The Neuroevolutionary Sources of Consciousness and Affect

FIGURE 15-1 A schematic summary of guinea pig brain regions where one can readily evoke social separation–induced vocalizations in young guinea pigs (as mapped in Barbara Herman’s PhD dissertation, Bowling Green State University, 1980). Very similar anatomies were observed in domestic chicks (Paul Bishop’s PhD dissertation, BGSU, 1984). In 1980 when Antonio Damasio et al. [5] published PET scan images of human beings feeling very sad, a very similar anatomy was evident, suggesting that all warm-blooded vertebrates share this social cohesions mediating PANIC/GRIEF system. The areas that lit up are anterior cingulate (AC), the dorsomedial thalamus (DMT) and the periaqueductal gray (PAG), and also regions in the most ancient parts of the cerebellum (CB). Animals showed remarkably similar anatomies including ventral septal area (VS), dorsal preoptic areas (dPOA), and the bed nucleus of the stria terminalis (BN), which are too small to be accurately identified on human PET images, thus the question mark there in the human depiction.

The PANIC System—Separation Distress and the Pain of Social Loss

One of the most intense forms of emotional “pain” that we humans experience is the death of loved ones, especially when we are young. Abundant data indicate that all other mammals, indeed birds born precocious (e.g., chickens, ducks, geese) also, exhibit pain-like crying when socially isolated from mothers. That is the kind of “psychological pain” that reflects the dynamics of social bonding—namely, the crying of separation-induced distress vocalizations (DVs). DVs primarily arise from social loss and probably at latter ages from ostracism (social marginalization). We have studied such emotional pains for 40 years [30, 31]. Why would we distinguish this from fearful anxiety? The key finding is that the behaviors, anatomies, and many chemistries of separation distress are quite distinct from fear-type anxiety responses [27, 39]. Such knowledge has abundant implications for the way we handle diverse medical problems, especially psychiatric ones such as depression and panic attacks.

While feeling of physical pain most probably emerged before the “psychological pain” of social loss, major regulatory features such as neurochemical controls were probably conserved. For instance, once primal physical pain had evolved, it could have been used as a foundation for various homeostatic and emotional pain (hunger pangs and separation distress). We initiated our work in the area with the hypothesis that “painful” feelings of social loss—the profound internal “ache” resulting from the loss of social support, whether by death or abandonment by a loved one—achieves part of its affective intensity from the same brain chemistries that emerged earlier to regulate physical pain, especially brain opioids, and the addictive qualities of opiates may reflect their capacity to mediate social bonding. Our research on the separation-distress (so-called PANIC) systems in socially bonded animals was guided by this evolutionary relationship [27]. In a sense, feelings engendered by social loss were comparable to the ache of bodily injury. One straightforward prediction was that brain opioid system also regulated the pain of social loss, and that relationship was abundantly supported; indeed, the reduction of separation-induced crying was reduced at the lowest dose of opioids ever used in the animal research (for earliest review, see reference [24]).

Considering how survival of mammalian young is critically depended on maternal care, it is easy to understand the strong survival value conferred by neurochemistries that elaborated both the affective intensity of physical pain and social bonds. In other words, once physically painful affect had evolved, it may have been relatively easy to use this solution for social cohesion purposes. There are many implications of this finding for clinical management of physical pain, for instance the power of placebos, as well as social influence, on the felt intensity of physical pain and psychological grief. One of the biggest impediments for scholars pursuing such ideas experimentally has been the long-standing controversy whether other animals (indeed infants who cannot yet speak) actually experience pain (also see Chapter 11) as opposed to just exhibiting nociceptive reflexes (e.g., see reference [45]). Indeed, animal models of physical pain have long been used in medicinal discoveries, and probably that will also apply for psychological pains that are of psychiatric significance, such as in the dysphoria of depression [42]. But first, let us consider possible linkages between emerging knowledge of psychological and physical pain.

HOW DOES THE BRAIN FEEL THE ACHE OF SOCIAL EXCLUSION AND A “Broken Heart”?

Evidence for evolutionary relationships between physical and social pain come from several lines of animal brain research: Localized DBS of various subcortical brain systems, long implicated in the regulation of physical pain, evoke separation cries which are auditorialy and sonographically similar to natural separation calls [12, 27, 32, 39]. Among the most prominent subcortical areas where DBS can evoke separation cries, even in adult animals, are dorsomedial thalamus, bed nuclei of the stria terminalis, ventral septal and dorsal preoptic regions, and most intensely and at the lowest current levels from midbrain PAG, where some of the evoked sounds are sonographically closer to pain squeals while at other nearby sites they more closely resemble separation cries. Indeed, the most intense emotional distress with the lowest current intensities is obtained from the dorsal PAG. Of course opiates are among the best medications for somatic pain, and the shared neurochemistries, highlighted most by endogenous opioids, suggest an evolutionary relationship between somatic and emotional pain [12, 53]. Indeed, it has been found that safe opioids such as buprenorphine at very low doses might be effective in reducing both depression and suicidal urges (for discussion, see reference [42, 52]).

Thus, once again, the psychological pain of social loss (grief and loneliness) may have arisen as evolutionary explanation from physical pain processes. Indeed, there is abundant evidence indicating that social support reduces affective pain intensity [3, 20], which is coded in part by anterior cingulate processes that are also highly responsive to being socially ostracized, as originally evaluated through the use of a video “cyberostracism game,” while emotional regulatory areas of prefrontal cortex exhibited diminished arousal [8]. These brain regions are well connected to other separation distress–mediating brain areas, especially PAG and dorsomedial thalamus, from where DVs can be evoked with DBS [39]. Indeed, such brain regions have exhibited strong arousals during PET imaging of human sadness [5, 18]. In this context several other brain chemistries have been identified that powerfully and specifically regulate separation distress, especially oxytocin [26], a neuropeptide that can also attenuate physical pain [44].

PLACEBO EFFECTS AND EMPATHY

With the discovery that the affective sting of social loss shares evolutionary relations to physical pain, novel avenues for understanding related phenomena such as empathy, as well as novel clinically intervention in psychiatric disorders related to social loss, such as depression, have opened up. Indeed, it has long been recognized that the quality of social environments may contribute much to our ability to cope with pain [11]. For instance the pain of childbirth can be substantially eased with social support [16], as can postoperative pain (see more extensive discussion in reference [30]). Indeed, these effects may have underlying similarities to how placebos control pain.

Might placebo effect be evolutionarily conceptualized as cerebral manifestations of the “healing touch” based in part on opioid release within the brain. Contact comfort in animals can release opioids [15, 32] as can joyful social play [34, 41]. Likewise, placebo analgesia in humans operates partly through opioid release [43]. Indeed, placebos may reduce arousal of anterior cingulate brain regions that are commonly overactive in depression and psychological distress [21], and participate in empathy-related brain responses [46]. For an extensive review of the preclinical (animal) findings in this area, see reference [40].

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