Who Needs Emotions? The Brain Meets the Robot

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and gonadal and adrenal steroids) influence the hypothalamus via circumventricular
organs such as the arcuate nucleus, which has dense receptors
for circulating chemical signals. The spinohypothalamic tract carries somatosensory
information (mostly to the lateral hypothalamus). Thus, many neural
and chemical sensory inputs to the behavioral control columns have been
identified, and it is clear that the architecture is elegantly designed for complex
coordination of adaptive motivated behavior.
Returning to Swanson’s model, a second route for critically important
inputs to the behavioral control column is via the cerebral cortex, including
massive direct and indirect afferents from such areas as the hippocampus,
amygdala, prefrontal cortex, striatum, and pallidum. Via these inputs, the
“reptilian core” has access to the highly complex computational, cognitive,
and associative abilities of the cerebral cortex. For example, hippocampal
inputs from the subiculum innervate the caudal aspect of the column involved
in foraging and provide key spatial information to control navigational
strategies; place cells are found in regions of the mammillary bodies as well
as the hippocampus, anterior thalamus, and striatum (Blair, Cho, & Sharp,
1998; Ragozzino, Leutgeb, & Mizumori, 2001). The amygdala’s role in reward
valuation and learning, particularly in its lateral and basolateral aspects
(which are intimately connected with the frontotemporal association cortex),
can influence and perhaps bias lateral hypothalamic output. Indeed,
recent studies have supported this notion; disconnection of the amygdalo–
lateral hypothalamic pathway does not abolish food intake but alters subtle
assessment of the comparative value of the food based on learning or sensory
cues (Petrovich, Setlow, Holland, & Gallagher, 2002); in some of our
recent work, inactivation of the amygdala prevents expression of ingestive
behavior mediated by striatal–hypothalamic circuitry (Will, Franzblau, &
Kelley, 2004). The potential for cellular plasticity in cortical and striatal
regions is greatly expanded compared to brain-stem and hypothalamic systems.
Indeed, gene expression patterns can reveal this expansion in evolutionary
development. An example from our material (Fig. 3.4) shows that
the cortex and striatum are rich in the protein product of the gene zif268,
which plays an important role in glutamate- and dopamine-mediated plasticity
(Keefe & Gerfen, 1996; Wang & McGinty, 1996). Levels of this gene
product are much lower in the brain stem and diencephalon. Thus, the phylogenetically
most recently developed and expanded brain region, the “neomammalian”
cerebral cortex, is intricately wired to communicate with and
influence the ancestral behavioral control columns and capable of complex
cellular plasticity based on experience.
As the origin of the term would suggest, motivation must ultimately result
in behavioral actions. The Canadian physiological psychologist Gordon
Mogenson and colleagues (1980) drew attention to this matter in their land-