Who Needs Emotions? The Brain Meets the Robot

organization of motivational–emotional systems 41
systems. For the purposes of the present discussion, we will focus on the prototypical
mammalian brain.
Modern neuroanatomical tracing methods combined with more advanced
cellular and chemical marking techniques have allowed investigators
to accrue an enormous amount of information about how the brain is
organized. However, as noted by Swanson (2000), such an array of detail
provides little insight without a synthetic perspective based on unifying
and simplifying principles. In a recent series of extensively detailed papers
by Swanson and colleagues, a model of brain architecture and function
has been proposed that is based on converging lines of evidence from neurodevelopment,
gene expression patterns, circuit connectivity, and function
and provides striking insight into the basic organizational patterns that have
NEOMAMMALIAN
(neocortex)
PALEOMAMMALIAN
(limbic cortex, hippocampus,
amygdala, septum,etc.)
REPTILIAN
basal ganglia)
(diencephalon, brainstem,
Figure 3.3. The triune brain, as conceptualized by Paul MacLean. MacLean
(1990) proposed that the mammalian brain is composed of three main
anatomical formations, which represent different levels of development in
evolution: the protoreptilian brain (represented in lizards and other reptiles
and composed of the diencephalic/brain-stem core as well as the basal ganglia),
the paleomammalian brain (represented in earlier mammals and composed of
limbic structures), and the neomammalian brain (reaching its most extensive
development in later mammals and primates and composed of the neocortex).
Behaviors necessary for survival—feeding, reproduction, social–communicative
behaviors—are hard-wired in protoreptilian circuits. As natural selection
proceeded, further behavioral flexibility was enabled, in a hierarchical fashion,
through the progressive expansion of the limbic and neocortical mantle.