336 CHAPTER 8
hippocampus is a critical gate-keeper of memory; without it, new information about
facts cannot be stored. If damage to the hippocampus prevents new information
from being stored, then such information is not available for later retrieval (even if
the hippocampus itself recovers). Given that many cases of dissociative amnesia are
characterized by “recovered” memories, it is not clear what brain systems would be
involved.Neural Communication How might the hippocampus get damaged, which then could
lead to some cases of dissociative amnesia? Hormones could be the culprit. As dis-
cussed in Chapter 2, our adrenal glands respond to stress by producing the hormone
cortisol. This hormone plays an important role in the fi ght-or-fl ight response, by al-
lowing the body to use stored energy more effi ciently; however, there are unfortunate
consequences if too much cortisol is released for too long a period. Specifi cally, many
researchers have shown in both monkeys and humans that excessive cortisol can
reduce the size of the hippocampus (Bremner et al., 1995; Sapolsky, 1996, 1997).
However, as intriguing as this idea is, there is as yet no good evidence that such
hippocampal damage has occurred in all patients with dissociative amnesia; further,
as noted above, such damage would prevent memories from being stored, and thus
reversible amnesia should not occur (but, at least in some cases, it does). Thus, it
is unlikely that too much cortisol is in fact responsible for all cases of dissociative
amnesia.Psychological Factors: Disconnected Mental Processes
Researchers have focused on two theories of how cognitive disturbances—especially
amnesia—arise with dissociative disorders: dissociation theory and neodissociation
theory. Both theories focus on how dissociation can arise in response to traumatic
experiences—specifi cally, how the normal processes of memory and its relation to
other cognitive processes might be disrupted. Although neither theory can com-
pletely explain the phenomenon of dissociative amnesia, both offer some insight—
and hence are worth considering. Let’s examine these two theories.Dissociation Theory The earliest theory of the origins of dissociative amnesia was
dubbed the dissociation theory (Janet, 1907). From our perspective today, the dis-
sociation theory appears poorly named, because it is the dissociation itself that
must be explained by any theory; a more descriptive name like “arousal disruption
theory” would seem more appropriate. Dissociation theory posits that very strong
emotions (as occur in response to a traumatic stressor) narrow the focus of atten-
tion and also disorganize cognitive processes, which prevent them from being inte-
grated normally. According to this theory, the poorly integrated cognitive processes
allow memory to be dissociated from other aspects of cognitive functioning, leading
to dissociative amnesia.
However, this theory does not specify whether the dissociation somehow blocks
or alters information processing or only interferes with later retrieval of the infor-
mation from memory (Guralnick, Schmeidler, & Simeon, 2000). At best the theory
provides only a broad explanation for dissociative amnesia; it does not outline spe-
cifi c mechanisms to account for the dissociation and possible later reintegration of
memory.Neodissociation Theory In contrast, neodissociation theory (Hilgard, 1994; Woody &
Bowers, 1994) proposes that an “executive monitoring system” normally coordi-
nates various cognitive systems, much like a chief executive offi cer coordinates the
various departments of a large company. However, in some circumstances (such
as while a person is experiencing a traumatic event) the various cognitive systems
can operate independently of the executive monitoring system. When this occurs,
the executive system no longer has access to the information stored or processed
by the separate cognitive systems. Memory thus operates as an independent cogni-
tive system, and an “amnestic barrier” arises between memory and the executive
system. This barrier causes the information in memory to be cut off from conscious
awareness—that is, dissociated.