By David Spiegel, M.D.
About David
Spiegel, M.D.
The controversial diagnosis of dissociative identity disorder (DID) has
replaced what once was called "multiple personality disorder." People
diagnosed with DID have trouble integrating their memories, sense of identity,
and aspects of consciousness into a unified whole. New research supports the
diagnosis and sheds light on what may have gone wrong in patients' brains, suggests
David Spiegel, M.D. Spiegel, who chaired the professional working group that
recommended the change of name in psychiatry's principle diagnostic
manual, notes that the disorder likely stems from trauma and can be considered
a severe form of post-traumatic stress disorder. Among the biological markers
he describes are a smaller hippocampus and certain neurotransmitters. A
better understanding of the importance of specific regions of the brain to
memory and emotion may help push research forward.
In pop culture, “multiple personality disorder” is often portrayed as
involving strategic, dramatic, and seductive battles among personalities that
are uncomfortably sharing one hapless body. On TV crime shows and in movies the
“split personality” is used as a dramatic excuse for mayhem or is feigned to
evade criminal responsibility. Some believe that the disorder is the creation
of credulous and overeager therapists. However, these and other common
perceptions are mistaken. This article is written to set the record straight,
to explain what this disorder is and what we understand about its causes, both
in early life experience and in the brain. Some people do have what scientists
now call “dissociative identity disorder” (DID), a
name change made official in 1994, when the American Psychiatric
Association published the fourth edition of its Diagnostic and Statistical
Manual of Mental Disorders. Sufferers experience sudden loss of episodic
memory, change from a sad, dependent, and helpless personality state to an
angry, demanding, hostile one in seconds, and may find themselves in situations
that they cannot understand. But they are the victims, not the authors, of
their own fragmentation.
One "identity" may inflict physical damage on their body as
"punishment" for another "personality" state, such as the
patient who carved "I hate Mary," another of her identities, into her
forearm with a knife. Mary was frightened and mystified about the injury. Such
memory loss is often asymmetrical—one identity may be aware when another is
prominent, but not vice versa.
The problem is not that there are "multiple personalities"
existing in one body, as the old name of the disorder implied, but rather that
the brain fails to integrate our different personae. We normally act like
"different people" at work and at a party (hopefully), but we have
continuity of memory and identity across the differences. Patients with DID do
not. In fact, the problem is not that they have more than one personality, but
rather that they have less than one—a fragmentation of self rather than a
proliferation of selves.
People with dissociative disorders are like actors
trapped in a variety of roles. They have difficulty integrating their memories,
their sense of identity and aspects of their consciousness into a continuous
whole. They find many parts of their experience alien, as if belonging to
someone else. They cannot remember or make sense of parts of their past.
Dissociative symptoms involving alterations in
identity, memory, consciousness, and body function are seen in cultures around
the world, described as "ataques de nervios" in many Hispanic cultures and as states
of trance and possession in
Controversy has swirled around the disorder, in part because it is extreme
and dramatic. But new research has helped us understand the origins of this
tragic condition, as well as how it is reflected in the brain.
Evidence is accumulating that trauma, especially early in life, repeated,
and inflicted by relatives or caretakers, produces dissociative
disorders. DID can be thought of as a chronic, severe form of
post-traumatic stress disorder. The essence of traumatic stress is
helplessness—a loss of control over one's body. The mental imprint of such
frightening experiences sometimes takes the form of loss of control over parts
of one’s mind—identity, memory, and consciousness—just as physical control is
regained. During and in the immediate aftermath of acute trauma, such as an
automobile accident or a physical assault, victims have reported being dazed,
unaware of serious physical injury, or experiencing the trauma as if they were
in a dream. Many rape victims report floating above their body, feeling sorry
for the person being assaulted below them. Sexually or physically abused
children often report seeking comfort from imaginary playmates or imagined
protectors, or by imagining themselves absorbed in the pattern of the
wallpaper. Some continue to feel detached and dis-integrated
for weeks, months or years after trauma.
Abuse by a trusted authority figure such as a parent creates special
problems. A child abused by a family member faces an ongoing dilemma: this
beloved figure is inflicting harm, pain, and humiliation, yet the child is both
emotionally and physically dependent. The child has to maintain two
diametrically opposing views of the same person, which creates considerable
tension and confusion, a situation described by psychologist Jennifer Freyd as "betrayal trauma."1 She
showed that people prone to dissociation have selective amnesia for
trauma-related words such as "incest." Freud wrote that “hysterics
[his term for people prone to dissociation] suffer mainly from
reminiscences." His point was that their often dramatic mental and
physical symptoms were the product of early life trauma and conflict over
sexually charged situations.
Humans process vast amounts of information. We can function only by being
strategically selective in our awareness. To do otherwise would be like having
every stored file in a computer open at once, or all the contents of one’s
office file cabinets spread out on the desk at the same time. Emotional arousal
typically leads to increases in recall—most of us remember
Research bears out that blocking emotion about a trauma can also block
memory of it. Neuroscientists Larry Cahill, James McGaugh
and colleagues at the University of California–Irvine had volunteers watch
slides of an accident. Before seeing the slides, one group was given a
beta-blocker, a drug that blocks the stress-induced increase in heart rate and
blood pressure triggered by the sympathetic nervous system. These subjects’
arousal-related increase in recall was also blocked, compared to the recall of
those subjects given a placebo rather than the beta-blocker.2 Other
research goes a step further, helping us understand what happens in the brain
when we suppress memories. John and Susan Gabrieli
and colleagues at Stanford and Michael Anderson at the
Evidence that this inhibition of memory happens in real life is more than
anecdotal. Linda Meyer Williams4 tracked down young women who
had been treated in hospital emergency rooms for physical and sexual abuse an
average of seven years earlier, during their childhood, and interviewed them
about their history of trauma. Thirty-eight percent of them could not remember
the episode that made a trip to the hospital necessary, although many discussed
other episodes of abuse in detail. Another 14 percent reported that they had
been unable to recall the traumatic episode for a period of time, lasting
months to years. One would think that anyone actually brought to a hospital
emergency room for treatment would recall the necessitating episode, yet a
substantial minority could not. While voluntary suppression of emotionally
laden memories is less likely to be successful than suppression of neutral
memories, psychologist Martin Conway of the University of Bristol in England
has found that when people are motivated to forget, they are more likely to do
so for trauma-related memories than for neutral ones.5
The pressure to forget is greater when children are abused by a trusted
caregiver, who might cue memory retrieval unavoidably. The only way to prevent
persistent recall of damaging memories would be to adapt internally and to
deliberately avoid thinking of such memories—in Freud’s terms, to push them
away from consciousness. A study published in 2007 by Geraerts
and colleagues at
Why does this happen? For one thing, people naturally enter an unusual
mental state during traumatic experiences. Their attention is narrowly focused.
“The prospect of the gallows concentrates a man’s mind wonderfully,” Samuel
Johnson famously noted. Mugging victims can often give a precise and detailed
description of the assailant’s gun, but can describe little about his
face. Dissociation can further isolate memories, by separating them from
common associative networks in the brain that would make associative memory
retrieval easier. Thus trauma can elicit dissociation, complicating the
necessary working through of traumatic memories. The nature of the acute
response may influence long-term adjustment.
Often people who have suffered trauma consciously try to suppress their
recollection of the painful events. Over time the forgetting becomes automatic
rather than willful, in the same way that riding a bicycle requires a great
deal of conscious mental and physical effort during the learning phase but
becomes automatic over time.
Trauma can be conceptualized as a sudden discontinuity in experience: one
minute everything is fine; the next, one is in serious danger. This may lead to
a process of memory storage that is similarly discontinuous with the usual
range of associated memories, which might explain the "off/on"
quality of dissociative amnesia, and its
reversibility with techniques such as hypnosis. However, though dissociated
information is out of sight, it is not out of mind. The information kept out of
consciousness nonetheless has effects on it.
Many people suffering from PTSD are unable to recall important aspects of
the trauma. Others feel detached or estranged from people afterward.
In a sample of 122 women seeking treatment for childhood sexual abuse, my
research team found that a majority (66, or 54 percent) experienced PTSD
symptoms. These women had more dissociative symptoms
than those who did not evidence PTSD symptoms.8 Furthermore,
among those with PTSD, dissociative
symptoms were associated with higher levels of childhood abuse. Those with
symptoms of dissociation also had more symptoms of physiological hyperarousal, such as a pronounced startle response after
hearing a loud noise, suggesting that there is an association between
psychological avoidance and physiological hyper-reactivity.
However, other studies provide evidence that dissociative
detachment after a traumatic experience numbs the body as well as the mind.
Psychologists Michael Griffin, Patricia Resick, and
Mindy Mechanic at the
Other studies reveal a distinction between the body’s immediate, neural
stress response and the secondary, hormonal response. Dissociation after trauma
is linked with higher levels of cortisol, a stress hormone that mobilizes
glucose into the blood to assist with the fight-or-flight response, in the
saliva, according to research in which cortisol levels were measured 24 hours after
a stressful interview among adult women who were sexually abused during
childhood.12 So while the immediate neural stress response system is
suppressed by dissociation, the secondary hormonal stress response system is
triggered by it.
Dissociative disorders involving fragmentation of
identity, memory and consciousness seem less mysterious if we conceptualize
identity as the product of mental effort rather than a given—a bottom-up rather
than a top-down model of how the brain processes information. Neural systems
that process the coincident firing of millions of neurons at a time must
extract coherence from all this activity, and it is not surprising that in some
cases these systems do not succeed. Neurons that fire together wire together,
but building large, complex, and yet coherent neural networks may not always
lead to a coherent sense of identity. Factors that restrict neurons from firing
in association may limit the continuity of identity that emerges from
experience and memory.
Hippocampal Volume
Another plausible neurobiological mechanism linking childhood trauma to dissociative difficulties with the integration of memory is
smaller hippocampal volume. As mentioned above, the
hippocampus, part of the limbic system situated in the middle portion of the
temporal lobe, organizes memory storage and retrieval. The hippocampus is rich
in glucocorticoid receptors, which are sensitive to
stress-induced exposure to cortisol. Researchers have provided strong evidence
in animals that early life experiences have lasting effects on the hormonal
stress response system, either making it unduly sensitive to stress or
protecting it from overreaction throughout life. Studies in humans show that
while minor stressors may produce resilience, childhood sexual abuse does the
opposite: it sensitizes the individual to subsequent stressors decades later.
This research indicates that chronically elevated cortisol levels may damage
the hippocampus, leading to smaller size and poorer function.
Imaging studies by Murray Stein at the University of California, San Diego,
and Eric Vermetten at Utrecht University in the
Netherlands have shown that people with a history of childhood abuse and dissociative disorders indeed have smaller hippocampi, and that the reduction in size correlates with
the severity of dissociative symptoms.13, 14 Vermetten also found reductions in the size of the amygdala, the seat of fear and anger conditioning.
Researcher Douglas Bremner found similarly smaller hippocampal size among veterans with PTSD symptoms.
However, Harvard psychiatrist Roger Pitman proposed an alternative explanation
for this relationship.15 He studied 35 pairs of identical twins, one
of whom had been exposed to trauma and one of whom had not. Pitman found that smaller
hippocampal volume is indeed a risk factor for PTSD
severity, but is not affected by exposure to trauma. A smaller hippocampus, he
reasoned, may underlie vulnerability to the development of PTSD symptoms rather
than occurring as a result of trauma exposure.
In any case, a smaller hippocampus would likely limit a person’s ability to
encode, store and retrieve memories and manage the emotions associated with
them. The hippocampus is a context generator, helping us to put information
into perspective. Wolf has shown that activity in the hippocampus buffers the
effects of stressful input on the hormonal stress response system.16 Ruth
Lanius demonstrated that those who dissociate in
response to listening to accounts of their traumatic experiences have decreased
activity in the brain adjacent to the hippocampus—they remember less and their
brain memory systems are less active.11 Limitations on hippocampal size and function hinder memory processing and
the ability to comprehend context, especially in light of contradictory memory
encoding and storage. Among patients with PTSD and dissociative
symptoms, research also indicates that there is higher connectivity between two
portions of the brain—the right insula and the left ventrolateral thalamus—that are involved in perception of
bodily processes and emotion and consciousness. This finding provides further
evidence that both mental and physical distress are
triggered by traumatic memories.
Neurotransmitter Activity
Neurotransmitters
convey information from one nerve cell to another, and a specific one may be
involved in dissociation. It has long been known that drugs that block the
activity of the N-methyl-d-aspartate (NMDA) subtype
of glutamate receptors in cortical and limbic brain regions produce dissociative symptoms, perhaps via a one-time release of
glutamate. Anti-anxiety medications such as lorazepam
stimulate the release of gamma amino butyric acid (GABA), a neurotransmitter
that inhibits rather than stimulates activity in many regions of the brain.
Yale researcher John Krystal has suggested that GABA
may also play a role in dissociative symptoms. His
work suggests that administering a drug that stimulates GABA increases
dissociation.17, 18
Two heads are not better than one when they share the same brain. The
fragmentation of mental function that can occur after a series of traumatic
experiences may both protect a person from distress and make it harder for the
individual to put the trauma into perspective. As we come to appreciate the
complexity of neural development, we also understand that early life
experiences have a profound effect on the developing brain. In dissociation,
achieving a sense of mental unity is such a difficult task that it can be
disrupted by events that challenge body integrity, emotional control, and the
development of relationships. Future research will reveal more about specific
genetic vulnerabilities that may make certain individuals especially
susceptible to the disorganizing effects of traumatic stress.
We also need to understand more about neural development and function: How
do specific regions of the brain facilitate or inhibit memory, emotion, and
their interaction? How can we use this knowledge to better treat individuals
suffering from dissociation? Current treatments primarily involve
psychotherapy, and increasing knowledge of brain structure and function may
provide necessary connections for therapists and their patients, helping these
individuals to understand and control their dissociative
tendencies while working through the consequences of traumatic experiences.
Other research may lead us to a specific medication that treats uncontrolled
dissociation; at present there is none.
As we better understand control systems in the brain that underlie
dissociation, we hope to enable people so that their response to trauma does
not reinforce feelings of helplessness but rather augments their control over
their identity, memory and consciousness.
More at: http://www.dana.org/news/cerebrum/