason to think that the mechanisms involved in psychiatric disorders are entirely neural, and that fMRI, or even a perfect science-fiction brain-scanner, would be capable of uncovering them. Psychiatric disorders, like numerous other cognitive processes, are liable to cross the brain–world boundary in such a promiscuous way as to be resistant to neural reduction.