Thursday, April 22, 2010

William L. Benzon - The Neural Self : Damasio, Kilmer-McCulloch, and Dissociated Identity Disorder

This is an interesting section of a much longer article from PsyArt: An Online Journal for the Psychological Study of the Arts.

Here is the relevant information:
First Person: Neuro-Cognitive Notes on the Self in Life and in Fiction

by William L. Benzon

We can think of the self as the result of interaction between subcortical systems for regulating the global brain state and largely cortical systems for representing the current body state and autobiography. The personal pronoun system is at the interface between the cortical and subcortical systems. By constructing a network model for the pronoun system that is grounded in basic machinery for social interaction we show how the pronoun system allows speakers to achieve self-reference and how this capacity engenders the illusion of a unified self. The same model allows us to see that there is no essential difference between reliving incidents from one's own past and giving life to imaginary characters in ritual and in literary works. Such imaginative experience may play a role in maintaining the coherence of the self through different emotions.
There is an interesting section in this much longer paper that looks at DID (dissociate identity disorder) using Antonio Damasio's neural self model.

3. The Neural Self : Damasio, Kilmer-McCulloch, and Dissociated Identity Disorder

In two recent books Antonio Damasio (1994, 1999b) has articulated a theory of the neural self. Damasio distinguishes between a core facet that is an integrated representation of one's body states and an autobiographical facet (1994, 236ff.; 1999, 171ff.). These selves--Damasio does refer to these systems as selves even as he refers to the neural self to mean both of these systems--are best conceived as processes, not things, and are subserved by extensive networks of interlinked neural areas. They are not physically continuous neural modules; the simple NS circle of the previous diagrams is thus a gross simplification (nor did the previous discussion say anything about the autobiographical self). Neither of these processes is the master process that runs the whole show--Damasio rejects the notion of such a process. As its name suggests, the autobiographical self organizes the historical events of one's life and imagines future events. The core self organizes sensations from the body's interior milieu and somesthetic and kinesthetic senses into an on-going evaluation of one's current body state.

Damasio's model is a rich one, but the purposes of this essay are most directly served by considering a single facet of it by considering anosognosia, a condition which disrupts the core self in a striking way (Damasio 1994, 62ff., 1999b, 209ff.). In this condition patients suffer brain damage that leaves them partially paralyzed, but they are completely unaware of their deficit and will deny that anything is wrong with them. Such, of course, is not always the case. It is possible, and common, to suffer brain damage that leaves one partially paralyzed but that doesn't spare one's awareness of that paralysis. It is this lost awareness of one's deficit that is characteristic of anosognosia.

Anosognosia generally occurs with extensive damage to the right hemisphere, leaving the left half of one's body extensively paralyzed--you'll recall that each cerebral hemisphere accepts input from the contralateral side of the body and sends output to that same side. The same pattern of damage to the left hemisphere will result in similar paralysis to the right half of the body but there is no lost awareness of one's disability. Anosognosia is a disruption of the integrated sense of one's body that is the foundation of the core neural self. What makes anosognosia so interesting to me is that it suggests a distinction primary neural systems that "run" the body and secondary systems that monitor the activities of those primary systems--a distinction we'll explore a bit later in conjunction with some experiments by Jean Piaget.

Anosognosia is a condition affecting the topology of the neural self, what is represented and what neural structures subserve that representation. There is another aspect of the neural self, one that has to do with the continuity and coherence of the representation. We can approach this issue by considering dissociative identity disorder (DID), an extreme pathology in which the neural self is fractured. In DID, also known as multiple personality disorder, one biological individual exhibits several different identities, each having different memories and personal style. In Thigpen and Cleckley's (1957) classic study Eve had three personalities; Schreiber's (1973) Sybil had sixteen (see also Rappaport 1971, Stoller 1973). Although there has been some controversy over whether or not DID is real or simply the effect of zealous therapeutic invention and intervention, there is no doubt that at least some cases are genuine (Schachter 1996, 236-242, Spiegel 1995, 135-138).

These different identities have different personal histories. The events in one personal history typically are unknown to the other histories. Each identity will have blank periods in its history, intervals, obviously, where another identity was being enacted. And the different "persons" are often unaware of one another. Further, the different identities seem to have different personal styles, different modes of speech, of movement, of dress, and so forth. Thus both the core and autobiographical selves seem to be riven. Using the conventions we employed above, Figure 7 is a simple depiction of DID:

Figure 7: Dissociative Identity Disorder

Notice that we now have two neural selves, NS1 and NS2, corresponding to two different identities. Of course, these two selves exist in the same body, so we have only one corresponding body in the external world.

We do not, so far as I know, understand why or how DID happens. It is not, however, the result of the sort of gross destruction of brain tissue that underlies anosognosia. One might imagine, for example, that the different selves reside in distinctly different patches of neural tissue, a speculation that Damasio (1999b, 355) himself has suggested for the autobiographical self (though he presents no evidence). This suggestion, however, has at least one problem: How does the nervous system switch from one identity to another? There is another way of explaining DID, equally speculative and equally without specific evidence, that eliminates this particular problem.

Noting that different identities seem to favor different moods and that "memories established in one mood state are often more readily recalled in that same mood state than in a different one," Daniel Schachter (1996, 238) suggests that "different moods and roles come to be labeled with separate names" (cf. LeDoux 1996, 211-212, McGaugh 1995, Cahill and McGaugh 1996). Different selves emerge to handle different desires and emotions. This suggests problems with brain neurochemistry, for our moods, emotions, and desires are subserved by complex chemical interactions in the nervous system (Bremmer et al. 1996, Freeman 1995, 117ff.; Joseph 1999, Panksepp 1998, 1999). The distribution of many of these neurochemicals is regulated by brain stem nuclei, at least some of which are in the system which Damasio (1999a, 1999b) calls the proto-self--which also includes cortical structures. While the activities of the core and autobiographical selves are conscious, those of the proto-self are not (though others have a different view of the structures of this proto-self, e.g. Panksepp 1998, 309ff.). However, the structures of the proto-self help constitute the conscious states in which the core and autobiographical selves operate (cf. Hobson 1999a, 1999b).

Among these brain stem nuclei are those of the reticular formation (RF), one of the oldest structures in the brain. Classically (Moruzzi and Magoun 1949) the reticular formation has been associated with sleep and arousal. However, others have argued that the RF plays a broader role. Thus Vanderwolf and Robinson (1981) have argued that the RF exerts a general role in the control of adaptive behavior through its ability to influence the cortex. More recently, Damasio has argued that the RF and closely associated structures play a critical role in "managing body states and representing current body states. Those activities are not incidental to the brain stem's well-established activation role: they may be the reason why such an activation role has been maintained evolutionarily and why it is primarily operated from that region" (Damasio 1999, 274).

These views are reminiscent of a very elegant model proposed by William Kilmer and Warren McCulloch, one of the "first models of decision making in neural circuitry to explicitly opt for cooperative computation, rather than executive control" (Amari and Arbib 1977, 119). Noting that "No animal can, for instance, fight, go to sleep, run away, and make love all at once." Kilmer-McCulloch went on to list fifteen "mutually incompatible modes of vertebrate behavior," all of them as basic as those already mentioned (Kilmer, McCulloch, and Blum 1969, 279). The exact number and identity of these modes is not important. What is important is that, at all times, an animal must be in one of these modes, and only one of them. Kilmer-McCulloch hypothesized that it was the RF that determined which mode the animal was committed to at any moment (cf. Benzon and Hays 1988, 296-298). The RF has extensive afferent connections from the rest of the brain and the structure of its internal connections seems well-suited to making a global evaluation of those inputs, thereby assessing the current state of the organism. The RF also has extensive efferent connections to the rest of the brain and is thus in a position to affect its state (cf. Panksepp 1999, 21ff.; Green 1999, 43). Specifically, the RF is in a position to affect the neurochemical ambiance of cortical tissue and thus can affect just which synapses are most arousable at any given moment.

In this view, if the animal is in eating mode, the world becomes an array of objects and events that either promise something to eat, or interfere with that promise. The cortical patterns most relevant to eating are readily arousable while those less relevant are less arousable. Similarly, if the animal is in mating mode, then the world becomes a set of opportunities for sexual satisfaction or frustration. The RF commits the brain to a pattern of activation that is suitable to the mode and the animal then seeks its satisfaction. Just what it does is not directly determined by the RF; that depends on other neural centers. Figure 8 is a highly schematic representation of mode:

Figure 8: Behavioral Mode

Here we see two different modes, A and B. I've used some arbitrary pattern to color the internal milieu and external world for each mode, thus indicating that the animal is committed to bringing about a certain kind of consonance between its inner milieu and the external world. I've depicted the modal arousal of the CNS by varying patterns of shaded squares, where the shading corresponds to level of arousal. I've used three levels of arousal, but there could be only two, there could be seven, or level of arousal could be continuously variable. For our immediate purposes it makes no difference. What's important is that we have two distinctly different patterns of arousal corresponding to two behavioral modes.

My suggestion about DID, then, is that the mechanism that switches between one identity and another is fundamentally neurochemical. Each identity favors a particular mode, or, more likely, a set of modes. An identity becomes regnant when brain neurochemistry favors it. The perceptions and memories relevant to the modes of that identity will become easily arousable while those relevant to other modes will be all but impossible to arouse. Among individuals unaffected by DID the neurochemical milieu will bias cortical tissue toward a particular set of perceptions and memories but will not necessarily make other perceptions and memories impossible to reconstruct. In the case of DID this neurochemical process is taken to an extreme where whole ranges of perceptions and memories become absolutely unavailable depending on what neurochemicals are currently active. The state space of the brain has become fractured along neurochemical lines, breaking the self into many selves.1

Note that this explanation of DID not only tells us how the brain switches from one identity to another--RF control over cortical arousal--but also suggests that the various neural selves do not have be in physically separate tissue. They can exist within the same volume of neural tissue for they are differentiated by chemical sensitivity, not by location.

Of course, one doesn't have to think about this model too long before suspecting that it gives us more than we've bargained for. After all, neurochemistry is known to be implicated in various neurological and psychiatric problems, and one can easily imagine it to be implicated in problems where we currently have no specific knowledge. Part of the way out of this difficulty is simply to point to the complexity of neurochemistry. There are well over 100 known neuroactive chemicals (Hobson 1999a, 159). That leaves plenty of room for a wide range of pathological conditions, only one or a few of which will produce DID. The trick, of course, is to identify just which disruption is responsible for DID. That job is surely beyond the scope of this essay. (However, later in the essay we will return to DID to refine our speculation just a bit.)

The more general point, then, is however we theorize about the neural self, we must consider more than topological issues. It is not enough to know what and where in the brain the body state and autobiography are represented. One does not automatically have access to all the events the brain has registered. Autobiographical continuity is not given in the nature of the nervous system. The continuity and coherence of the neural self depends on complex matters of the neurochemistry of mood and emotion.

I would like to conclude this section by counterpointing DID against the perfectly normal activity of playacting (recall Figure 6). In playacting one deliberately assumes a different identity. One chooses to act like another and does so for a limited period of time. When the time is over one returns to one's own identity without, generally, ever having completely lost touch with that identity. Playacting is thus different from identity switching in DID, which is involuntary.

Children routinely engage in pretense during play. While adults are less likely to engage in playacting, one can certainly argue that reading novels and stories and seeing movies and plays involves something very like pretending to be someone else. You may not enact another person through gesture and voice, but you identify with fictional characters, enacting their feelings and desires in your nervous system, in your core self, and constructing autobiographies for them. Just as you can, in appropriate circumstances, reconstruct events from your past so vividly that you reexperience the feelings that attended them, so you can treat events in the life of a fictional character as though that life were your own and thereby experience that imaginary life as your own. Beyond this, of course, skilled actors can enter into a role quite deeply, creating physical and vocal styles appropriate to the character, imagining a lifetime of events in the character's life, not just those depicted in the script. In the case of a good actor, the transformation can be so great that one is confronted with the question of whether or not the actor becomes the character.

I have more to say about playacting but I want to say it after we have had a chance to delve into the cognitive mechanisms surrounding the personal pronouns. Those mechanisms will tell us a bit how a nervous system can pretend to be someone else. That investigation, for the most part, is about operations at the interface between the proto-self and the core self. With that discussion in hand we can revisit these neurochemical matters, concluding with the speculation that ritual and art contribute to the maintenance of an internal milieu which is not neurochemically fractured.

For now, it is time to consider the infant and how she interacts with others even in the first hour of life. That is where we will find the mechanisms upon which we will construct our account of the personal pronoun system.

* * * *

A Note on Conceptual Frameworks: David Hays and I have developed a fairly extensive cognitive model organized on several levels, which we choose to call degrees (Hays 1981, Benzon 1978, Benzon and Hays 1988). Henceforth, when I use the term "degree" I will be referring to that model. I use this model as the most general framework for this essay and, in particular, for the technical detail of the model for first and second person pronouns. Damasio's theory of the neural self, of course, is the other major framework for this discussion. Given that Damasio's model has been developed for rather different purposes, and employs a different evidentiary base, there is no clean correspondence between his model and ours. Roughly speaking, our modal degree contains at least some of the subcortical components of Damasio's proto-self. Our sensorimotor degree would handle some of the functions of both the proto-self and the core-self, but none of the functions of the autobiographical self. His autobiographical self would be implemented in our episodic and gnomonic degrees, though I suspect the core self has a gnomonic aspect as well. (See Note 9 for further remarks on the episodic and gnomonic degrees.)

The table below summarizes the approximate relationships between Damasio's theory and the Hays-Benzon model. In particular, the neural correlates more accurately reflect the Hays-Benzon model, which is about perception, action, and cognition in general, than Damasio's model. The notion of primary, secondary, and tertiary cortex is that of A. R. Luria (1973).

Hays-Benzon Neural Damasio
modal brainstem proto-self
sensorimotor limbic system
basal ganglia
proto, core
systemic primary, or
projection cortex
proto, core
episodic secondary cortex
(temporal, frontal)
gnomonic tertiary cortex

Read the whole article.

No comments: