Who Needs Emotions? The Brain Meets the Robot

organization of motivational–emotional systems 43
aging/exploratory behaviors. Within the rostral column reside nuclei mediating
sexual dimorphic behaviors: medial preoptic nucleus, ventrolateral
ventromedial nucleus, and ventral premammillary nucleus (these areas contain
high levels of estrogen receptor mRNA). Other nuclei, the anterior
nucleus, dorsomedial part of the ventromedial nucleus, dorsal premammillary
nucleus, mediate defensive responses including defense of territory (and have
abundant levels of androgen receptor mRNA). The main hypothalamic controllers
for food and water intake are found in the periventricular zone and
include the ventromedial and dorsomedial nuclei, the descending part of the
paraventricular nucleus, the subfornical organ, and the arcuate nucleus. The
more caudal segment of the column includes the mammillary body, the ventral
tegmental area, and the reticular part of the substantia nigra. This area,
whose efferents ultimately reach parts of voluntary motor circuits via the thalamus
and superior colliculus, is proposed to mediate forward locomotion and
may also play a role in eye, head, and upper body orientation to salient environmental
stimuli. The lateral hypothalamus is not specifically included in
Swanson’s behavioral control column scheme but probably plays a critical role
in arousal, control of behavioral state, and reward-seeking behavior. The lateral
hypothalamus has long posed an enigma to investigators, not the least
because rats will press a lever thousands of times per hour to deliver electrical
stimulation to this region (Olds, 1958).
Central to this basic model of motivated behavior is an appreciation of
the main inputs to these hypothalamic systems, the features of its organization
with regard to other major brain regions, and its targets. As elaborated
above, motivational–emotional systems are triggered into action by specific
signals—energy deficits, osmotic imbalances, olfactory cues, threatening
stimuli—that impinge on the system and initiate (as well as terminate) activity
in specific brain pathways, thereby effecting responses. In higher mammals,
these signals reach the behavioral control column in multiple ways.
Multiple sensory inputs from the external world reach the hypothalamus
both directly and indirectly (Risold, Thompson, & Swanson, 1997). For
example, it receives direct input from the retina; olfactory and pheromonal
information is conveyed via a massive projection from the medial amygdala
and bed nucleus of the stria terminalis. Cues relating to territory and identification
of individuals as prey or predators arrive to the rostral control column;
those important for visceral (including pain, temperature, and heart
rate) and gustatory processing reach the hypothalamus principally through
the brain-stem nucleus of the solitary tract and parabrachial nuclei, which
bring in information about taste and visceral sensations. This information
influences the periventricular zone involved in ingestion as well as the lateral
hypothalamus. Metabolic and humoral information (circulating levels
of glucose, salt, fatty acids, hormones such as insulin and leptin, angiotensin,