Evolution of cognitive function via redeployment of brain areas

studies are understood to be those specifically responsible for the cognitive function
under investigation.

In order to evaluate the three predictions, several values need to be calculated for this
data set. First, we need to know how many brain areas are activated by a typical
cognitive task, and whether this varies by task category. Second, we need to know how
many cognitive tasks a typical brain area supports, and how these tasks are distributed
across the four categories. Third, we need to measure the “scatter” of the areas
participating in each task, and the variance of this value by task category. Finally, we
need to correlate these values with phylogenetic age.

To calculate the first two values was primarily a matter of counting. Cabeza and Nyberg
use a coding scheme for activations that forces a decision between lateral and medial
activation, such that it is not possible to show both a medial and a lateral activation in a
given brain area for a given task. Instead, the possible activations for each brain area are
left lateral (LL), right lateral (RL), bilateral lateral (BL); left medial (LM), right medial
(RM), bilateral medial (BM). Thus, for instance, they list the following activations for a
task involving hearing words vs. a resting condition (Muller 1997): an LL activation in
Brodmann area 47, and BL activations in areas 21 and 22. For the purposes of counting
areas activated by a task, I treated bilateral activations of an area as two participants, one
left and one right (medial or lateral). Thus, the language task above would have five
participants, three LL participants (areas 47, 21 and 22) and two RL participants (areas 21
and 22). For the purposes of counting redeployments (areas activated by more than one
task), I matched LL activations in an area to other LL activations of that area, as well as

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