346 CHAPTER 8
P SNelectrical activity on the scalp to show that the brain responds as if the patient with
DID recognizes previously learned words, even when the learning took place when
one alter was dominant and the testing occurred when another alter was dominant
(Allen & Movius, 2000). For example, if an adult alter were taught the words, a child
alter might claim to have no memory of them—but the brain responses to the familiar
words are the same, regardless of which alter is dominant when the test is done.
However, additional research has provided evidence that patients with DID are
inhibited from recalling stored information when a different alter is dominant, even if
they are capable of doing so (Elzinga et al., 2003). Why might some memories be made
unavailable for easy recall by particular alters? Putnam (1995) has offered a theory,
which other researchers have extended to specify brain mechanisms. Specifi cally, the
orbital frontal cortex (the lower part of the frontal lobe, behind the eyes)—which regu-
lates many other brain regions used in various cognitive and emotional processes—may
play a key role in the development of DID (Forrest, 2001). According to this theory,
early abuse may prevent this area of the brain from maturing normally, and hence it
is not able to integrate representations of the self normally. If memories are associated
with particular representations of the self (that is, with individual alters), each represen-
tation will cue only some specifi c memories—which will be easier to recall than ones
that are not cued by that representation.
Perhaps the key characteristic of DID is that each alter has a different “sense of
self.” To the individual with DID, it feels as if different personalities “take over” in
turn. To explore the neural bases of this phenomenon, Reinders and colleagues (2003)
asked 11 DID patients to listen to stories about their personal traumatic history while
their brains were scanned using PET. Each patient was scanned once when an alter
who was aware of the past trauma was dominant and once when an alter who was
not aware of the past trauma was dominant. Two results are of particular interest:
First, and most basic, the brain responded differently for the two alters. This alone
is evidence that something was neurologically different when the person was in the
two states. Second, the traumatic history activated brain areas known to be activated
by autobiographical information—but only when the alter that was aware of that
information was dominant during the PET scanning. Moreover, a brain area known
to process emotional information (the parietal operculum) was much more strongly
activated when the participant was an alter that was aware of the trauma, compared
to when the participant was an alter unaware of the trauma. Thus, from the brain’s
point of view, different information was in fact accessible to the two alters.
However, it is diffi cult to interpret the results of many studies that investigate
neurological differences among alters because the studies do not include an appro-
priate control group (Merckelbach, Devilly, & Rassin, 2002). Researchers have
found that hypnosis can alter brain activity (Kosslyn et al., 2000), so it is possible
that at least some of the neurological differences between alters refl ect a form of
self-hypnosis. That is, the person with DID—perhaps unconsciously—hypnotizes
himself or herself, which produces different neurological states when different alters
come to the fore.Neural Communication DID is thought to be associated with early childhood abuse,
and it is well known that such abuse affects a wide range of stress-related hor-
mones, cortisol being just one. These stress-related hormones clearly disrupt brain
development and subsequent brain functioning, including that of the hippocampus
and the frontal lobes—both of which play major roles in memory (Teicher et al.,
2002). However, researchers do not yet understand what might cause stress-related
hormones to affect specifi cally those brain systems that in turn would produce the
symptoms of the disorder.Genetics Using a questionnaire, a team of researchers assessed the capacity for dis-
sociative experiences in monozygotic and dizygotic twins in the general population
(Jang et al., 1998). This questionnaire did not address DID directly, but it did assess
the capacity for both “normal” dissociations (such as becoming very absorbed in a
television show or a movie) and “abnormal” dissociations (such as not recognizingP SN