Transcript Conflicting Views on Inter-Identity Amnesia in Patients with

Can Inter-Identity Amnesia in Dissociative Identity Disorder be Accurately Described by Current Studies?
Ioanna Georgopoulos
Introduction
Procedure
Subjects (31 DID patients, 25 controls, and 25 simulators)
were taught two word lists as shown below.
DID patients
List A
List B
Controls
Identity 1
Normal ID
Identity 2
Normal ID
Normal ID
Simulated
“amnesic” ID
•Sample word lists are
shown at right
List A
List B
2
1
Sample word lists
•The researchers used two
unshared categories,
vegetables and animals.
•An unshared category was
used as a control. List A
contained names of flowers
and list B of furniture.
DID patients
List A
List B
broccoli
cabbage
cat
zebra
tulip
chair
Directed forgetting between, but not
within, dissociative personality states
Elzinga et al, 2003
•12 DID patients were tested on a directedforgetting task.
•They were taught nonsense word pairs and
told to specifically remember or forget them
when switching states.
Procedural memory in dissociative identity disorder: When can interidentity amnesia be truly established?
Huntjens et al, 2005b
Procedure
•Subjects (31 patients, 25 simulators,
and 25 controls) were given a serial
reaction time task (shown below).
•The task involves pressing the letter
on the keyboard that corresponds to
the position on the screen (Z,X,N,M).
•Response time was measured and
analyzed across trials.
•Procedures vary considerably between studies, so
3 representative papers are presented here that
each employ different procedures and memory
tasks.
Trial
Task
Baseline
Random sequence
Trial 1a
A series of 12 positions were shown 10
times for each trial (same for all three
trials)
Trial 2a
Trial 3a
Personality
Switch
Patients and simulators switched
personalities, controls took break
Trial 1b
The same exact sequence was shown
as in trials 1a, 2a, and 3a
X
Future Experiments
•Experiments should be simulation-resistant to
focus on actual memory processes.
•Limitations on subjects should be relieved to
increase the sample size.
•More objective memory tests need to be devised to
avoid patient bias.
•fMRI studies should focus on changes between
personality states.
References
Results
Personality A
1000
800
600
400
200
0
Personality B
Ra
nd
om
b
a
Tri
al
3
Tri
al
3
a
Tri
al
2
b
a
Tri
al
1
Controls
Simulators
Patients
lin
e
Response time (ms)
Emotional
Forget
Neutral
Forget
•This study is inconclusive because of
the small sample size and lack of
control subjects.
•Results show that inter-identity amnesia does not
occur.
•However, patients do report having no knowledge
of events taking place in other personalities.
•It is possible that patients have an incorrect belief
about their memory function, not a problem with
the memory function itself.
A new random sequence used
Random
M
N
Response Time on a Serial Reaction Time Task
•To-be-forgotten words were in fact
forgotten when patients switched states
regardless of emotional valence. To-beremembered words were also lost
across states, but to a lesser degree.
Conclusions
Trial 3b
Z
State 1
State 2
Outline of Procedure
Trial 2b
Ba
se
Inconclusive
40
30
20
10
0
Emotional
Remember
7
6
5
4
3
2
1
0
Percent Cued Recall on a Directed
Forgetting Task
Neutral
Remember
Number of Recent Articles Dealing
with Inter-Identity Amnesia in
Dissociative Identity Disorder
Percent Cued Recall
•The resulting articles were then limited to those
produced in the last ten years.
Simulators
• Patients showed interference between words learned in list A
and list B.
• Interference indicates that words from list A taught in
personality one were recalled by personality two.
• Patients showed a reduced capacity to recognize and recall
words in general.
Serial reaction time task
•Pubmed was used with search terms “dissociative
identity disorder” and amnesia
Controls
Inconclusive Evidence Regarding Inter-Identity Amnesia
Method
Against
3
0
Results
Supporting
4
Tri
al
2
Does inter-identity amnesia occur in
dissociative identity disorder patients?
5
Simulators
Procedure
Problem
List-Dependent Recall for Shared
Categories
b
•DID often involves various types of amnesia
•Loss of memory for current episodes
•Loss of autobiographical memory (usually from
childhood)
•Appearance of pseudo-memories
•Symmetric amnesia
•Asymmetric amnesia
•Only people who could fully control and maintain
identity switch were chosen.
•Not all identities for each patient were tested.
•Patients were chosen so that one of the identities
did not know of the others.
•Small sample sizes, typically less than 30 cases at
once, were tested.
•It is often difficult to tell if the memory tests were
measuring the proper form of memory and nothing
else because simulation is possible.
•Patients did not come from a very diverse
background.
•Details about subjects were largely based on selfreport.
Huntjens et al, 2003
•DID patients lose their lives to suicide at a higher
rate than patients suffering from any other
psychiatric disorder.
•Two conflicting theories
•Posttraumatic model – personality is divided as
a protective reaction to trauma. Memories of
traumatic events are stored in dissociated
states.
•Sociocognitive model – multiple identities are
created and maintained in response to therapist
influences, media portrayals and cultural
expectations.
Interidentity amnesia for neutral, episodic information in dissociative identity disorder
Tri
al
1
•It affects 1% of the population, making it as
prevalent as other debilitating mental health
disorders such as schizophrenia
Limitations of These Studies
Mean Scores
•Dissociative Identity Disorder (DID) is defined as
“a failure to integrate various aspects of identity,
memory, and consciousness.”
Evidence Against Inter-Identity Amnesia
•The jump in the graph for patients indicates that whatever was learned in
the first state was lost in the switch to the second.
•However, the identical jump in the simulators makes it unclear if the
patients truly forgot what was learned or were also simulating amnesia.
Bear MF, Connors BW, Paradiso MA (2001) Neuroscience: Exploring the Brain. Lippincott
Williams & Wilkins. 2nd Edition.
Dorahy MJ (2001) Dissociative identity disorder and memory dysfunction: the current state
of experimental research and its future directions. Clinical Psychology Review 21(5):
771-795.
Elzinga BM, Phaf RH, Ardon AM, van Dyck R (2003) Directed forgetting between, but not
within, dissociative personality states. Journal of Abnormal Psychology 112(2): 237243.
Forrest KA (2001) Toward an etiology of dissociative identity disorder: A
neurodevelopmental approach. Consciousness and Cognition 10: 259-293.
Huntjens RJC, Peters ML, Postma A, Woertman L, Effting M, van der Hart O (2005a)
Transfer of newly acquired stimulus valence between identities in dissociative identity
disorder (DID). Behaviour Research and Therapy 43: 243-255.
Huntjens RJC, Peters ML, Woertman L, Bovenschen LM, Martin RC, Postma A (2006).
Inter-identity amnesia in dissociative identity disorder: a simulated memory
impairment? Psychological Medicine 1-7.
Huntjens RJC, Postma A (2003) Interidentity amnesia for neutral, episodic information in
dissociative identity disorder. Journal of Abnormal Psychology 112(2): 290-297.
Huntjens RJC, Postma A, Woertman L, van der Hart O, Peters ML (2005b) Procedural
memory in dissociative identity disorder: When can inter-identity amnesia be truly
established? Consciousness and Cognition 14: 377-389.
Merck Manual (1995-2006). Merck & Co., Inc., Whitehouse Station, NJ
<http://www.merck.com/mrkshared/mmanual/section15/chapter188/188d.jsp>
Spanos, NP (1994) Multiple identity enactments and multiple personality disorder: A
sociocognitive perspective. Psychological Bulletin 116(1): 143-165.