Pain Perception As a Model for the Study of Consciousness
The pain model seeks to determine the characteristics of physical systems that are sufficient for the emergence of consciousness. Although many theories presently under investigation focus on the cognitive mechanisms of highly evolved systems, the pain model is especially valuable because it aspires to understand the evolution of primitive awareness systems. The primary problem with past attempts to study primitive awareness has been the inability to recognize consciousness in simpler organisms; however, current research has suggested a “self-report” animal model based on rodent ultrasonic vocalizations (Panksepp 2002). The pain model intends to use vocalizations and other forms of self-report in animals to study awareness in systems less complex than the human. In some cases, consciousness entails the ability to reflect and rationalize, so 1 use the term awareness to mean the most elemental aspect of conciousness, raw experience without cognition.
Because consciousness is a convenient term for a multitude of characteristics, the specificity of the pain model is a significant advantage. This approach explores pain perception, a mode of awareness that is more quantifiable than others, in the hope that the knowledge gained about this mode can be generalized to other modes of awareness. By narrowing the study of consciousness to primitive affective experience, and further selecting the affective experiences associated with pain, this model intends to gain a definitive understanding of the mechanisms of one aspect of primitive consciousness before elaborating on the complexities of the human experience.
Two Types of Consciousness
Previous research models for consciousness studies can be roughly divided into brain-based models and organism-based models. The Neural Correlate of Consciousness (NCC) hypothesis, a proponent of the former, claims that consciousness, like other cognitive functions, can be reduced to the electrical patterns in specific brain modules. The NCC requires that for any sensory experience, there is a neural representational system whose activation is the minimal neural pattern sufficient for the experience, and there must be a match between the content of experience and the content of the neural system. The requirement of a common structure, a one-to-one correspondence, between the elements of the experience and the elements of activity in the minimal neural substrate ensures that there is an intelligible connection beyond simple correlation that would relate the experience to the neural substrate. In recording the response of neurons to stimuli in various parts of the brain, researchers hope to find a network of neurons that satisfy these conditions for a neural correlate of consciousness.
Pioneers in the search for the NCC, Crick and Koch have suggested an unconscious homunculus that combines the neuronal signals from the NCC into a conscious, sensory experience (Crick and Koch 2000). Just as the body has specific organs to translate sensory images like sound into an electrical code the body understands, this theory suggests that there is one region or system in the brain to translate into a conscious experience the electrochemical events of the neural environment, extending from sensory perception to introspective dialogue. Recognizing that neurons can be empirically correlated only with the contect of consciousness and not consciousness itself, the NCC hypothesis assumes that consciousness consists only of sensory content. In other words, no conscious thought is independent of a sensory experience that can be linked to a specific neuronal firing pattern, even internal perceptions like solving a math problem or feeling emotion. Based on the assumption that all modalities and forms of consciousness work by a common mechanism, they hypothesize that the NCC will perceive both the events of the inner world and the events of the outer world as sensory events.
While the NCC is conceptualized as a distinct region or network, the neuromatrix conceptualizes the self’s inner representation as a dynamic integrated system extending throughout the brain (Melzack 1993). The phantom limb phenomenon suggests that there is a neurological representation of the bodyself that persists even when input from a part of the body is gone. This theoretical network, the neuromatrix, consists of extensive loops between cortex and thalamus as well as cortex and limbic regions. These cyclical processing patterns create a unique neurosignature that integrates all the peripheral input into a single representation of the body-self experience. The constant stream of neurosignatures created by the neuromatrix constitutes the experience of continuous awareness, felt as a unified body but generated in the brain.
Though the neuromatrix has not yet been demonstrated in research, the theory has enormous explanatory power. The neuromatrix is the context against which incoming sensations are interpreted and could represent psychological moods that influence the subjective interpretation of stimuli. Not only does the genetically programmed body-self template explain why sensation can persist when the peripheral inputs are destroyed, but it also suggests a solution to the binding problem encountered by NCC theorists by postulating one system on which multiple input units converge and become imprinted as a unit. Each multidimensional experience is represented by characteristic neurosignature patterns of nerve impulses generated by a widely distributed neural network (Melzack 1999). The neuromatrix is, in effect, a new conceptualization of the original NCC, but rather than localizing to one region, the neuromatrix extends through most of the brain, creating one continuous stream of output from multiple systems.
There is a second group of theories identified by their claims that though consciousness is not independent of the nervous system, it is also not identical with any part of it. In response to Crick and Koch’s claim that all experience contains only sensory content, Jaak Panksepp argues that “exteroceptive senses provide a rich content for our consciousness, but not the essential fabric from which consciousness is woven” (2000, 25). Affective interpretations of consciousness focus on the internal disposition and motor tendencies of the subject, and require a chain of complementary systems to encode the sensory information into a symbolic language understood by the whole organism. The integration of multiple physical systems by this affectively colored intentionality may have been the core of self/world awareness that allowed for the evolution of self-consciousness and cognitive abilities.
Like affective theory, the sensori motor integration theory described by Alva Noe claims that the feeling of immersion in the experiential world cannot be isolated in a brain that manipulates a dumb body. Rather, this experiential aspect is described by the integration of sensory input gained through the biological interactions (and possible interactions) between the organism and his environment (Noe 2002). Lawful changes in the neural influx that occur as a function of the movement of the body are the sensorimotor contingencies that allow a subject to perceive and predict external activity (O’Regan 2001). For example, when viewing the Necker Cube (optical illusion of a transparent cube that appears to lean toward the observer and away from the observer at the same time), one bistable image is experienced rather than two alternating images because the change in the perception is not in the visual image of the cube, but in the implications for interaction. This understanding requires prediction and depends on past experience, making it an inherently temporal process that cannot be reduced to a sequence of instantaneous inputs and outputs represented in an information processing device like the neuromatrix or minimal neural substrate.
Though at first the multiple-system explanations of consciousness seem incompatible with the brain-based interpretations, evidence for two types of consciousness suggests that these theories may be describing two different mechanisms for awareness that are equally valid. Intentional interaction with an environment involves the organism as a functional system, and the associated implicit consciousness is better described by affective moods and emotive systems than distinct sensory images represented in neural structures. The vision studies of Crick and Koch, however, are ideal for the study of reflective cognitive functions in complex organisms with a developed attentional system and working memory. Barresi and Moore suggest a theory of consciousness that distinguishes the intentional or “core” consciousness described by affective theories from the reflective consciousness described by NCC theories (Barresi and Moore 2002).
While humans have a complex of cognitive abilities that enhance their conscious experience, core consciousness has been described as a transient sense of knowing that requires neither language nor working memory, but that may exist in virtue of an organism’s sensorimotor capacities (Barresi and Moore 2002). Core consciousness consists simply of awareness directed at objects, and little specific content regarding the objects. Although the subject does experience the object, the subject cannot reflect on its \experience because the self is only implicit in this relation. Far from the popular feeling that primates alone experience the world, this theory suggests that all mammals engage in the lowest level of reflective consciousness, while the entire spectrum of intentional consciousness is characteristic of species existing prior to the evolution of the mammal. This type of consciousness raises the question of how physical systems developed mental properties.
Though core awareness might be attributed to an organism in its entirety, the specific, attentional aspects of reflective awareness are unlikely to be experienced equally by the periphery and central nervous system. The explicit self requires a working memory and the ability to focus attention, both of which are cognitive functions localized in the brain. This type of consciousness is multifaceted and involves levels of development, which Barresi and Moore explain using their theory of intentional relations. Reflective consciousness likely evolved later and built on the systems for intentional awareness because reflective consciousness takes the basic awareness of the environment and turns it on the agent of experience. This type of consciousness raises the question of how a mind can become aware of itself.
Pain Model
Theory
Because intentional and reflective conscious states each raise different philosophical and biological issues, studying the complexities of reflective consciousness in humans is unlikely to take us any closer to the understanding of the mechanism by which matter came to be aware of its environment.
A study of core consciousness encounters the original question of how the mechanical interactions of physical systems developed mental properties. The relationship of these two experientially opposite types of events has been referred to as the explanatory gap. The jump between physical and mental appears insurmountable when studied in the human because the symbolic reflections have become so far removed from their original referents. Human mental events might entail a large number of intentional relations, for example “She knew that he claimed to have heard her speaking about his belief in God.” Although the human brain and its reflective abilities may be the site of a Cambrian explosion of mental life, prior to this there was a long history of tedious development of basic awareness. If the simple relations that make up this complex representation could be studied in primitive conscious systems, then the gap between being and awareness of being would be reduced. In theory, the more primitive the awareness, the less distance there is between the mental and physical events.
Many physical theories, with the exception of some theories of affect, remain unconcerned with the explanatory gap because they assume that the need for mental terms will disappear once they have a thorough analysis of physical systems. The pain model, on the other hand, incorporates conscious affective experience as a vital part of its analysis of physical systems. By acknowledging conscious affective experiences as causal events, the pain model is closer to presenting a physical interpretation of the explanatory gap than other models that avoid the philosophical dilemma. It offers a method of approaching the explanatory gap that might eventually lead to an answer.
The pain model attempts to answer the metaphysical question by first answering the epistemological question, how do we know that other organisms experience the world. This model responds by acknowledging that all organisms must possess some level of awareness in order to experience pain as an affective state. An extensive study of pain perception in non-human species should indicate a primitive conscious system, complex enough to experience pain, yet simple enough that the physical mechanism of consciousness might be within the grasp of modern science.
Rather than studying the specifics of human consciousness, the pain model is ideal for understanding the function of intentional awareness prior to the evolution of reflective awareness and cognition. The understanding gained from these simpler systems might better prepare us for understanding the complexities of our own minds. The interactions between the two mechanisms of consciousness are undoubtably complex and it may not be possible to extricate one from the other in recently evolved organisms. However, a method for studying consciousness in simple organisms might allow scientists and philosophers to focus on the physical requiremerits of core consciousness. This is what the pain model intends to contribute to the picture of consciousness expressed in previous theories.
Advantages of Pain
Defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, pain describes a relation between sensations, cognition, and emotions, the three basic components of reflective consciousness. The experience of pain is unique because, unlike other psychological states that describe the interrelation of the three elements of consciousness, pain can be quantified and manipulated as it has been in past research with both humans and non-humans. Robert Melzack has studied the physical mechanisms of pain extensively, and he originally suggested the neuromatrix theory to account for the psychological experience of pain. Since there was no reason to assume this neural system was specialized to pain, Melzack postulated the neuromatrix as a mechanism for all self-conscious experience (Melzack 1999). The pain model takes a similar specific-to-general approach to a theory of consciousness; however, while the neuromatrix is centered in the brain and descriptive of reflective consciousness, the pain model includes the behavior, physiology, and neurology of the whole organism in its analysis of core consciousness.
Pain is ideal for differentiating between core and reflective awareness because the two types of consciousness can be linked with two pathways for pain perception by their similar qualities. Although these pathways are not completely independent, the primitive paleospinothalamic pathway will be more useful to this method of study than the more complex neospinalthalamic pathway. Different neural mechanisms have been shown to mediate different types of pain, and even the analgesic effects of morphine vary in different pain systems (Abbott 1982). Current research demonstrates that the paleo-pathway projects sensory data from the C-fibers, which sense pain in the peripheral nervous system, to the most primitive base of the brain, including the reticular formation and the periaqueductal gray. The data is further translated up into the limbic systems and the hypothalamus, but not directly to the cortex where the NCC is proposed to exist. Being unmyelinated, C-fibers transmit information more slowly and in humans are associated with dull, diffuse, and burning pain. This system, present in lower animals as well as primates, is not point specific and is likely experienced as a constant low-grade aching. Due to its activity in the limbic regions, this primitive pain system is more likely to affect mood and motivation than the precise pain information of the neospinalthalamic pathway. This relationship between the primitive pain perception associated with core consciousness and emotion suggests the affective theory will influence the hypotheses generated by the pain model.
Additionally, pain is useful because it may be the most primitive perception that is the content of a conscious experience. By our definition, pain elicits the psychological experience of fear or anxiety, and the similarity of fear responses across species is indicative of its early evolution. Of all affective systems, pain has the most significant evolutionary advantages because it allows an organism to perceive and react to tissue damage despite the destruction of preprogrammed reactions, compels communication of danger, and enhances the encoding of the experience into emotional memory banks. Thus, the primitive perception of pain is an ideal model for determining the minimal requirements for awareness in the simplest conscious system. From an evolutionary perspective, pain appears to be the most universal and the most adaptive of any primitive psychological experience, so it is a natural candidate for the most primitive conscious experience.
Describing the most primitive system of awareness is a great advantage in the attempt to understand the evolution of the mind. David Marr argued that determining the evolutionary function of the system is essential to understanding the structure and action of a biological system (Gazzaniga 2002, 597). Because information processing devices such as the brain evolved to solve some problem faced by the organism, the structure of the system can only be explained when what problem it originally solved is known. Theories for the function of pain perception might suggest a possible mechanism to be explored in pain research and integrated into the current consciousness research.
The most primitive consciousness addressed by this model is defined by the perception of pain. This argument does not assume that an animal that does not feel pain is not capable of experiencing other aspects of consciousness, only that the perception of pain is sufficient for the attribution of awareness. This definition is practical because the experience of pain is quantifiable by many measures and is expressed by many different systems throughout an organism, as will be described in the next section. Though there may be levels of awareness excluded by this definition, this definition is morally useful because only organisms that experience pain require humane treatment. After identifying the simplest organism that expresses the definitive characteristics of pain perception, the possible mechanisms of awareness can be studied in the\se species.
Conversely, the appearance of consciousness has often been the reason to infer that an organism could experience pain, the logic being that if an organism could not recognize itself, it could not recognize that it was in pain. This inference is faulty mainly because consciousness was defined by human consciousness, a level of reflective consciousness commonly thought to involve extended working memory, directed attention, the ability to generate thoughts independently of sensory inputs, and a theory of mind. Core consciousness requires none of these capacities, yet is sufficient for the experience of pain. Analyses of the two levels of consciousness imply that primitive organisms perceived pain before they perceived themselves, so a study of core consciousness is more appropriately defined by the experience of pain with the associated affective states than by self-perception.
Finally, pain is an important area of research independent of the philosophical significance it may have for consciousness research. Relatively little is known about the mechanisms of pain, despite the fact that pain is the most common health complaint. Even if research in the pain model yields no evidence relevant to the nature of consciousness, the knowledge gained will likely improve pharmacological and psychological treatment of pain associated with the primitive pathway in humans.
Empirical Indications of Pain
Although pain perception is surely enhanced by the specificity of the neospinothalamic pathway and cognition, the perception of pain from the primitive pathway is evidence of an implicit awareness of self. Thus, it is possible to determine the sufficient requirements for awareness, and perhaps the necessary requirements, by first determining the minimal biological and affective requirements for primitive pain. This is the first step in implementing the pain model as an approach for the study of consciousness.
We can verify whether an organism has the capacity for visual awareness by determining if it has organs for perceiving light, neurological networks for interpreting the light pattern, and the behavioral reactions to visual stimuli. To determine which species experience pain, we must determine the basic physiological and neurological requirements for the affective experience of pain and become familiar with the behavioral expression of pain in nonhuman species.
In an attempt to compile evidence of the nature of perception, neuroscientists often study the physical events correlated with mental events. The assumption is that this correlation is not mere temporal coincidence, but that there is some necessary relation between the events. Similarly, the pain model assumes that the behavioral, physiological, chemical, hormonal, and neurological events correlated with pain are more than coincidence and even more than conditioned correlations; rather, pain is the experience of these events.
Because pain is not identical to tissue damage, this thesis will utilize the definition of pain given by the first Subcommittee on Taxonomy of the International Association for the Study of Pain: “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” For example, anesthesia may interrupt the flow of information to the brain, so no pain will be perceived by the organism even though the sensory nerves are reporting damage. Also pain can be experienced in the absence of tissue damage, or even tissue existence, as is the case for amputees who feel pain in a nonexistent limb. To determine which species experience pain, it is necessary to describe the manifestation of the unpleasant sensory and emotional experience in terms of physical systems, including physiological fluctuations, the activation of expected limbic structures, individual behavioral patterns, the activity of nociceptive and opioid compounds, and the evolutionary validation of the experience.
Physiological fluctuations associated with strong emotional distress include galvanic skin responses, blood pressure, sweating, heart rate, salivatory secretion, respiration rate and depth, skin temperature, pupillary response, metabolic rate, tremor of muscles, and eye movements. Polygraph tests measure psychological discomfort by the resulting physiological changes like heart rate, perspiration, and temperature. Although this evidence is not infallible, the use of these tests in important legal capacities supports the claim that physiological fluctuations are powerful indicators of psychological experiences. These are the easiest expressions of distress to quantify, but it is difficult to measure emotional suffering by the associated physiological changes because these general changes are associated with a variety of emotional states.
Stress is known to activate endogenous pain inhibitory systems, and the paraventricular nucleus of the hypothalamus, located well below the cortex, plays an important role in stress-induced analgesia (Fuchs 1996). Supposedly, this inhibitory mechanism evolved to keep the affective pain experience from distracting the organism in the presence of a greater threat. If this is the case, then it is logical to assume that organisms with these inhibitory systems experience pain as a psychological state than to assume that these inhibitory systems are superfluous mechanisms in organisms that cannot be psychologically distracted by pain. The evolution of this inhibitory system in precortical animals implies that animals gained the capacity to experience pain prior to the development of the cortex.
The numerous parallels between human psychophysical responses to pain and responses of animal nociceptive responses and animal neural responses make it possible to assume that stimuli that evoke pain in humans evoke the same qualitative experience in animals (Price 1988). Indeed, this assumption is essential in pain research that uses animal behavior to predict the effects of drugs on the pain experienced by human subjects. A person who does not feel the pain associated with tissue damage will not automatically go through the motions of exhibiting pain beyond spinal reflexes as a reaction to the tissue damage. Given the similarity of human and nonhuman autonomie physiology, there is no reason to assume that animals would go through the motions of exhibiting pain merely as a reaction to tissue damage when humans only exhibit these reactions in response to the psychological experience of pain.
To determine if an organism has seen a visual stimulus, scientists analyze its behavior to identify some reaction to the stimulus. If there is no reaction, one might infer that it did not see the stimulus, though the organism might be behaving deceptively. Likewise, if an animal reacts to a painful stimulus as if it were in pain, it seems only logical to infer that it experienced pain. Without this inference, the explanation for variations in individual reactions requires that each organism has an individually programmed response, but this conclusion is inconsistent with the simple survival patterns wrought by evolution. The inference of experienced emotion is the most parsimonious and useful explanation for variations between individual reactions to stressful stimuli.
Just as the mere presence of a visual stimulus does not imply that the organism saw it, the pain experienced by the subject cannot be inferred by merely observing whether or not something in the environment is acting on it in a harmful way. Rather, pain must be inferred by the organism’s expression of pain, either in an attempt to communicate pain or an attempt to escape from the cause of the distress. Common behavioral expressions of pain include species- typical vocal or facial expressions, violent thrashing and muscle contraction, attempt to escape, loss of appetite, restricted movement, and antisocial behavior. Though there are some patterns, emotional reactions in humans are specific to the individual, and etheologists have found this to be true in animals as well. Different chimps might express frustration by scratching, ducking the head, restlessness, moaning, whimpering, or any combination thereof (Hebb 1946). Because of the individual subjective nature of psychological experiences, the attribution of emotion might require an analysis of behavior in terms of the individual’s baseline behavior as opposed to the normal behavior of the species. If different individuals of the same species can vary to this extent, the variability between species in their expression of emotion should not be a justification for denying the emotional experience of animals unlike humans unless it is also a justification for denying the emotional experience of atypical human individuals.
Because pain is defined as a psychological experience, the physiological requirements may be necessary but not sufficient for the experience of pain. The experience of fear and distress are also necessary for pain perception. To postulate the experience of pain in the animal, there must be some explanatory power to the affective experience beyond mere mechanical reaction. Using extant species as a living timeline, affective theorists aim to answer this question by studying the evolution of consciousness in primitive systems. Panksepp explores two emotional systems, reward-seeking and separation distress that may have been evolutionarily designed to signal an increase or decrease in fitness (Panksepp 2002). He also postulates that affective neurosymbolic states may have become conscious through an implicit knowing system of the brain, programmed throughout history (Panksepp 1994). Antonio Damasio suggests that core consciousness is another level of biological systems that works to maintain the homeostatic balance within an organism, which means that self-representation is not a superfluous subjective accompaniment but critical to t\he biological development of the organism (Damasio 2000, 2001).
Affective states associated with pain might have provided the motivation to escape that would persist in case of damage to preprogrammed escape systems, compel communication of danger, and facilitate learning and memory. Originally, automatic responses to threatening situations may have been programmed into organisms as they evolved. But as the situations faced by the organism became more complex, procedural memory and motor reflexes were no longer sufficient. Emotions have been described as “genetic memories” that encode biological values that aid in survival (Panksepp 1994). This original perception is likely to have been better described not as the perception lhat “I am in pain,” but rather “Move!” The affective experience of pain provides the organism with a psychological compulsion to find a way to escape, even in a novel environment where preprogrammed responses would be useless. This experience consisted of a sufficiently strong biological response to imprint the internal representation of the stimulus into the nervous system for future recognition. It is possible that primitive procedural memory evolved until the nervous system was capable of interpreting pain and affect, which allowed for the imprinting of emotional memories. This implicit memory is a significant evolutionary advantage, and it is dependent on subjective affective experience.
The requirement of an evolutionary advantage to justify the inference of pain allows for the discrimination between mobile and immobile organisms. If an organism is unable to react to a painful stimulus either by escaping from it or warning other members of its species, there seems to be no evolutionary value to the perception of pain. By this logic, the affective experience of pain would not be inferred for immobile organisms, like plants, regardless of their reaction to painful stimuli. On the other hand, the affective experience of pain would be inferred for any organism that exhibited the reactions expected during a painful experience and utilized some evolutionary benefit of the affective experience beyond mechanical routines.
No matter how many requirements of pain are described and observed, it cannot be certainly established that animals who express pain actually experience it; however, neither can it be established that other humans experience pain, or that anything exists apart from what is personally experienced. Because the inference of animal affective states is necessary to explain animal behavior, Panksepp urges us to emulate particle physicists who were forced to infer unseen entities to explain their observations. The more we learn about the physiological changes associated with pain in humans and nonhuman expressions of affect, the better we can predict which physical events indicate the perception of pain in non- humans.
Objections
Verbal Reports
Despite all of the behavioral and physiological evidence for the experience of pain in non-human animals, some philosophers as well as neuroscientists are reluctant to concede the psychological experience of pain to nonhuman animals that lack the capacity for linguistic expression. Most well-known is Rene Descartes’ dualistic argument against the mental experience of animals other than humans (Descartes 1971). Descartes describes nonhumans as animated machines, lacking both reason and emotion. Descartes observes the gradually increasing complexity in the behavior of species and concludes that there is no reason to grant conscious experience to some animals and not to others because there is no distinction, no break in the gradual climb to complex, mind-like behavior. That is, until he considered humanity. Descartes claims that the obvious gap between humans and nonhuman animals justifies the attribution of consciousness to humanity, but no other species. Language, according to Descartes, is the defining characteristic of consciousness. He claims linguistic capacity is a sufficient condition for the attribution of consciousness because one must have a mind to make use of language.
When Descartes explains the intentional behavior of nonhuman animals in terms of “passions,” he doesn’t mean emotional desires, but purely mechanical drives. These drives are involuntary, unknown to the organism, and motivate behaviors through a series of biochemical signals. It is incorrect to interpret the intentional actions brought about by robotic involuntary processes as phenomenally experienced desires and goals, but human behavior can be explained in terms of mechanical processes as well as nonhuman animal behavior. Yet, Descartes does interpret humans’ intentional actions as the product of internal desires and goals. Descartes admits there are mechanical causes of human mental events, but he claims that the self-reporting by humans of their mental experience justifies the assumption of other human minds. Descartes does not observe animals self-reporting their mental experiences, and so he sees no justification for the assumption of nonhuman minds.
However, there is no certain evidence that a verbal expression is any more a report of internal states than is a behavioral reaction. A verbal expression of internal states may be described as a verbal wince, no more justifiable as a report than other behavioral indications. Verbal reports and expressions are merely one kind of behavior and one kind of expression among many, some of which might be a more reliable source of knowledge about the internal states of other organisms than verbal expression. Aside from the assumed propositional content, there is no observable difference between a verbal report and a behavioral response. A yelp of pain, for example, can be given by a human or a dog, but the human’s yelp has no more symbolic reference to an internal state than does the dog’s. If the person replaces the yelp with the verbal content “ouch” or “my hand,” there is still no reason to believe that this report is any more credible than that of the dog, although it may indeed be more precise because language grants the human greater capacity for categorization. The fact remains that both actions are behavioral manifestations of an internal state, but one is dubbed an instinctive reaction while the other is assumed to have some inexplicable status as a report.
Since there is no logical justification for accepting a verbal report as indication of internal mental states as opposed to other behavioral signals, the justification must lie in the practicality of this assumption in daily interactions. Linguistic specifics are only the most superficial layer of many levels of communication, and understanding based on vocal fluctuations, facial expressions, or pure intuition may just as well occur between non-linguistic organisms. Self reports are often inconsistent with accompanying behavioral indications, and research shows that subjects are more likely to attribute emotions consistent with the tone of voice even when the verbal report contradicted the tone in which the words were spoken (Mehrabian, Weiner 1967). This finding raises doubts about the extent to which verbal reports of emotional states are relied on in making everyday judgments. If daily judgments rely more on behavioral and tonal cues than the symbolic meaning of verbal reports, then we have no reason to deny the same justification to the inference of emotional states in animals who do not utilize a symbolic system.
Verbal labels are most useful in discriminating between similar emotional states differentiated primarily by the context in which they occurred, like disgust, scorn, and contempt. The fact that nonhuman animals are unable to make these distinctions does not deny the possibility that they do differentiate between basic emotional states like approach/withdraw, and so on. Research has shown that mammals with no capacity for verbal representation do in fact make behavioral and tonal reports of their emotional states. After extensive research, P. T. Young (1969) concluded that choice behavior reveals the states of pleasure and pain experienced by the individual; however, two similar behaviors might be motivated by very different emotions, such as affection and curiosity, which cannot be distinguished by choice behavior.
Even if self-reporting is more reliable than other signs that indicate the psychological experience of pain, research done by Jaak Panksepp may provide evidence of the self-reporting of internal emotions of rats. The 50 kHz vocalizations were unconditionally associated with reward anticipation elicited by amphetamine injections, suggesting that these specific vocalizations indicate the general emotional state of the rodent (Burgdorf 2000, 2001). Positive rewarding social interactions as well as tickling of rats elicited these vocalizations, which suggests that the vocalizations might be a useful behavioral marker of positive social affect in rats (Panksepp 2000;Knutson 1999).
Animal reports might be compared to humans who are unable to reflectively evaluate and express their emotional experiences with appropriate verbal labels. Monkeys deprived of social contact huddled in a corner, rocked, and whimpered, much as a human child might do in similar circumstances (Harlow et al. 1972). Although mere similarity of behavior is not a logical justification for attributing emotional experience to some animals but not to others, we can use some of the same techniques used to measure emotion in children and disabled adults to measure emotions in animals. The scales tested were based on the presence of behaviors associated with emotional states, and those rating the emotions were asked to evaluate only the observable expressions of the emotional state of the subject. Other scales weight the presence of some behaviors as being more essential to the relevant emotional experience and record their frequency asa measure of intensity. In another study observers could correctly identify surprise in infants despite the lack of verbal or facial expression (Camras 2002). Thus, humans can judge the existence of nonhuman emotion in the same way they judge the existence of emotion in other humans-that is, by observing the normal behavior, expression, and state, and inferring that internal experiences cause the external variations.
The validity of the verbal report assumes that the symbolic labeling chosen after introspective discovery is more reliable than objective observation of the physiological and behavioral deviations from the baseline activity of that individual. This seems a contradictory and surprising view for a scientist to hold. Though typically scientists abstain from subjective interpretations, introspective self-reports are commonly used in the study of emotion. Empirical observation and comparison of emotional reactions may be not only more reliable and predictive, but also less restrictive than verbal reports that limit emotional research to the study of primates.
Pain vs. Mechanical Reaction
Although the lack of self-report is a challenge, the larger difficulty of this search is expected to be distinguishing the animals that experience pain as a negative affective state rather than automatic reaction to threatening stimuli. Daniel Dennett (1996) cautions against attributing the emotional motivation of pain to behaviors that can be explained by conditioning and negative reinforcement. He suggests that the simple mechanisms of negative reinforcement shape behavior just as pain does, but without the mental aspect of psychological pain. Since neurochemical substances associated with the experience of pain do not necessitate the experience, and the experience might occur without the activation of these substances, the physiological effects of pain might be merely automatic functions shaped by natural selection over eons of evolution.
To distinguish the psychological experience of pain from mere conditioned responses, we need a way to empirically determine the presence of this negative affect. Dennett claims that suffering can be discerned by observing what lhe creatures are doing as a whole organism, not just what individual processes are going on in the brain or the body (Dennett 1996). He expects that if no suffering is expressed by the organism, then no suffering is experienced, and that when suffering is expressed and observed, suffering is indeed experienced. But observation is interpretation and subject to individual biases. Because the expression of suffering by nonhumans may not be similar to humans, we may not recognize it when we see it. Dennett does not elaborate on what counts as an expression of suffering or what kinds of behaviors require the attribution of psychological pain rather than programmed reactions.
While the physiological components of pain might be no more than negative feedback, the affective components that we know from our own experience must be measured in others by their physiological manifestations. The experience of fear, distress, discomfort, or the feeling of “This is bad” in general, are components of pain/ suffering, but not components of negative reinforcement. The organism experiences the physiological changes associated with fear, and the psychological experience of fear motivates him to escape. This hypothesis is difficult to test, however, because if the psychological experience is inferred from physiological and behavioral changes, then the impact of the emotion on these patterns cannot be determined.
Panksepp suggests one way to differentiate motivational drives from affective motivations might be to prove that drives are reactions to sensory stimuli and do not necessarily involve motor programming, which he believes to be intimately connected to affective systems (Panksepp 1994). For example, the drive to satisfy thirst might be initiated by the sight of water, but the motor strategy to accomplish that drive might be motivated by the affective state of the organism in that particular circumstance. Thus, an affective state might be inferred by the activation of motor regions for choice behavior.
The strong link between emotion and memory can also help establish evidence for the attribution of affective states in nonhuman animals. Because memory is biased to encode only emotionally salient experience, it is plausible that the affective quality of experiences was necessary for the development of episodic memory. Of course, procedural memory systems might have stored reflexive motor movements without the influence of affect; however, such responses require repetition, while an emotional experience has immediate impact on future behavior. Emotional memory requires only one encounter with a predator to program an appropriate response rather than multiple occasions on which the predator might overtake it, so emotional memory is an enormous survival advantage for the organism. Emotional events also elicit an attentional bias, so emotion may have been selected for its promotion of decision-making abilities that require an organism to select salient details from the environment (Kulas 2003). This is evidence that affective motivation in addition to mere mechanical programming was necessary to the survival of some animals.
Cortical Theory of Consciousness
The only way to explain primates’ reactions as conscious and nonprimates’ reactions as mechanical is to assume that conscious experience only occurs in a developed cortex. As described by Joseph LeDoux, the argument for this theory assumes that consciousness requires a working memory with the capacity to relate many stimuli current and past to create a context for the experience (LeDoux 1996). Though the physiological components of emotion are initiated in the brainstem, this theory claims that the activation of these affective systems is not sufficient for the experience of emotion. Rather, emotional experience results from the interpretation by the orbital frontal cortex of these physiological fluctuations with respect to the context in which they occur. If emotions result only when the organism becomes aware of the activation of an emotional system in the brain, emotion would entail second order awareness, which dramatically limits the number of species that enjoy sentience (awareness of an emotion or feeling).
Despite the lack of encoding in an explicit memory system, implicit emotional memories can have a significant influence in behavior. For example, a woman with extreme long-term memory deficits refused to shake the hand of the experimenter who had earlier hidden a pin in his hand. Independently of any conscious contextual interpretation, the thought of shaking his hand distressed her (Gazzaniga 2002, 342). This explains why the most effective way to motivate cognitive processes of thought, strategy, and memory is to activate the emotional systems (Gray 1990). This influence of emotion is implicit in experimentation designed to analyze the nature of memory and learning, and experimenters must work to make the experiment salient for the organism. This phenomenon illustrates that events can be emotionally experienced in the absence of explicit long-term memory and complex contextual interpretation.
Of course, cognitive interpretation has a great power to manipulate the instinctual emotional patterns, but the conscious interpretation of context is not necessary to differentiate between emotions. Proponents of cortical consciousness argue that the physiological similarity between such opposite emotions as love and hate proves that the activation of the systems that stimulate the physiological changes cannot be identified with psychological experiences. However, the opposite behavioral manifestations of love and hate indicate that there is some difference for the organism. Specific emotions may become empirically differentiated as our knowledge of affective systems becomes more detailed. Panksepp urges affective neuroscientists to detail the properties of affective systems so that they might be able to precisely specify how various behavioral and physiological patterns are orchestrated by these systems (Panksepp 1994). Furthermore, the neurochemical makeup of affective states may prove to be a powerful indicator of specific affective states (Panksepp 1993). By pairing neuropeptides, like oxytocin and opioids, with human emotions, it might be possible to make more precise differentiations among nonhuman emotions based on the presence, location and influence of these neuropeptides.
Contrary to the cortical theory of consciousness, even if distinct feelings gain their affective intensity from common physiological mechanisms, they may be initiated by distinct parts of the brain. If this is true, then brain imaging might be more beneficial in discriminating between emotions than studying physiological differences in emotional experiences (Ekman et al. 1990; Zappulla et al. 1991). According to Dr. Verne Bingman, artificial stimulation of the subcortical hypothalamus has been shown to elicit emotional experiences in humans, and different emotions are associated with the activation of different regions of the hypothalamus.
There is no reason to require the cortical interpretation of this activation in animals when the activation is sufficient for causing the experience in humans.
Pain research offers evidence that the affect associated with pain perception occurs well below the cortical level and is associated with core awareness rather than reflective consciousness. The gate control theory of pain recognizes even the dorsal horns of the brainstem as active sites at which inhibition, excitation, and modulation occurred. The five inputs that contribute to the neurosignature of pain are sensory inputs from somatic receptors, sensory inputs from other modalities, cognitive and emotional inputsfrom the brain, neural inhibitory modulation, and the body’s stress-regulation systems, including cytokines, the endocrine, autonomie, immune, and opioid systems (Melzack 1999). Apart from the cognitive modulation, none of these inputs require the specific cortical extension of the primate’s central nervous system.
It has been suggested that these inputs must converge on some cortical region which creates the unified perception of pain for the organism, but this may just as well occur at the superior colliculus and reticular formation areas suggested by Panksepp and Damasio as at the cortical areas presumed by other theories. Panksepp suggests the superior colliculus as the first primitive site of self- awareness because motor information is processed in a self-oriented manner and also because it is the center of massive convergence of multimodal information (1994). Just below the colliculi, the central gray is a convenient passage for the exchange of self- representation and affective processes. Other research suggests that nuclei in the brainstem reticular formation may constitute the basic set of somato-sensing structures necessary for core consciousness and the emergence of a core self (Parvizi 2001).
Extended consciousness is enhanced by memory and language, which allow the creation of conceptual memories and an autobiographical self; however, it is hard to believe that consciousness and the entire human experience jumped into existence from pure mechanics with the evolution of these cognitive abilities. The pain model employs the theory that consciousness is not one characteristic that evolved at some critical level of development, but rather a convenient name for many distinct characteristics that evolved independently or interdependently. As the various systems grew more complex and gained the ability to accomplish more complex tasks, what we consider the “mind” grew more complex as well. This view implies that there was no magic moment of consciousness when this system responsible for “becoming conscious of” the body evolved. One does not “become conscious of the emotional systems; rather, the existence and activation of these systems is the experience. Using a memory to guide behavior and conscious remembering are the same event, though one might entail an explicit reflection on the activity. The distinction between the bodily experiences and the awareness of the mind may be a remnant of Cartesian dualism that still pervades the way we think about mind and body.
Accepting that mind is body and body is mind is the first step towards understanding consciousness from a physical perspective. If consciousness is nothing over and above the physical systems that are responsible for different functions of consciousness, then contrary to popular theories, there is no specific location of consciousness. Rather, different elements that are considered components of consciousness are located in different parts of the brain and body, and not one of them on its own could be considered conscious. As time goes on and no “center of consciousness” is found, the methods of research aimed at finding it will be far less productive and will gain less attention than methods that accept the mind as a function of the body.
Conclusion
Though resources are already divided among many differing theories, the variety of research programs is likely to multiply rather than divide the results of labor toward understanding this multifaceted experience. If each theory studies a different part of the elephant of consciousness, the initially contrary reports will likely be integrated into one comprehensive analysis of the capacities associated with consciousness. The pain model has been suggested as an approach to the study of consciousness not to contradict or replace any existing theories, but to contribute to the research by raising new questions and a new perspective that addresses some issues neglected by other research methods.
In the past, science has avoided the explanatory gap by denying either the validity of subjective experience or the ability of science to study internal states. Similar to some affective theories, the pain model aspires to open the realm of affective conscious experience to scientific exploration. The circumstantial evidence is overwhelming that other animals do have internal feelings that are as influential as those in primates, yet animal consciousness has been avoided by most scientific research. Panksepp compares the inference of nonhuman emotions to the inference of protons and electrons to explain microphysical phenomena because without the inference of affective experiences, the explanation of animal behavior becomes a useless jumble of contradictory heuristics (Panksepp 1994). The varied expressions of a painful experience cannot be expressed in terms of a preconditioned behavioral formula, but these observations can be explained, and must be explained, in terms of the sensory and emotional experience of pain.
The conscious experience of nonhuman animals is an issue of significance on moral, political, and psychological dimensions as well as metaphysical. Morally, we are obligated to respond with empathy to other sentient beings, and the intentional causation of pain to another sentient being is reprehensible in almost any moral theory. The United States Congress recognized this moral duty when it enacted the Animal Welfare Act in 1966. Currently, this law only applies to warm-blooded animals used for research purposes, but depending on the extent of animal consciousness defined by pain perception this may or may not be the moral answer. To minimi/e the experience of pain, however, we need to determine which organisms have the ability to experience pain. Using pain as a model for consciousness research will contribute to this moral pursuit.
Beyond these pragmatic consequences of accepting pain as a model for the study of consciousness lies the metaphysical quandary: What is consciousness and how does it work? Studying the details of human cognition, although technologically valuable, only distracts from the primary philosophical question and unnecessarily complicates the search for the basic mechanism of awareness. The pain model has been suggested to focus science on the emergence of core consciousness in primitive systems in order to confront the explanatory gap that riddles current theories of consciousness.
Relatively little is known about the mechanisms of pain, despite the fact that pain is the most common health complaint.
The inference of experienced emotion is the most parsimonious and useful explanation for variations between individual reactions to stressful stimuli.
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Brystana Kaufman was born in Wooster, Ohio, and in 2003 earned a Bachelor of Arts in Philosophy from Bowling Green State University. While studying at BGSU, she also received the Undergraduate Research Award in 2002 and the Mayieux Honors Thesis award in 2003. CuiTently, she is working with the Ohio House of Representatives in Columbus, Ohio.
Copyright HELDREF PUBLICATIONS Summer 2004