One of the most vexing pathologies identified by DSM-IV is dissociative identity disorder (“DID”), formerly known as multiple personality disorder. From a philosophical standpoint the main reason why DID is interesting is because it implicates issues involving personal identity. We are inclined to say that one’s personal identity persists over time. One has certain features or properties that are necessary (and may be sufficient) for some past or future instance of oneself still to be “me,” no matter how much one might change physically or psychologically. These predicates truthfully can be ascribed to one no matter where one is situated spatially or when one is living on the temporal continuum of life. It is their continuity and consistency that makes it possible for there to be a stable concept of self despite changes to a myriad of other factors comprising “personality.”
Physiologically, while one’s body certainly changes, one still is “in” one’s body. Thanks to modern medical technology it’s possible to substitute various organs, but one still remains one’s self. There is no such thing as a brain transplant that would carry over one’s memories and beliefs from one physical incarnation or instantiation to another. For that matter it’s unlikely there ever could be, given the close connection between the brain and the physical body. Being-in-the-world (experiencing emotion, for example) is possible only because of these psychosomatic links.
From a psychological standpoint one is connected to one’s past. One has memories involving previous instances of one’s self (although forgetting these memories doesn’t mean one isn’t one’s self, nor does being unconscious or unaware of experience as it occurs). One only can “remember” one’s own past experiences, not those of somebody else. One has beliefs about the world and characterological traits and tendencies, all derived from prior experience.
According to DSM-IV 300.14, dissociative identity disorder involves the following elements:
A. The presence of two or more distinct identities or personality states (each with its own relatively enduring pattern of perceiving, relating to, and thinking about the environment and self).
B. At least two of these identities or personality states recurrently take control of the person’s behavior.
C. Inability to recall important personal information that is too extensive to be explained by ordinary forgetfulness.
D. The disturbance is not due to the direct physiological effects of a substance (e.g., blackouts or chaotic behavior during alcohol intoxication) or a general medical condition (e.g., complex partial seizures).
DID implicates at least two selves: one’s “real” self and then another “self.” In principle there’s no reason why there can’t be multiple selves; the literature reports cases of over a dozen. Each personality is an integrated unit with a distinct history, self-image and identity. For example, gender, age and personality characteristics may be different. The different selves alternately take control of behavior. The world each personality inhabits is phenomenologically distinct and internally consistent with its own objects, people, roles, objectives and other features. There literally is a “split” in the “mind” or “consciousness,” understood as the outcome or precipitate of neurochemical activity.
Even so there still is common ground between personality states. If we imagine the self as comprising a set with a myriad number of traits, characteristics or other ascriptive predicates, then there is some overlap or intersection between these sets. There can be some cross-communication between personalities (although events occurring during control by other personalities may not be remembered). Autobiographical memory may be impaired but there is not complete inter-identity amnesia. Studies show for example that word priming at identity #1 significantly enhances recollection at identity #2.
Even more puzzling is that all of these various selves inhabit the same body with the same brain anatomy and neurochemistry. They share the same sensory inputs such as irradiations on the retina and vibrations in the auditory canal, in turn routed to the thalamus for further processing by the relevant areas of the cerebral cortex. The epistemology of DID therefore is daunting because it is hard to see where these multiple selves reside and how to define the neurophysiological world they inhabit. Considerable research needs to be done on differences in brain activity and neurochemistry during personality switches and different identity states.
Until this research is completed the best way to think about DID may be by analogy to the many-worlds or multiverse interpretation of quantum mechanics. This hypothesis is to the effect that in addition to the physical world we inhabit there are other parallel worlds. A world is a totality of facts, beliefs, states of affairs and other things or occurrences that might be said to be ontologically real in that they actually exist. While another world may be spatially elsewhere it exists in our same universe and is parallel in time. Whenever something happens in our world all possible variations or outcomes occur simultaneously in each other possible world. These variations include all possible different spatio-temporal outcomes or states of affairs. As inhabitants of our world we’re only aware of the outcome that occurs in it. The relationship between these multiple worlds is unclear; at the least it’s based on a correspondence between events in our world and our experiences, and those taking place in the other alternative worlds. It may not however have the same cause-effect relationships.
Each of us physically exists in each of these possible worlds. It’s possible to evaluate and describe one’s physical condition and one’s neuroanatomy and neurochemistry. Given this overlap in somatic and psychological states, do each one of these other instances or instantiations of oneself still comprise the same person? What about the criteria for personal identity we discussed in connection with DID such as continuity of memories, beliefs, past experiences and future prospects? Are they just copies of me, or genuinely somebody else?
Maybe the patient that presents with symptoms of DID actually is a window into these different possible world states.