Higher-Level Cognition - Computational Explorations in Cognitive Neuroscience - page 376

Chapter Organization

After a brief discussion of the biological organization
of the frontal cortex, we begin with the first explo-
ration, which covers a model of the Stroop task and il-
lustrates how the prefrontal cortex can exhibit strategic,
goal-directed control over cognitive processing by sim-
ply maintaining appropriate goallike representations in
active memory. Then, we explore a version of the cate-
gorization task described previously that is based on the
widely-studied Wisconsin Card Sorting Task. We sim-
ulate performance of intact and frontally-lesioned mon-
keys on this task.
Having explored two important principles of frontal
function, we then consider a broader range of data re-
garding the role of frontal cortex in humans and mon-
keys (e.g., lesion data, electrophysiology, neuroimag-
ing). These data provide a more general sense of frontal
contributions to cognitive functioning, which we can
then account for using the mechanisms developed in the
explorations. We also discuss other major theoretical
frameworks for understanding frontal function.
Having focused primarily on the role of the frontal
cortex in higher-level cognition, we conclude with a
broader perspective on the interactions among different
brain areas as they contribute to controlled processing.

ventro−
medial

sma

Figure 11.2: Primary subdivisions of the frontal cortex,
shown for both a lateral (top panel) and medial (bottom panel)
perspective.

The frontal cortex can be subdivided into a number of
different regions, and lesions of these different regions
can have different effects on behavior, as we discuss
later. Figure 11.2 shows the primary subdivisions of
frontal cortex, including the more posterior motor and
supplementary motor areas, and the dorsolateral (top
and side) and ventromedial (bottom and middle) pre-
frontal areas. The cingulate cortex, located in the me-
dial wall, is typically included in discussions of frontal
cortex.
In general, one can think of the frontal representa-
tions as becoming progressively more abstract in the di-
rection from the posterior (primary motor) to the more
anterior (prefrontal) areas. The supplementary (also
called premotor) areas constitute an intermediate level
of abstraction, consisting of larger-scale motor plan rep-
resentations that integrate a number of more basic mo-
tor movements. By extension, one can think of the pre-
frontal areas as having yet more abstract action plans.

11.2 Biology of the Frontal Cortex

From a biological perspective, the emphasis we place
on activation-based processing in higher-level cognition
clearly points to an important role for the prefrontal
cortex, with its ability to sustain robust yet rapidly
updatable activation-based memories (see chapter 9).
Thus, we focus primarily on the properties of this sys-
tem. However, it is important to keep in mind that the
true complexity and power of human higher-level cog-
nition is undoubtedly an emergent property involving
important contributions from posterior cortical systems
as well as other brain areas such as the hippocampus.
Unfortunately, the complexity of developing models of
these emergent phenomena is prohibitive at this time.
We focus on the prefrontal cortex to develop the central
theme of activation-based processing and to introduce
an important set of principles.