Neural Reuse and the Modularity of Mind: Where to Next for Modularity?

Abstract

The leading hypothesis concerning the “reuse” or “recycling” of neural circuits builds on the assumption that evolution might prefer the redeployment of established circuits over the development of new ones. What conception of cognitive architecture can survive the evidence for this hypothesis? In particular, what sorts of “modules” are compatible with this evidence? I argue that the only likely candidates will, in effect, be the columns which Vernon Mountcastle originally hypothesized some 60 years ago, and which form part of the well-known columnar hypothesis in neuroscience—systems that cannot handle gross cognitive functions (vision, olfaction, language, etc.) as distinct from strictly exiguous subfunctions (such as aspects of edge detection, depth discrimination, etc.). This is in stark contrast to the modules postulated by much of cognitive psychology, cognitive neuropsychology, and evolutionary psychology. And yet the fate of this revised notion is unclear. The main issue confronting it is the effect of the neural network context on local function. At some point the effects of context are so strong that the degree of specialization required for modularity is not able to be met. Still, despite indications from neuroimaging that peripheral and central systems deploy shared circuitry, some skills clearly do seem to display modularization and autonomy. This article: (1) provides an in-depth analytical and historical review of the fortunes of modular thinking in cognitive science; (2) offers a systematic calibration of brain regions in terms of degrees of functional specificity and robustness; and (3) suggests another way of accounting for the partially encapsulated character of expertise and other highly practiced skills without having to resort to domain-specific modules.