Who Needs Emotions? The Brain Meets the Robot

organization of motivational–emotional systems 61
mediate food “liking” or the pleasurable affective state induced by calorically
dense foods. Thus, it seems that the positive emotional state induced
by tasty, energy-dense foods is in part mediated by brain opioids. It interesting
to speculate that this system may be responsible for the effect that “comfort
foods” have on mood and general emotional state in humans. Supportive
of this notion is the finding that in humans and other animals consumption
of high-fat or sweet foods induces analgesia (Kanarek, Przypek, D’Anci, &
Marks-Kaufman, 1997), suggesting that their consumption can literally reduce
pain. Consumption of chocolate or sugar activates brain circuits encoding
emotion and increases pleasurable feelings (Small et al., 2001).
In sum, opioid peptide-coded neural networks in striatal, limbic, and
brain-stem regions appear to be fundamental substrates for certain affects.
Lowered opioid peptide levels may signal distress, pain, and aversive motivation;
enhanced peptide levels appear to be associated with safety and contentment.
It is therefore not surprising that for thousands of years humans
have chosen to activate this system artificially with opium, heroin, cannabinoids,
and alcohol, all of which interact strongly with opioid systems.
Addictive Drugs and Artificial Stimulation of Emotions
Neurochemically coded brain circuits have evolved to serve as critical internal
signals in guiding adaptive behavior and in maximizing fitness and
survival. We have seen from the above account that the development of
emotional–motivational systems in mammals has its molecular roots in ancestral
behaviors of organisms millions and even billions of years ago. These
systems enable animals to seek stimuli that enhance availability of resources
(food, mating opportunities, safety, shelter) and to avoid danger or defend
against predators. In humans, derangement or imbalance in these systems
can lead to poor coping skills, emotional and mental distress, and psychopathologies
such as anxiety, depression, and obsessive–compulsive disorder.
For thousands of years, humans have used drugs that artificially stimulate
these emotional systems. In the context of the present chapter, it is of interest
to consider the use of drugs by humans within this evolutionary framework.
Considerable advances have been made in understanding the neurobiological
concomitants of addiction; however, it is only relatively recently that
researchers have considered drug use and addiction from an evolutionary
perspective (Nesse & Berridge, 1997; Panksepp, Knutson, & Burgdorf, 2002;
Sullivan & Hagen, 2002).
Drugs serving as reinforcers are not a uniquely human phenomenon.
Many species, such as rats, mice, and nonhuman primates, will directly selfadminister
most drugs that are used or abused by humans, such as alcohol,