What Does Any Part of the Brain Do?
The actual research;
Modules and brain mapping
This article has been cited by other articles in PMC.
Abstract
This
review highlights the key role of modularity and the additive factors
method in functional neuroimaging. Our focus is on structure–function
mappings in the human brain and how these are disclosed by brain
mapping. We describe how modularity of processing (and possibly
processes) was a key point of reference for establishing functional
segregation as a principle of brain organization. Furthermore,
modularity plays a crucial role when trying to characterize distributed
brain responses in terms of functional integration or coupling among
brain areas. We consider additive factors logic and how it helped to
shape the design and interpretation of studies at the inception of brain
mapping, with a special focus on factorial designs. We look at
factorial designs in activation experiments and in the context of
lesion–deficit mapping. In both cases, the presence or absence of
interactions among various experimental factors has proven essential in
understanding the context-sensitive nature of distributed but modular
processing and discerning the nature of (potentially degenerate)
structure–function relationships in cognitive neuroscience.
Keywords: Additive factors, Modularity, Factorial, Connectivity, Degeneracy
This
review is essentially a narrative about how some of the fundaments of
experimental design and interpretation of human brain mapping studies
have developed over the past two decades. Its focus is on the role of
modularity and additive factors logic in guiding these developments.
This is a somewhat self-referential account, which allows us to describe
how our earlier misconceptions gave way to more enduring perspectives—
perspectives that help guide our current research into
structure–function relationships in the brain.
This
review comprises four sections. The first considers, briefly, the
rationale for modularity and its place within distributed neuronal
processing architectures. We consider evolutionary imperatives for
modularity and then a slightly more abstract treatment that underpins
the analysis of functional and effective connectivity. The second
section is a short historical perspective that covers the rise and fall
of cognitive subtraction and the emergence of factorial designs in
neuroimaging. Our focus here is on the role of additive factors logic
and the connection to conjunction analyses in neuroimaging. The third
section pursues the importance of interactions in factorial
designs—specifically, their role in disclosing context-sensitive
interactions or coupling among modular brain areas. We illustrate this
using the notion of dynamic diaschisis and psychophysiolopical
interactions. The final section turns to lesion–deficit mapping and
neuropsychology (in the sense of using lesions to infer functional
architectures). Here, we review the concept of necessary and sufficient
brain systems for a given task and how these led to the appreciation of
degenerate structure–function mappings. Additive factors logic again
plays a key role but, in this instance, the combination rule (Sternberg, 2011
this issue) becomes probabilistic and acquires a multiplicative aspect.
We rehearse the importance of degenerate mappings in the context of
multilesion–deficit analysis and conclude with some comments on the role
of cognitive ontologies in making the most of neuroimaging data.
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