functions. Again, the reasoning is simple: the more brain areas there are when a given
cognitive capacity is evolving, the more likely that one of them will already serve some
purpose useful for the emerging capacity, and there is little reason to suppose that the
most useful areas will be grouped together (and less reason to suppose this as
evolutionary time passes, making available more functions supported by more areas).
Approach and methods
To evaluate the predictions made by the redeployment hypothesis, I performed some
statistical analyses of 135 brain-imaging experiments, collected by Cabeza and Nyberg
(2000). They survey 275 fMRI and PET experiments, in ten task categories. Here I focus
on only four categories: attention, perception, imagery, and language. The 39 attention
tasks included things like tone detection and Stroop tasks (naming colored words); the 42
perception tasks included such things as object identification and facial recognition; the
18 imagery tasks include mental rotation and landmark visualization; and the 36 language
tasks included reading out loud and silently, lexical decision tasks (discriminating words
from non-words), and the like.
For each task, Cabeza and Nyberg catalog the brain areas reported to be activated by that
task from a list including 26 numbered Brodmann areas, plus the insula and MT, and
three subcortical areas—basal ganglia, thalamus and cerebellum—for each hemisphere.
Each area was divided into a lateral and medial segment, for a total of 124 brain regions.
Note that the reported activations do not represent the full network of brain areas
activated by a given cognitive task, but those remaining after the relevant
control/comparison tasks have been subtracted out. That is, the areas identified in the