Summing Up

The Adaptable Mind: What Neuroplasticity and Neural Reuse Tell Us about Language and Cognition - John Zerilli 2021

Summing Up

This book has been concerned with a specific feature of the organization of biological systems. Livers, hair, eyes, skin, hearts—each exhibits in its own way a certain richness of inner structure it would be foolish to suppose stops the moment one reaches the brain. Happily, no one denies the brain’s intricacy of structure and function. The debate has always been over what form this complexity takes. The most influential answer to this question for over 60 years—and the most controversial for almost 40—is that the mind is composed of modules. I took the canonical expression of this concept from Fodor, but isolated it from some of its peculiarities, most especially the notion of strict domain specificity and sensory transduction. I put this refined concept to the test and ended up with a mixed bag of results. Fodorian modules survive in some ways, but die in others. The modules that survive are functionally and anatomically exiguous when set against those postulated by mainstream evolutionary psychologists. They do not handle gross cognitive functions. In effect, they are the columns that Vernon Mountcastle originally hypothesized some 60 years ago, and form part of the well-known “columnar hypothesis” in neuroscience. These modules extend throughout the cortex, so there can be no real sense in which central systems are not modular. This is to say that the cortex appears to be modular in the general sense that it exhibits a limited (and as yet undetermined) degree of functional specialization consistent with the reuse of neural resources. There seems to be no particular difference in this regard between peripheral systems and central systems. Low-level sensory systems appear as reliant on domain-general mechanisms as central ones. Perceptual and linguistic systems do not exhibit the defining characteristics of Fodorian modularity.

Still, the fate of this revised notion of modularity is not certain. The main issue confronting modularity in this revised sense is the effect of neural network context on local function. At some point, the effects of context are so strong that the degree of specialization required for modularity cannot be met. This does not mean that such brain regions are infinitely plastic, prey entirely to the whims of the neural network in which they find themselves: their plasticity is actually impressively constrained, and they exhibit a considerable degree of developmental robustness. Nevertheless, the extent of strong context effects may turn out to be great enough to put a decisive end to modularity’s long reign. Recent work in neurobiology is thus forcing a redefinition of the architecture of cognition, principally in terms of patterns of interconnectivity, partial specialization, and emergent specialization. As Giordana Grossi summarizes recent trends:

. . . cognitive and brain systems that are specialized in adults develop in a highly interconnected brain where regions co-develop with other brain regions, not in isolation. What a brain region or neuron does, in terms of function, depends on its interaction with other regions and neurons[;] it even depends on the state of distributed neural networks. . . . Within this framework, the specialization of neural systems (modularity) assumes a different meaning, one that is anchored into the physical system of a developing organism. . . . (2014, p. 346)

Turning to the language module, we saw that there probably is no such thing, not at any rate in the conventional sense, and that dissociations that are otherwise compelling evidence of domain specificity can be adequately explained by the Redundancy Model, which predicates functional inheritance across tasks and task categories even when the tasks are implemented in spatially segregated neural networks.

All up, this is a brave new world. It offers a clearer, cleaner, and far more realistic picture of how the mind works. It is respectful of advances in psychology and philosophy over the past half century, but is anchored firmly in the neurobiological evidence. It strikes what I think is an ideal balance between different approaches to the investigation of the mind/brain. I hope it proves as clarifying and useful to others as it has to me.