Where in the brain is the self?
Introduction
Along with the explosion of interest in the biological basis of consciousness, scientists have become increasingly interested in the neurobiology and neuroscience of the self. Indeed, it is difficult if not impossible to imagine consciousness without some form of self as a subject of that consciousness, and therefore, without selves, consciousness as we usually understand it cannot exist. As noted by John Searle:
We know furthermore that all such conscious states are subjective in the sense that they only exist as experienced by a human or animal subject. Conscious states require a subject for their very existence. They do not exist in a neutral or third-person fashion, they have an existence that depends on their first-person subjective qualities, and that is just another way of saying that a conscious state must always be someone’s conscious state (Searle, in press).
But what is the “self”? Is it “real” in the sense that a brain is real? Kant was a firm believer in the existence of the self and he placed a primordial and unified ego at the center of his philosophy. William James on the other hand argued in his The Principles of Psychology that the “Ego” was nothing but “a ‘cheap and nasty’ edition of the soul.” Although James conceded that selves exist, he denied that there is anything that could be called an “I” or “ego” at their center. He argues that all that really existed were passing states of consciousness, and our belief in ourselves as unified beings is due to the fact that we experience successive mental states in our stream of consciousness that are uniquely our own. Indeed, James asserted that if several independent minds shared a common experience and past, one could produce the same mental unity among several minds that we as single minds experience. “Metaphysics or theology may prove the Soul to exist; but for psychology the hypothesis of such a substantial principle of unity is superfluous.” (James, 1892).
Dennett, in his book Consciousness Explained, sums up nicely why the belief in selves remains controversial and why great minds have come down on both sides of the issue:
Since the dawn of modern science in the 17th century, there has been nearly unanimous agreement that the self, whatever it is, would be invisible under a microscope, and invisible to introspection, too. For some, this has suggested that the self was a nonphysical soul, a ghost in the machine. For others, it has suggested that the self was nothing at all, a figment of metaphysically fevered imaginations. And for still others, it has suggested only that a self was in one way or another a sort of abstraction, something whose existence was not in the slightest impugned by its invisibility. After all, one might say, a center of gravity is just as invisible—and just as real. Is that real enough?… The question of whether there really are selves can be made to look ridiculously easy to answer, in either direction… (Dennett, 1991).
There are at least three reasons why the self remains such an elusive concept, and all three are in many respects identical with questions regarding the nature of consciousness in general. The first reason the idea of the self is problematic is that while we subjectively experience ourselves as single and unified beings, the brain is actually composed of millions of individual neurons. The manner in which neuronal assemblies are synchronized to produce unification in perception and action is an active area of research in neuroscience, but even if we fully understood the mechanism or neural synchronization, there still appears to be a fundamental difference—an unbridgeable gap—between the unified self and the divisible brain. This is the problem of the unification of the self.
Another reason the notion of the self is problematic, as pointed out by Descartes over 300 years ago, and reiterated by Dennett in the above quote, is that unlike a brain or a body, and in common with consciousness itself, the self cannot be objectively observed, but only subjectively experienced. The subject that represents the “I” in the sentence“I exist” cannot be weighed or measured. We can refer to this as the problem of the subjectivity of the self.
Finally, even if we accept that there is a unified entity in the world that can appropriately be called a self, we do not know where in the brain or which brain structures are most important for its creation. This is the problem of the location of the self.
In prior publications, one of us (TEF) has offered solutions to these problems (Feinberg, 2000, Feinberg, 2001a, Feinberg, 2001b, Feinberg, in press). The proposed solution to the problem of mental unification is based upon the hierarchical organization of neural systems. For instance, the processing streams of all perceptual systems are hierarchical. This organization allows for neural assemblies at an early stage of perceptual processing to create higher order perceptual features subserved by specialized “hypercomplex” neurons that are located further “downstream.” This process is known as topical convergence (Zeki, 1993). But the idea that the neural substrate of the unified self converges at a particular place in the brain (as proposed by Descartes) or alternatively that the mind or the self emerges at the pinnacle of the neural hierarchy (as proposed by Sperry, 1990) cannot be correct. In visual perception, for example, while it is true that cells of the brain project to levels in a hierarchical fashion to code for increasingly specific complex and abstract properties, the information coded by cells earlier in the process is not and cannot be lost to awareness. Both lower order and higher order neurons make a contribution to consciousness. By the same token, the analysis of action demonstrates that intention or will does not emanate solely from the highest most explicitly conscious levels of the neural hierarchy. Rather, the neural substrate of a voluntary action is actually distributed across multiple hierarchical levels.
The principal problem with prior accounts of the neural hierarchy with reference to mental unification is that these accounts view the mind as a non-nested hierarchy. A non-nested hierarchy has a pyramidal structure with a clear-cut top and bottom. A non-nested model of sensory awareness would posit that consciousness would emerge at the summit of the neural hierarchy at the peak of a processing stream. In a similar way, a non-nested hierarchical model of intentional action would propose that unified action emanates from a “ghost in the machine” at the summit of the motor hierarchy.
Feinberg, 2000, Feinberg, 2001a, Feinberg, 2001b, Feinberg, in press has proposed an alternative framework for viewing the mind/brain relationship. The model proposes that the mind operates—as do all living things—as a compositional or nested hierarchy. The important difference between non-nested and nested hierarchies is the relationship between lower and higher levels of the hierarchy. In a non-nested hierarchy, the lower and higher levels of the hierarchy are physically independent entities. The top of the hierarchy is not physically composed of the bottom of the hierarchy. In an organic nested hierarchy, in contrast, the elements comprising the lower levels of the hierarchy are physically combined or nested within higher levels to create increasingly complex wholes. In the nested hierarchy of a unified mind, lower order features combine in the mind as “part of”—or nested within—higher order features. Elements that are bound to other elements in awareness are represented dependently and are nested together. In this manner, neurons at both lower and higher levels of the hierarchy are able to contribute to sensory consciousness, and mental unification is possible. Similarly, intentional action does not emanate from a “ghost in the machine” at the pinnacle of the neural hierarchy. Rather, the unification of action is embodied within the entire hierarchical system across multiple hierarchical levels.
According to this account, mental unification occurs because the highest level of meaning provides the constraint required for the unification of sensory awareness while the highest level of purpose provides the constraint that underlies volitional action.
With these considerations in mind, we can turn to another obstacle to a neurological understanding of the self, the problem of subjectivity. The problem of subjectivity has several aspects, but one in particular can be elucidated by neural hierarchy theory considered above. This is the question of whether the self and the mind as subjectively experienced can be entirely reduced to the brain as objectively observed. Searle, among others, has argued that the mind cannot be reduced to the brain. He points out that traditionally a successful scientific reduction entirely removes subjective factors from the analysis. In this way, an observation that “appears” a certain way in non-reduced form is ultimately reduced to its scientific “reality.” However, in the case of mental events, Searle suggests that “the ontology of the mental is an irreducibly first-person ontology” (Searle, 1992, p. 95).
There are numerous and fairly basic reasons from the standpoint of neurology why the mind and self cannot be reduced to the brain, and that the mind and self are indeed ontologically subjective (Feinberg, 1997b, Feinberg, 2001b). While some of these reasons go beyond the purposes of this review, we have already laid the groundwork to consider one. We have explained how hierarchical sensory neural systems create higher order perceptual features by topical convergence. When a neural hierarchy is objectively analyzed, it indeed appears to have the structure and functional characteristics of a non-nested hierarchy, with lower order neurons successively converging upon higher order neurons to create higher order perceptual features. However, we have also seen how the same neural system, when subjectively experienced, functions and is experienced as a nested hierarchy. In a similar fashion, while the nested nature of the motor system provides the subjective experience of unified action, that unification also exists only from the subjective point of view, since the neurons that contribute to a voluntary action are actually distributed across multiple neurological levels. It should be fairly obvious and not terribly mysterious, based upon these facts alone, why the objective and subjective aspects of a complex and conscious neural system are mutually irreducible. It is not possible to ontologically reduce the self or mind to the brain because from the objective standpoint the system appears as a distributed non-nested hierarchy, while from the subjective standpoint the same neural system functions and is experienced as a unified nested hierarchy.
These considerations lead us to the third problem, the location of the self. If the unified self is distributed across multiple neurological levels, are there particular brain structures especially critical for its creation and maintenance? One approach to this problem is by studying patients who have disturbances of the self as a result of brain damage. For most of us, the relationship between the self and one’s physical body, between the self and the outside world, or between one’s personal boundaries and those of others are well defined. However, there are a number of clinical neurological conditions in which these boundaries become disturbed. As noted by Sigmund Freud:
Pathology has made us acquainted with a great number of states in which the boundary lines between the ego and the external world become uncertain or in which they are actually drawn incorrectly. There are cases in which parts of a person’s own body, even portions of his mental life—his perceptions, thoughts, and feelings—appear alien to him and as not belonging to his ego; there are other cases in which he ascribes to the external world things that clearly originate in his own ego and that ought to be acknowledged by it. Thus even the feeling of our own ego is subject to disturbances and the boundaries of the ego are not constant (Freud, 1930, p. 66).
Freud observed that, under certain pathological conditions, the margins between the ego and the world might be transformed. He further opined that the transformations or perturbations of the self might be of two complimentary types. In the first, entities that were once personally significant to the individual may become alienated from the self. Alternatively and conversely, entities that were normally related to the self become externalized into the world.
Neurology provides for us many conditions in which there is a disturbance of self–self or self–other relationships, and these disorders provides a unique insight into the self and its origins in the brain. By turning to these cases, we can gain a better understanding of the role the brain plays in creating the self.
Section snippets
Delusional misidentification and reduplication
Among the many neurological conditions that affect the brain and behavior there is a subset of disorders that specifically affect the self. These are conditions that alter the relationship between the individual and their body as seen directly or in a mirror, or their personal relationship to significant persons, places, or objects in their environment. Some of best-defined and most common clinical disorders that fit this general description are the syndromes of delusional misidentification and
Delusional misidentification/reduplication syndromes and focal Neuropathology
There are a minimum of six DMS/DRS that are reported as occurring in neurological patients with focal brain pathology.
Anatomical analysis of cases of delusional misidentification and reduplication
In a recent review (see Feinberg, Roane, & Solms, in press) we analyzed a series of previously published cases of these conditions (Table 1). The disorders were organized into six categories:
- 1.
Capgras syndrome for person(s).
- 2.
Capgras syndrome for environment.
- 3.
Capgras syndrome for arm (asomatognosia).
- 4.
Frégoli syndrome for person(s).
- 5.
Frégoli syndrome for environment.
- 6.
Delusional reduplication (without misidentification) for the self or other persons.
The data indicated a bias for the right frontal damage (
Imaging the self
How does the neuroimaging data support the findings in DMS/DRS patients? Is there a right hemisphere bias in self/other distinctions? The neuroimaging data appear to support the findings in patients. Before examining the data, however, it is wise to realize that 1:1 relationships are rare in terms of brain:behavior relationships. In localizing any cognitive or behavioral event in terms of brain function, one of us (J.P.K.) has suggested that the brain be visualized as a mobile (Keenan, 2001).
The brain, the right hemisphere, and the self
The findings regarding the clinical disorders of the self, as well as the experimental and imaging studies, strongly suggest that the right hemisphere plays a special role in the creation of the self. We do not wish to make the claim, however, that the self “resides” in the right hemisphere. Rather these findings suggest that the right hemisphere is dominant for these aspects of the self.
But an intriguing question remains: What special functions of the right hemisphere create its dominance for
Acknowledgments
Some portions of this article, and some of the cases described in the article, are adapted from Feinberg (2001b), Feinberg and Keenan (in press), and Feinberg et al. (in press). The original DMS/DRS case review analysis is adapted from Feinberg et al. (in press). J.P.K. thank the Kennedy Foundation for their support.
References (76)
- et al.
A PET exploration of the neural mechanisms involved in reciprocal imitation
Neuroimage
(2002) - et al.
Shared representations between self and other: A social cognitive neuroscience view
Trends in Cognitive Science
(2003) - et al.
Neural correlates of action attribution in schizophrenia
Psychiatry Research
(2004) - et al.
Modulating the experience of agency: A positron emission tomography study
Neuroimage
(2003) - et al.
Multiple Fregoli delusions after traumatic brain injury
Cortex
(1999) - et al.
Other minds in the brain: A functional imaging study of theory of mind in story comprehension
Cognition
(1995) - et al.
Reduplication after right middle cerebral artery infarction
Brain and Cognition
(1993) - et al.
Recognizing one’s own face
Cognition
(2001) - et al.
Confabualtion and delusional misidentification: A four year follow-up study
Cortex
(1999) Right hemispheric self-awareness: A critical assessment
Consciousness and Cognition
(2002)
Neural substrates for recognition of familiar voices: A PET study
Neuropsychologia
Where am I. The neurological correlates of self and other
Cognitive Brain Research
A region of right posterior superior temporal sulcus responds to observed intentional actions
Neuropsychologia
Cortical activations during judgments about the self and an other person
Neuropsychologia
Self recognition and social awareness in the deconnected minor hemisphere
Neuropsychologia
Passive and active recognition of one’s own face
Neuroimage
Une observation anatomo-clinique de fabulation (ou délire) topografique
Cortex
Mind reading: Neural mechanisms of theory of mind and self-perspective
Neuroimage
Capgras syndrome: A reduplicative phenomenon
Neurology
Amnesia autobiographical memory and confabulation
Reduplicative paramnesia
Neurology
Self-duplication shifted in time: A particular form of delusional misidentification syndrome
Neurocase
The evolution of spontaneous confabulation, delusional misidentification and a related delusion in a case of severe head injury
Neurocase
Delusional paramnesic misidentification
L’illusion des “sosies” dans un delire systematise
Bulletin de Society Clinique de Medicine Mentale
Delusional hyper-identifications of the Fregoli type
Acta Psychiatrica Scandinavica
The syndrome of Capgras
British Journal of Psychiatry
Syndrome d’ilusion de Frégoli et schizophrenie
Bulletin de Society Clinique de Medicine Mentale
In search of the self: A positron emission tomography study
Psychological Science
Personification of paralyzed limbs in hemiplegics
British Medical Journal
Frégoli syndrome after cerebral infarction
Journal of Nervous and Mental Diseases
Consciousness explained
Some interesting perturbations of the self in neurology
Seminars in Neurology
The irreducible perspectives of consciousness
Seminars in Neurology
The nested hierarchy of consciousness: A neurobiological solution to the problem of mental unity
Neurocase
Why the mind is not a radically emergent feature of the brain
Journal of Consciousness Studies
Altered egos: How the brain creates the self
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2020, CortexCitation Excerpt :Among brain-damaged patients presenting CD, right-hemisphere lesions are known to be the most frequent ones, so that it could be assumed that the cohabitation in the right hemisphere of both visuo-limbic lesion and frontal neurodegeneration may have been crucial determinants for I.F. psychopathology (Gainotti, 2007). Indeed, in light of the acknowledged role of right hemisphere in producing the experience of familiarity (Gainotti, 2007), some authors argued that delusional misidentification syndromes (including CD) could develop from a general deficit of familiarity judgement (Feinberg & Keenan, 2005a, 2005b; Gainotti, 2007). Even outside pathological models, it has been largely demonstrated that the right hemisphere plays a fundamental role in the generation of familiarity feelings related to the perception of known faces (for a comprehensive review see Gainotti, 2007).