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Interhemispheric Interaction and Saccadic Horizontal Eye MovementsImplications for Episodic Memory, EMDR, and PTSD



The growing body of literature on the effects of bilateral saccadic eye movements, patterned after those employed in eye movement desensitization and reprocessing (EMDR), on memory is reviewed. Research indicates that engaging in bilateral saccadic eye movements prior to lab-based memory testing results in significant improvement in episodic memory across a wide range of memory tests. Other effects of these types of eye movements on hemispheric activation and emotional state are also discussed. The findings are interpreted within a framework suggesting that bilateral saccadic eye movements, such as those employed in EMDR, increase interaction between the left and right cerebral hemispheres. This framework is also used to explain the effects of such eye movements on memory during EMDR treatment of posttraumatic stress disorder.
Journal of EMDR Practice and Research, Volume 2, Number 4, 2008 269
© 2008 EMDR International Association DOI: 10.1891/1933-3196.2.4.269
An important advance in our understanding
of the neural bases of human memory was
provided by Tulving and colleagues, who
proposed the Hemispheric Encoding/Retrieval Asym-
metry (HERA) model of episodic memory (Tulving,
Kapur, Craik, Moscovitch, & Houle, 1994). The HERA
model argues that the left versus right cerebral hemi-
spheres are specialized for the encoding and retrieval,
respectively, of episodic memories (in contrast, both
the encoding and retrieval of semantic memories are
handled by the left hemisphere only). Subsequent
brain imaging studies have provided further support
for the HERA model (e.g., Babiloni et al., 2006; Cabeza
& Nyberg, 2000; Habib, Nyberg, & Tulving, 2003).
Although much of the work following up on the
HERA model has focused on the questions of which
specifi c left hemisphere regions are involved in encod-
ing and which right hemisphere regions are involved
in retrieval (e.g., Buckner, 1996; Prince, Tsukiura, &
Cabeza, 2007), we have focused on the implications
of the HERA model for interhemispheric interaction.
Specifi cally, the fact that episodic encoding and re-
trieval processes take place in different hemispheres
implies an important role of the corpus callosum,
the primary tract of axons connecting the left and
right hemispheres, in episodic memory. Over the
past several years, we have published a series of arti-
cles demonstrating an interhemispheric basis for the
retrieval of episodic memories (Christman, Garvey,
Propper, & Phaneuf, 2003; Christman & Propper,
2001; Christman, Propper, & Brown, 2006; Christ-
man, Propper, & Dion, 2004; Propper & Christman,
2004; Propper, Christman, & Phaneuf, 2005).
One factor that we have found to infl uence epi-
sodic memory and interhemispheric interaction is
saccadic horizontal eye movements (EMs), which
may induce statelike changes in both the accuracy of
episodic memories and in the amount or quality of
interhemispheric interaction. In this article, we exam-
ine the conceptual and empirical bases for the effects
of saccadic horizontal EMs on memory and on inter-
hemispheric interaction.
Interhemispheric Interaction and Saccadic
Horizontal Eye Movements
Implications for Episodic Memory, EMDR, and PTSD
Ruth E. Propper
Merrimack College, North Andover, Massachusetts
Stephen D. Christman
University of Toledo, Ohio
The growing body of literature on the effects of bilateral saccadic eye movements, patterned after those
employed in eye movement desensitization and reprocessing (EMDR), on memory is reviewed. Research
indicates that engaging in bilateral saccadic eye movements prior to lab-based memory testing results in
signifi cant improvement in episodic memory across a wide range of memory tests. Other effects of these
types of eye movements on hemispheric activation and emotional state are also discussed. The fi ndings
are interpreted within a framework suggesting that bilateral saccadic eye movements, such as those em-
ployed in EMDR, increase interaction between the left and right cerebral hemispheres. This framework
is also used to explain the effects of such eye movements on memory during EMDR treatment of post-
traumatic stress disorder.
Keywords: eye movements; episodic memory; eye movement desensitization therapy; handedness;
interhemispheric interaction
270 Journal of EMDR Practice and Research, Volume 2, Number 4, 2008
Propper and Christman
Posttraumatic Stress Disorder
and Episodic Memory
The notion that saccadic horizontal EMs might (a) in-
crease episodic memory and ( b) do so via interhemi-
spheric interaction originally came from research on
posttraumatic stress disorder (PTSD). PTSD is a de-
bilitating disorder affecting, by some accounts, up to
14% of the population and can follow an individual’s
exposure to a traumatic event in which “the person ex-
perienced, witnessed, or was confronted with an event
or events that involved actual or threatened death or
serious injury . . . [to] the self or others, and the per-
son’s response involved intense fear, helplessness, or
horror” (American Psychiatric Association, p. 428).
Traumatic events resulting in PTSD can include being
threatened by or witnessing car accidents, natural di-
sasters, muggings, rape, assault, military combat, or
any other circumstance wherein an individual feels as
if his or her life is threatened or wherein an individual
learns of the life-threatening events of a loved one or
friend (e.g., a mother learning of the life-threatening
illness of her child).
Symptoms of PTSD vary, but one hallmark of the
disorder is memory disturbance. Such disturbances can
include the persistent experiencing of “recurrent and
intrusive distressing” memories of the event. These
reexperiencings can occur during wakefulness—for
example, in the form of uncontrolled images or
thoughts of the trauma—or in a sense of reliving the
event. Uncontrolled memories can also occur during
sleep, in the form of nightmares that seemingly accu-
rately refl ect the traumatic events. In fact, up to 50%
of posttraumatic dreams may be considered to ve-
ridically represent the trauma (Wittmann, Schredl, &
Kramer, 2007). Additionally, traumatized individuals
may also experience physiological reactivity to events
or objects that remind them of the traumatic experi-
ence (American Psychological Association, 1994).
In addition to the intrusive, uncontrollable recall
of the traumatic event diagnostic of PTSD, research
demonstrates evidence of impaired retrieval of other
episodic memories in this disorder. For example, in-
dividuals may also have diffi culty recalling specifi c
memories that are unrelated to the trauma. When
asked to report a specifi c memory that demonstrates
the word relax, individuals with PTSD may state a
general memory, such as “when I go for walks in the
park.” This is in contrast to specifi c, time-dated mem-
ories reported by nontraumatized individuals, such
as “when I went for a walk in the park last Tuesday
with my wife.” Individuals with PTSD persist in re-
porting overgeneral memories even when repeatedly
prompted for specifi c information (McNally, Lasko,
Macklin, & Pitman, 1995).
Thus, one characteristic of PTSD is a dysfunction
of episodic memory, as evidenced by intrusive re-
call while both awake and asleep, and in an inability
to recall specifi c, relative to general, nontraumatic
Saccadic Horizontal EMs:
Relation to Memory Abilities
We reasoned that if one aspect of PTSD is a dysfunc-
tion of episodic memory, then treatments that relieve
PTSD symptoms may offer clues to memory function
even in the absence of trauma. One such treatment
that seemed promising is eye movement desensitiza-
tion and reprocessing (EMDR; Shapiro, 1989). EMDR
is a structured psychotherapy approach, during which
participants focus on the components of a targeted
memory while engaging in simultaneous bilateral
stimulation (alternating left–right tactile or auditory
stimuli or, most frequently, eye movements) at the
rate of approximately two movements per second, for
a “set” of about 30 seconds. At the end of the set, the
therapist asks the client, “what do you notice now?”
This procedure is designed to elicit other aspects of
the memory, or other related information, including
other episodic memories. The client is then instructed
to focus on the new material while engaging in an-
other set of bilateral stimulation. The procedure con-
tinues, in accordance with standard protocols, until
new, more adaptive information is integrated with
the original memory.
We decided to focus on the bilateral stimulation
used in EMDR; we suggest that changes in episodic
memory in PTSD following EMDR (e.g., Rogers
et al., 1999; Sandström, Wiberg, Wikman, Willman,
& Högberg, 2008) might be based on neurophysi-
ological mechanisms involved in memory generally.
If so, then bilateral stimulation might alter episodic
memory, regardless of whether such memories are
In fact, we have published a series of articles
demonstrating superior episodic memory follow-
ing saccadic horizontal EMs (Christman et al., 2003,
2004, 2006) relative to vertical, smooth-pursuit, or
to no EMs. In these studies, we used stimulation
designed to be similar to that used in EMDR: bilat-
eral visual stimulation with left–right alternating in-
formation, presented at the rate of two stimuli per
second. Specifi cally, participants watched a dot ap-
pear alternately on the left and right sides of a com-
puter screen for 30 seconds, with dots alternating
Journal of EMDR Practice and Research, Volume 2, Number 4, 2008 271
Interhemispheric Interaction and Saccadic Horizontal Eye Movements
left–right position every 500 milliseconds. Christman
et al. (2003) contrasted this saccadic horizontal EM
condition with (a) a vertical saccadic EM condition,
wherein the computer screen was turned on its side;
(b) two smooth-pursuit conditions—one horizontal,
the other vertical—in which a dot moved smoothly
and continuously from one side of the monitor to the
other; and (c) a central fi xation condition, wherein a
dot changed colors twice a second in the center of the
computer screen. In the fi rst two conditions, partici-
pants followed a black dot as it moved continuously
back and forth across the computer screen with the
same spatial extent and periodicity as that of the sac-
cadic EM conditions. The third control condition in-
volved periodic visual stimulation but in the absence
of EMs.
We report surprising, but robust, results. For exam-
ple, we examined the effects of EMs on the retrieval of
episodic memories (Christman et al., 2003). In Experi-
ment 1, we used a standard laboratory-based memory
procedure directly adapted from that developed by
Tulving, Schacter, and Stark (1982). In this task, par-
ticipants viewed a total of 36 words on a computer
screen, one at a time for 5 seconds each. Then, after
a 30-minute retention interval, they were given either
a blank sheet of paper and asked to recall as many
of the 36 words as they could, or they were given a
list of 72 word fragments (36 were new, and 36 cor-
responded to the previously studied words) and were
asked to complete as many fragments as they could
(no reference was made to the list they had previously
seen) as a test of implicit memory. Immediately prior
to memory testing, participants were assigned to one
of fi ve EM conditions: (1) saccadic horizontal EMs,
(2) saccadic vertical EMs, (3) smooth-pursuit hori-
zontal EMs, (4) smooth-pursuit vertical EMs, or (5) a
no-EM control condition (in all EM conditions, par-
ticipants engaged in EMs for a 30-second period).
Episodic recall was enhanced only in the saccadic
horizontal EM condition; the other four conditions
were not statistically signifi cantly different from one
another (although there was a marginal trend for sac-
cadic vertical EMs to be associated with enhanced re-
call relative to the smooth-pursuit and no-EM control
conditions). This pattern of results likely refl ects the
fact that saccadic EMs generate much more activity
in frontal lobe regions that have been implicated in
episodic retrieval (e.g., Cabeza & Nyberg, 2000) than
do smooth-pursuit EMs, which are largely controlled
by subcortical structures (O’Driscoll et al., 1998) . In
contrast to the results for episodic memory, there
were no differences among the fi ve EM conditions in
performance on the word fragment completion task,
indicating that EMs have no effect on the retrieval of
nonepisodic memories.
The fact that only the saccadic horizontal EM con-
dition resulted in increased episodic memory has very
important implications for the use of EMs in EMDR
therapy, because many of the experimental and clini-
cal protocols used in EMDR research and therapy ap-
pear to induce smooth-pursuit, not saccadic, EMs. For
example, Montgomery and Ayllon (1994) claimed to
induce bilateral saccadic eye movements by waving a
nger in front of the patient. The fi nger was moved
back and forth two times a second across a spatial
extent of approximately 35°–45° of visual angle; this
is similar to the stimulation employed in the current
study to induce smooth-pursuit eye movements, lead-
ing to the possibility that the participants of this study
may in fact have engaged in smooth-pursuit, not sac-
cadic, eye movements. This problem is widespread,
because many studies of EMDR follow Shapiro’s
(1995) protocol (e.g., Bates, McGlynn, Montgomery,
& Mattke, 1996; Devilly & Spence, 1999; Levin, Laz-
rove, & van der Kolk, 1999), in which the therapist
waves a fi nger back and forth in front of the patient—
a procedure more likely to elicit pursuit than saccadic
eye movements. Because pursuit eye movements did
not enhance episodic retrieval in the Christman et al.
(2003) study, it is possible that many of the negative
reports on the effi cacy of EMDR refl ect the fact that
procedures used induced smooth-pursuit, not sacca-
dic, eye movements. Future work testing the effi cacy
of EMDR needs to explicitly distinguish between sac-
cadic and pursuit eye movements.
Because our results indicated that it is saccadic
horizontal EMs that increase memory (rather than
smooth-pursuit or vertical), in other experiments
we compared these types of EMs with the central
xation condition described above. In Experiment
2 (Christman et al., 2003) memory for real-world
events was studied. Participants began by keep-
ing a daily journal for a week in which they wrote
down a couple of notable events each day. They
were instructed to not write down common, ev-
eryday events (e.g., “I woke up and got dressed”),
but instead to record distinctive events. Responses
included statements such as “I stubbed my toe re-
ally bad,” “I went to a funeral,” and “I went to the
park with my cousin and had some ice cream.” Par-
ticipants were not informed of the purpose of the
journal and turned them in at the end of the week.
About a week later, participants were randomly as-
signed to a saccadic horizontal dot condition or to
a color-changing dot condition. After viewing their
respective stimuli for 30 seconds, participants were
272 Journal of EMDR Practice and Research, Volume 2, Number 4, 2008
Propper and Christman
asked to recall the gist of all the previous journal
entries that they could remember. Once again, the
results indicated that, following saccadic horizontal
EMs, individuals recalled more of the journal entries
and had fewer false recalls . Thus, the superior mem-
ory following saccadic horizontal EMs was observed
for both lab-based and real-world memories.
In another study, we examined the effect of EMs
on false memories (Christman et al., 2004). Partici-
pants engaged in the false memory task popularized
by Roediger and McDermott (1995): the Deese-
Roediger-McDermott paradigm. In this task, subjects
listen to lists of words that are comprised of verbal
associates to a critical lure item that is not included
in the list. For example, participants would hear a list
of words like thread, eye, sewing, sharp, thimble, hay-
stack, syringe, etc.—all of which are close associates
of the word needle, which did not appear in the list.
Following saccadic horizontal EMs, participants dem-
onstrated a decreased false recall for the critical lures
compared to following a color-changing stimulus.
Interestingly, EMs did not result in decreased false
recall for words unrelated to the lists. Our fi ndings
have been replicated using a recognition task (Parker
& Dagnall, 2007) ; following saccadic horizontal EMs,
individuals had increased accurate recognition and
decreased false recognition for the critical lure com-
pared to vertical EMs and an EM movement control.
We have extended the EM paradigm to other
memory tasks (Christman et al., 2006). In a study of
the offset of childhood amnesia (the inability to ex-
plicitly remember events from the fi rst few years of
life), we found that the average age for earliest mem-
ory following saccadic horizontal EMs was reported
5.33 years, while the average age for earliest memory
following the no-EM condition was 5.92 years—a
signifi cant difference. Given that such early memo-
ries are encoded and consolidated years previously,
these differences between groups likely refl ect an ef-
fect of EMs on the retrieval (and not at other memory
stages such as encoding or consolidation) of episodic
Others have replicated our fi ndings of superior
episodic memory following saccadic horizontal EMs
(e.g., Lyle, Logan, & Roediger, 2008; Parker & Dag-
nall, 2007; Parker, Relph, & Dagnall, 2008). For exam-
ple, as mentioned above, Parker and Dagnall (2007)
reported that, following saccadic horizontal EMs,
individuals had increased recognition and decreased
false recognition for nonpresented critical lures in the
Deese-Roediger-McDermott paradigm (Roediger &
McDermott, 1995), compared to vertical EMs and a
no-EM control.
Parker et al. (2008) in Experiment 1 found increased
hits and decreased false alarms on a word recognition
test following saccadic horizontal EMs relative to
vertical or to no EMs. Additionally, they also report
increased “remember” responses following saccadic
horizontal EMs compared to the other two conditions,
but no between-group differences in the number of
“know” responses. Because “remember” responses
are thought to be indicative of episodic memory
processes, while “know” responses are analogous to
semantic memory (Gardiner, 1988; Tulving, 1985),
these results offer direct support for the hypothesis
that saccadic horizontal EMs are involved in episodic
memory processes. Parker et al. (2008) also reported
increased hits and decreased false alarms for paired as-
sociates following the saccadic horizontal EMs condi-
tion. In Experiment 2, following saccadic horizontal
EMs, individuals were more accurate in recalling the
spatial location and the color of previously presented
words compared to vertical and no-EM conditions.
Lyle et al. (2008) report increased word list recall
(Experiment 1) following saccadic horizontal EMs
relative to central fi xation in strongly right-handed
subjects. Interestingly, these authors also report in-
creased accuracy in recognition, and decreased false
recognition (Experiment 2), following saccadic hori-
zontal EMs and following vertical EMs, relative to
spontaneous EMs or to central fi xation, in strongly
right-handed individuals.
Although not a direct replication of our methodol-
ogy, it is worth noting that at least one study of the
effects of EMs on memory reported a decrease in the
vividness of personal autobiographical nontraumatic
positive and negative memories following EMs, but
not following fi nger tapping or “imagery” conditions
(van den Hout , Muris, Salemink, & Kindt, 2001). It
is not clear how this fi nding of decreased vividness
might be related to increases in episodic memory rec-
ollection generally.
To summarize, a rapidly growing literature indicates
that saccadic horizontal EMs, relative to non-EM con-
trol conditions such as spontaneous EMs, and smooth-
pursuit EMs result in superior episodic memory. As a
whole, such superior episodic memory takes the form
of improved recall and/or recognition for list words;
increased identifi cation of the spatial location of previ-
ously presented stimuli; increased identifi cation of the
color of previously presented information; increased
accuracy for recall of paired associates; increased ac-
curacy for recently experienced autobiographical in-
formation; an earlier age of fi rst childhood memory;
increased recollection for previously presented stimuli
in the form of increased “remember” responses during
Journal of EMDR Practice and Research, Volume 2, Number 4, 2008 273
Interhemispheric Interaction and Saccadic Horizontal Eye Movements
recognition; and decreased false recall or recognition
of previously presented information. See Table 1 for a
summary of the effects of EMs on memory.
Although the exact locus in memory processing of
these effects is still not clear, two things are apparent.
First, the benefi cial effects of EMs are at the retrieval
stage, not at other memory stages such as encoding
or consolidation; in fact, there is evidence that sac-
cadic horizontal EMs immediately prior to encoding
impair subsequent memory performance (Christman
& Butler, 2005). Second, the benefi cial effects of EMs
at retrieval appear to be driven in large part by better
source memory, as evidenced by the decreased false
memory rate associated with such EMs.
Although some studies have reported increased re-
call following other types of EMs (i.e., during vertical
EMs; Christman et al., 2003, Experiment 1; Lyle et al.,
2008, Experiment 2), such reports are infrequent, and
it is unknown whether the mechanisms resulting in
increased episodic memory following these saccadic
vertical EMs are similar to those that result in increased
episodic memory following saccadic horizontal EMs.
For example, Stickgold (2002) has proposed an alter-
native neurobiological account of the effects of EMs
on memory, arguing that “the repetitive redirecting
of attention in EMDR induces a neurobiological state,
similar to that of REM sleep, which is optimally con-
gured to support the cortical integration of traumatic
memories into general semantic frameworks” (p. 61).
That is, any procedure that induces repetitive redi-
recting of attention, be it left–right (as with horizontal
EMs) or up–down (as with vertical eye movements),
TABLE 1. Summary of Research on the Effects of Bilateral Saccadic Eye Movements
on Memory Retrieval (All Studies Involve Eye Movements Immediately Prior
to Retrieval Except Where Noted)
Task Findings Citation
Recognition of words Eye movements are benefi cial Christman, Garvey, Propper, &
Phaneuf, 2003
Recognition of words Eye movements are benefi cial for
consistent-handers, detrimental
for inconsistent-handers
Lyle, Logan, & Roediger, in press
Recognition of words Eye movements are benefi cial Parker, Relph, & Dagnall, 2008
Free recall of words Eye movements are benefi cial Christman, 2004
Free recall of words Eye movements are benefi cial for
consistent right-handers, detri-
mental for inconsistent-handers
Lyle, Logan, & Roediger, in press
Associative recognition Eye movements are benefi cial Parker, Relph, & Dagnall, 2008
Recall of early childhood memories Eye movements are benefi cial Christman, Propper, & Brown, 2006
Source memory (DRM paradigm) Eye movements are benefi cial Christman, Propper, & Dion, 2004
Source memory (DRM paradigm) Eye movements are benefi cial Parker & Dagnall, 2007
Know vs. remember judgments of
recognized words
Eye movements result in increased
number of “remember” responses
Parker, Relph, & Dagnall, 2008
Color memory Eye movements are benefi cial Parker, Relph, & Dagnall, 2008
Spatial location memory Eye movements are benefi cial Parker, Relph, & Dagnall, 2008
Vividness of memory Eye movements decrease vividness van den Hout, Muris, Salemink, &
Kindt, 2001
Response bias Eye movements induce more
conservative response bias
Christman, Garvey, Propper, &
Phaneuf, 2003
Encoding Eye movements are detrimental at
Christman & Butler, 2005
Implicit word fragment comple-
tion (old minus new fragments
Eye movements have no effect Christman, Garvey, Propper, &
Phaneuf, 2003
Semantic memory (total fragments
Eye movements have no effect Christman, Garvey, Propper, &
Phaneuf, 2003
274 Journal of EMDR Practice and Research, Volume 2, Number 4, 2008
Propper and Christman
may benefi t the consolidation of memory traces. The
“interhemispheric interaction” (proposed here, see
below) and “redirecting of attention” accounts are not
mutually exclusive, and the combined results from the
studies by Christman, Garvey, Propper, and Phaneuf
(2003) , Parker and colleagues (2008), and Lyle and col-
leagues (2008) suggest that both accounts may have
Saccadic Horizontal EMs and
Interhemispheric Interaction
Although the clinical effi cacy of EMDR has been
demonstrated (e.g., Russell, 2006; Tufnell, 2005), the
therapy remains controversial, in large part because
of a lack of knowledge of its underlying neural mecha-
nisms (e.g., Spector & Read, 1999).We suggest that
because EMDR helps patients overcome memory
dysfunction associated with PTSD, it is possible that
EMDR is effi cacious due to its action on neuroana-
tomical structures involved in memory. In particular,
we have proposed that the alternating left–right stim-
ulation used in EMDR facilitates episodic memory
via neural mechanisms involved in hemispheric com-
munication. Our neurobiological framework sug-
gests that the bilateral stimulation in EMDR enhances
memory processing through increased interhemi-
spheric interaction via the corpus callosum (Christ-
man et al., 2003, 2004, 2006). Support for the notion
that saccadic horizontal EMs in particular might in-
crease interhemispheric interaction comes from sev-
eral lines of investigation.
First, there is evidence that leftward and rightward
EMs selectively activate the contralateral hemisphere
(Bakan & Svorad, 1969). Thus, repeated left–right EMs
should result in simultaneous activation of both hemi-
spheres. This was confi rmed by Christman and Gar-
vey (2001), who reported that engaging in left–right
EMs reduced preexisting asymmetries in hemispheric
activation, as indexed by perceptual asymmetries
on a free-vision chimeric faces task (Kim, Levine, &
Kertesz, 1990; Levy, Heller, Banich, & Burton, 1983).
Thus, leftward–rightward eye movements may equal-
ize the activation of both hemispheres.
Second, because one hemisphere is typically more
activated than the other (Klein & Armitage, 1979),
such equalization may foster interhemispheric com-
munication; if the two hemispheres possess different
levels of activation, it may be diffi cult for the less acti-
vated hemisphere to keep pace and interact effi ciently
with the more active hemisphere.
Third, direct evidence linking left–right EMs and fa-
cilitation of interhemispheric interaction can be found
in studies of brain activity during rapid eye movement
(REM) sleep. Evidence indicates that interhemispheric
electroencephalographic (EEG) coherence increases
signifi cantly during REM sleep (e.g., Barcaro et al.,
1989; Dumermuth & Lehman, 1981). Furthermore, the
increase in interhemispheric EEG coherence has been
specifi cally linked to the presence of EMs (Dionne,
1986). Because the majority of eye movements during
REM sleep are horizontal (Hansotia et al., 1990), this
evidence suggests that left–right EMs are associated
with increased interhemispheric interaction.
A direct study of the effects of saccadic horizontal
EMs in particular on interhemispheric interaction also
supports the hypothesis. Following saccadic horizon-
tal EMs, individuals demonstrated increased Stroop
interference, relative to pre-eye movement baseline
measures (Christman & Garvey, 2003), and such in-
terference has been shown to arise at least in part
from increased interhemispheric interaction (Christ-
man, 2001).
Our hypothesis of increased interhemispheric in-
teraction following saccadic horizontal EMs does not
preclude the possibility that such increased interac-
tion is inhibitory in nature. That is, communication
between the cerebral hemispheres may be either ex-
citatory or inhibitory; there is no a priori reason to
suspect that increased communication is by defi ni-
tion excitatory. Furthermore, any neurophysiologi-
cal change in hemispheric communication, while
presumably associated with a concomitant change in
behavior, is not necessarily associated with a similar
change in behavior. Therefore, increased excitatory
interaction at the physiological level will not necessar-
ily be associated with increased excitatory interaction
at the behavioral level (however excitatory behavioral
interaction might be defi ned). For example, a behav-
ioral study (Christman & Garvey, 2003) suggested that
increased interaction following saccadic horizontal
EMs is associated with interference between the two
processing modes of the hemispheres, a result that
could be interpreted as indicative of either excitatory
interaction (e.g., the hemispheric processing modes
are directly interfering with each other) or inhibitory
interaction (e.g., the hemispheres are independently
competing for response). For example, in that study,
participants demonstrated increased Stroop interfer-
ence following saccadic EMs; it was suggested that
left hemisphere word-naming processes and right
hemisphere color-detection processes interfered with
each other, resulting in increased reaction times. Such
decreased performance following EMs may have oc-
curred because the left and right hemispheres actively
attempted to suppress, via the corpus callosum, the
Journal of EMDR Practice and Research, Volume 2, Number 4, 2008 275
Interhemispheric Interaction and Saccadic Horizontal Eye Movements
other hemisphere’s response (i.e., excitatory interac-
tion), or because each hemisphere attempted to re-
spond independently, with information within a given
hemisphere actively kept separate from the other (i.e.,
inhibitory interaction) resulting in a bottleneck, and
decreased performance, at the level of response.
The distinction between physiological versus behav-
ioral interaction is especially important to consider in
light of the results of a recent study. We directly tested
the hypothesis that saccadic horizontal EMs result in a
change of interhemispheric connectivity by examining
interhemispheric EEG coherence following saccadic
horizontal EMs versus following central fi xation (Prop-
per, Pierce, Geisler, Christman, & Bellorado, 2007).
Interhemispheric EEG coherence compares the rela-
tionship between EEG signals from (usually) homolo-
gous sites in the two hemispheres as a function of the
signals’ frequencies. Interhemispheric EEG coherence
is thought to refl ect corpus callosum–mediated com-
munication between the two cerebral hemispheres
(Montplaisir et al., 1990; Nielsen, Montplaisir, & Las-
sonde, 1992 ). Increased levels of coherence are believed
to refl ect increased callosal activity and thus indicate
increased hemispheric connectivity, while decreased
levels of coherence are thought to refl ect the opposite.
Some evidence supporting this interpretation of inter-
hemispheric EEG coherence comes from Montplaisir
et al. (1990), who reported decreased coherence in epi-
leptics following partial callosotomy, and Nielsen et al.
(1992), who reported decreased coherence in individu-
als with agenesis of the corpus callosum—particularly
at frontal, parietal, and temporal sites compared to in-
dividuals with an intact corpus callosum .
We recorded EEG from the left and right anterior
frontal lobes (Fp1 and Fp2) prior to and immediately
following either saccadic horizontal EMs or a central
xation condition (eye movements cause artifact in
frontal sites, and EEG could not therefore be examined
during eye movements). We examined theta (4–8 Hz)
and gamma (35–54 Hz) frequencies because they have
frequently been associated with episodic memory
processing (e.g., Babiloni et al.; 2004; Burgess & Gru-
zelier, 1997; Klimesch, Schimke, & Schwaiger, 2004 ;
Weiss, Müller, & Rappelsberger, 2000). Because alpha
has been associated with semantic memory processes
(e.g., Klimesch et al., 2004, Mima, Oluwatimilehin,
Hiraoka, & Hallett, 2001), we also examined alpha
(8–13 Hz) frequency in order to rule out a general,
nonepisodic memory–related effect of stimuli condi-
tion on interhemispheric interaction.
Contrary to our hypothesis of increased interhemi-
spheric interaction following saccadic horizontal EMs,
we found a decrease in gamma frequency coherence.
While surprising, the fi ndings correspond nicely with
a recent functional magnetic resonance imaging study.
Umeda et al. (2005) reported decreased functional con-
nectivity between the left and right hemispheres in
anterior prefrontal cortex during an episodic retrieval
task. Given that the cortical locations of Fp1 and Fp2
(Brodmann’s area 10; Homan, Herman, & Purdy,
1987) coincide with the location of the anterior frontal
cortex in which decreased functional interhemispheric
connectivity was reported (Umeda et al., 2005), it seems
likely that our EEG results are related to the fi ndings of
Umeda et al. Specifi cally, the eye movement manipu-
lation we used, and that has been reported to facilitate
episodic memory, resulted in decreased interhemi-
spheric EEG coherence in anterior prefrontal cortex.
As mentioned, a decrease in interhemispheric EEG
coherence does not necessarily indicate a decrease in
functional interhemispheric interaction. As noted by
Uttal (2001), changes in measures of brain activity do
not always map directly onto changes in cognitive
function (i.e., increases in activation of a brain region
associated with a specifi c task do not necessarily indi-
cate that that region is primarily responsible for that
task). To illustrate, decreases in gamma-band inter-
hemispheric EEG coherence have been reported as
subjects become better at a bimanual motor task in
which the movements of the left and right hands, and
hence right and left hemisphere processing, need to
be coordinated (Gerloff & Andres, 2002). Thus, the
current results should be interpreted as refl ecting EM-
induced changes in interhemispheric interaction, not
necessarily EM-induced decreases in interhemispheric
interaction. For example, increased interhemispheric
EEG coherence implies that the two hemispheres are
doing similar things, while increased interhemispheric
interaction implies that the two hemispheres are doing
coordinated, but not necessarily similar, things.
Finally, recent pilot data from our lab suggests that,
in addition to enhancing the recall of episodic memo-
ries, saccadic horizontal EMs may also have effects on
participants’ emotional states (Christman & Stieber,
2005). Davidson (1992, 1995) has argued that the left
and right frontal lobes are specialized for approach-
versus withdrawal-related behaviors, respectively. For
example, individuals with depression show decreased
activation of the left frontal lobe (Henriques & Da-
vidson, 1991), whereas individuals with high levels of
well-being show increased activation of the left fron-
tal lobe (Davidson, 2004). Accordingly, it was hypoth-
esized that, to the extent to which saccadic horizontal
EMs equalize levels of activation over the left and
right frontal lobes, then such EMs should also result
in a neutralization of affective state. Indirect support
276 Journal of EMDR Practice and Research, Volume 2, Number 4, 2008
Propper and Christman
for this hypothesis comes from a study by Compton
and Mintzer (2001), who found that interhemispheric
interaction served to reduce stress and worry. More
direct support comes from studies reporting that
EMDR therapy is associated with reduced negative
affect associated with traumatic memories (e.g., Bar-
rowcliff, Gray, Freeman, & McCulloch, 2004; Kava-
nagh, Freese, Andrade, & May, 2001).
To test this hypothesis, we induced happy or sad
moods in participants. Participants then rated their
current mood, engaged in either our standard sacca-
dic horizontal EM procedure or the no-EM control
condition, and then rated their mood again. Among
those participants for whom the mood induction pro-
cedure was effective, saccadic horizontal EMs led to
signifi cant neutralization of mood relative to controls
(i.e., “happy” participants became less happy, and
“sad” participants became less sad); although both
the EM and no-EM groups showed neutralization of
affect, this effect was signifi cantly larger in the EM
condition.. This last fi nding, in conjunction with the
well-documented effects of saccadic horizontal EMs
on episodic retrieval, suggests that the EMs employed
in EMDR may work on at least two levels: (1) helping
patients overcome their episodic memory dysfunc-
tion and (2) reducing their levels of negative emotion
induced by retrieval of traumatic memories.
Theoretical Considerations
and Future Directions
Although our research has focused on the effects of
saccadic horizontal eye movements on interhemi-
spheric interaction and memory, other types of
bilateral stimuli have also been used in EMDR (e.g., bi-
lateral tapping, bilateral tones, alternating fi st clench-
ing), as have smooth-pursuit eye movements (e.g.,
Rothbaum, 1997). It is not clear whether increased
interhemispheric interaction occurring as a result of
saccadic horizontal EMs relies on mechanisms that
would be applicable to other forms of bilateral stimu-
lation. Future research could directly compare other
forms of bilateral stimulation on memory and inter-
hemispheric interaction.
Finally, our work examining effects of saccadic
horizontal EMs on memory and on interhemispheric
interaction offer suggestions for theories of neuro-
physiological correlates of PTSD. For example, there
is evidence that PTSD may be characterized by a
dysfunction of interhemispheric interaction. Such
evidence comes from sleep disturbances in PTSD, in
individual differences in susceptibility to dissociation,
from research demonstrating altered corpus callosum
size in individuals with PTSD, and from our own
work examining saccadic horizontal EMs.
First, REM sleep, that stage of sleep associated
with increased interhemispheric interaction (Barcaro
et al., 1989; Dumermuth & Lehman, 1981), may be
disturbed in individuals with PTSD. Disturbances
may include increased awakenings from REM (Bres-
lau et al., 2004), increased eye movement density
during REM, decreased latency to REM sleep, and
increased REM sleep (see Harvey, Jones, & Schmidt,
2003, for review), although these latter two fi ndings
have not always been replicated. Furthermore, re-
search has suggested that the PTSD-related veridical
replay of the traumatic experience in dreams occurs
during REM sleep (see Phelps, Forbes, & Creamer,
2007). In those who do not have PTSD, REM dreams
rarely replay daily events (Stickgold, Hobson, Fosse,
& Fosse, 2001). The physiological REM disturbances
found in individuals with PTSD, in conjunction with
the phenomenological abnormalities, suggest the
possibility that the interhemispheric interaction asso-
ciated with REM sleep (Barcaro et al., 1989; Dumer-
muth & Lehman, 1981) may be somehow altered in
the sleep of individuals with PTSD.
Second, individual differences in susceptibility to
PTSD also suggest that this disorder may be charac-
terized by a dysfunction in interhemispheric interac-
tion. Christman and Ammann (1995) reported that
strong right-handedness was associated with a signifi -
cantly higher frequency of dissociative experiences,
suggesting that strong-handedness may be associated
with increased risk for developing dissociative disor-
ders such as PTSD. This framework is reinforced by
evidence that patients with PTSD have smaller corpus
callosa (Kitayama et al., 2007; Villareal et al., 2004).
Moreover, strong-handedness is also associated with
both smaller corpus callosum size (Clarke & Zaidel,
1994; Denenberg, Kertesz, & Cowell, 1991; Habib et
al.1991; Witelson & Goldsmith, 1991) and decreased
interaction between cognitive processes known to
be functionally lateralized to opposite hemispheres
(Christman, 1993, 2001; Christman, Bentle, & Nie-
bauer, 2007 ; Christman, Geers, Kosbab, & Weiland,
2006; Jasper & Christman, 2005; Niebauer, Aselage, &
Schutte, 2002 ).
Surprisingly, however, published reports have in-
dicated a decreased incidence of PTSD among strongly
handed individuals (e.g., Boscarino & Hoffman, 2007;
Chemtob & Taylor, 2003; Chemtob, Taylor, Woo, &
Coel, 2001). The results of the Chemtob studies are
inconclusive due to the idiosyncratic way in which the
degree of hand preference was assessed: participants
were asked a single question concerning whether
Journal of EMDR Practice and Research, Volume 2, Number 4, 2008 277
Interhemispheric Interaction and Saccadic Horizontal Eye Movements
they did anything better with their nondominant
hand. The problem here is that, even for very strongly
right-handed people, they are likely, for example, to
be better at catching objects with their nondominant
hand. The handedness inventory used in our studies
does not ask about catching. However, the study by
Boscarino and Hoffman (2007) measured handedness
in a way very similar to the studies from our lab and
still found an association between mixed-handedness
and PTSD. Finally, a recent study by Choudhary and
O’Carroll (2007) reported that PTSD diagnoses were
elevated for strongly left-handed, relative to mixed-
and strongly right-handed, individuals. At present,
the basis for these discrepancies remains unclear and
should be addressed by further research.
Third, more direct support for the notion that al-
terations in interhemispheric interaction may, in part,
underlie the memory disturbances associated with
PTSD comes from research directly examining the
corpus callosum in individuals with PTSD. In PTSD
pediatric populations, there is evidence for decreased
organization of the medial and posterior corpus cal-
losum, as measured via diffusion tensor imaging,
compared with children who do not have PTSD
( Jackowski et al., 2008). Research examining adults
with PTSD indicate decreased corpus callosum size
in these individuals (Villarreal et al., 2004). Presum-
ably, reduced size of this structure would be associ-
ated with decreased interhemispheric interaction in
individuals with PTSD.
Fourth, support for the hypothesis that interhemi-
spheric interaction may be disturbed in PTSD comes
from our research on saccadic horizontal EMs and its
similarity to the stimuli used in EMDR. Our proposal
that saccadic horizontal EMs increase episodic mem-
ory via increased interhemispheric interaction (e.g.,
Christman et al., 2003, 2004, 2006 ), suggests that sac-
cadic horizontal EMs, or saccadic horizontal EMs-like
stimuli used in EMDR, increase interhemispheric in-
teraction in individuals with PTSD, thereby reducing
memory disturbances in PTSD. In this light, however,
it is interesting to note that: (1) Forbes et al. (2006)
reported that patients with PTSD and mixed lateral
preference responded more poorly to treatment, and
(2) the benefi cial effects of saccadic horizontal EMs on
episodic retrieval may be restricted to strong right-
handers only (Lyle et al., 2008), suggesting that dif-
ferent therapeutic approaches may be more effective
with different handedness groups.
It is, of course, diffi cult to reconcile the admit-
tedly somewhat contradictory fi ndings regarding the
relationship between interhemispheric interaction,
memory, EMDR, PTSD, and bilateral stimulation;
however, we believe our hypothesis offers a fi rst step
toward understanding the cortical connections under-
lying episodic memory for both the mundane and the
traumatic. For example, our hypothesis of increased
interhemispheric interaction following saccadic hori-
zontal EMs was not supported in our study examining
interhemispheric EEG coherence in anterior frontal
lobe—a fi nding that deserves further study.
Similarly, at a behavioral level, our, and other
research groups’ (e.g., Lyle et al., 2008; Parker &
Dagnall, 2007; Parker, Relph, & Dagnall, 2008) fi nd-
ings of increased episodic memory following saccadic
horizontal EMs seems to be in direct contrast with
the reduction of intrusive episodic memories found
following EMDR in individuals with PTSD. One pos-
sible explanation for these opposite effects of EMs on
nontraumatic versus traumatic memories is that EMs
reinstate an optimal level of hemispheric communica-
tion necessary for episodic memory, beyond which is
detrimental to recall. This interpretation is supported
by Lyle and colleagues (2008), who found a negative
effect of EMs on memory in non–right-handers. This
nding may help explain why mixed-handedness is as-
sociated with poorer response to treatment for PTSD
(Forbes et al., 2006).
These latter fi ndings, in conjunction with research
indicating increased interhemispheric interaction and
a larger corpus callosum in the non–right-handed
(e.g., Christman, 1993, 2001; Christman, Bentle, &
Niebauer, 2006; Clarke & Zaidel, 1994) suggest that
beyond some optimal level of interhemispheric inter-
action, negative effects of EMs on memory may occur.
Another possibility is that saccadic horizontal EMs in
patients with PTSD reinstate a level of interhemi-
spheric interaction that encourages the transforma-
tion of episodic information into semantic memory,
with a concomitant reduction in the intrusive episodic
memories (e.g., Stickgold, 2002). Future research
could directly compare these two possible mecha-
nisms of action of saccadic horizontal EMs in EMDR.
How these fi ndings are related to the decreased cor-
pus callosum size found in individuals with PTSD
(e.g., Villarreal et al., 2004) is currently unknown.
We leave it to others to determine the exact na-
ture of how the saccadic horizontal EMs used in
EMDR affect aspects of interhemispheric interac-
tion and activation from both functional and neu-
rophysiological perspectives and how those effects
infl uence individuals’ memory retrieval abilities and
emotional states, especially in clinical populations
such as patients with PTSD. We hope this review
article stimulates interesting and fruitful avenues of
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Acknowledgments. The fi rst author (REP) would like to
thank Lorraine Reneé Propper for discussions of theory
and concept.
Correspondence regarding this article should be di-
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Toledo, Ohio, 43606. E-mail: stephen.christman@uto-
... The alternating bilateral nature of the EMs suggested to cognitive researchers that lateralized information-processing mechanisms are at play in SIRE. Inspired by the hemispheric encoding/retrieval asymmetry model (HERA; Tulving et al., 1994), which claims that episodic memory encoding is predominantly associated with left prefrontal activity and retrieval with right prefrontal activity, Propper and Christman (2008) posited the interhemispheric interaction (IHI) hypothesis. According to HERA, collaboration of the two hemispheres' prefrontal areas is required for retrieval of the encoded memories. ...
... This aspect is virtually neglected in theorizing about SIRE. As a notable exception, Propper and Christman (2008) suggested in their IHI account that saccades would neutralize both positive and negative affective valence by equalizing activations across the left and right frontal lobes. Not only does the IHI account no longer appear tenable (e.g., Lyle & Martin, 2010;Petit et al., 2015;Samara et al., 2011), but this suggestion is also contradicted by valence-specific EM findings (Phaf, 2017;Phaf et al., 2021). ...
... 33 Additionally, interhemispheric electroencephalographic interactions increase significantly during rapid eye movement (REM) sleep, and these interactions have been specifically linked to left and right saccadic horizontal eye movements. 32 However, many studies have reported significant saccadeinduced enhancements in memory retrieval in individuals who are strongly right-or left-handed, but not individuals who are mixed-handed. 10 Individuals who are mixedhanded have a larger corpus collosum, which might enhance the communication between hemispheres. ...
DEPARTMENT EDITORS Julie P. Gentile, MD Professor and Chair, Department of Psychiatry, Wright State University, Boonshoft School of Medicine, Dayton, Ohio Allison E. Cowan, MD Associate Professor, Department of Psychiatry, Wright State University, Boonshoft School of Medicine, Dayton, Ohio EDITORS' NOTE The patient cases presented in Psychotherapy Rounds are composite cases written to illustrate certain diagnostic characteristics and to instruct on treatment techniques. The composite cases are not real patients in treatment. Any resemblance to a real patient is purely coincidental. ABSTRACT Eye movement desensitization and reprocessing (EMDR) is a specific treatment modality that utilizes bilateral stimulation to help individuals who have experienced trauma. This stimulation can occur in a variety of forms, including left-right eye movements, tapping on the knees, headphones, or handheld buzzers, known as tappers. This type of psychotherapy allows the individuals to redefine their self-assessment and responses to a given traumatic event in eight defined steps. While EMDR is relatively new type of psychotherapy, existing literature has demonstrated positive results using this form of therapy when treating patients with post-traumatic stress disorder (PTSD) by utilizing eye movements to detract from negative conceptualizations as a response to a specific trigger, while reaffirming positive self-assessments. Research indicates that EMDR could be a promising treatment for mental health issues other than PTSD, including bipolar disorder, substance use disorders, and depressive disorders. In this article, the eight fundamental processes of EMDR are illustrated through a composite case vignette and examined alongside relevant research regarding its efficacy in treating PTSD.
... Esto se ve respaldado por la observación de que las personas que desarrollan TEPT suelen tener una tendencia a reactivar de manera involuntaria e intrusiva aspectos sensoriales (predominantemente visuales) del recuerdo traumático mientras que muestran disfunciones para recordar otro tipo de memorias no traumáticas (por ejemplo, componentes episódicos del recuerdo). Esta hipótesis es respaldada por resultados de investigaciones que muestran que movimientos oculares bilaterales realizados previamente a un testeo de memoria episódica generan una mejora significativa en la misma (Propper & Christman, 2008), basados en que los movimientos oculares incrementan la interacción entre los hemisferios cerebrales (Christman & Propper, 2001). Mediante una tarea computarizada en la cual los participantes debían seguir un círculo que se movía de izquierda a derecha (condición horizontal) o de arriba hacia abajo (condición vertical); se evidenció que únicamente movimientos oculares horizontales realizados previamente a la evaluación de una lista de palabras generaban una mejora significativa en la memoria episódica (Christman et al., 2003). ...
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Flashbacks, memories with powerful visuospatial components, are one of the main symptoms of Post Traumatic Stress Disorder (PTSD). In this work, strategies that have been effective in reducing PTSD symptoms will be exposed, such as eye movements, drawing, a repetitive audio task, counting backward, and playing Tetris. Although there is currently no consensus about the mechanism of action by which these tasks interact with memory, two main hypotheses are discussed: a) eye movements generate an improvement in episodic memory due to interhemispheric interaction; b) tasks that require the use of working memory during memory reactivation, generate a decrease in involuntary intrusions. Future research could address a new hypothesis based on the type of stimulus, considering that the proposed interventions could reduce the visual components of the traumatic memory and improve the episodic components.
... The majority of previous research has focused on interfering with previously encoded memories (Holmes et al., 2004). Conversely, some researchers suggest that rapid horizontal eye-movements possess the potential to enhance memory retrieval due to stimulation of the visuomotor and somatosensory systems from the alternating stimulation of the brain hemispheres (Nieuwenhuis et al., 2013;Propper & Christman, 2008). Others have found more tenuous results and implicate the potential influence of handedness (Lyle & Martin, 2010), which we did not assess. ...
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Visual mental imagery has been proposed to be an underlying mechanism of music-induced emotion, yet very little is known about the phenomenon due to its ephemeral nature. The present study utilised a saccadic eye-movement task designed to suppress visual imagery during music listening. Thirty-five participants took part in Distractor (eye-movement) and Control (blank screen) conditions, and reported the prevalence, control, and vividness of their visual imagery, and felt emotion ratings using the GEMS-9 in response to short excerpts of film music. The results show that the eye-movement task was highly effective in reducing ratings for prevalence and vividness of visual imagery, and for one GEMS item, Nostalgia, but was not successful in reducing control of imagery or the remaining GEMS items in response to the music. This represents a novel approach to understanding the potentially causal role of visual imagery on music-induced emotion, on which future research can build by considering the attentional mechanisms that a distraction task may pose during music-induced visual imagery formation.
Bilateral eye movement (EM) is a critical component in eye movement desensitization and reprocessing (EMDR), an effective treatment for post-traumatic stress disorder. However, the role of bilateral EM in alleviating trauma-related symptoms is unclear. Here we hypothesize that bilateral EM selectively disrupts the perceptual representation of traumatic memories. We used the trauma film paradigm as an analog for trauma experience. Nonclinical participants viewed trauma films followed by a bilateral EM intervention or a static Fixation period as a control. Perceptual and semantic memories for the film were assessed with different measures. Results showed a significant decrease in perceptual memory recognition shortly after the EM intervention and subsequently in the frequency and vividness of film-related memory intrusions across one week, relative to the Fixation condition. The EM intervention did not affect the explicit recognition of semantic memories, suggesting a dissociation between perceptual and semantic memory disruption. Furthermore, the EM intervention effectively reduced psychophysiological affective responses, including the skin conductance response and pupil size, to film scenes and subjective affective ratings of film-related intrusions. Together, bilateral EMs effectively reduce the perceptual representation and affective response of trauma-related memories. Further theoretical developments are needed to elucidate the mechanism of bilateral EMs in trauma treatment.
L'articolo ha l'obiettivo di fare il punto su quanto sappiamo sulla memoria traumatica e sull'eventuale possibilità di alterarla producendo "falsi ricordi", dal punto di vista sia della psicologia clinica che della psicologia giuridica. Negli ultimi anni ci sono state molte pubblicazioni e ricerche su come le esperienze traumatiche sono immagazzinate e codificate in memoria e sulle reazioni post-traumatiche che presentano le persone esposte a situazioni da stress estremo. Questo ha avuto un effetto importante nel campo della psicoterapia e del trattamento dei disturbi post-traumatici, contribuendo alla loro comprensione e dando strumenti utili per la loro risoluzione. Allo stesso tempo, negli anni '90 è nato un movimento opposto, chiamato "false memory syndrome", dove spesso gli psicoterapeuti venivano accusati di produrre falsi ricordi di abusi sessuali nei loro pazienti. Sotto accusa erano finiti metodi come l'ipnosi, le terapie di gruppo, le tecniche di immaginazione guidata o di interpretazione dei sogni: ma in generale sotto accusa era finita l'attività psicoterapeutica in ogni sua forma. Ad oggi il dibattito continua, sollevando dubbi specie sulle psicoterapie mirate alla risoluzione degli esiti post traumatici. L'articolo percorre i vari aspetti di questa diatriba e cerca di fare luce sulla comprensione degli aspetti clinici particolarmente complessi di situazioni traumatiche croniche, rispondendo agli autori che sostengono che la psicoterapia può creare falsi ricordi.
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One of the most crucial points of consideration in criminal investigative settings is the collection of victim and eyewitness testimonies. Moreover, it is also important to evaluate the investigative value of such collected testimonial evidences by analyzing its validity, reliability, and more. This review examines the possible applications of neurocognitive principles under investigative settings by exploring various memory enhancement/evaluation techniques, including horizontal saccadic eye movement (HSEM), electroencephalogram (EEG)/event-related potential (ERP) component analyses, and a hybrid EEG-fNIRS memory accuracy evaluation modality. Furthermore, this review discusses the neurocognitive theories underlying each technique, the current trends of related research, the general characteristics of victim/eyewitness memory, as well as the limitations of cognitive neuroscience research in applying them to real-life investigative circumstances. By utilizing the theories and techniques discussed, we anticipate not only increased scientific credibility of testimony collection/ evaluation processes, but also improved efficiency of the victim/eyewitness investigative framework overall.
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We have devised a new free-vision task to index functional cerebral asymmetry for processing facial characteristics. Confirming its sensitivity to properties of lateralized hemispheric functions, left- and right-handers were clearly differentiated on this task with respect to several aspects of performance that conform with known differences between handedness groups in hemispheric asymmetry. Additionally, there were highly reliable and stable individual differences in perceptual asymmetries within handedness. Analyses of items in the task revealed that most of the differences between items in the asymmetries they elicited were random.
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Two experiments (modeled after J. Deese's 1959 study) revealed remarkable levels of false recall and false recognition in a list learning paradigm. In Experiment 1, subjects studied lists of 12 words (e.g., bed, rest, awake ); each list was composed of associates of 1 nonpresented word (e.g., sleep). On immediate free recall tests, the nonpresented associates were recalled 40% of the time and were later recognized with high confidence. In Experiment 2, a false recall rate of 55% was obtained with an expanded set of lists, and on a later recognition test, subjects produced false alarms to these items at a rate comparable to the hit rate. The act of recall enhanced later remembering of both studied and nonstudied material. The results reveal a powerful illusion of memory: People remember events that never happened.
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Two experiments examining effects of eye movements on episodic memory retrieval are reported. Thirty seconds of horizontal saccadic eye movements (but not smooth pursuit or vertical eye movements) preceding testing resulted in selective enhancement of episodic memory retrieval for laboratory (Experiment 1) and everyday (Experiment 2) events. Eye movements had no effects on implicit memory. Eye movements were also associated with more conservative response biases relative to a no eye movement condition. Episodic memory improvement induced by bilateral eye movements is hypothesized to reflect en-hanced interhemispheric interaction, which is associated with superior episodic memory (S. D. Christman & R. E. Propper, 2001). Implications for neuropsychological mechanisms underlying eye movement desensitization and reprocessing (F. Shapiro, 1989, 2001), a therapeutic technique for posttraumatic stress disorder, are discussed. Christman and Propper (2001) reported that the explicit retrieval of episodic memories is facilitated by increased interaction between the two cerebral hemispheres. In one experiment, familial left-handedness, associated with lesser cerebral asymmetry and greater interhemispheric interaction (e.g., Gorynia & Egenter, 2000; Marino & McKeever, 1989; McKeever, VanDeventer, & Suberi, 1973), was associated with superior performance on a test of episodic memory. In a second experiment, inter-versus intrahemispheric pro-cessing was directly manipulated by sequentially presenting input to either the same or a different visual field. Superior episodic memory was associated with between-hemispheres presentation of input, whereas semantic memory was supe-rior for within-hemisphere presentation. These findings pro-vide a complement to research indicating that patients who have undergone a commisurotomy (split-brain procedure), who exhibit no direct interhemispheric interaction, display impaired episodic but normal semantic memory (e.g., Cro-nin-Golomb, Gabrieli, & Keane, 1996; Zaidel, 1995). Further support for an interhemispheric basis of episodic memory comes from brain imaging studies. Cabeza and Nyberg (2000) reviewed 275 studies comparing brain ac-tivity during different memory tasks with activity under baseline conditions. During episodic encoding, "prefrontal activations were always left-lateralized" (p. 23), whereas "prefrontal activations during episodic retrieval are some-times bilateral, but they show a clear tendency for right-lateralization" (p. 26). In contrast, "activity during semantic memory tasks has been almost always found in the left hemisphere but not in the right" (p. 20). Thus, encoding and retrieval of episodic memories is distributed across both hemispheres, whereas semantic encoding and retrieval (at least for verbal material) is restricted to areas within the left hemisphere. These results are consistent with an inter-ver-sus intrahemispheric basis for episodic versus semantic memories, respectively. The current study addressed the inter-versus intrahemi-spheric bases for different types of memory by examining a potential method for enhancing interhemispheric interac-tion, independent of participant (e.g., handedness) and task (e.g., within-vs. between-hemispheres presentation of in-put) manipulations as used by Christman and Propper (2001). Bilateral eye movements were used as a means of temporarily increasing the amount of interhemispheric in-teraction. The underlying logic for the use of bilateral eye movements is as follows. First, there is a link between eye movements and hemi-spheric activation, with lateral eye movements leading to a sustained increase in activation of the contralateral hemi-sphere (Bakan & Svorad, 1969). Thus, sequences of left– right bilateral eye movements presumably result in simul-taneous activation of both cerebral hemispheres. As the protocol used by Bakan and Svorad (1969) was not de-signed to measure the time constant of this activation, it is possible that alternating left–right eye movements might result in rapidly alternating, instead of simultaneous, acti-vation of the two hemispheres. For current purposes, how-ever, it is assumed that either possibility may result in increased bihemispheric activation, which in turn is hypoth-esized to enhance interhemispheric interaction. Research from our lab (Christman & Garvey, 2001) dem-onstrated that engaging in 30 s of bilateral saccadic eye
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Casualties from the Iraqi War were evacuated to a field hospital in Rota, Spain, and were screened for combat-related stress conditions. Four combat veterans requested immediate relief of their posttraumatic symptoms prior to returning to the United States. A single session of Eye Movement Desensitization and Reprocessing (EMDR) led to significant improvement in their acute stress disorder and posttraumatic stress disorder symptoms. A detailed account of those treatment sessions, as well as the proposed alterations of standard protocols for time-limited fleldwork, is presented. Compared to other early interventions, EMDR may be better suited for combat veterans. The results are promising but in need of further research. (PsycINFO Database Record (c) 2013 APA, all rights reserved)
Objectives: Vivid and intrusive memories of extreme trauma can disrupt a stepwise approach to imaginal exposure. Concurrent tasks that load the visuo-spatial sketchpad (VSSP) of working memory reduce memory vividness during imaginal exposure. Such tasks may help maintain a progressive exposure protocol while minimizing distress during treatment. The current study tested whether relief of distress from a competing VSSP load during emotive imagery is at the cost of impaired desensitization. Design: This study examined repeated exposure to emotive memories using 18 unselected undergraduates, using a within-subjects design. Method: Participants recalled three positive and three negative self-related memories, and rated the vividness and emotiveness of the image. Participants then received all three conditions (Eye Movements; Visual Noise; Control) in a counterbalanced order. One positive and one negative recollection were used for each condition. They then rated the vividness of the image and their emotional response before proceeding to the next trial. There were 8 trials for each image. At a noninterference session one week later, participants recalled each image, rating its vividness and their emotional response. Results: Consistent with previous research, vividness and distress during imaging were lower during eye movements than in exposure alone, with passive visual interference giving intermediate results. A small reduction in emotional responses a week later was of similar size for the three conditions.
The following values have no corresponding Zotero field: ID - 47
Recent neuroimaging studies have provided a wealth of information about areas within prefrontal cortex involved in long-term memory. These studies prompted a proposal by Tulving and colleagues (Tulving, Kapur, Craik, Habib, & Houle, 1994) that prefrontal contributions to memory function are related to laterality differences (the hemispheric encoding/retrieval asymmetry model). This review goes beyond a general characterization of prefrontal lobes to a more specific analysis of distinct areas within the prefrontal cortex. Separate prefrontal areas, sometimes within the same hemisphere, are discussed in terms of selective contributions that they might make to memory retrieval. In the end, it is concluded that a framework which tries to understand prefrontal function in terms of specific areas is a useful complement to models, like HERA, which attempt to find unifying principles across multiple areas.
This article describes the treatment of post-traumatic stress disorder (PTSD) using eye movement desensitization and reprocessing (EMDR) with four pre-adolescent children. EMDR has been shown to bring rapid relief in adults with PTSD. Studies are beginning to show that it can also be useful in work with young children. However, the standard protocol requires some adjustment to make it suitable for use with young children. In addition, in situations where children have complex difficulties in addition to PTSD, EMDR may need to be used alongside other interventions within a complex treatment package. This study describes brief work carried out with four pre-adolescent children with PTSD. Three of these children had received no treatment despite suffering from significant and chronic symptoms for some years. One had suffered a recent traumatic bereavement. All had additional problems that required intervention. EMDR was used as part of a multimodal treatment package. In all cases, the children’s PTSD symptoms resolved within 2-4 sessions of EMDR. The maximum total number of sessions was 7. The children's symptomatic improvements were maintained at 6-month follow-up. EMDR can be adapted for use with pre-adolescent children. It can provide rapid and lasting symptomatic relief. EMDR can be a useful part of a multi-modal treatment package for young children with PTSD and additional mental health problems.