For animals, many biological values, such as finding food and shelter, avoiding predators, etc., have to do homeostasis―namely maintaining overall physiological states within the range required for survival (Damasio 1999, 2010; Panksepp 1998, 2005). To explain this, both Damasio and Panksepp propose that the brain has distinctive emotion systems and self-systems (the “proto-self” and the “core-self”). These inter-connected systems regulate homeostasis by integrating external information from perception with internal information from the body.[25] Despite their differences, Damasio and Panksepp share the following views: (1) emotions and homeostasis play essential roles in explaining how the sense of self is generated in the brain; (2) the key brain areas related to the self involve not only cortical but also sub-cortical regions, especially the brain stem possessed by both humans and many animals; (3) those brain areas are crucial, because multifarious types of neural information are integrated in those regions and provide representations of the whole body; (4) both Damasio and Panksepp believe that their accounts explain not only the sense of self-as-object but also the sense of self-as-subject. In the following I elucidate these points and then examine whether their goals are achieved.
According to Damasio, animal brains have what he calls the proto-self system, which is “a dynamic collection of integrated neural processes, centered on the representation of the living body” (2010, p. 9). The neural processes of this system represent “moment by moment, the most stable aspects of the organism’s physical structure”, on the one hand, and “the externally directed sensory portals”, on the other (2010, p. 190). This generates primordial feelings that “reflect the current state of the body” and “provide a direct experience of one’s own living body, wordless, unadorned, and connected to nothing but sheer existence” (2010, p. 21, p. 185). The proto-self system and primordial feelings account only for the sense of self-as-object (2010, p. 9, p. 202). The sense of self-as-subject is generated when an animal interacts with the environment such that a neural representation of the interaction is generated in the brain (2010, pp. 9–10, p. 91, p. 202). By interacting with external objects, the current state of the body and the proto-self system are modified. This modification activates the core-self system, which enhances attention to external objects and “engenders a sense of ownership” (2010, pp. 202–203). This is closely related to the sense of experiential ownership discussed above. It is part of what Damasio calls core consciousness, which “displays […] moment by moment, that you rather than anyone else are doing the reading and the understanding of the text” (1999, p. 10).
Damasio’s key idea is that the brain produces not only first-order representations of external objects and of the body (2010, p. 76, p. 84, pp. 91–97), but also second-order representations of the relationship between objects and the organism (1999, pp. 169–170; 2010, pp. 71–72, p. 181). These are “the source of the sense of the self in the act of knowing” (1999, p. 169). When the core-self is felt (1999, p. 172), i.e. when the second-order representations become conscious states (2010, p. 248), core consciousness emerges. This includes a minimal sense of self-as-subject, a transient sense that “it is you […] doing the seeing” (1999, p. 169; cf. 2010, p. 168), or the sense that I am the subject of current experiences (cf. 2010, p. 185, p. 203, p. 209). As we can see, this account is highly relevant to our current investigation.
Damasio emphasizes that the most crucial neural structures related to the proto-self and the core-self systems are found in the subcortical regions, especially the brain stem (2010, p. 195, p. 205).[26] They include, among others, the nucleus tractus solitarius (NTS), the parabrachial nucleus (PBN), the periaqueductal gray (PAG), the hypothalamus, and the superior colliculus (2010, pp. 98–99, pp. 191–192; 1999, pp. 180–183). Why are these neural structures so critical for the core-self and core consciousness? According to Damasio, core consciousness results from integration of interoceptive, proprioceptive, and exteroceptive information, which produces second-order representations (2010, p. 76, p. 97, pp. 190–196, p. 199, p. 203, pp. 206–209). The brain areas just mentioned receive input from many other regions, which process information about external objects and internal bodily conditions (2010, p. 78, p. 80, pp. 84–85, p. 94, pp. 99–100, pp. 207–209). Thus it is in these areas that integration is thought to take place. Integration in those areas constitutes core consciousness because they provide neural representations of the organism’s whole body (2010, p. 68, pp. 94–97, p. 209, pp. 244–245), and the integration is implemented by neural synchrony in the gamma range (2010, p. 20, pp. 86–87).
Panksepp points out seven basic innate emotion-systems in mammals: seeking, rage, fear, lust, care, panic, and play.[27] These emotion-systems generate affective feelings, which characterize how animals respond to environmental challenges. Panksepp & Northoff (2009) also postulate that the proto- and core-self systems monitor and regulate homeostasis. The proto-self is ‘the most ancient form of coherent body representation’, and the core-self gives rise to “affective consciousness”.[28] Both systems are causally mediated by what they call affective self-related processing, which integrates interoceptive information from the body and exteroceptive stimuli from the environment. The main mechanism that underlies this processing is a subcortical-cortical midline system (SCMS) (2009, p. 197). The subcortical parts of this network include “the Periaqueductal gray (PAG), the superior colliculi (SC), and the adjacent mesencephalic locomotor region (MLR), as well as preoptic areas, the hypothalamus, and dorsomedial thalamus (DMT)” (2009, p. 201). On the superior colliculi (SC) and the periaqueductal gray (PAG), they tell us that:
The colliculi and the PAG are among the most richly connected areas of the brain; both receive afferents from several exteroceptive sensory regions (occipital, auditory, somatosensory, gustatory, and olfactory cortex) and, at the same time, afferents from other interoceptive subcortical regions. In addition, the PAG and the colliculi are connected with the cortical midline structures (CMS). (2009, p. 201)
Like Damasio, Panksepp and Northoff believe that the SC and the PAG play important roles in instigating the core-self system because they are the central areas where exteroceptive sensory information and interoceptive bodily information are integrated. They suggest that, due to anatomical convergence and neural synchronizations within the SCMS, “an archaic scheme of the entire body may be constituted in brain regions as low as the medial brainstem” (2009, p. 202; my emphasis).
Panksepp and Northoff claim that their theory explains what philosophers call the ‘experiential self’ and the ‘primitive form of selfhood’ (2009, p. 209). Self-related processing “intrinsically integrates affectivity, appropriateness and belongingness, and the phenomenal dimension of mineness into the ownership of experience” (2009, p. 199; my emphasis). This comes very close to the sense of experiential ownership that I discussed above. They consider self-related processing by the SCMS to be the mechanism not only of affective consciousness but also of the sense of self-as-subject.
In sum, Damasio, Panksepp and Northoff suggest that the sense of self-as-subject can be explained by full-body representations implemented by neural synchrony or by the SCMS. Now the key issue is: Do their accounts really specify the neural mechanisms that produce the sense of self-as-subject? Or do they specify only the mechanisms of the sense of self-as-object, i.e., of consciousness of oneself as a physical body interacting with the world? I argue that they address only the sense of self-as-object; they do not really provide a genuine account of the sense of self-as-subject.[29] Below I raise this theoretical issue; empirical arguments will follow in the next section.
Damasio claims that core consciousness is constituted by a second-order neural representation of the relation between animal and the environment. But this seems to require more explanation. Yet an explanation is not really provided by Damasio. I can agree that, for the sense of self-as-object, one must not only represent the external world, but also the body. But we cannot assume that the same account will automatically apply to the sense of self-as-subject. The problem with Damasio’s account is that the theoretical link between full-body representation and the sense of self-as-subject is lacking. And Panksepp and Northoff’s account is afflicted with the same defect. It might be that full-body representations are part of the biological conditions necessary for generating the sense of self-as-subject. But since they are also necessary for the sense of body ownership and the sense of self-as-object, it is far from obvious whether they are sufficient for the sense of self-as-subject. Let me elaborate.
Consider the full-body illusion mentioned in section 1. According to Blanke & Metzinger (2009), this illusion contains three central features related to self-consciousness. The first is self-identification. When the subjects experienced OBE during the experiment, “they felt as if the virtual body was their own” (2009, p. 12). We can see that this feature turns on the question “Is that body mine?” rather than “Am I the one who is having this experience?” So self-identification is about the sense of full-body ownership rather than the sense of experiential ownership. The second feature is self-location, which concerns “where my body is located in space and time”. Again, this is about the spatiotemporal position of the body rather than the sense of experiential ownership. Blanke and Metzinger call the third feature a weak first-person perspective, defined as a geometrical point of projection and nothing more (2009, p. 8). So construed, even a camera could possess such a perspective. Hence, this feature does not specify the sense of self-as-subject, either.
The point is that, in the OBE experiment, the sense of experiential ownership is not in question and hence not measured. This means that explanations of the mechanisms of full-body representation or the sense of body ownership do not necessarily apply to the sense of experiential ownership. As such, self-related processing can help explain full-body representation without explaining the sense of self-as-subject. Damasio, Panksepp and Northoff neglect the theoretical gap between full-body representation and the sense of self-as-subject, hence their accounts do not really explain the sense of self-as-subject. They suggest that the sense of self-as-subject results from integration by neural synchrony in the brain stem or the SCMS. But it remains unexplained why and how this could be so. To investigate these worries, I examine in the next section the two major proposals by neuroscientists regarding the mechanisms of the sense of self-as-subject: neural synchrony and processing in the SCMS.