American Journal of Law & Medicine

Pain detection and the privacy of subjective experience.(Brain Imaging and the Law)


A neurologist with abdominal pain goes to see a gastroenterologist for treatment. The gastroenterologist asks the neurologist where it hurts. The neurologist replies, "In my head, of course." (1) Indeed, while we can feel pain throughout much of our bodies, pain signals undergo most of their processing in the brain. Using neuroimaging techniques like functional magnetic resonance imaging ("fMRI") and positron emission tomography ("PET"), researchers have more precisely identified brain regions that enable us to experience physical pain. (2) Certain regions of the brain's cortex, for example, increase in activation when subjects are exposed to painful stimuli. (3) Furthermore, the amount of activation increases with the intensity of the painful stimulus. (4) These findings suggest that we may be able to gain insight into the amount of pain a particular person is experiencing by non-invasively imaging his brain.

Such insight could be particularly valuable in the courtroom where we often have no definitive medical evidence to prove or disprove claims about the existence and extent of pain symptoms. In fact, pain is one of the easiest medical complaints to feign. (5) Yet, given that pain and suffering awards may represent about half of personal injury damage awards, (6) if even a small percentage of those awards involve feigned or grossly exaggerated symptoms, billions of dollars may be redistributed each year to malingering plaintiffs. On the other hand, if litigants raise genuine claims that we fail to recognize, billions of dollars may fail to reach those who properly deserve compensation for injuries. (7) In this symposium article, I will argue that, despite many conceptual and technological challenges, neuroimaging may someday play a critical role in the evaluation of pain claims.

In recent years, a burgeoning literature has developed on how neuroimaging may inform our understanding of deception, (8) moral and legal responsibility, (9) behavior prediction, (10) and much more. (11) There has been very little analysis, however, of the societal implications of neuroimaging technologies that provide insight into our subjective experiences, (12) even though researchers have used neuroimaging to observe our brains while we experience not only pain but also happiness, sadness, anger, fear, and disgust. (13) While we are still a long way from understanding these complicated phenomena, neuroimaging has been and will continue to be at the forefront of neuroscience research into the nature of subjective experience. It may well be time to consider some of the legal and ethical issues that such technology may raise. (14)

Subjective experiences such as pain are private in two quite different senses. First, they are private in the descriptive sense. No one else knows exactly what I am feeling at a particular moment, and no one else can directly experience my feelings. While I can infer that others are in pain, ! have uniquely direct access to my own pain. "One does not say that one is in pain on the grounds that one is groaning and assuaging one's injured limb." (15) Rather, "it is because I can introspect that I can say how things are with me without observing what I do and say." (16)

Second, subjective experiences are private in the normative sense. In some cases, we ought not be forced to reveal information about what we are feeling. For example, one might reasonably believe that we have some interests in keeping private when we are in pain, how much pain we are in, what triggers our pain, and how sensitive we are to pain. Such privacy interests may partially explain why we legally restrict disclosure of medical records. Similarly, we may have interests in keeping private other subjective experiences like embarrassment and sexual arousal. Even though we sometimes betray our own emotions involuntarily through comments, gesticulation, and facial expressions, in some cases, we may plausibly have rights to be free from certain unwanted inquiries into our subjective experiences.

In Part II, I provide general background on the nature of pain and the ways in which we develop evidence that other people are in pain. In Part III, I describe how neuroimaging may, in the not-too-distant future, supplement our evaluations of pain claims by supporting genuine claims or, possibly, impugning malingered ones. In addition, I suggest that basic research into pain imaging may, in the more distant future, provide increasingly objective methods of assessing the severity of a person's pain and comparing that to the pain of other people. Finally, in Part IV, I discuss some of the legal and ethical issues raised by imaging technologies that reveal subjective experiences like pain. I suggest that future pain imaging technologies are likely to raise rather manageable privacy concerns because they would permit only limited intrusion into the privacy of our thoughts and character.



There is much disagreement over exactly what pain is, as no simple definition adequately captures the concept. The International Association for the Study of Pain has influentially defined the phenomenon as "[a]n unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." (17) This description highlights the fact that pain has several phenomenological components. Sensory components of pain include its perceived intensity, location in the body, (18) and texture (for example, pain can be sharp, burning, or stinging). (19) The process of sensing such aspects of pain is called nociception. (20) Affective and evaluative components of pain include the emotional distress or unpleasantness we associate with a sensation of pain, (21) characterized by words like "tiring, sickening, and annoying." (22)

The sensory and affective aspects of pain are processed, at least in part, in different regions of the brain. (23) In fact, some patients with disrupted cognitive abilities due to frontal lobotomies, cingulotomies, or certain drugs, such as morphine, report that they feel the sensory component of pain but find it "less distressing or bothersome." (24) Similarly, those with "pain asymbolia" do not have aversive reactions to the pain of small cuts or burns, yet they still recognize these experiences as being, in some sense, painful. (25) In rare cases, people are born completely insensitive to physical pain, having neither sensory nor affective reactions to painful stimuli. (26) This condition can be quite devastating as the afflicted are quite prone to cuts, bruises, and more serious injuries that those with normal pain responses know more instinctively to avoid. (27)

Because pain has both sensory and affective components, our reactions to pain depend on more than just sensory stimuli. Pain responses are "significantly influenced by psychosocial context, the meaning of the pain to the individual, the patient's cultural background, and the individual's beliefs and coping resources." (28) Emotional states like anxiety and depression also "dramatically influence[]" pain perception. (29) Thus, "severity of pain does not bear a simple relationship to the degree of tissue damage." (30) To take a dramatic example, the pain associated with an injury that occurs while saving a child from a burning building may feel far less distressing than the pain from an otherwise identical injury that prevents a person from saving a child. (31) Furthermore, when pain is induced in medical experiments, researchers tell subjects that their pain is only temporary and that subjects can cease to participate in the experiment whenever they so decide. (32) This affects the nature of the pain experience and makes it difficult to create well-controlled experiments that induce the kinds of pain we are likely to experience outside the laboratory.

Pain can be roughly classified as acute or chronic, though there is little precision in the distinction. (33) Typically, acute pain is viewed as more temporary or more a function of nociceptive input than chronic pain, which is thought of as more long term and more heavily influenced by psychological and social influences. (34) Among these influences, several studies suggest that those involved in litigation over personal injuries tend to have worse treatment outcomes than similarly injured people who are not seeking compensation. (35) Some cite these results to challenge compensation schemes that, through conscious or unconscious processes, seem to increase the severity of people's symptoms. (36)


When we, ourselves, are in pain, we know it automatically through introspection. Under the traditional view, "[p]ains are said to be private to their owners in the strong sense that no one else can epistemically access one's pain in the way one has access to one's own pain, namely by feeling it and coming to know one is feeling it on that basis." (37) While we might infer that someone else is in pain based on his behavior, we need not resort to such observations to know our own pains. "[I]f it seems to me that I am in pain and I believe so on that basis, I am in pain." (38) According to this view, no evidence of pain can ever be more persuasive than one's honest, immediate first-person perceptions of the phenomenon. Thus, "if a person avows that he is not in pain, yet evidence from PET or fMRI suggests that he is, the latter is defeated by the agent's sincere utterance, and the inductive correlations of the data from PET and fMRI with the subject's being in pain need to be reexamined." (39)

Pain has also been deemed essentially subjective "in the sense that [its] existence seems to depend on feeling [it]." (40) Thus, it is not at all clear whether a person can be in pain without knowing it. On the one hand, I might plausibly say, "I was awakened by a pain in my shoulder," which seems to suggest that my pain precedes my awareness of it. On the other hand, I might more precisely say that I was awakened by a pain precursor and that I did not actually experience pain until I was at least partially awake. (41)

While pain is typically thought to be fundamentally private and subjective, there is plenty of room for science to improve our understanding of our reactions to pain. For example, though we have unique introspective access to our own pain, the mere act of introspecting draws attention to pain in a manner that intensifies the phenomenon. (42) Seeking to analyze one's pain thereby alters its nature. Similarly, distraction from pain can ease its intensity. (43) Expectations that pain will subside can also ease pain intensity. When we unwittingly take placebos to treat pain, we expect our pain to subside, and it frequently does. (44)

Furthermore, while we may be experts about our own pain while it occurs, our memories of pain are often inaccurate. For example, our evaluations of painful episodes are heavily influenced by particular moments during the episode (such as the moment when the pain is most intense) and do not necessarily reflect accurate judgments of the total pain experienced during the episode. (45) Similarly, in a famous study, researchers showed that when we experience physically painful circumstances that extend over a period of time, we tend to remember especially the amount of pain felt at the end of the interval. (46) In the study, both control and experimental subjects received a colonoscopy, a screening procedure for colorectal cancer where a colonoscope is inserted through a patient's rectum into the lower gastrointestinal region. (47) In experimental subjects, however, after an ordinary colonoscopy, the colonoscope was left in patients' rectums for an average of one additional minute. (48) During this period, patient discomfort was somewhat less than it was when the colonoscope was more deeply inserted. The amount of pain experienced by experimental subjects at the end of the procedure proved particularly salient to their overall memory of the event. After the procedure, compared to control subjects, experimental subjects remembered less total pain, rated the discomfort of the colonoscopy to be less unpleasant, and were more likely to return for follow-up colonoscopies in subsequent years. (49) This was true even though the experimental subjects, on average, had longer colonoscopies and, as an objective matter, probably experienced more total pain. (50)


Despite the uniquely first-person aspects of pain, we can nevertheless still make judgments, with some level of objectivity, about the pain of others. For example, when a radiologist reviews a simple X-ray image of a severely fractured leg, he can typically report with great confidence that the patient is in pain. …

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