Who Needs Emotions The Brain Meets the Robot - Fellous & Arbib Part 3 pdf

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This page intentionally left blank PART II BRAINS This page intentionally left blank 3 Neurochemical Networks Encoding Emotion and Motivation An Evolutionary Perspective ann e. kelley Specific and phylogenetically ancient motivational systems exist in the brain that have evolved over the course of millions of years to ensure adaptation and survival. These systems are engaged by perception of environmental events or stimuli, and when so engaged generate specific affective states (positive or negative emotions) that are powerful drivers of behavior. Positive emotions generally serve to bring the organism in contact with potentially beneficial resources—food, water, territory, mating or other social opportunities. Negative emotions serve to protect the organism from danger—mainly to ensure fight-or-flight responses, or other appropriate defensive strategies such as submissive behavior or withdrawal, protection of territory or kin, and avoidance of pain. Brain systems monitor the external and internal world for signals, and control the ebb and flow of these motivational states. Their elaboration and expression, when elicited by appropriate stimuli, are instantiated in complex but highly organized neural circuitry. Cross talk between cortical and subcortical networks enables intimate communication be- tween phylogenetically newer brain regions, subserving subjective aware- ness and cognition (primarily cortex), and ancestral motivational systems that exist to promote survival behaviors (primarily hypothala- mus). Neurochemical coding, imparting an extraordinary amount of 30 brains specificity and flexibility within these networks, appears to be conserved in evolution. This is exemplified by examining the role of dopamine in reward and plasticity, serotonin in aggression and depression, and opioid peptides in pain and pleasure. Moreover, across the course of thousands of years, humans, through interactions with plant alkyloids, have dis- covered how to facilitate or blunt emotions with psychoactive drugs. Thus, while neurochemical systems mediating emotion generally serve a highly functional and adaptive role in behavior, they can be altered in maladaptive ways in the case of addiction. In attempting to understand the elements out of which mental phenomena are compounded, it is of the greatest importance to remember that from the protozoa to man there is nowhere a very wide gap either in structure or in behavior. —Bertrand Russell (The Analysis of Mind, 1921) Emotions are necessary for the survival of the individual and the species. Therefore, a simple answer to the title of this book is that all organ- isms on earth need emotional systems, in their broadest biological defini- tion. Emotional systems enable animals to more effectively explore and interact with their environment, eat, drink, mate, engage in self-protective and defensive behaviors, and communicate. Thus, a robot designed to sur- vive in the world as successfully as its living counterparts undoubtedly would require an equivalent system, one that instills urgency to its actions and decisions—in short, one that motivates and directs. Along with exquisitely designed perceptual, cognitive, and motor networks, evolution has enabled built-in affective mechanisms that in essence constitute a powerful, readily available energizer that ensures efficiency and maximizes survival. The basic premise of this chapter is that emotions are derived from complex, neurochemically coded systems, structured by evolution, that are present in one form or another from single-celled bacteria to primates. Of course, human subjective awareness of a negative emotion such as dejection or hu- miliation and a crayfish displaying a submissive posture following a struggle with a conspecific are vastly different events; yet one is struck by shared features that characterize neurochemical coding and behavioral mechanisms throughout the evolutionary development of affective systems. Within the rich array of diverse molecules, proteins, neurotransmitters, receptors, and neurohormones in living organisms—some of which have become special- ized for emotion—there is a striking phylogenetic conservation of chemical signaling molecules, many of which have played apparently related roles organization of motivational–emotional systems 31 throughout evolution. In the lobster, serotonin biases dominant behavior, acting as a “gain-setting” device in aggressive conspecific encounters; in hu- mans, serotonin is thought to be a key modulator of mood and control of impulse and aggression. Nuclear transcription factors such as cyclic adenos- ine monophosphate (cAMP) response element binding protein (CREB), by interacting with genes that encode synaptic modeling molecules, enable plas- ticity and flexibility of motivated behavior in both fruit flies and mammals. Dopamine receptors likely play a role in reward learning in honeybees, mollusks, mice, and primates. This richness and complexity of behavioral and affective coding presents a great puzzle for behavioral neuroscientists, but the challenge for computational neuroscientists or roboticists modeling emotion is even more daunting. Computational modeling has tackled cer- tain processes, such as sensation, learning, and motor control, with some success; but to incorporate an organism’s genome and the combinatorial encoding enabled by its protein products and to relate this to emotional states introduces a different and much more formidable level of complexity. Can knowledge of chemical signaling and transmission inform theories about emotion? Can emotional processes be modeled by machines? PHYLOGENETIC DEVELOPMENT OF MOTIVATIONAL– EMOTIONAL SYSTEMS Most chapters or treatises on emotion attempt to define what is meant by such terms as emotion, affect, and feelings. This is a traditional sticking point in the science of emotion as it is notoriously difficult to define what one means by a “feeling”; historically, such endeavors have often led to the philosophy of subjective experience (Russell, 1921) or invited ridicule and the tempo- rary demise of mental science (Watson, 1924). However, in recent decades, a number of testable theories of emotion within the domains of psychology and neuroscience have been developed (Buck, 1999; Damasio, 1996; Ekman & Davidson, 1994; Izard, 1993; MacLean, 1990; Panksepp, 1991; Tomkins, 1982). Buck (1999) nicely summarizes a common thread in these viewpoints: “Rather than stemming from higher-order cognitive appraisal processes, emotions are seen to be based on biologically structured systems that are phylogenetic adaptations, that is, are innate” (p. 302). The concep- tual framework of the present chapter is based on ideas emerging from these theorists and on present knowledge of anatomy, neurochemistry, gene ex- pression patterns, molecular evolution, and function of basic brain motiva- tional circuits. It is clear that much of what we conceive of as emotional processing can be accounted for by a growing understanding of motivational circuits and chemical mechanisms within the brain. 32 brains It is useful to begin with two important premises: first, that specific and phylogenetically ancient motivational systems exist in the brain and have evolved over the course of millions of years to ensure adaptation and sur- vival and, second, that these systems are engaged by perception of environ- mental events or stimuli, that is, information, and when so engaged generate specific affective states (positive or negative emotions) that are temporarily powerful drivers and/or sustainers of behavior. Positive emotions generally bring the organism in contact with potentially beneficial resources: food, water, territory, mating, or other social opportunities. Negative emotions protect the organism from danger: mainly ensuring fight-or-flight responses or other appropriate defensive strategies such as submissive behavior or withdrawal, protection of territory or kin, and avoidance of pain. Brain sys- tems monitor the external and internal (bodily) worlds for signals and con- trol the ebb and flow of these emotions (see Fig. 3.1). Regarding the first premise, the vertebrate brain contains multiple se- lective systems that are adapted for specific purposes, such as mating, social communication, and ingestion. Corresponding systems exist in the inverte- brate brain. These were termed “special purpose” systems by Buck (1999; in contrast to general purpose systems, see below) and, within an anatomical framework, behavioral control columns by Swanson (2000). A typical example is a system designed to procure water under conditions of dehydration. Sen- sory information indicating a need for water (dry mouth, stimulation of volume receptors, osmoreceptors) is conveyed via specifically designed ana- tomical and neurochemical routes (e.g., neural information converging on the periventricular nucleus of the hypothalamus and the neurohormone angiotensin II detected in the subfornical organ). Hypothalamic output path- ways connect to the motor system, and the motivated, thirsty animal seeks and procures water. Depending on how thirsty the animal is, the behavior is more or less vigorous and sustained. Other complex neurochemically, ana- tomically, and hormonally coded systems, discussed in detail below, exist to optimize survival of the individual and the species, ranging from opioids signaling distress calls in rat pups separated from their mother to sex ste- roids directing sexual differentiation and reproductive behavior. Thus, hun- ger, thirst, sex, aggression, the need for air and water, and the need for shelter or territory—what Paul MacLean (1969) calls “the primary affects”—are specific drive states that exist to goad the organism to seek the stimuli that will address its basic survival. Among these are the needs to breathe, to have freedom of movement, to rid the body of filth and excrement, and to rest or sleep. Descriptive words for the primary affects associated with many of these basic needs come readily to mind, for example, hunger, thirst, suffocation, fatigue, pain. organization of motivational–emotional systems 33 However, these are not activated at all times (with the exception of breathing); only in response to particular conditions, states, or needs will motivational circuits be utilized. Buck (1999) develops a very useful notion concerning the concepts of motivation and emotion. Motivation, he postu- lates, is “potential for behavior that is built into a system of behavioral con- trol” [my italics]. It exists whether activated or not; in contrast, emotion is Emotions Motivational states, shaped by natural selection, that allow modulation of physiological and behavioral responses ensuring survival, reproduction and fitness Cope with threat. Avoid danger. Defensive reactions. Procure food and water. Seek reproductive opportunities. Shelter/safety. NEGATIVE EMOTIONS POSITIVE EMOTIONS Learning, Plasticity Flexibility/ adaptation 'Fearful' Defense Figure 3.1. Emotions serve as adaptive states that energize and direct survival behaviors, as discussed in the text. Emotions with negative valence (fear, anger, aggression) protect the organism from danger; an example of defensive burying by the ground squirrel faced with threat is shown (photograph by John Cooke, from Coss & Owings, 1989, with permission). Emotions with positive valence are generally associated with appetitive behaviors such as food seeking, sex, and social bonding; shown are facial expressions from neonates given sucrose solution on the tongue (from Steiner, 1973, with permission). Although the potential for species-specific affective behaviors is hard-wired in brain circuits, motivational–emotional systems are capable of flexibility and plasticity due to experience. [...]... 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... behaviors, whereas if the brain is transected below the hypothalamus, the animal displays only fragments of these behaviors, enabled by motor pattern generators in the brain stem Stimulation and lesion studies during the first half of the 20th century indicated that the motor instructions for species-specific motivated behaviors were instantiated within the hypothalamic circuitry and its brain- stem motor targets... patterning as well as the modifiability and flexibility in the expression of these behaviors For example, in the male blue spiny lizard defending its territory, there are degrees of aggressive display depending on the nature of the encounter If the intruder merely approaches, there is a “warning, take-notice” display If the intruder does not heed this, there is a “challenge” display, in which the lizard expands... with the neocortex MacLean (1990) is perhaps best known for his espousal of the notion of the triune brain, which is particularly interesting with regard to the viewpoint of the present chapter He proposed that the mammalian brain was essentially composed of three formations, which together represent different levels of development in evolution: the protoreptilian brain (represented in lizards and other... (Adler, Hazelbauer, & Dahl, 19 73; Qi & Adler, 1989; Tso & Adler, 1974) Like primordial nervous systems, these cells possess sensory reception, an integrating and transmitting mechanism, and an excitation/effector pathway (see Fig 3. 2) 36 brains NH4Cl 5 Bacteria in capillary x 10 -4 A 4 LiCl NaCl 3 KCl 2 RbCl CsCl 1 0 0 100 200 30 0 400 Salt in capillary, mM B 1 SENSORY RECEPTION other attractants attractants... 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 such as the hippocampus, amygdala, and related structures like the septum), and the neomammalian brain (reaching its most extensive development in later mammals and primates and composed of the neocortex) The general idea is that... 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... bitter/sour (negative hedonic) stimulus is applied to the tongue (Steiner, Glaser, Hawilo, & Berridge, 2001; and see Fig 3. 1) 38 brains Although instinctual behaviors in animals may not reflect the complexity of human emotions, the origin of the word instinct, from the Latin instiguere meaning “to incite, to impel,” reminds us of the Latin origins of the word emotion (“to move out”) and suggests a conceptual.. .34 brains the readout of that system when activated, that is, the manifestation of the potential For example, all organisms have instinctive, built-in mechanisms for defensive behavior in the face of threat or danger; when threat is present, the systems are activated and species-specific defensive behavior ensues The latter point leads to the second premise, that these mechanisms are... make it larger and exposes the blue coloration on his belly If the intruder still fails to retreat, the tenant rushes for him, taillashes, and bites the tail of the offending conspecific (sometimes tails are lost) One way or another, the encounter ends with one member engaging in a sub- organization of motivational–emotional systems 39 missive bow and retreating Thus, the particular behaviors aimed . pain. Brain sys- tems monitor the external and internal (bodily) worlds for signals and con- trol the ebb and flow of these emotions (see Fig. 3. 1). Regarding the first premise, the vertebrate brain. nucleus, the subfornical organ, and the arcuate nucleus. The more caudal segment of the column includes the mammillary body, the ven- tral tegmental area, and the reticular part of the substantia. At the end of the day, the lizard retires and the next day the routine repeats itself. One sees the fixed, routine patterning as well as the modifiability and flexibility in the expression of these