AT FIRST the unhappy 33-year-old-let鈥檚 call her Marnie-didn鈥檛 stand out from the hundreds of patients that psychiatrist Don Condie saw every month at the Massachusetts General Hospital in Boston. Indeed, he treated Marnie for depression for two-and-a-half years without ever suspecting her secret. Then her mother died and Marnie began to reveal her true selves.
After her mother鈥檚 death, Marnie became withdrawn and felt hopeless. She hoarded her medicines, hinted at suicide and needed a spell in hospital. While she was there Condie saw her, but instead of the depressed patient he expected to see, he found himself talking to a bright, energetic and optimistic woman-nothing like the usual Marnie. She even introduced herself to him as if they hadn鈥檛 met before, not as Marnie, but as Mimi. Mimi told him that she could fool everyone by imitating Marnie so well that they wouldn鈥檛 notice the switch-even Marnie didn鈥檛 know she existed.
Mimi gradually began to unveil Marnie鈥檚 horrifying past, including years of beatings, sexual abuse and psychological torment at the hands of her alcoholic, criminally violent mother. Mimi explained that her job was to deal with problems that were just too painful for Marnie, such as the explosion of feelings unleashed by her mother鈥檚 death. As he listened, Condie realised that Marnie was suffering from something far more mysterious and difficult to treat than depression-multiple personality disorder or MPD.
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After years of therapy with Marnie, Mimi, and the several other personalities that subsequently emerged, Condie teamed up with Guochuan Tsai, a neurobiologist and brain imaging expert at the McLean Hospital in Belmont, Massachusetts. They realised that, with Marnie鈥檚 help, they could do something nobody had done before-peer inside a human brain as it shrugs off one identity and slips into another. Their findings are helping to piece together a brain-based understanding of this mysterious, personality-splintering disease.
A physical basis for MPD, and even the reality of the condition, is by no means a given. Many psychiatrists, especially in Britain, think the disorder is nonsense (快猫短视频, 17 June 1995, p 14). They鈥檝e seen it mutate over the past decade from a condition so rare that most therapists never saw a single case into a near epidemic, especially in North America. They scoff at reports of patients who spin off hundreds or even thousands of personalities.
Tom Fahy, a psychiatrist at the Maudsley Hospital, London, is one of the critics who believe most MPD cases are the creation of misguided therapists. Through the use of hypnosis, drugs and group pressure, he suspects, aggressive therapists persuade vulnerable patients into believing and acting as multiples. Other critics say MPD is trumped up by attention-seeking patients, or by criminals trying to dodge responsibility for their crimes.
But after years of debate, Fahy wants to move on. 鈥淚t鈥檚 silly to argue whether it exists or not,鈥� he says. 鈥淵ou can鈥檛 deny that MPD patients exist. The question is, how has this patient got into such a bizarre mental state?鈥� While Fahy is looking primarily to cultural causes, Condie and Tsai chose to address the question by studying Marnie鈥檚 brain in action.
Therapists who believe in MPD have developed a more or less consistent psychological explanation, that it is the mind鈥檚 escape from unendurable childhood abuse, usually before the age of five-an explanation popularised by the film Sybil. 鈥淚t鈥檚 chronic trauma,鈥� says Condie, 鈥渨here you know you鈥檙e going to be abused over and over again, by the same person, and there鈥檚 no escape. The only escape is inside your own mind.鈥�
But if it is a form of escape, then surely it is like escaping into a nightmare. Imagine competing for control of mind and body, not to mention your home and bank balance with a terrified child, strangers with different sexual proclivities, and a collection of hostile or suicidal toughs. You never meet them and don鈥檛 know what they鈥檙e up to, although some of them know all about you. But you find their clothes in your closet, you鈥檙e blamed for their bad behaviour and you have to clean up the messes they make. And even when you manage to stay in charge, you鈥檙e plagued by them arguing, shouting or crying inside your head. No wonder Marnie, like most people with MPD, hid this terrifying reality for years.
But how in escaping does one personality fragment into many others? Some theorists suggest that the overwhelming stress of living such a chaotically divided life tears at the fragile web of a child鈥檚 developing memory, so the child cannot weave experiences together into a coherent whole. Instead, islands of memory and behavioural traits develop independently. Eventually they emerge as autonomous personalities competing for control of mind and body.
For example, as a child, Marnie learned to trick her mother into thinking she鈥檇 already punished her by pounding on her own thighs until they were covered in bruises. Eventually, a separate male personality developed to inflict the beatings. The outcome is too close to Invasion of the Body Snatchers to be believed without a fight. Perhaps that鈥檚 one reason MPD is such a contentious diagnosis. That and a reluctance to admit that anyone could so grossly mistreat a child.
Traumatic shrinkage
The continuing battle over the diagnosis makes it all the more exciting that Condie and Tsai have finally been able to peer into the brain of a patient with MPD. Their preliminary studies showed what鈥檚 now been found in many people who鈥檝e lived through protracted trauma: a dramatically shrunken hippocampus. All the other areas of Marnie鈥檚 brain were well within the average volumes, while her hippocampus was less than half the normal size-as shrunken as if she suffered from Alzheimer鈥檚 disease.
Brain researchers have known for years that the hippocampus, a pair of finger-sized curls of tissue cradled between the temples, plays a key role in memory. It is most active when a person consciously recalls information they have learned-lists of words for example, but more importantly, personal experiences-what you have heard, seen and felt. In addition, patients with severe hippocampal damage can neither build nor recall new memories. 鈥淚f it鈥檚 damaged bilaterally,鈥� says John Aggleton, a neuroscientist at the University of Wales, in Cardiff, 鈥渢hen you get a profound loss of new learning. You can鈥檛 remember conversations you鈥檝e had, places you鈥檝e been, or what you鈥檝e done. Yet your other cognitive abilities remain intact.鈥�
To some, her shrivelled hippocampus did not come as a complete surprise. In 1995, researchers at Yale University and at the University of California, San Diego, reported that patients with combat-related post-traumatic stress disorder (PTSD), and adults with PTSD following childhood abuse, also have smaller hippocampuses, along with memory and thinking deficits. Stress and depression are closely linked; indeed one study of women with a history of depression also uncovered a degree of hippocampal damage and memory problems.
After surveying human and animal studies linking stress and hippocampal decline, Robert Sapolsky from Stanford University suggests that extreme levels of glucocorticoids, steroid hormones released by the body under stress, are toxic to the hippocampus. They can disrupt cell function, cause structural changes and eventually cell death. Conversely, Barry Jacobs and Casimir Fornal at Princeton University showed that Prozac, used for treating depression, stimulates the birth of new neurons in the hippocampus (快猫短视频, 6 November, p 6). 鈥淲e know that stress hormones can be neurotoxic,鈥� says Condie. 鈥淏ut we don鈥檛 know if it鈥檚 neurotoxicity or a combination of things causing the volume change.鈥�
A large number of studies have shown that the memory formation controlled by the hippocampus is also intimately linked to emotion, probably modulated by its next-door neighbour, the amygdala. The hippocampus reacts strongly to stress hormones and also to drugs like Valium and the body鈥檚 own anti-anxiety agents. Recent research in rats shows that emotional arousal, for example from a mild electric shock, switches a protein called CREB from an inactive to an active form in the hippocampus. High levels of activated CREB help lay down long-lasting memories, while low levels cause amnesia (快猫短视频, 27 March, p 16).
Joseph LeDoux, a neuroscientist at New York University, adds that someone with an intact amygdala but a damaged hippocampus may form emotional memories, for example, fear of a certain place or person, without conscious memory of what caused the fear. 鈥淵ou get a powerful emotional memory, but a weaker memory for the experience,鈥� he says.
Putting all this together-a shrunken, damaged hippocampus and wildly fluctuating levels of stress hormones and neurotransmitters-makes memory distortions seem inevitable. And, as Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego, pinpoints in his idea of the mnemonic self, memory underlies who we are. Store memories abnormally and you may never be able to find them again. Land on a different island of memories and you鈥檙e a different person.
Stanford University鈥檚 John Gabrieli, who studies the neuroscience of human memory, also links it to personality formation. 鈥淭he hippocampus binds together information from many different parts of the brain into a memory of an experience,鈥� he says. 鈥淲ithout access to these memories, your identity can鈥檛 grow or develop.鈥� And the absence of coherent memory for personal experiences, the kind of amnesia caused by hippocampal damage, is MPD鈥檚 calling card.
What Condie and Tsai really wanted to know was what lies beneath the memory separation and the switch from one dissociated personality to another. They used functional magnetic resonance imaging, fMRI, to address this question. By the time they did their study, a dozen years had passed since Marnie鈥檚 mother鈥檚 death. Marnie was working steadily in a professional role and seemed to be coping better with her personal life too. Intriguingly, through years of therapy, she had also developed an unusual ability to shift personalities at her therapist鈥檚 request, allowing the researchers a unique opportunity to watch the change happening.
The fMRI scanner records hundreds of images per second, revealing in exquisite detail where brain activity is drawing oxygen from the blood. Condie and Tsai monitored Marnie鈥檚 brain for a total of 90 minutes, in two sessions separated by several weeks. Using taped directions, Condie directed Marnie to switch to a personality named Guardian, an 8-year-old girl who appeared frequently during therapy. Guardian鈥檚 role since childhood had been to watch over Marnie, for example, while her mother tormented her. In the experiment, Guardian would press a button to signal to the experimenters that she had taken control, a process that took about 30 seconds. Marnie would signal her return the same way.
To see whether real personality switches were different from the effects of imagination or effort, Marnie was also asked to imagine being an 8-year-old girl named Player, who was not a real alter ego. Although she found it exhausting, Marnie made the transitions dozens of times while the researchers measured how the activity in the different regions of Marnie鈥檚 brain changed as each personality or the imagined character emerged.
As suspected from the preliminary studies, the hippocampus emerged as the star of the identity-shifting drama. But just what its activity means is not easy to interpret. As Marnie鈥檚 awareness faded and Guardian took centre stage, activity throughout the hippocampus and in the surrounding temporal cortex ebbed. And as Guardian stepped aside and Marnie re-emerged, the right side of the hippocampus lit up with renewed activity (see Diagram). When Marnie pictured herself as Player, rather than a real alter ego, her brain activity didn鈥檛 change.
These findings, coupled with the known links between stress, hippocampal damage and memory abnormalities, have led Tsai towards a brain-based theory of MPD. 鈥淭he label is misleading,鈥� he says. 鈥淚t鈥檚 not multiple personalities in the same body, but the brain鈥檚 reaction to damage. I think it鈥檚 a form of brain damage from repetitive and overwhelming stress in early childhood or from overwhelming trauma in life.鈥�
Flashback
The American Psychiatric Association has already acknowledged the problem with the name of the condition, and since 1993 has labelled it Dissociative Identity Disorder, or DID. Dissociation is a disruption in normally integrated consciousness. It ranges from the everyday, such as momentarily forgetting a familiar name or realising you鈥檝e driven miles while thinking of something else, to the pathological-episodes of amnesia, flashbacks or periods of highly abnormal behaviour. At dissociation鈥檚 extreme, say believers, lurks multiplicity-coexisting selves with distinct life experiences, memories and personalities.
Tsai speculates that Marnie鈥檚 abnormally small hippocampus, almost certainly the result of the abuse she suffered early in life, may misfire in a way that makes possible the extreme dissociation required to switch personalities. He points out that everyone can dissociate, when they daydream, for example. 鈥淏ut some people鈥檚 brains get changed early in life, become more vulnerable to trauma, so the switch can go back and forth more easily,鈥� he says. 鈥淲e really don鈥檛 know, but if the wiring is not as sound as it should be, it might easily get inhibited or over-excited, and that might tip the balance between the two personalities.鈥�
David Healy, who heads the department of psychological medicine at the University of Wales College of Medicine in Bangor, finds the brain imaging results intriguing. 鈥淭here would have to be some physiological underpinnings to the phenomenon of MPD,鈥� he says. 鈥淵ou could describe this as a very graphic illustration of the idea that when a particular personality comes into play, it doesn鈥檛 have access to the full range of brain resources.鈥�
He thinks differences between children鈥檚 brains might determine who would react to extreme stress by developing dissociative symptoms and eventually MPD. And he鈥檚 not surprised to find the hippocampus lurking at the heart of MPD. 鈥淚t鈥檚 no surprise that it鈥檚 the structure that might be involved when people are asked to remember what they did, or who they are.鈥�
It is tempting to suggest that decreased hippocampal activity as Guardian emerges is suppressing and preventing access to memories that are Marnie, while the upsurge of activity as Marnie returns is the vital trigger to bring her memories back online. But the researchers and other experts are quick to point out that their findings are too preliminary to support such detailed conclusions.
Daniel Schacter, a brain researcher at Harvard University, warns about pushing the findings too far. 鈥淚t鈥檚 certainly very suggestive,鈥� he says, 鈥渂ut it鈥檚 one finding, one patient, one study. Imaging studies are very easy to over-interpret, especially in an exotic subject like this.鈥�
While agreeing with Condie and Tsai鈥檚 interpretation of what the hippocampus does, Fahy, the Maudsley psychiatrist, echoes Schacter鈥檚 cautionary note. 鈥淭he important thing with these kinds of studies is not to take them literally, to think that a light flashing in one part of the brain represents a different personality,鈥� he says. 鈥淭hat would be absurd.鈥�
Although Tsai very much wants to repeat their findings with other MPD patients, getting to watch Marnie鈥檚 injured brain perform its remarkable sleight of hand has strengthened his belief that neuroscience鈥檚 high-powered new tools can illuminate the damage or dysfunction in more detail, and eventually lead to better treatments for MPD and many other mental disorders. But for now, it鈥檚 no small feat that they have spotlighted the hippocampus as the battleground where traumatic stress, memory and our sense of who we are collide.