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HYPOTHESIS AND THEORY
published: 05 April 2018
doi: 10.3389/fphar.2018.00330
Edited by:
Ede Frecska,
University of Debrecen, Hungary
Reviewed by:
Alfredo Meneses,
Centro de Investigación y de Estudios
Avanzados del Instituto Politécnico
Nacional (CINVESTAV-IPN), Mexico
Dasiel Oscar Borroto-Escuela,
Karolinska Institute, Sweden
*Correspondence:
Antonio Inserra
antonio.inserra@live.com
Specialty section:
This article was submitted to
Neuropharmacology,
a section of the journal
Frontiers in Pharmacology
Received: 28 November 2017
Accepted: 21 March 2018
Published: 05 April 2018
Citation:
Inserra A (2018) Hypothesis:
The Psychedelic Ayahuasca Heals
Traumatic Memories via a Sigma 1
Receptor-Mediated
Epigenetic-Mnemonic Process.
Front. Pharmacol. 9:330.
doi: 10.3389/fphar.2018.00330
Hypothesis: The Psychedelic
Ayahuasca Heals Traumatic
Memories via a Sigma 1
Receptor-Mediated
Epigenetic-Mnemonic Process
Antonio Inserra1,2,3*
1Mind and Brain Theme, The South Australian Health and Medical Research Institute, Adelaide, SA, Australia, 2Department
of Psychiatry, College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia, 3Centre for Neuroscience,
Flinders University, Adelaide, SA, Australia
Ayahuasca ingestion modulates brain activity, neurotransmission, gene expression and
epigenetic regulation. N,N-Dimethyltryptamine (DMT, one of the alkaloids in Ayahuasca)
activates sigma 1 receptor (SIGMAR1) and others. SIGMAR1 is a multi-faceted stress-
responsive receptor which promotes cell survival, neuroprotection, neuroplasticity,
and neuroimmunomodulation. Simultaneously, monoamine oxidase inhibitors (MAOIs)
also present in Ayahuasca prevent the degradation of DMT. One peculiarity of
SIGMAR1 activation and MAOI activity is the reversal of mnemonic deficits in pre-
clinical models. Since traumatic memories in post-traumatic stress disorder (PTSD)
are often characterised by “repression” and PTSD patients ingesting Ayahuasca
report the retrieval of such memories, it cannot be excluded that DMT-mediated
SIGMAR1 activation and the concomitant MAOIs effects during Ayahuasca ingestion
might mediate such “anti-amnesic” process. Here I hypothesise that Ayahuasca,
via hyperactivation of trauma and emotional memory-related centres, and via its
concomitant SIGMAR1- and MAOIs- induced anti-amnesic effects, facilitates the
retrieval of traumatic memories, in turn making them labile (destabilised). As Ayahuasca
alkaloids enhance synaptic plasticity, increase neurogenesis and boost dopaminergic
neurotransmission, and those processes are involved in memory reconsolidation and
fear extinction, the fear response triggered by the memory can be reprogramed and/or
extinguished. Subsequently, the memory is stored with this updated significance.
To date, it is unclear if new memories replace, co-exist with or bypass old ones.
Although the mechanisms involved in memory are still debated, they seem to require
the involvement of cellular and molecular events, such as reorganisation of homo
and heteroreceptor complexes at the synapse, synaptic plasticity, and epigenetic re-
modulation of gene expression. Since SIGMAR1 mobilises synaptic receptor, boosts
synaptic plasticity and modulates epigenetic processes, such effects might be involved
in the reported healing of traumatic memories in PTSD patients. If this theory proves
to be true, Ayahuasca could come to represent the only standing pharmacological
treatment which targets traumatic memories in PTSD. Lastly, since SIGMAR1 activation
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
triggers both epigenetic and immunomodulatory programmes, the mechanism here
presented could help understanding and treating other conditions in which the cellular
memory is dysregulated, such as cancer, diabetes, autoimmune and neurodegenerative
pathologies and substance addiction.
Keywords: Ayahuasca, DMT, sigma 1 receptor, trauma, post-traumatic stress disorder, epigenetics, fear
extinction, cellular memory
INTRODUCTION
Ayahuasca is a psychoactive plant brew containing N,N-
dimethyltryptamine (DMT) and β-carboline alkaloids (harmine,
harmaline, and tetrahydroharmine) traditionally used in
the Amazon basin for therapeutic and spiritual purposes
(Schultes et al., 1979;Frecska et al., 2016). The hallucinogenic
tryptamine DMT is obtained from Psychotria viridis and
it binds to SIGMAR1, the serotonin receptors (5HTR)
1A/1D/1E/2A/2B/2C/5A/6/7, the serotonin transporter, the
dopamine receptor D1 (D1R), the adrenergic receptors alpha
1A/1B/2A/2B/2C, the imidazoline 1 receptor and the trace
amine associated receptor (Deliganis et al., 1991;Smith et al.,
1998;Bunzow et al., 2001;Fontanilla et al., 2009;Ray, 2010).
β-carbolines are obtained from Banisteriopsis caapi and function
as monoamine oxidase inhibitors (MAOIs) to render DMT orally
active (Riba et al., 2003).
Ayahuasca seems to hold therapeutic potential in psychiatry.
Recently, fast onset antidepressant effects were reported
following administration of a single dose of Ayahuasca in
patients diagnosed with recurrent depression (Sanches et al.,
2016). Similarly, anecdotal evidence suggests that Ayahuasca
might be beneficial in the treatment of post-traumatic stress
disorder (PTSD) (Nielson and Megler, 2014). However, no
pre-clinical or clinical studies to date have investigated this
possibility.
In this work, based on converging layers of evidence from
in-vitro, pre-clinical and clinical studies, I postulate a mechanism
involving the activation of discrete brain areas and receptor
systems which triggers the recall of traumatic memories and
their reconsolidation (and potentially fear extinction learning)
hypothetically via modifying the epigenetic signatures of the
memory.
AYAHUASCA INGESTION MODULATES
BRAIN ACTIVITY
The deep changes in perception and cognition elicited by
Ayahuasca ingestion are underlined by a profound activation
of limbic, paralimbic and neocortical brain areas, which are
Abbreviations: 5HT, Serotonin; BDNF, Brain-derived neurotrophic factor;
CB1, Cannabinoid receptor 1; DMN, Default mode network; DMT, N,N-
Dimethyltryptamine; GABA, Gamma-aminobutyric acid; HDAC, Histone
deacetylase; IFG, Inferior frontal gyrus; LVGCC, L-type voltage-gated
calcium channels; MAOI, Monoamine oxidase inhibitor; MDMA, 3,4-
methylenedioxy-methamphetamine; NFKB, Nuclear factor kappa-B; NMDA,
N-methyl-D-aspartate; PTSD, Post-traumatic stress disorder; SIGMAR1, Sigma 1
receptor.
involved in trauma, memory formation, memory retrieval and
emotional regulation, as well as a region-specific shift of electrical
activity. These changes lead to an altered state of awareness
underlined by introspection, retrieval of traumatic memories,
and visions. Imaging studies have shown that Ayahuasca
hyperactivates the inferior frontal gyrus (IFG) and the anterior
insula, the right anterior cingulate/subcallosal gyrus and the
left amygdala/parahippocampal gyrus, while decreasing activity
within relevant hubs of the default mode network (DMN),
such as the precuneus/posterior cingulate cortex and the medial
prefrontal cortex (Riba et al., 2006;Palhano-Fontes et al., 2015).
The inferior frontal gyrus (IFG) is a brain area involved in
semantic unification, emotion perception and regulation and
processing of negative emotional stimuli (Etkin et al., 2011;
Zhu et al., 2012;Tabei, 2015;Urgesi et al., 2016). This suggests
that activation of this brain area during Ayahuasca ingestion
could be involved in the processing of trauma. Significantly,
veterans diagnosed with PTSD display decreased IFG activation
in response to contextual cues, suggesting that modulation of this
brain area might be beneficial in PTSD treatment (van Rooij et al.,
2014). Similarly, the anterior insula is hyperactivated following
Ayahuasca ingestion, and this region is involved in emotional
processing and in the conscious perception of errors (Phillips
et al., 1998;Ullsperger et al., 2010). The amygdala is involved
in fear response, emotional arousal processes, reconsolidation
of fear memories and fear memory extinction, and this brain
region has been shown to be hyper-responsive in PTSD (Riba
et al., 2006;Shin et al., 2006;Myers and Davis, 2007;Palhano-
Fontes et al., 2015). Ayahuasca-induced hyperactivity of this
brain area therefore supports the processing and reconsolidation
of traumatic memories and the extinction of the fear memory
associated with recall of the traumatic memory (Riba et al., 2006;
Shin et al., 2006;Myers and Davis, 2007;Palhano-Fontes et al.,
2015).
The subcallosal gyrus is involved in the processing of
sadness and sad memories (Mayberg et al., 1999). Increased
activity of this brain region is observed when patients are
asked to rehearse sad autobiographic scripts, in line with the
hypothesis presented here. Significantly, co-activation of the IFG,
amygdala and hippocampus is a prerequisite for autobiographical
memory retrieval, and specific sub-regions of these brain
areas are activated following Ayahuasca ingestion (Greenberg
et al., 2005;Riba et al., 2006). Moreover, parahippocampal
gyrus activity is increased during memory retrieval tasks,
and Ayahuasca hyperactivates this brain area (Maguire and
Mummery, 1999).
Much like other psychedelic compounds such as psilocybin
and lysergic acid diethylamide (LSD), Ayahuasca ingestion
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
dampens activity and connectivity of crucial hubs within the
DMN, such as the precuneus/posterior cingulate cortex and the
medial prefrontal cortex (Carhart-Harris et al., 2012;Palhano-
Fontes et al., 2015;Speth et al., 2016). Of relevance, the medial
prefrontal cortex is involved in the process of fear extinction, and
its activity is modulated by Ayahuasca (Myers and Davis, 2007;
Palhano-Fontes et al., 2015).
AYAHUASCA INGESTION MODULATES
NEUROTRANSMISSION
To date, only one study has investigated the effects of Ayahuasca
administration on neurotransmission (de Castro-Neto et al.,
2013). In this study, the authors orally administered rats
three Ayahuasca doses and studied post-mortem amino acid
and monoamines levels in the hippocampus and amygdala.
Gamma-aminobutyric acid (GABA), the main inhibitory
neurotransmitter in the human brain, was dose-independently
increased in the hippocampus while it was increased in the
amygdala at the lowest dose and decreased at the highest
concentrations. Moreover, in the amygdala, noradrenaline,
serotonin and dopamine levels were increased at all doses
studied, while in the hippocampus only serotonin was increased
in rats receiving the two highest doses. Furthermore, the
turnover of serotonin, noradrenaline and dopamine was
drastically reduced in the amygdala but not in the hippocampus
of Ayahuasca-treated rats (de Castro-Neto et al., 2013).
These findings suggest that Ayahuasca ingestion exerts
profound monoaminergic effects in the amygdala, increasing
the levels of excitatory and decreasing those of inhibitory
neurotransmitters, while decreasing monoamine utilisation. The
findings that GABA is decreased and dopamine is increased in
the amygdala following Ayahuasca administration is relevant
for the hypothesis here presented, since the GABAergic system
mediates the amnesic effects of chemical compounds, and
negative modulation of the GABAergic system has anti-amnesic
effects, while amygdalar dopamine is involved in the extinction of
conditioned fear (Rau et al., 2009;Abraham et al., 2014). Thus, the
decreased levels of amygdalar GABA might be at least partially
responsible for the anti-amnesic-like effects of Ayahuasca on
the retrieval of repressed memories in PTSD patients, while the
increased levels of amygdalar dopamine might play an important
role in the process of fear extinction (discussed below).
Further studies should investigate if similar changes in
neurotransmission are replicable in humans. This could be
possible via in vivo approaches, by using neuroimaging
techniques to a) directly measure the levels of neurotransmitter
release following Ayahuasca ingestion or b) indirectly, by
measuring the relative drug occupancy at receptors for each of the
neurotransmitter of interest (Badgaiyan, 2014;Kumar and Mann,
2014). However, until otherwise proven, it seems likely that
Ayahuasca ingestion might trigger similar neurotransmission
patterns in humans. These changes could be involved in the
reported antidepressant effects of Ayahuasca and in the anecdotal
reports of Ayahuasca consumption in the healing of trauma
(Dominguez-Clave et al., 2016;Sanches et al., 2016).
AYAHUASCA INGESTION MODULATES
NEUROGENESIS
Aside from their monoaminergic effects, the alkaloids present in
Ayahuasca have been shown to increase neurogenesis in vitro
and in vivo at least partially via SIGMAR1-mediated upregulation
of brain-derived neurotrophic factor (BDNF) (Fortunato et al.,
2009;Fujimoto et al., 2012;Lenart et al., 2016;Morales-
Garcia et al., 2017). The processes of memory reconsolidation
and fear extinction (discussed below) both require synaptic
plasticity enhancement and hippocampal neurogenesis, which
are modulated by BDNF (Radiske et al., 2015;Suarez-Pereira and
Carrion, 2015). Therefore, it seems likely that the Ayahuasca-
induced synaptic plasticity and neurogenesis, which are required
for mnemonic processes and fear extinction, might be involved
in the healing of traumatic memories experienced by Ayahuasca
users.
SIGMA-1 RECEPTOR
SIGMAR1 is a transmembrane protein with neuroprotective,
neurotrophic, and immunomodulatory properties found in high
concentrations in limbic areas of the human brain and in
immune cells (Ishikawa et al., 2007;Fujimoto et al., 2012;
Frecska et al., 2013;Szabo et al., 2014). SIGMAR1 can be
membrane-bound at the mitochondria-associated endoplasmic
reticulum (ER) membrane, where it acts as a molecular
chaperone, or translocate to the nuclear envelope, the cytosol
and the plasma membrane. (Hayashi and Su, 2007;Tsai et al.,
2015). At the nuclear envelope, SIGMAR1 recruits chromatin-
remodelling molecules to control gene expression (Tsai et al.,
2015). Aside from its effects at the ER and nuclear level,
SIGMAR1 also plays an important role at the synaptic level both
via forming heteroreceptor complexes with G-protein coupled
receptors (GPCRs) and via directly interacting with voltage-
gated ion channels, therefore controlling the reorganisation of
several homo and heteroreceptor complexes and modulating
neurotransmission. (Kourrich et al., 2013;Balasuriya et al.,
2014;Beggiato et al., 2017;Feltmann et al., 2018;Ortiz-
Renteria et al., 2018) Dysregulation of SIGMAR1 function is
implicated in neuropsychiatric and neurodegenerative disorders,
drug addiction, cancer, cardiovascular diseases, immune-related
pathologies, stroke and neuropathic pain [Reviewed in (Tsai et al.,
2009;Frecska et al., 2016)].
One peculiarity of the human SIGMAR1 gene is that, unlike
any other, it only shares 30.3% homology with any other
mammalian protein, while sharing 66.7% identity with the
enzyme sterol isomerase found in fungi, which is involved
in the biosynthesis of ergosterol (Hanner et al., 1996;Weete
et al., 2010). Ergosterol is a compound found in the cell
membrane of fungi and protozoa first identified in the fungus
Claviceps Purpurea (Weete et al., 2010). Interestingly, this
fungus produces ergot alkaloids amongst which lysergic acid,
a precursor of the synthetic LSD (Miedaner and Geiger,
2015). Some authors have suggested that, unlike the traditional
view that 5HT receptors mediate the psychedelic effects of
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
tryptamines, SIGMAR1 might also be involved in those effects
(Fontanilla et al., 2009). Although such discussion is beyond
the scope of this work and shall be argued elsewhere, the
author believes that SIGMAR1 might represent the real gateway
to psychedelic states. Further studies should investigate this
possibility.
Sigma 1 Receptor Activation Is
Anti-amnesic
Aside from its neuroprotective and immunomodulatory
properties, SIGMAR1 activation has been shown to reverse
experimental-induced amnesia in rodents, possibly via
enhancement of the cholinergic and N-methyl-D-aspartate-
(NMDA) glutamatergic neurotransmitter systems (Earley et al.,
1991;Maurice et al., 1998;Antonini et al., 2009). Interestingly,
peak densities of SIGMAR1 are found in brain areas relevant
to traumatic memory formation, retrieval and updating, such
as the amygdala and the hippocampal formation, suggesting
that Ayahuasca-induced SIGMAR1 activation in such brain
areas could be involved in the reported retrieval and updating
of traumatic memories (Mash and Zabetian, 1992). Supporting
this notion, the parahippocampal gyrus, one of the brain
areas hyperactivated by Ayahuasca ingestion, is involved
in the modulation of memory retrieval (Woodcock et al.,
2015).
Accordingly, SIGMAR1, D2R and 5HT2AR are enriched in
the amygdala, while SIGMAR1-D2R and D2R-5HT2AR have
been shown to interact to form heteroreceptor complexes at the
post-junctional membrane of synapses. (Beggiato et al., 2017;
Feltmann et al., 2018) The term “junctional neurotransmission”
identifies a type of neurotransmission which is “non-synaptic”
and refers to the neurotransmission at neuro-non-neural
effectors, that is the connexion between neuronal and non-
neuronal cells (such as smooth muscle cells). Such non-
synaptic neurotransmission is achieved by means of GPCRs
metabotropic receptors signalling, and produces a slower (second
to minutes) response compared to synaptic neurotransmission.
(Goyal and Chaudhury, 2013) Given that (a) SIGMAR1 plays
an important role in junctional neurotransmission via forming
heteroreceptor complexes with other metabotropic receptors
such as 5HT2AR and D2R and that (b) DMT has high affinity
for SIGMAR1 and 5HT2AR, and the latter forms heteroreceptor
complexes with both SIGMAR1 and D2R, and that (c) D2R-
5HT2AR oligomerization enhances D2R promoter recognition
and signalling, it could be plausible that this mechanisms at
the post-junctional synapse might enhance the effects of DMT
on dopaminergic neurotransmission in the amygdala, a crucial
event in memory retrieval and reconsolidation. (Borroto-Escuela
et al., 2010, 2014, 2017;Lukasiewicz et al., 2010;Albizu et al.,
2011)
Therefore, it seems possible that the elicited patterns of brain
activation arising from Ayahuasca ingestion, accompanied by the
DMT-induced SIGMAR1 activation leading to gene expression
regulation, and by the formation of heteroreceptor complexes
to boost dopaminergic neurotransmission, might mediate the
retrieval of repressed traumatic memories. This kind of retrieval
process forms an essential step in the re-elaboration and re-
contextualization of such memories. Interestingly, MAOI activity
has also been shown to be beneficial in pre-clinical models
of amnesia, and Ayahuasca contains MAOIs (Botwinick and
Quartermain, 1974).
Sigma 1 Receptor Activation Modulates
Epigenetic Processes
Recently, SIGMAR1 has been shown to modulate epigenetic
processes. In fact, cocaine-induced SIGMAR1 activation triggers
SIGMAR1 translocation to the nuclear envelope, where it
interacts with proteins which regulate gene expression by
affecting chromatin compaction (Tsai et al., 2015). Specifically,
SIGMAR1 was shown to create a dose-dependent interaction
between emerin and histone deacetylase (HDAC) 1, HDAC2
and HDAC3 and to therefore affect chromatin compaction
and gene expression (Demmerle et al., 2012;Tsai et al.,
2015). Therefore, for the first time, a study has described
an involvement of SIGMAR1 on the epigenetic regulation
of gene expression. This is in line with the hypothesis
here presented, since reconsolidation and fear extinction of
traumatic memories both seem to require the involvement of
epigenetic mechanisms (Graff et al., 2014;Kwapis and Wood,
2014).
Sigma 1 Receptor Activation Disrupts
the Reconsolidation of Fear Memories
Aside from promoting anti-amnesic and regulating epigenetic
intracellular pathways, activated SIGMAR1 modulates the
cannabinoid receptor 1 (CB1)/NMDA receptor interaction
to prevent NMDA receptor dysfunction (Sanchez-Blazquez
et al., 2014). In support of the hypothesis here presented,
CB1 receptors are enriched in the basolateral amygdala (a
region involved in conditioned fear), and pharmacological
agonists that activate CB1 or NMDA receptors during traumatic
memory retrieval disrupt the reconsolidation of fear memories,
preventing subsequent fear expression (McDonald and Mascagni,
2001;Lee et al., 2017). This mechanism could be involved
in the extinction of fear memory and healing of traumatic
memories reported by Ayahuasca users (Nielson and Megler,
2014).
MEMORY, PTSD AND TRAUMATIC
MEMORIES
Memory formation is the ensemble of highly dynamic processes
that permit specific aspects of an event to be stored in
the brain (Nadel et al., 2012). The mechanisms involved in
memory formation, retrieval and reconsolidation have long
been investigated. However, because of the highly complex
nature of such processes, and because of the difficulties in
studying them, the exact nature of these mechanisms are still
debated. It is, however, accepted that mnemonic processes (i.e.,
memory consolidation, retrieval and reconsolidation) require
the involvement of cellular and molecular mechanisms, such as
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
synaptic plasticity and the transcriptional modulation of specific
sets of genes in relevant neuronal subpopulations, which are likely
to be mediated by epigenetic modifications (Jarome and Lubin,
2014).
Several hypotheses have been formulated trying to describe
the elusive mechanisms of memory formation, retrieval and
reconsolidation. Although diverging in some aspects, these
hypotheses are not necessarily mutually exclusive, and they could
hold the key to explain slightly different mechanisms of the
same paradigm. The “synaptic plasticity” hypothesis suggests
that activity-dependent plasticity is achieved at appropriate
synapses and is necessary and sufficient for storage, retrieval
and reconsolidation of the memory engram. (Martin et al.,
2000;Takeuchi et al., 2014) The “memory indexing theory” or
“hippocampal hypothesis of memory,” suggests that the pattern
of neocortical and other brain areas activated by an event
are initially indexed (i.e., “photographed”) in the hippocampus
only to be subsequently stored in other brain regions, such as
the neocortex. (Teyler and DiScenna, 1985) The “consolidation
hypothesis” disputes that new memories consolidate slowly
over time unless new information is learnt shortly after the
initial learning. (McGaugh, 2000) The “cholinergic hypothesis”
proposes that cholinergic neurons are central player in the
formation and storage of memory, and that cholinergic
dysfunction is involved in memory and cognitive deficits. (Bartus
et al., 1982;Contestabile, 2011) The “vasopressin hypothesis”
argues that vasopressin is the fundamental peptide that enhances
memory given that vasopressin delayed memory extinction.
(Strupp and Levitsky, 1985) The “fragmentation hypothesis”
holds that a specific memory is stored as fragments of the
specific perceived situation. It has been suggested that this
mechanisms might be relevant to PTSD via the phenomenon of
“dissociative encoding”, the insufficient encoding of the trauma
memory following peritraumatic dissociation which prevents
future re-elaboration of the traumatic memory (Bedard-Gilligan
and Zoellner, 2012).
Nonetheless, some authors have suggested that long-term
memory might be mediated by the allosteric reorganisation
of populations of homo- and heteroreceptor complexes in
the post-junctional membranes, which in turn affect the pre-
junctional receptor complexes to facilitate the new pattern
of transmitter release to be learned. (Borroto-Escuela et al.,
2015, 2017;Fuxe and Borroto-Escuela, 2016b) Specifically, the
transformation of sub-regions of heteroreceptor complexes into
transcription factors, upon formation of specific adapter proteins,
can consolidate the heteroreceptor complexes into long-term
units. Those influence gene expression via altered promoter
recognition, signalling and trafficking as well as via the formation
of novel allosteric sites, which can lead to changes in promoter
function and pharmacology. (Fuxe and Borroto-Escuela, 2016a;
Borroto-Escuela et al., 2017) Hence, given that SIGMAR1
controls the reorganisational pattern of several homo- and
heteroreceptor complexes at the synapses, it cannot be excluded
that these mechanisms might be involved in the reported retrieval
and healing of traumatic memories following DMT-mediated
SIGMAR1 activation. This might result in a “new post-junctional
transmission learning” mediated by a long term modulation of
the neuronal networks in which the memory is encoded. Further
studies are warranted to explore this possibility.
Traumatic Memories and Brain Activity
in PTSD
When a traumatic event is experienced, the extent of circulating
glucocorticoids and adrenalin seem to determine the formation
fate of a memory of the event. For example, when the stressor
is particularly intense and the levels of stress hormones (such
as glucocorticoids) become particularly elevated, formation of
the memory can be impaired [Reviewed by (Schwabe et al.,
2010)]. Following such events, deficits in declarative memory (the
difficulty of recalling the traumatic event) can be experienced
(Samuelson, 2011). Exposure to highly traumatic situations can
lead to the development of PTSD, a disorder characterised by
intrusive thoughts, repression of trauma memory, flashbacks,
nightmares, hyperarousal, startle response, and changes in
memory and concentration (Bremner, 2006).
Individuals diagnosed with PTSD display changes in brain
function and structure, such as alterations of the hippocampus,
amygdala and medial prefrontal cortex (including anterior
cingulate cortex). Crucially, Ayahuasca ingestion modulates
activity of these brain areas (Bremner et al., 1997;Lanius
et al., 2001;Bremner, 2006;Riba et al., 2006;Palhano-Fontes
et al., 2015). Human studies suggest that PTSD patients present
disorder-specific epigenetic regulation of genes involved in
pathways relevant to this disorder (Zannas et al., 2015). Given
that SIGMAR1 activation is involved in chromatin remodelling
and epigenetics regulation of gene expression, it cannot be
excluded that DMT-mediated SIGMAR1 activation might affect
aberrant gene expression and/or epigenetic signatures in PTSD
(Tsai et al., 2015;Zannas et al., 2015).
Dissociative Amnesia and Brain Activity
Changes
A subset of individuals diagnosed with PTSD experience
dissociative amnesia, a condition characterised by impaired
retrograde memory functioning and loss (or repression) of
autobiographic traumatic memory, which is not related to
structural brain damage or other cognitive impairments (Brand
et al., 2009;Staniloiu and Markowitsch, 2014).
In one imaging study, dissociative amnesia patients displayed
hypometabolic functioning of the right inferolateral prefrontal
cortex and left supramarginal gyrus (Brand et al., 2009).
Another study suggested that dissociative amnesia patients
present increased activity in the prefrontal cortex and decreased
activity in the hippocampus during a memory retrieval task
(Kikuchi et al., 2010). Since Ayahuasca increases brain activity
in the parahippocampal region, a brain area involved in memory
retrieval, and the hippocampus is underactive during memory
retrieval tasks in dissociative amnesia patients, it seems plausible
that Ayahuasca might be beneficial in the process of memory
recovery in dissociative amnesia patients (Riba et al., 2006;
Kikuchi et al., 2010). Interestingly, after treatment for dissociative
amnesia, this aberrant pattern of brain activity is reversed
(Kikuchi et al., 2010).
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
Traumatic Memory Recall in PTSD
During traumatic memory recall in PTSD patients, abnormal
brain activity changes can be observed, such as decreased
activation of the hippocampus, parietal cortex and decreased
activation of the inferior frontal gyrus (the latter is upregulated by
Ayahuasca). Moreover, traumatic memory recall hyperactivates
the amygdala and posterior cingulate cortex (the latter is
hypoactivated following Ayahuasca ingestion) (Bremner, 2006;
Palhano-Fontes et al., 2015). Recall and reactivation of a
traumatic memory create a plastic window in which the memory
becomes labile and has the potential to be updated via epigenetic
regulation of neuroplasticity-related gene expression, which can
lead to an attenuation (or extinction) of the fear response
associated with the memory itself (Nader et al., 2000;Graff
et al., 2014). This timeframe (considered to last around 6 h)
offers healing potential in PTSD, dissociative amnesia and in any
individual that has been exposed to traumatic events (Schiller
et al., 2010).
Memory Reconsolidation and Fear
Extinction
The notion that memories are a stable and unchangeable entity
has long been disproven. It is now accepted that when memories
are retrieved (reactivation of the trace memory), they enter a
labile (deconsolidation) state with potential for the memory to
be updated (reconsolidation), so that when the memory will be
recalled in future, the “new” version of the memory is recalled
(Alberini and Ledoux, 2013). However, debate still exists as to
whether the new trace memory replaces or co-exists with the
old one. Either way, the potential to update memory presents
considerable therapeutic implications (Jarome and Lubin, 2014).
The term fear extinction refers to the loss of the fear response
associated with the recall of a traumatic memory, and it is
an important step in the healing of traumatic memories, such
as those experienced by PTSD patients (Myers and Davis,
2007). BDNF-mediated neurogenic processes seem to be essential
for this process. (Radiske et al., 2015) In fact, the extinction
of the fear responses associated with traumatic memories is
mediated by BDNF signalling, and pharmacological BDNF
activation after fear extinction hinders the re-emergence of
fear (Radiske et al., 2015). Since Ayahuasca increases BDNF
signalling, and BDNF mediates fear extinction, it seems plausible
that this effect might be involved in the reported processing and
amelioration of traumatic memories and in the extinction of
the fear response associated with traumatic memories following
Ayahuasca ingestion (Fortunato et al., 2009;Morales-Garcia
et al., 2017).
Involvement of Epigenetic Mechanisms
in Memory Formation
Epigenetic modifications refer to changes in chromatin
compaction which enhance or represses gene transcription
and that are not mediated by changes in the underlying DNA
sequence (Goldberg et al., 2007). A central role has been
suggested for epigenetic regulation in memory processes, since
gene transcription seems to be a critical modulator of the
processes underlying memory acquisition, retrieval and updating
[Reviewed by (Jarome and Lubin, 2014)]. Gene expression shifts
result in synaptic functional and structural changes, which lead
to changes in synaptic efficacy, thought to underlie the storage
and plasticity of memories (Kandel, 2004;Mayford et al., 2012).
Involvement of Epigenetic Mechanisms
in Memory Reconsolidation
The term reconsolidation refers to the updating of an existing
memory following retrieval, which results in the updated version
of the memory being retrieved in subsequent recall (Alberini and
Ledoux, 2013). Relatively little is known about the molecular basis
of reconsolidation processes, which are thought to be regulated
by intracellular pathways upstream of gene transcription, such as
protein kinase A, extracellular signal-regulated kinase/mitogen-
activated protein kinase and cAMP responsive element binding
protein [Reviewed by (Jarome and Lubin, 2014)].
The nuclear factor kappa-B (NFKB) pathway seems to be
critically involved in the epigenetic underpinnings of memory
reconsolidation via increasing global histone H3 phosphorylation
and acetylation (Lubin and Sweatt, 2007). Significantly, the
DMT analogue 5-methoxy-N,N-dimethyltryptamine as well as
the synthetic psychedelic 2,5-Dimethoxy-4-iodoamphetamine
downregulate this pathway, suggesting that DMT and Ayahuasca
might present at least same degree of NFKB pathway modulation
(Yu et al., 2008;Dakic et al., 2017). It could therefore
be argued that Ayahuasca enhances the process of memory
reconsolidation via modulating NFKB-mediated regulation of
epigenetic modification at the histone level. In support of this
notion, a recent study found that activated SIGMAR1 forms a
complex with HDAC 1, 2, and 3 and other chromatin remodelling
factors to modulate gene expression (Tsai et al., 2015).
Lastly, NMDA receptor activation seems to be essential for
memory destabilisation and reconsolidation and it is thought to
occur upstream of the mechanisms modulating the epigenetic
regulation of gene expression (Gazarini et al., 2014;Jarome
and Lubin, 2014). Since activated SIGMAR1 interacts with
this receptor, it could be hypothesised that such interaction
is involved in the reported beneficial effects of Ayahuasca on
memory updating (Sanchez-Blazquez et al., 2014).
Involvement of Epigenetic Mechanisms
in Fear Extinction
Fear extinction is described as a decline in conditioned fear
response following exposure to a non-reinforced fearful stimulus
(i.e., exposure to a context in which the aversive stimulus
associated with that context is not presented) (Myers et al.,
2006). Fear extinction is thought to involve the “new learning”
of a memory that competes with the traumatic one rather than
the updating of an old one. Systemic or localised modulation
of HDAC activity (and in particular HDAC1 inhibition, which
results in histone acetylation and methylation of target genes)
seems to be beneficial to fear extinction learning [Reviewed in
(Kwapis and Wood, 2014). Since activated SIGMAR1 interacts
with HDAC1 and other HDACs, which are involved in fear
extinction, and DMT activates SIGMAR1, is possible that DMT
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
and Ayahuasca might be beneficial in erasing the fear response
associated with traumatic memories (Tsai et al., 2015).
Similarly, studies have shown that L-type voltage-gated
calcium channels (LVGCCs) are involved in the extinction of
conditioned fear (McKinney et al., 2008;Davis and Bauer,
2012;Temme and Murphy, 2017). Interestingly, DMT, harmaline
and harmane all modulate LVGCCs (Splettstoesser et al., 2005;
Johannessen et al., 2009;Gao et al., 2012). Therefore, it seems
plausible that such effect might be involved in the Ayahuasca-
induced extinction of conditioned fear memories.
“Stronger” memories seem to be more resistant to
reconsolidation, and they can become labile only if the retrieval
session is prolonged (Besnard et al., 2012). Moreover, the process
of extinction of the fear response coupled to a traumatic memory
is possible within a window of 6 h after reactivation, while the
memory is labile (Schiller et al., 2010). Therefore, the prolonged
biological effects arising from Ayahuasca ingestion (3–6 h) could
represent a beneficial timeframe for the retrieval, reconsolidation
and/or fear extinction of traumatic memories.
HYPOTHESIS: AYAHUASCA
RECONSOLIDATES TRAUMATIC
MEMORIES VIA MODULATING BRAIN
ACTIVITY, NEUROTRANSMISSION AND
EPIGENETICS
Given the available evidence from cellular, pre-clinical and
clinical studies, supported by ample anecdotal evidence, I
hypothesise that Ayahuasca ingestion can be helpful in the
processing and healing of traumatic memories. I postulate that
such effects might be mediated by a multilevel mechanism
involving (a) changes in patterns of brain activity conducive
to memory retrieval, memory reconsolidation and fear
extinction, (b) activation of receptors which trigger anti-
amnesic intracellular signalling pathways conducive to the
retrieval of traumatic memories, (c) changes in neurotransmitter
systems in discrete brain regions which are beneficial to memory
updating and fear extinction, (d) enhancement of synaptic
plasticity and neurogenesis, and (e) involvement of epigenetic
mechanisms, which update the previous emotional association of
the memory via modifying the epigenetic signature and cellular
memory of the neurons that physically store the traumatic
memory. I suggest that these processes result in the memory
being updated, to a less- or even non-traumatic form.
Given that Ayahuasca ingestion (a) hyperactivates brain
areas involved in the retrieval of memories (parahippocampal
gyrus), regulation of emotional processing and perception of
errors (anterior insula), regulation and processing of negative
emotional stimuli (IFG) and emotional arousal (amygdala),
and (b) boosts dopaminergic neurotransmission, an essential
requisite for memory retrieval and reconsolidation, I postulate
that Ayahuasca creates a pattern of brain activity which is
conducive to the recall and/or re-experiencing of traumatic
memories, or memories that have a negative connotation
(Phillips et al., 1998;Ullsperger et al., 2010;Etkin et al., 2011;
Zhu et al., 2012;Tabei, 2015;Urgesi et al., 2016). This process
is assisted by the anti-amnesic effects of SIGMAR1 activation,
which are potentially mediated by enhanced cholinergic, NMDA-
glutamatergic and dopaminergic neurotransmission and might
be involved in the retrieval of repressed memories (Earley et al.,
1991;Maurice et al., 1998;Antonini et al., 2009).
When the traumatic memory is recalled, it enters a labile
state, which allows for the memory to be updated and
reconsolidated and/or for the fear response associated with
the memory to be erased (fear extinction). In line with this
notion, Ayahuasca hyperactivates the subcallosal gyrus, which is
involved in the rehearsing and processing of “sad” autobiographic
memories, while hyperactivating and boosting dopaminergic
neurotransmission in the amygdala; these processes are involved
in fear extinction (Mayberg et al., 1999;Riba et al., 2006;Myers
and Davis, 2007;Palhano-Fontes et al., 2015). These effects
suggest the instauration of a pattern of brain activity which is
conducive to the processing of traumatic memories and to the
extinction of the conditioned fear response associated with such
memories (Mayberg et al., 1999;Myers and Davis, 2007).
SIGMAR1 has been shown to modulate the CB1/NMDA
receptor interaction (Sanchez-Blazquez et al., 2014). Since CB1
receptors are enriched in the amygdala (one of the brain areas
hyperactivated by Ayahuasca), and given that CB1 or NMDA
agonists prevent fear expression during traumatic memory
retrieval, this supports a role for Ayahuasca in the updating and
reconsolidation of traumatic memories by modulating the fear
responses associated with the traumatic memory (McDonald and
Mascagni, 2001;Lee et al., 2017). The hypothesis presented in this
paper is also supported by the fact that each of the main alkaloids
present in Ayahuasca modulate LVGCCs, which are involved
in the extinction of conditioned fear (Splettstoesser et al., 2005;
McKinney et al., 2008;Johannessen et al., 2009;Davis and Bauer,
2012;Gao et al., 2012;Temme and Murphy, 2017).
Moreover, given the neurotrophic and neurogenic effects of
the alkaloids present in Ayahuasca, it cannot be excluded that
these effects too could be involved in the processes of memory
reconsolidation and/or fear extinction, since those mnemonic
processes require increased synaptic plasticity (Fortunato
et al., 2009;Radiske et al., 2015;Morales-Garcia et al., 2017).
Furthermore, Ayahuasca ingestion increases dopaminergic
and decreases GABAergic neurotransmission in the amygdala
(de Castro-Neto et al., 2013). In line with the hypothesis here
presented, the former is involved in fear extinction learning,
while negative regulation of the latter is conducive to anti-
amnesic effects (Barad et al., 2006;Rau et al., 2009). These lines
of evidence support a role for Ayahuasca in the retrieval of
traumatic, repressed memories and in the extinction of the fear
associated with such memories in PTSD and dissociative amnesia
(Barad et al., 2006;de Castro-Neto et al., 2013).
Finally, SIGMAR1 interacts with the epigenetic modulators
HDAC1, 2 and 3, and these proteins are involved in
transcriptional regulation and chromatin remodelling,
representing crucial modulators of memory updating and
reconsolidation in the amygdala (Maddox and Schafe, 2011).
Hence, I hypothesise that DMT-mediated SIGMAR1 activation,
via the recruitment of HDAC and other chromatin remodelling
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
molecules, results in the updating of the traumatic memory. This
occurs by means of epigenetic modifications in the neurons that
previously stored the traumatic memory; these modifications
delete the transcriptional “instructions” to trigger the fear
response that is associated with the memory updating the
memory to become a non-traumatic one.
To the best of the author’s knowledge, no formal study
has investigated the potential of Ayahuasca or its alkaloids in
isolation in the updating of traumatic memories and in fear
extinction processes. However, one study has investigated the
potential of psilocybin in the extinction of fear conditioning.
In that study, mice receiving low doses (but not high doses) of
psilocybin, exhibited a facilitated extinction of the fear response
in a paradigm for hippocampal-dependent trace conditioning
paradigm (Catlow et al., 2013). A mechanistic explanation
for such differences was not investigated in that study. The
authors suggested that, since psilocybin increases dopaminergic
neurotransmission, and since drugs that increase dopamine
availability are beneficial to fear extinction, psilocybin might
be beneficial to fear extinction via enhancing dopaminergic
neurotransmission (Aghajanian and Marek, 1999;Vollenweider
et al., 1999;Vazquez-Borsetti et al., 2009;Catlow et al., 2013).
A similar study investigating the effects of 3,4-methylenedioxy-
methamphetamine (MDMA) on fear extinction in rodents found
that MDMA enhanced fear extinction when administered before
fear extinction learning while increasing BDNF signalling in the
amygdala following extinction learning (Young et al., 2015).
TRANSLATIONAL IMPLICATIONS OF
AYAHUASCA-MEDIATED HEALING OF
CELLULAR MEMORY
Cellular memory is the maintenance of gene expression and
silencing patterns in a cell through the processes of DNA
replication and packaging, which almost never involves changes
in DNA sequence (Turner, 2002;Henikoff and Greally, 2016).
This type of intrinsic DNA-bound memory is crucial during
development and later in life to rule out cellular transformation
(Jacobs and van Lohuizen, 2002). Given the influence of activated
SIGMAR1 on epigenetics processes and chromatin compaction,
it seems possible that DMT and Ayahuasca might modulate
cellular memory (Tsai et al., 2015).
Cellular memory is mediated by proteins and short non-
coding RNAs which, following DNA replication, ensure the
perpetuation of repressed and active transcriptional states in the
offspring. Examples are proteins belonging to the polycomb and
trithorax families, and microRNAs, which are involved in cellular
memory, reprogramming and differentiation by controlling the
expression of hundreds of target genes (Steffen and Ringrose,
2014;Stuwe et al., 2014;Hwang et al., 2017).
Cellular memory seems to be dysregulated in many
conditions, including but not limited to PTSD, cancer, epilepsy,
neurodegenerative and gastrointestinal disorders and gut
microbiome-mediated diseases (Jacobs and van Lohuizen, 2002;
Paul et al., 2015;Zannas et al., 2015;Hwang et al., 2017;Kiese
et al., 2017). Drugs that modulate cellular memory have the
potential to reverse pathological cellular phenotypes mediated by
dysregulated cellular memory. Examples include molecules able
to change the fate of cells with dysregulated cellular memory in
cancer and those able to restore neuron-mediated synaptogenesis
and learning in neurodegeneration (Henikoff and Greally, 2016;
Hwang et al., 2017).
Therefore, given that SIGMAR1 interacts with the
epigenetic machinery, and given that the alkaloids present
in Ayahuasca have neurogenic, neuroplastic, neuroprotective
and immunomodulatory properties, it seems plausible that
these compounds might be useful in diseases such as those of
neurodegenerative and transformative nature (i.e., Alzheimer’s
disease and cancer) (Jacobs and van Lohuizen, 2002;Fortunato
et al., 2009;Tsai et al., 2015;Hwang et al., 2017;Morales-Garcia
et al., 2017). This represents a tentative suggestion and further
studies should investigate this possibility.
FUTURE DIRECTIONS
Further studies are required to determine if the hypothesis
here presented is indeed confirmed by experimental evidence.
If the theory here postulated proves to be true, Ayahuasca
could represent the first pharmacological therapy which targets
traumatic memories in PTSD and dissociative amnesia.
Double-blind, placebo-controlled studies are warranted to
determine the efficacy of Ayahuasca treatment in PTSD and
dissociative amnesia. Brain activity in PTSD patients could be
assessed via imaging techniques before and during Ayahuasca
ingestion, to assess potential regional changes in activity
which could indicate improvements of PTSD symptoms. PTSD
and dissociative amnesia patients could be asked to rehearse
traumatic memory during Ayahuasca ingestion to determine
if this could indeed represent a helpful approach in relieving
the traumatic connotation of those memories. Moreover, follow
up studies could investigate if the abnormal patterns of brain
activation in PTSD and dissociative amnesia patients can be
altered by Ayahuasca ingestion and if such alterations are stable
over time (Lanius et al., 2001;Brand et al., 2009). Particular
care should be taken in these settings, because the retrieval
of repressed traumatic memories could inadvertently result
in re-traumatization (Nielson and Megler, 2014). Therefore,
psychological support should be available before, during and after
such trials, to ensure adequate care for the well-being of the
participants. Nevertheless, because fear extinction is generally
considered to be susceptible to change rather than permanent, it
is important to follow-up PTSD patients that undergo Ayahuasca
therapy for the healing of traumatic memories; there exists the
possibility that the fear memory might be reinstated,renewed, or
spontaneously recovered (Myers and Davis, 2007).
Pre-clinical studies could investigate the potential of
Ayahuasca treatment through paradigms of fear extinction. Such
paradigms include contextual fear conditioning and cued fear
conditioning. Contextual fear conditioning involves (a) placing
the animal in a novel environment, (b) presenting them with
an aversive stimulus, (c) removing the animal, (d) subsequently
returning the animal to the same environment and quantifying
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Inserra Ayahuasca, Epigenetics and Traumatic Memories
“freezing” behaviour without presenting the aversive stimulus.
Cued fear conditioning paradigms are similar to contextual ones
with the difference that the aversive stimulus is preceded by a
contextual cue (i.e., a sound or a light). When the animals are
returned to the testing environment, the cue is presented but
the aversive stimulus is not and freezing behaviour is quantified.
The freezing behaviour derives from the fact that the animal has
learned that the specific environment is unpleasant and being
placed in such environment will likely result in the aversive
stimulus being re-presented (Curzon et al., 2009). If Ayahuasca-
treated animals present decreased freezing behaviour in those
paradigms, this might suggest that indeed Ayahuasca is beneficial
in the extinction of fear conditioning, as it was previously
demonstrated with 3,4-methylenedioxymethamphetamine and
low-dose psilocybin (Catlow et al., 2013;Young et al.,
2015).
To the best of the author’s knowledge, no study has
investigated the effects of Ayahuasca or other psychedelic
compounds on processes involving epigenetic regulation of
gene expression. However, studies investigating gene expression
changes stemming from LSD and proteomic changes induced by
the DMT analogue 5-MeO-DMT have been reported (Nichols
and Sanders-Bush, 2002;Nichols et al., 2003;Dakic et al.,
2017). An early investigation into long-term Ayahuasca drinkers
suggested that long-term Ayahuasca consumption increases 5HT
binding sites in platelets (Callaway et al., 1994). Although this
study did not suggest an involvement of epigenetic processes in
the changes observed, it cannot be excluded that the differences
observed might be mediated by changes in epigenetic regulation
of the 5HT receptor gene or neighbouring regulatory DNA
regions.
Further studies should investigate the possibility that
Ayahuasca affects epigenetic processes and epigenetic markers
thereof (such as histone acetylation, methylation and
phosphorylation and DNA methylation). Such studies could
involve either epigenome-wide interrogation or analyses at
specific DNA (or histone) sites of interest in specific pathologies,
such as PTSD, depression, and autoimmune disorders.
Finally, in order to investigate if Ayahuasca has effects
on cellular memory mechanisms, studies could be performed
analysing the expression levels and epigenetic signatures of
proteins involved in cellular memory regulation, such as those
belonging to the polycomb and trithorax families, which,
respectively, sustain repressed and active transcriptional states
of hundreds of genes (Steffen and Ringrose, 2014). If Ayahuasca
indeed affects the transcription, translation, post-translational
modification or epigenetic regulation of those proteins, it
could mean that Ayahuasca has an effect on cellular memory
processes. If this proves to be true, it could be that the
beneficial effects observed and reported in several diseases and
conditions following Ayahuasca ingestion might be mediated
by its SIGMAR1-mediated effects on those master regulatory
mechanisms (Frecska et al., 2016;Henikoff and Greally, 2016).
CONCLUSION
In this work a mechanism that might explain the healing
effects of Ayahuasca ingestion on traumatic memories has
been hypothesised. I have highlighted the effects of Ayahuasca
on the modulation of brain activity, neurotransmission, and
neurogenesis, which are consistent with the reported effects of
Ayahuasca on the retrieval of traumatic memories. Moreover, I
have explored the effects of DMT-mediated SIGMAR1 activation
on the modulation of anti-amnesic pathways and on the
regulation of epigenetic processes, which might be involved in
the healing of traumatic memories via memory reconsolidation
and/or fear extinction. Moreover, given the effects of SIGMAR1
on epigenetic processes, the author suggests that Ayahuasca
might be useful in the treatment of disorders in which the cellular
memory is dysregulated, such as cancer and neurodegenerative
and autoimmune diseases. Further efficacy studies should aim at
optimising therapeutic Ayahuasca doses while investigating the
hypothesis here presented in randomised controlled trials with
PTSD and dissociative amnesia patients and/or in pre-clinical
models of PTSD, memory reconsolidation and fear extinction.
Clinical trials should be coupled to preliminary psychiatric
assessments, ongoing psychological treatment and integration
to avoid negative psychological outcomes, such as fear renewal,
fear reinstatement or psychosis. If the hypothesis here presented
proves to be true, it might help guide evidence-based informed
policy decisions. Such decisions could help alter the legal status
of Ayahuasca and lead toward the utilisation of Ayahuasca in
psychiatry and other fields of medicine.
AUTHOR CONTRIBUTIONS
The author confirms being the sole contributor of this work and
approved it for publication.
ACKNOWLEDGMENTS
The author acknowledges the contribution of Dr. Dennis
Schiaroli to the development of the hypothesis presented
here and the invaluable contribution of Dr. Sarah Pearce to
proofreading and editing this manuscript.
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conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
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Frontiers in Pharmacology | www.frontiersin.org 13 April 2018 | Volume 9 | Article 330
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