Who Needs Emotions? The Brain Meets the Robot

organization of motivational–emotional systems 59
response to stress, and reinforcement (Van Ree et al., 2000). Much of the
investigation of central opioids has been fueled by an interest in understanding
the nature of addiction. Indeed, when naturally occurring opioid compounds
were discovered, there was much excitement about the possibility that studies
of endorphins and enkephalins would lead to the development of nonaddictive
pain medications or improved treatment of narcotic addictions.
However, it was clear from the intense research that soon followed these
discoveries that endogenous opioids had very similar physiological profiles
to exogenous opiate drugs such as morphine and heroin (i.e., tolerance and
dependence). Nevertheless, studies of opioid peptide systems and the effects
of exogenous opiate drugs have provided important insights into the
nature of physical pain and psychological distress.
Although opioids mediate diverse functions in different brain regions
and these functions may differ across species, several commonalities characterize
them. Increased opioid function is clearly associated with positive
affective states—for example, relief of pain; feelings of euphoria, well-being,
or relaxation; feelings or behavior associated with social attachment; and
pleasurable states associated with highly palatable foods. Herman and
Panksepp (1981) and Panksepp et al. (1980) have conducted pioneering work
on the role of opioids in behaviors related to social attachment and separation.
A considerable body of research demonstrates that activation of opioid
receptors promotes maternal behavior in mothers and attachment behavior
and social play in juveniles. Separation distress, exhibited by archetypal
behaviors and calls in most mammals and birds, is reduced by opiate agonists
and increased by opiate antagonists in many species (Panksepp, 1998);
maternal separation in rat pups also causes an opiate-mediated analgesia
(Kehoe & Blass, 1986b). This distress behavior in the young serves as a powerful
determinant of maternal behavior; upon such calls, mothers characteristically
come back to and comfort their young. It has been theorized that
touch, a powerful signal of care, activates endogenous opiate signals; for
example, motivation for allogrooming in primates appears to be mediated
by opiates (Graves, Wallen, & Maestripieri, 2002; Keverne, Martensz, &
Tuite, 1989; Martel et al., 1993).
Perhaps the most remarkable effect of opiates is the reduction or elimination
of pain. Pain is generally conceptualized to have both a physical and
an affective component; often, we can describe the physical sensation induced
by a painful stimulus, but additionally it induces a negative emotional
state. Opiate drugs can act on both components of pain, probably at the spinal
and cortical levels; they clearly augment the pain threshold but also induce
statements in patients such as “I still feel the pain, but I don’t mind it as
much.” Pain clearly serves as an enormously adaptive component in protecting
the organism from further danger and eliciting escape responses. Why