The default dream network (DDN), named so be- cause the brain “defaults” to this state when not otherwise occupied, is a set of regions in the brain that are metabolically active during rest/sleeping and seem to play a key role in dreaming. During rest, “stimulus- independent thought,” or thought unrelated to current perceptions, predominates. This type of thinking allows visualizing and rehearsing scenarios. The dorsal medial subsystem of the DDN includes the dorsomedial prefron- tal cortex, the temporoparietal junction/anterior inferior parietal lobule, the lateral temporal cortex, and the tem- poropolar cortex (the anterior pole of the temporal lobe), and is activated by instructions to think about the present situation or a present mental state (“present self”). On the other hand, the medial temporal subsystem includes the ventral medial prefrontal cortex, posterior inferior pari- etal lobule, retrosplenial cortex, parahippocampal cortex, and hippocampal formation, and is activated by thinking about personal situations and decisions in the future (“fu- ture self”). The left hemisphere generates the narrative organization of the dream, and the right hemisphere gen- erates the visual-spatial and visual-constructive elements of the dream. A biophysical pathway common to dreams and temporal lobe epilepsy is conceivable since dreamlike symptoms are sometimes experienced during temporal lobe seizures and have been elicited by direct stimulation of the temporal lobes. Besides neuroimaging studies, some knowledge about the process of dreaming comes from case reports demon- strating that damage to regions of the DDN corresponds to certain abnormalities in dreaming. For example, occipital lobe pathologies (usually bilateral) resulted in an isolated loss of visual dream imagery (Charcot’s variant). A global dreaming loss (Wilbrand’s variant) has been seen with le- sions in the posterior regions around the parieto-temporal- occipital junction. Various conditions in the transitional zone between the anterior diencephalon and the basal forebrain have been reported to lead to excesses of dream- ing. All of these studies, however, lack dream content data obtained before the damage was inflicted on the brain. To our knowledge, no studies have ever been under- taken to assess dreaming in the setting of brain surgery. Not infrequently, patients will spontaneously complain or remark about changes to sleep or even dreams postopera- tively. In this study, we prospectively applied the validated coding system developed by Calvin S. Hall and Robert Van de Castle to written home-recorded dream contents of patients with drug-resistant epilepsy prior to and after anterior temporal lobectomy (ATL). The primary objec- tive was to register a possible change in dream content and thus shed more light on the temporal lobe’s role in the
MethodsStandard of Care and Referral Process Participants in this study were diagnosed with drug- resistant epilepsy and underwent presurgical assessment for epilepsy surgery. As part of the standard assessment, patients were monitored in the epilepsy monitoring unit. In cases in which the seizure onset zone could not be de- lineated by semiology in conjunction with noninvasive di- agnostic methods such as prolonged video-electroenceph- alography performed with scalp electrodes, neuropsychol- ogy, and structural and functional imaging, patients were subjected to invasive monitoring according to our institu- tional SEEG protocol. Since no brain tissue is removed during SEEG implantation, this group was invited to be part of the control arm (SEEG group). Those who quali- fied for epilepsy surgery underwent resection of the sei- zure onset zone. Patients eligible for ATL were recruited as part of the treatment arm (ATL group). Exclusion criteria were age < 16 years, inability to doc- ument dreams in written form (e.g., because of language barrier, illiteracy, cognitive impairment, or dementia), or major psychiatric comorbidities, as well as previous cra- nial surgery. DDN. Serving as controls were patients who underwent depth electrode implantation for stereoelectroencephalog- raphy (SEEG). The secondary objective was to elicit/rule out any impact of general anesthesia on dream content.
Dream Collection and AnalysisThe publicly available Most Recent Dream form asks the patient to record the most recent dream they re- call having. The form specifically requests information re- garding the dream setting and its familiarity to the patient, people and animals in the dream and their characteristics, as well as how the patient felt in the dream. To control for varying dream length, content beyond the first 300 words was disregarded. Dream reports were coded for dream elements as previously described by Hall and Van de Castle. The Most Recent Dream form was provided, to be returned to the study coordinators by mail prior to the procedure (SEEG or ATL). In the postoperative follow-up, patients were again asked to complete the Most Recent Dream forms. In the SEEG group, postoperative dreams were collected relatively soon after surgery, at 1 month, in order to pick up potential effects from anesthesia, whereas the ATL group did not provide the dreams recorded in the Most Recent Dream forms until after 3 months. The rationale for the longer follow-up in the latter group was to ascertain that any potential changes in dream content could be attributed to the removal of brain tissue and not anesthesia or the mere fact that the patients had surgery. The coder (C.G.) was blinded to the patients’ diagnoses and procedures.
Ethical AdherenceThis study was approved by the ethics board of Western University and the London Health Sciences Centre (proj- ect ID 107654) and the trial was registered at clinicaltrials. gov (identifier NCT02731443) (https://clinicaltrials.gov/ct2/show/NCT02731443). Informed consent was obtained from all study participants according to the Declaration of Helsinki. The Most Recent Dream forms were anony- mized with study numbers. Statistical Methods Differences in dream content between study groups were calculated using Cohen’s h statistic. Major indica- tors for main content categories in the Hall/Van de Castle system were compared before and after the index proce- dure, and p values < 0.01 were considered significant to correct for multiple comparisons. A normative dataset of previously analyzed contents of 500 men’s and women’s dreams were assumed to be representative of the general population and used as another control. All statistical analysis beyond using the Automated Dream Data Entry System and Statistical Analysis Tool to calculate the occurrence of various features in the dreams among sub- groups of patients was performed in R version 3.5.1. The R package ggplot2 was used for graphing. IBM SPSS version 24 (IBM Corp.) was used for sta- tistical analysis of the group’s baseline parameters. Con- tinuous variables were tested using the Mann-Whitney U- test. Fisher’s exact test was applied to compare categorical variables, and p values < 0.05 were considered statistically significant.
Results
Patient PopulationBetween March 2016 and March 2018, 56 (72.7%) out of 77 eligible patients were excluded after screening, mostly because they declared that they usually do not recall any dream content (n = 47). Two patients rejected study participation and 5 did not find the time to journal their dreams. In one instance, the dreams were “too vivid to put into words.” Another patient was retrospectively ex- cluded since his dreams were clearly too mixed with likely day-time posttraumatic stress disorder content from child- hood, which was not picked up during study recruitment. In total, 21 patients (15 females, 6 males) participated. In the control group, 18 patients (13 females, 5 males) provided 55 pre- and 60 post-SEEG dreams. Sufficient intraoperative monitoring information was obtained in all SEEG cases after an average of 10.5 ± 7.1 monitoring days with 9.8 ± 3.6 electrodes. Out of 18 patients, 15 were considered surgical candidates. Three patients from this group later also became part of the ATL group, and their pre-SEEG dreams were used as the baseline for the as- sessment of changes in dream content. With the addition of another 3 ATL patients without prior SEEG, a total of 6 patients (4 females and 2 males) provided 30 pre- and 21 post-ATL dreams. The cohort’s baseline characteristics are given in Table 1. There was no visible mesial temporal sclerosis in the ATL group on preoperative imaging. An- esthesia time (intubation to extubation) was significantly shorter for the SEEG patients (199.8 ± 68.6 minutes) than the ATL patients (333.2 ± 71.1 minutes; p < 0.01); this was also the case for operation time (skin to skin), which was 105.8 ± 42.4 minutes in the SEEG patients versus 262.7 ± 69 minutes in the ATL patients (p < 0.01). Anesthesia was induced with propofol and lidocaine as well as midazolam in some cases. Maintenance was achieved using desflurane and sevoflurane. In the ATL group, laterality was right in 4 and left in 2 patients. One left ATL was performed in a patient under awake condition for intraoperative language cortical mapping. The neocortex was removed at 4 to 5 cm behind the temporal pole and the mesial structures resect- ed to 1 cm behind a coronal plane of the posterior surface of the midbrain, according to Girvin. No complications occurred in either group. Surgical seizure outcome at 3 months was Engel class I in 3 and Engel class II in 2 patients. One patient had unfavorable seizure outcome (Engel class IV), but showed worthwhile improvement (Engel class III) in the further course. Pathology of the resected temporal lobes revealed gliosis in 2 patients, gliosis in combination with a focal cortical dysplasia type 1 in 3 patients, and no abnormali- ties in 1 patient.
Patients With Drug-Resistant Epilepsy Compared to Historical NormsCompared to publicly available normative dreams, the ATL patients’ preoperative dreams were not statisti- cally different (Fig. 1). SEEG patients were preoperatively more likely to have dreams with indoor settings compared to the norms (p < 0.01; Fig. 2).
Preoperative Dreams Compared to Postoperative DreamsPatients who underwent ATL were significantly less likely to have dreams involving physical aggression fol- lowing surgery (p < 0.01; Fig. 3). There are three indi- vidual categories related to this: “aggressor,” “physical aggression,” and “aggression.” All of them are separate entities. It should be noted that the categories “aggressor” and “aggression” were not significantly different and pos- sibly even more frequent in post-ATL patients by trend. There were no significant differences in the dream content of patients prior to and after SEEG procedures across the major categories analyzed (Fig. 4).
DiscussionSupporting the role of the temporal lobe in dream pro- duction, Bentes et al. showed that the dream content of patients with temporal lobe epilepsy differs from that of the general population. For 5 consecutive days, 52 patients recorded their dreams while being monitored with electroencephalography in-hospital for epilepsy surgical assessment. These patients had decreased dream recall, dreams with a higher percentage of familiar settings, and fewer dreams featuring dreamer success. This is in contrast to our analysis, which detected no difference in setting familiarity or success compared to normative data. Instead, we found that pre-SEEG patients had more dreams featuring indoor settings than the historical norm. As social isolation often prevails in these patients’ lives, incorporation of daily experiences into their dreams as so- called “day’s residues” could explain this observation. However, direct comparison is difficult for two reasons. First, many of our SEEG patients had extratemporal lobe epilepsy, and second, the SEEG patients were compared to externally obtained norms rather than a healthy matched control group who recorded dreams for 5 days at home.
ATL and Dream ContentAs a primary finding of this prospective study on a co- hort of patients with drug-resistant epilepsy, significantly less (in fact no) physical aggressive features were seen in dream content of patients following ATL. On the contrary, the “aggressor” and “aggression” remained unchanged. The reason behind this is that the latter categories repre- sent the total aggression, which also includes nonphysi- cal aggression, such as yelling or arguing, for example. Within the limitations of the study design in mind, two careful explanations of this observation can be attempted. ATL entails amygdalectomy, and the amygdala, which is time locked to be activated during rapid eye movement (REM) sleep, has previously been attributed to fear con- ditioning in dreams. The amygdala even takes a cen- tral role in Revonsuo’s threat-simulation theory of the an- cestral human. By means of deep brain amygdala stimu- lation, Lai et al. provoked dreamy states enriched with vivid and bizarre emotional elements in 2 patients with posttraumatic stress disorder. Further evidence comes from De Gennaro et al., who established a correlation of volumetric and ultrastructural measures of the amygdala with dream emotional load and bizarreness in 34 healthy subjects. In 8 patients with Urbach-Wiethe disease (a rare condition with bilateral calcification of the basolateral amygdala), Blake et al. showed that threatening dream content still occurred, but was less negatively charged and thus perceived as more pleasant. As several lines of evidence converge on the amygdala as a node for affective salience, we hypothesize that the unilateral resection of a (potentially dysfunctional) amyg- dala may have exerted a “taming effect” on dream con- tent in our patients.
None of the ATL patients preoperatively stood out with peri- or interictal aggressive behaviors. Absence or a markable reduction of seizures, which was achieved in 5 out of the 6 ATL patients at 3 months, is therefore unlikely to directly account for a decrease in aggression states in these patients’ lives and—presumably—dream content. However, it is conceivable that the indirect positive ef- fect of a favorable seizure outcome by means of ATL on the patients’ well-being created a more at-ease mindset. This, in turn, might be subconsciously reflected by more peaceful dream contents. Notwithstanding, this argument is not further substantiated and it should be acknowledged that various psychological factors may have influenced the inner life of our patients. For example, it is possible that anxiety in anticipation of their upcoming operation might have unfolded aggression in dreams during the preopera- tive waiting period. Anxiety peaks have previously been described in a hospitalized neurosurgical patient’s dream content. However, this situation would have applied to the SEEG group as well, who showed no pre- and post- operative dream content differences. Antiepileptic drugs can also facilitate aggression in certain individuals with epilepsy. Among those with the strongest evidence for ag- gression are levetiracetam, perampanel, and possibly topi- ramate. However, these antiepileptic drugs in question were distributed in equal parts in both groups, and left un- changed up to at least 9 months after surgery at our insti- tution. Another explanation for the observed decrease in physical aggression in postoperative ATL patients’ dreams might be a change in sleep patterns. McNamara et al. discovered that aggressive social interactions were more characteristic of REM than non-REM sleep phases or wake reports. Although no reports on sleep patterns after brain surgery exist, it is known that patients with traumatic brain injury spend less time in REM sleep and perhaps this holds true for ATL patients as well.
SEEG and Dream ContentAs a secondary finding, the effect of general anesthe- sia on dream content in patients undergoing depth elec- trode insertion for SEEG (if present at all) was statistically negligible. The inclusion of this control group undergoing “sham surgery” is a unique strength of the study concept. Some patients were later re-recruited into the surgical group, thus raising intergroup homogeneity. The fact that pre- and post-SEEG dream content with a shorter follow- up of 1 month remained stable also strengthens the robust- ness of the changes seen in the ATL group, who had a longer follow-up of 3 months. For anesthesiologists and patients receiving general anesthesia, it is interesting to know that dream content will remain unaffected. Howev- er, confirmatory studies for patients undergoing extraneu - rological surgery and anesthesia with different anesthetics are needed.
Study Strengths and LimitationsTo the best of our knowledge, we are the first to in- vestigate the change of dream content in patients elec- tively undergoing brain surgery. This prospective study has a higher scientific value over the previous case reports summarized by Solms that did not capture prelesional dream content. In comparison to tumor-invaded brain, for example, the resected temporal lobes in our temporal lobe epilepsy cohort can be regarded as relatively healthy. However, epileptic brain tissue is always dysfunctional to some degree. Since resective brain surgery is not under- taken for healthy brains, the current cohort is closest to the normal population in a neurosurgical setting. The low study participant inclusion rate—especially in the ATL group—in a high-volume epilepsy surgery center over 2 years is a major shortcoming mainly attributable to lack of dream recall. This is unsurprising in a population with epilepsy and confirms the findings of previous studies. Bentes et al. showed that patients with drug-resistant temporal lobe epilepsy have lower dream recall (71.2%) than healthy controls (87.8%). More than half of the pa- tients who consulted our clinic for presurgical investiga- tions could not participate because they never or very rarely remembered their dreams. The much lower dream recall rate in our patients compared to that in the temporal lobe epilepsy patients reported by Bentes et al. is likely explained by the fact that many of the patients in the pres- ent study had extratemporal epilepsy and also generalized seizures. Bonanni et al. showed that dream recall was half as likely in patients with generalized seizures as in pa- tients with complex partial seizures. Perhaps writing up the most recent dream posed an inconvenience to some of our patients. Whereas some patients might therefore not have tried to remember their dreams in the morning, oth- ers perceived this as interesting to do, which leads to se- lection bias. The gold standard remains laboratory dream reports; however, home-recorded dream reports provide valid data and have therefore been used by others. Interestingly, home-recorded dreams show a higher pre- ponderance of physical aggression than dreams recalled in the laboratory. More qualitative dream assessment tools to provide further insight into the emotional component, such as bizarreness or the occurrence of parasomnias such as nightmares, for example, would have been desirable. Ideally, a second later follow-up had been included. Likely, however, more drop-outs would have weakened the long- term results. Last, our results may not be generalizable as aggression in particular differs by culture and gender. Taking into account the limitations, this study can be re- garded as a pilot paving the way for future high-volume dream studies in neurosurgery.
ConclusionsThe study results suggest that perhaps the temporal lobe with the amygdala as an emotional integrator for dreaming plays a role in the generation of aggressive dream content within the DDN. As a result of ATL, ag- gression is less predominant in patients’ dreams. All pa- tients receiving general anesthesia can be counseled that their dream content will remain unaffected. With the re- sults of the current study and findings of future studies assessing different brain regions that belong to the DDN, the generation of dream content will be further unraveled. Last, neurosurgeons and physicians involved in the care of patients with drug-refractory epilepsy or other neu- rological conditions are encouraged to become more at- tuned to their patients’ inner life, which may be accessible through their dreams.
We have made strides in the field of dream research, utilizing brain imaging techniques and studying neural activity during sleep. However, these methods only scratch the surface, providing a mere glimpse into the complex tapestry of our dreams. We are left with abstract patterns of brain activity, but no true visual representation of what occurs within the dreamer's mind.
Dreams are deeply personal experiences, and being unable to share or visually communicate them poses a significant limitation. How marvelous it would be if we could express the surreal landscapes, vibrant colors, and fantastical characters that dance within our dreams! Such visuals could foster greater understanding and connection among individuals, as we would be able to explore the depths of our collective subconscious.
Artists and writers have long attempted to capture the essence of dreams through their work, but these interpretations often fall short of the true experience. The frustration intensifies when we realize that no matter how skilled the artist, their depiction remains a mere approximation, an interpretation of an experience they did not personally witness.
I express my disappointment and frustration with the current limitations in visualizing dreams.
Let us strive for a future where dreams are not only experienced but also visually shared, understood, and celebrated.
CLINICAL ARTICLE
The default dream network (DDN), named so be-
cause the brain “defaults” to this state when not
otherwise occupied, is a set of regions in the brain
that are metabolically active during rest/sleeping and seem
to play a key role in dreaming. During rest, “stimulus-
independent thought,” or thought unrelated to current
perceptions, predominates. This type of thinking allows
visualizing and rehearsing scenarios. The dorsal medial
subsystem of the DDN includes the dorsomedial prefron-
tal cortex, the temporoparietal junction/anterior inferior
parietal lobule, the lateral temporal cortex, and the tem-
poropolar cortex (the anterior pole of the temporal lobe),
and is activated by instructions to think about the present
situation or a present mental state (“present self”). On the
other hand, the medial temporal subsystem includes the
ventral medial prefrontal cortex, posterior inferior pari-
etal lobule, retrosplenial cortex, parahippocampal cortex,
and hippocampal formation, and is activated by thinking
about personal situations and decisions in the future (“fu-
ture self”). The left hemisphere generates the narrative
organization of the dream, and the right hemisphere gen-
erates the visual-spatial and visual-constructive elements
of the dream. A biophysical pathway common to dreams
and temporal lobe epilepsy is conceivable since dreamlike
symptoms are sometimes experienced during temporal
lobe seizures and have been elicited by direct stimulation
of the temporal lobes.
Besides neuroimaging studies, some knowledge about
the process of dreaming comes from case reports demon-
strating that damage to regions of the DDN corresponds to
certain abnormalities in dreaming. For example, occipital
lobe pathologies (usually bilateral) resulted in an isolated
loss of visual dream imagery (Charcot’s variant). A global
dreaming loss (Wilbrand’s variant) has been seen with le-
sions in the posterior regions around the parieto-temporal-
occipital junction. Various conditions in the transitional zone between the anterior diencephalon and the basal
forebrain have been reported to lead to excesses of dream-
ing. All of these studies, however, lack dream content
data obtained before the damage was inflicted on the
brain. To our knowledge, no studies have ever been under-
taken to assess dreaming in the setting of brain surgery.
Not infrequently, patients will spontaneously complain or
remark about changes to sleep or even dreams postopera-
tively. In this study, we prospectively applied the validated
coding system developed by Calvin S. Hall and Robert
Van de Castle to written home-recorded dream contents
of patients with drug-resistant epilepsy prior to and after
anterior temporal lobectomy (ATL). The primary objec-
tive was to register a possible change in dream content
and thus shed more light on the temporal lobe’s role in the
MethodsStandard of Care and Referral Process
Participants in this study were diagnosed with drug-
resistant epilepsy and underwent presurgical assessment
for epilepsy surgery. As part of the standard assessment,
patients were monitored in the epilepsy monitoring unit.
In cases in which the seizure onset zone could not be de-
lineated by semiology in conjunction with noninvasive di-
agnostic methods such as prolonged video-electroenceph-
alography performed with scalp electrodes, neuropsychol-
ogy, and structural and functional imaging, patients were
subjected to invasive monitoring according to our institu-
tional SEEG protocol. Since no brain tissue is removed
during SEEG implantation, this group was invited to be
part of the control arm (SEEG group). Those who quali-
fied for epilepsy surgery underwent resection of the sei-
zure onset zone. Patients eligible for ATL were recruited
as part of the treatment arm (ATL group).
Exclusion criteria were age < 16 years, inability to doc-
ument dreams in written form (e.g., because of language
barrier, illiteracy, cognitive impairment, or dementia), or
major psychiatric comorbidities, as well as previous cra-
nial surgery.
DDN. Serving as controls were patients who underwent
depth electrode implantation for stereoelectroencephalog-
raphy (SEEG). The secondary objective was to elicit/rule
out any impact of general anesthesia on dream content.
Dream Collection and AnalysisThe publicly available Most Recent Dream form
asks the patient to record the most recent dream they re-
call having. The form specifically requests information re-
garding the dream setting and its familiarity to the patient,
people and animals in the dream and their characteristics,
as well as how the patient felt in the dream. To control for
varying dream length, content beyond the first 300 words
was disregarded. Dream reports were coded for dream
elements as previously described by Hall and Van de
Castle. The Most Recent Dream form was provided, to
be returned to the study coordinators by mail prior to the
procedure (SEEG or ATL). In the postoperative follow-up,
patients were again asked to complete the Most Recent
Dream forms. In the SEEG group, postoperative dreams
were collected relatively soon after surgery, at 1 month, in order to pick up potential effects from anesthesia, whereas
the ATL group did not provide the dreams recorded in
the Most Recent Dream forms until after 3 months. The
rationale for the longer follow-up in the latter group was
to ascertain that any potential changes in dream content
could be attributed to the removal of brain tissue and not
anesthesia or the mere fact that the patients had surgery.
The coder (C.G.) was blinded to the patients’ diagnoses
and procedures.
Ethical AdherenceThis study was approved by the ethics board of Western
University and the London Health Sciences Centre (proj-
ect ID 107654) and the trial was registered at clinicaltrials.
gov (identifier NCT02731443) (https://clinicaltrials.gov/ct2/show/NCT02731443). Informed consent was obtained
from all study participants according to the Declaration
of Helsinki. The Most Recent Dream forms were anony-
mized with study numbers.
Statistical Methods
Differences in dream content between study groups
were calculated using Cohen’s h statistic. Major indica-
tors for main content categories in the Hall/Van de Castle
system were compared before and after the index proce-
dure, and p values < 0.01 were considered significant to
correct for multiple comparisons. A normative dataset of
previously analyzed contents of 500 men’s and women’s
dreams were assumed to be representative of the general
population and used as another control. All statistical
analysis beyond using the Automated Dream Data Entry
System and Statistical Analysis Tool to calculate the
occurrence of various features in the dreams among sub-
groups of patients was performed in R version 3.5.1. The
R package ggplot2 was used for graphing. IBM SPSS version 24 (IBM Corp.) was used for sta-
tistical analysis of the group’s baseline parameters. Con-
tinuous variables were tested using the Mann-Whitney U-
test. Fisher’s exact test was applied to compare categorical
variables, and p values < 0.05 were considered statistically
significant.
Results
Patient PopulationBetween March 2016 and March 2018, 56 (72.7%)
out of 77 eligible patients were excluded after screening,
mostly because they declared that they usually do not
recall any dream content (n = 47). Two patients rejected
study participation and 5 did not find the time to journal
their dreams. In one instance, the dreams were “too vivid
to put into words.” Another patient was retrospectively ex-
cluded since his dreams were clearly too mixed with likely
day-time posttraumatic stress disorder content from child-
hood, which was not picked up during study recruitment.
In total, 21 patients (15 females, 6 males) participated.
In the control group, 18 patients (13 females, 5 males)
provided 55 pre- and 60 post-SEEG dreams. Sufficient
intraoperative monitoring information was obtained in
all SEEG cases after an average of 10.5 ± 7.1 monitoring
days with 9.8 ± 3.6 electrodes. Out of 18 patients, 15 were considered surgical candidates. Three patients from this
group later also became part of the ATL group, and their
pre-SEEG dreams were used as the baseline for the as-
sessment of changes in dream content. With the addition
of another 3 ATL patients without prior SEEG, a total of
6 patients (4 females and 2 males) provided 30 pre- and
21 post-ATL dreams. The cohort’s baseline characteristics
are given in Table 1. There was no visible mesial temporal
sclerosis in the ATL group on preoperative imaging. An-
esthesia time (intubation to extubation) was significantly
shorter for the SEEG patients (199.8 ± 68.6 minutes) than
the ATL patients (333.2 ± 71.1 minutes; p < 0.01); this was
also the case for operation time (skin to skin), which was
105.8 ± 42.4 minutes in the SEEG patients versus 262.7 ±
69 minutes in the ATL patients (p < 0.01). Anesthesia was
induced with propofol and lidocaine as well as midazolam
in some cases. Maintenance was achieved using desflurane
and sevoflurane. In the ATL group, laterality was right in
4 and left in 2 patients. One left ATL was performed in a
patient under awake condition for intraoperative language
cortical mapping. The neocortex was removed at 4 to 5 cm
behind the temporal pole and the mesial structures resect-
ed to 1 cm behind a coronal plane of the posterior surface
of the midbrain, according to Girvin. No complications
occurred in either group.
Surgical seizure outcome at 3 months was Engel class
I in 3 and Engel class II in 2 patients. One patient had
unfavorable seizure outcome (Engel class IV), but showed
worthwhile improvement (Engel class III) in the further
course. Pathology of the resected temporal lobes revealed
gliosis in 2 patients, gliosis in combination with a focal
cortical dysplasia type 1 in 3 patients, and no abnormali-
ties in 1 patient.
Patients With Drug-Resistant Epilepsy Compared to Historical NormsCompared to publicly available normative dreams, the ATL patients’ preoperative dreams were not statisti-
cally different (Fig. 1). SEEG patients were preoperatively
more likely to have dreams with indoor settings compared
to the norms (p < 0.01; Fig. 2).
Preoperative Dreams Compared to Postoperative DreamsPatients who underwent ATL were significantly less
likely to have dreams involving physical aggression fol-
lowing surgery (p < 0.01; Fig. 3). There are three indi-
vidual categories related to this: “aggressor,” “physical
aggression,” and “aggression.” All of them are separate
entities. It should be noted that the categories “aggressor”
and “aggression” were not significantly different and pos-
sibly even more frequent in post-ATL patients by trend.
There were no significant differences in the dream content
of patients prior to and after SEEG procedures across the
major categories analyzed (Fig. 4).
DiscussionSupporting the role of the temporal lobe in dream pro-
duction, Bentes et al. showed that the dream content of
patients with temporal lobe epilepsy differs from that of
the general population. For 5 consecutive days, 52 patients recorded their dreams while being monitored with
electroencephalography in-hospital for epilepsy surgical
assessment. These patients had decreased dream recall,
dreams with a higher percentage of familiar settings,
and fewer dreams featuring dreamer success. This is in
contrast to our analysis, which detected no difference in setting familiarity or success compared to normative
data. Instead, we found that pre-SEEG patients had more
dreams featuring indoor settings than the historical norm.
As social isolation often prevails in these patients’ lives, incorporation of daily experiences into their dreams as so-
called “day’s residues” could explain this observation.
However, direct comparison is difficult for two reasons.
First, many of our SEEG patients had extratemporal lobe
epilepsy, and second, the SEEG patients were compared to
externally obtained norms rather than a healthy matched
control group who recorded dreams for 5 days at home.
ATL and Dream ContentAs a primary finding of this prospective study on a co-
hort of patients with drug-resistant epilepsy, significantly less (in fact no) physical aggressive features were seen in
dream content of patients following ATL. On the contrary,
the “aggressor” and “aggression” remained unchanged.
The reason behind this is that the latter categories repre-
sent the total aggression, which also includes nonphysi-
cal aggression, such as yelling or arguing, for example.
Within the limitations of the study design in mind, two
careful explanations of this observation can be attempted.
ATL entails amygdalectomy, and the amygdala, which
is time locked to be activated during rapid eye movement
(REM) sleep, has previously been attributed to fear con-
ditioning in dreams. The amygdala even takes a cen-
tral role in Revonsuo’s threat-simulation theory of the an-
cestral human. By means of deep brain amygdala stimu-
lation, Lai et al. provoked dreamy states enriched with vivid and bizarre emotional elements in 2 patients with
posttraumatic stress disorder. Further evidence comes
from De Gennaro et al., who established a correlation of
volumetric and ultrastructural measures of the amygdala
with dream emotional load and bizarreness in 34 healthy
subjects. In 8 patients with Urbach-Wiethe disease (a rare
condition with bilateral calcification of the basolateral
amygdala), Blake et al. showed that threatening dream
content still occurred, but was less negatively charged and
thus perceived as more pleasant.
As several lines of evidence converge on the amygdala
as a node for affective salience, we hypothesize that the
unilateral resection of a (potentially dysfunctional) amyg-
dala may have exerted a “taming effect” on dream con-
tent in our patients.
None of the ATL patients preoperatively stood out
with peri- or interictal aggressive behaviors. Absence or a
markable reduction of seizures, which was achieved in 5
out of the 6 ATL patients at 3 months, is therefore unlikely
to directly account for a decrease in aggression states in
these patients’ lives and—presumably—dream content.
However, it is conceivable that the indirect positive ef-
fect of a favorable seizure outcome by means of ATL on
the patients’ well-being created a more at-ease mindset.
This, in turn, might be subconsciously reflected by more
peaceful dream contents. Notwithstanding, this argument
is not further substantiated and it should be acknowledged
that various psychological factors may have influenced the
inner life of our patients. For example, it is possible that
anxiety in anticipation of their upcoming operation might have unfolded aggression in dreams during the preopera-
tive waiting period. Anxiety peaks have previously been
described in a hospitalized neurosurgical patient’s dream
content. However, this situation would have applied to
the SEEG group as well, who showed no pre- and post-
operative dream content differences. Antiepileptic drugs
can also facilitate aggression in certain individuals with
epilepsy. Among those with the strongest evidence for ag-
gression are levetiracetam, perampanel, and possibly topi-
ramate. However, these antiepileptic drugs in question
were distributed in equal parts in both groups, and left un-
changed up to at least 9 months after surgery at our insti-
tution. Another explanation for the observed decrease in
physical aggression in postoperative ATL patients’ dreams
might be a change in sleep patterns. McNamara et al. discovered that aggressive social interactions were more
characteristic of REM than non-REM sleep phases or
wake reports. Although no reports on sleep patterns after
brain surgery exist, it is known that patients with traumatic
brain injury spend less time in REM sleep and perhaps
this holds true for ATL patients as well.
SEEG and Dream ContentAs a secondary finding, the effect of general anesthe-
sia on dream content in patients undergoing depth elec-
trode insertion for SEEG (if present at all) was statistically
negligible. The inclusion of this control group undergoing
“sham surgery” is a unique strength of the study concept.
Some patients were later re-recruited into the surgical group, thus raising intergroup homogeneity. The fact that
pre- and post-SEEG dream content with a shorter follow-
up of 1 month remained stable also strengthens the robust-
ness of the changes seen in the ATL group, who had a
longer follow-up of 3 months. For anesthesiologists and
patients receiving general anesthesia, it is interesting to
know that dream content will remain unaffected. Howev-
er, confirmatory studies for patients undergoing extraneu -
rological surgery and anesthesia with different anesthetics
are needed.
Study Strengths and LimitationsTo the best of our knowledge, we are the first to in-
vestigate the change of dream content in patients elec-
tively undergoing brain surgery. This prospective study has a higher scientific value over the previous case reports
summarized by Solms that did not capture prelesional
dream content. In comparison to tumor-invaded brain,
for example, the resected temporal lobes in our temporal
lobe epilepsy cohort can be regarded as relatively healthy.
However, epileptic brain tissue is always dysfunctional to
some degree. Since resective brain surgery is not under-
taken for healthy brains, the current cohort is closest to
the normal population in a neurosurgical setting. The low
study participant inclusion rate—especially in the ATL
group—in a high-volume epilepsy surgery center over 2
years is a major shortcoming mainly attributable to lack
of dream recall. This is unsurprising in a population with
epilepsy and confirms the findings of previous studies.
Bentes et al. showed that patients with drug-resistant temporal lobe epilepsy have lower dream recall (71.2%)
than healthy controls (87.8%). More than half of the pa-
tients who consulted our clinic for presurgical investiga-
tions could not participate because they never or very
rarely remembered their dreams. The much lower dream
recall rate in our patients compared to that in the temporal
lobe epilepsy patients reported by Bentes et al. is likely
explained by the fact that many of the patients in the pres-
ent study had extratemporal epilepsy and also generalized
seizures. Bonanni et al. showed that dream recall was half
as likely in patients with generalized seizures as in pa-
tients with complex partial seizures. Perhaps writing up
the most recent dream posed an inconvenience to some of
our patients. Whereas some patients might therefore not
have tried to remember their dreams in the morning, oth-
ers perceived this as interesting to do, which leads to se-
lection bias. The gold standard remains laboratory dream
reports; however, home-recorded dream reports provide
valid data and have therefore been used by others.
Interestingly, home-recorded dreams show a higher pre-
ponderance of physical aggression than dreams recalled in
the laboratory. More qualitative dream assessment tools
to provide further insight into the emotional component,
such as bizarreness or the occurrence of parasomnias such
as nightmares, for example, would have been desirable.
Ideally, a second later follow-up had been included. Likely,
however, more drop-outs would have weakened the long-
term results. Last, our results may not be generalizable as
aggression in particular differs by culture and gender.
Taking into account the limitations, this study can be re-
garded as a pilot paving the way for future high-volume
dream studies in neurosurgery.
ConclusionsThe study results suggest that perhaps the temporal
lobe with the amygdala as an emotional integrator for
dreaming plays a role in the generation of aggressive
dream content within the DDN. As a result of ATL, ag-
gression is less predominant in patients’ dreams. All pa-
tients receiving general anesthesia can be counseled that
their dream content will remain unaffected. With the re-
sults of the current study and findings of future studies
assessing different brain regions that belong to the DDN,
the generation of dream content will be further unraveled.
Last, neurosurgeons and physicians involved in the care
of patients with drug-refractory epilepsy or other neu-
rological conditions are encouraged to become more at-
tuned to their patients’ inner life, which may be accessible
through their dreams.
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We have made strides in the field of dream research, utilizing brain imaging techniques and studying neural activity during sleep. However, these methods only scratch the surface, providing a mere glimpse into the complex tapestry of our dreams. We are left with abstract patterns of brain activity, but no true visual representation of what occurs within the dreamer's mind.
Dreams are deeply personal experiences, and being unable to share or visually communicate them poses a significant limitation. How marvelous it would be if we could express the surreal landscapes, vibrant colors, and fantastical characters that dance within our dreams! Such visuals could foster greater understanding and connection among individuals, as we would be able to explore the depths of our collective subconscious.
Artists and writers have long attempted to capture the essence of dreams through their work, but these interpretations often fall short of the true experience. The frustration intensifies when we realize that no matter how skilled the artist, their depiction remains a mere approximation, an interpretation of an experience they did not personally witness.
I express my disappointment and frustration with the current limitations in visualizing dreams.
Let us strive for a future where dreams are not only experienced but also visually shared, understood, and celebrated.