Large-Scale Brain Area Functional Organization - Computational Explorations in Cognitive Neuroscience - page 208

in figure 7.3, and explored in more detail in subsequent
chapters as indicated. Based on anatomical distinctions,
primarily in the thicknesses of different cortical layers,
the cortical lobes were further subdivided into process-
ing areas by Brodmann, as shown in figure 7.4. We will
use the following standard terminology for describing
locations (figure 7.5): superior or dorsal = upper; in-
ferior or ventral =lower; posterior or caudal =toward
the back; anterior or rostral = toward the front; lateral
= toward the sides; medial = toward the middle.

The posterior regions contain the primary and higher-
level motor output representations, which is consis-
tent with the executive nature of this lobe in control-
ling behavior.

7.3.2 Limbic System

The limbic system is a group of subcortical brain areas
tucked inside the medial surface of the cortex, and con-
sists principally of the hippocampus , cingulate cor-
tex ,and amygdala , and also contains the anterior tha-
lamus , hypothalamus ,andthe mammillary bodies .
These areas, which are mutually interconnected, were
originally thought to process emotional information.
However, it is probably not useful to group them all
together as one system, because they are now known
to have very different individual roles and can be better
understood in terms of their relationship with the cortex.
For example, the hippocampus, which sits just me-
dial to the temporal cortex, is quite important for rapidly
learning new information of many different types (not
just emotional), is richly interconnected with the me-
dial portions of the temporal cortical association areas,
and can be viewed as sitting at the top of the cortical
hierarchy by virtue of this connectivity. The cingulate,
which is located just inferior to the frontal cortex, ap-
pears to be important for tasks that the frontal cortex
is also specialized for, including motor control and ac-
tion selection. Thus, these two areas should probably be
thought of more as specialized cortical-like areas, even
though they are evolutionarily more ancient archicortex
(protocortex).
Unlike the hippocampus and cingulate, the amygdala
is still thought to be primarily specialized for emotional
processing (see Armony, Servan-Schreiber, Cohen, &
LeDoux, 1997 for a modeling approach), and the cogni-
tive roles of the other components of the limbic system
are not well documented.

Occipital Lobe: Specialized for visual processing,
with area V1 (Brodmann area 17) in the central poste-
rior region receiving the main visual inputs from the
thalamus, and the other areas (e.g., V2, V4) perform-
ing higher levels of transformations (chapter 8).

Temporal Lobe: Specialized for a mix of functions,
including primary and higher level auditory per-
ception (superior regions), higher-level visual form
and object representations (posterior inferior regions,
chapter 8), language processing (superior and medial
lateral regions, chapter 10), and longer-term episodic
representations (e.g., stories, life events) (anterior in-
ferior regions). Medial regions feed into the hip-
pocampus and play an important role in rapid learn-
ing of arbitrary information (see following and chap-
ter 9). There is obviously an important relationship
between language and audition (i.e., speech percep-
tion) that might contribute to their colocalization.

Parietal Lobe: Also specialized for a mix of functions,
including spatial processing (e.g., representing where
things are located in space, chapter 8), and task spe-
cific perceptual processing (e.g., organizing and tun-
ing reaching movements via visual perception). The
most anterior and superior regions house the primary
and higher-level somatosensory processing areas. In-
ferior areas near the temporal lobe are important for
language (especially in the left hemisphere).
Frontal Lobe: Specialized for maintaining represen-
tations in an active state ( active maintenance ), and
(consequently) for “executive” control of processing
in other areas (more on this below and in chapter 11).

7.3.3 The Thalamus

The thalamus is a subcortical area with many special-
ized nuclei (subdivisions) that provides sensory input to
the cortex, by relaying information from sensory sys-
tems. We will discuss the lateral geniculate nucleus of