Assessing the Psychedelic "After-Glow" in Ayahuasca Users: Post-Acute Neurometabolic and Functional Connectivity Changes Are Associated with Enhanced Mindfulness Capacities [Formatted Article]

Abstract

Background: Ayahuasca is a plant tea containing the psychedelic 5-HT2A agonist N,N-dimethyltryptamine and harmala monoamine-oxidase inhibitors. Acute administration leads to neurophysiological modifications in brain regions of the default mode network, purportedly through a glutamatergic mechanism. Post-acutely, ayahuasca potentiates mindfulness capacities in volunteers and induces rapid and sustained antidepressant effects in treatment-resistant patients. However, the mechanisms underlying these fast and maintained effects are poorly understood. Here, we investigated in an open-label
uncontrolled study in 16 healthy volunteers ayahuasca-induced post-acute neurometabolic and connectivity modifications and their association with mindfulness measures.
Methods: Using 1H-magnetic resonance spectroscopy and functional connectivity, we compared baseline and post-acute neurometabolites and seed-to-voxel connectivity in the posterior and anterior cingulate cortex after a single ayahuasca dose.
Results: Magnetic resonance spectroscopy showed post-acute reductions in glutamate+glutamine, creatine, and N-acetylaspartate+N-acetylaspartylglutamate in the posterior cingulate cortex. Connectivity was increased between the
posterior cingulate cortex and the anterior cingulate cortex, and between the anterior cingulate cortex and limbic structures in the right medial temporal lobe. Glutamate+glutamine reductions correlated with increases in the “nonjudging” subscale of the Five Facets Mindfulness Questionnaire. Increased anterior cingulate cortex-medial temporal lobe connectivity correlated with increased scores on the self-compassion questionnaire. Post-acute neural changes predicted sustained elevations in nonjudging 2 months later.
Conclusions: These results support the involvement of glutamate neurotransmission in the effects of psychedelics in humans. They further suggest that neurometabolic changes in the posterior cingulate cortex, a key region within the default mode network, and increased connectivity between the anterior cingulate cortex and medial temporal lobe structures involved in emotion and memory potentially underlie the post-acute psychological effects of ayahuasca.

Full text

Received: October 4, 2016; Revised: May 10, 2017; Accepted: May 17, 2017
© The Author 2017. Published by Oxford University Press on behalf of CINP.
International Journal of Neuropsychopharmacology (2017) 00(00): 1–14
doi:10.1093/ijnp/pyx036
Advance Access Publication: June 13, 2017
Regular Research Article
1
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  
Assessing the Psychedelic “After-Glow” in Ayahuasca
Users: Post-Acute Neurometabolic and Functional
Connectivity Changes Are Associated with Enhanced
Mindfulness Capacities
Frederic Sampedro, MSc; Mario de la Fuente Revenga, PhD;
Marta Valle, PhD; Natalia Roberto, MSc; Elisabet Domínguez-Clavé, MSc;
Matilde Elices, PhD; Luís Eduardo Luna, PhD; José Alexandre S. Crippa, PhD;
Jaime E. C. Hallak, PhD; Draulio B. de Araujo, PhD; Pablo Friedlander, MSc;
Steven A. Barker, PhD; Enrique Álvarez, PhD; Joaquim Soler, PhD;
Juan C. Pascual, PhD; Amanda Feilding, MSc; Jordi Riba, PhD
School of Medicine, Autonomous University of Barcelona, Barcelona, Spain (Mr Sampedro); Human
Neuropsychopharmacology Research Group, Sant Pau Institute of Biomedical Research, Barcelona, Spain
(Dr de la Fuente Revenga, Ms Roberto, and Dr Riba); Pharmacokinetic and Pharmacodynamic Modelling and
Simulation, Sant Pau Institute of Biomedical Research, Barcelona, Spain (Dr Valle); Centre d’Investigació de
Medicaments, Servei de Farmacologia Clínica, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain (Drs
Valle and Riba); Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Spain (Drs Valle,
Elices, Álvarez, Soler, Pascual, and Riba); Department of Pharmacology and Therapeutics, Autonomous
University of Barcelona, Barcelona, Spain (Dr Valle); Department of Psychiatry, Hospital de la Santa Creu i
Sant Pau, Barcelona, Spain (Ms Domínguez-Clavé and Drs Elices, Álvarez, Soler, and Pascual); Department
of Psychiatry and Forensic Medicine, School of Medicine, Universitat Autònoma de Barcelona, Barcelona,
Spain (Ms Domínguez-Clavé and Drs Elices, Álvarez, and Pascual); Research Center for the Study of
Psychointegrator Plants, Visionary Art and Consciousness, Florianópolis, Santa Catarina, Brazil (Dr Luna);
Department of Neuroscience and Behavior, Medical School of Ribeirão Preto, University of São Paulo, São
Paulo, Brazil and National Institute for Translational Medicine, Ribeirão Preto, Brazil (Drs Crippa and Hallak);
Brain Institute/Hospital Universitario Onofre Lopes, Natal, Brazil (Dr de Araujo); The Beckley Foundation,
Beckley Park, Oxford, United Kingdom (Mr Friedlander and Mrs Feilding); Department of Comparative
Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive at
River Road, Baton Rouge, Louisiana (Dr Barker); Department of Clinical and Health Psychology, School of
Psychology, Autonomous University of Barcelona, Barcelona, Spain (Dr Soler).
Correspondence: Jordi Riba, PhD, Human Neuropsychopharmacology Research Group, IIB-Sant Pau.C/Sant Antoni María Claret 167, 08025, Barcelona,
Spain (jriba@santpau.cat).

2 | International Journal of Neuropsychopharmacology, 2017
Abstract
Background: Ayahuasca is a plant tea containing the psychedelic 5-HT2A agonist N,N-dimethyltryptamine and harmala
monoamine-oxidase inhibitors. Acute administration leads to neurophysiological modications in brain regions of the
default mode network, purportedly through a glutamatergic mechanism. Post-acutely, ayahuasca potentiates mindfulness
capacities in volunteers and induces rapid and sustained antidepressant effects in treatment-resistant patients. However,
the mechanisms underlying these fast and maintained effects are poorly understood. Here, we investigated in an open-label
uncontrolled study in 16 healthy volunteers ayahuasca-induced post-acute neurometabolic and connectivity modications
and their association with mindfulness measures.
Methods: Using 1H-magnetic resonance spectroscopy and functional connectivity, we compared baseline and post-acute
neurometabolites and seed-to-voxel connectivity in the posterior and anterior cingulate cortex after a single ayahuasca dose.
Results: Magnetic resonance spectroscopy showed post-acute reductions in glutamate+glutamine, creatine, and
N-acetylaspartate+N-acetylaspartylglutamate in the posterior cingulate cortex. Connectivity was increased between the
posterior cingulate cortex and the anterior cingulate cortex, and between the anterior cingulate cortex and limbic structures
in the right medial temporal lobe. Glutamate+glutamine reductions correlated with increases in the “nonjudging” subscale of
the Five Facets Mindfulness Questionnaire. Increased anterior cingulate cortex-medial temporal lobe connectivity correlated
with increased scores on the self-compassion questionnaire. Post-acute neural changes predicted sustained elevations in
nonjudging 2months later.
Conclusions: These results support the involvement of glutamate neurotransmission in the effects of psychedelics in humans.
They further suggest that neurometabolic changes in the posterior cingulate cortex, a key region within the default mode
network, and increased connectivity between the anterior cingulate cortex and medial temporal lobe structures involved in
emotion and memory potentially underlie the post-acute psychological effects of ayahuasca.
Keywords: ayahuasca, psychedelic after-effects, magnetic resonance imaging, mindfulness, human
Introduction
Psychedelics are the object of renewed interest as potential
therapeutic tools in psychiatry (Sessa, 2005; Vollenweider and
Kometer, 2010; Grob etal., 2011). Among these substances is
ayahuasca, an Amazonian psychoactive beverage typically
obtained from the plants Banisteriopsis caapi and Psychotria
viridis. The ayahuasca tea contains a combination of the psy-
chedelic indole N,N-dimethyltryptamine (DMT) from P. viridis,
and β-carboline (harmala) alkaloids with monoamine-oxidase-
inhibiting properties from B. caapi (McKenna etal., 1984). DMT is
a classical serotonergic psychedelic that stimulates the 5-HT2A
receptor (Carbonaro etal., 2015). Agonism at this level by DMT
and other psychedelics recruits glutamatergic neurotrans-
mission (Carbonaro et al., 2015), induces neuronal excitatory
effects (Kłodzinska etal., 2002), and increases glutamate release
(Scruggs et al., 2003; Muschamp etal., 2004). However, unlike
psilocybin or LSD, DMT is orally inactive due to extensive deg-
radation by monoamine-oxidase (Riba etal., 2015). Interestingly,
the presence of β-carbolines in the ayahuasca tea inhibits DMT
metabolism, allowing for psychoactive effects after oral intake
(Riba et al., 2003). Additionally, DMT shows neuroprotective
effects mediated through interaction with the sigma-1 receptor
(Szabo etal., 2016).
Interest in the general pharmacology and therapeutic
properties of ayahuasca has greatly increased in recent years
(Domínguez-Clavé et al., 2016). Acute administration to healthy
volunteers induces a transient introspective state character-
ized by dream-like visions with eyes closed, recollection of per-
sonal memories, and intense emotion (Riba et al., 2001, 2003).
Neurophysiological studies show a suppression of the inhibitory
alpha rhythm in the occipital and parietal cortex, including the
posterior cingulate cortex (PCC) (Schenberg et al., 2015; Valle et
al., 2016), a key node of the default mode network (DMN) with
a prominent role in self-reection and consciousness (Vogt and
Laureys, 2005). Furthermore, decreased activity for the most
part of the DMN and reduced connectivity of the PCC have been
observed during the acute effects of ayahuasca (Palhano-Fontes
et al., 2015). On the other hand, radiotracer data shows increased
blood ow in the anterior cingulate cortex (ACC) and in the
insula, amygdala, and hippocampus, brain areas involved in cog-
nitive control, emotion, and memory (Riba et al., 2006). Recently,
Signicance Statement
Psychedelics are intriguing drugs that induce transient but intense modications in perception, emotion, and cognition. Despite
human use dating back millennia, their mechanism of action is still poorly understood. Recent research in patients has shown
that ayahuasca, a plant psychedelic used traditionally in the Amazon for religious and medicinal purposes, exerts rapid and
potent antidepressant effects in treatment-resistant patients. These benecial effects are observed after a single dose and
intriguingly persist for weeks, long after the immediate acute effects have disappeared. Here we demonstrate using 2 neuroim-
aging techniques that during the post-acute phase, that is within 24 hours after intake, ayahuasca leads to metabolic and con-
nectivity changes in the brain. These changes are associated with enhanced psychological capacities that are benecial in the
therapeutic context. These ndings provide a biological basis for the post-acute or “after-glow” stage of psychedelic effects, and
contribute to elucidate the therapeutic mechanisms of these substances.

Sampedro et al. | 3
ayahuasca was found to induce post-acute increases in “decen-
tering” ability, that is, the capacity to observe one’s thoughts
and emotions in a detached manner, and to reduce automatic
negative judgmental attitudes and inner reactivity (Soler et al.,
2016). It thus enhanced a series of “mindfulness” capacities tra-
ditionally cultivated by meditation schools and that are known
to be impaired in many forms of psychopathology (Soler et al.,
2014b). In a subsequent review, the authors postulated that the
mindfulness-enhancing properties of ayahuasca could be used
in a therapeutic context to facilitate emotional reprocessing in
patients with depression, addiction, and personality disorders
(Domínguez-Clavé et al., 2016).
In line with the above, 2 recent open-label uncontrolled clini-
cal studies have found rapid reductions in psychopathology after
administration of single ayahuasca doses to depressed patients.
Remarkably, antidepressant effects appeared within hours after
dosing and were maintained for 3 weeks (Osório et al., 2015;
Sanches etal., 2016). Analogous improvements have also been
observed after psilocybin (Carhart-Harris et al., 2016b). In all
cases, sustained antidepressant effects were in sharp contrast
with the much shorter duration of the acute psychedelic state.
This disparity of time courses suggests that 5-HT2A stimulation
leads to persistent effects beyond the time frame of the acute
inebriation. In fact, early researchers coined the term “after-glow”
to designate a positive post-acute phase of psychedelic drug
effects characterized by elevated mood and openness (Pahnke
etal., 1970). This post-acute phase has been reported to extend
between 6 and 8 weeks after the acute psychedelic effects and
characterized as a window of opportunity for therapeutic inter-
vention (Halpern, 1996; Winkelman, 2014). Recent clinical studies
have described persisting positive after-effects following psilocy-
bin and LSD (Grifths etal., 2008; Lebedev etal., 2016).
Here, we investigated the neural correlates of the psychedelic
“after-glow” in healthy volunteers to improve our understanding
of the neural mechanisms potentially involved in the rapid and
sustained therapeutic effects observed in patients. Using 2 differ-
ent neuroimaging techniques, we assessed post-acute neuromet-
abolic and connectivity changes induced by ayahuasca in healthy
volunteers. Our study focused on the PCC and the ACC, 2 brain
regions that have consistently been identied as targets of psych-
edelics (Carhart-Harris etal., 2012, 2016a; Palhano-Fontes etal.,
2015; Valle etal., 2016). We postulated 3 hypotheses. First, that
excitatory effects in PCC and ACC during acute ayahuasca would
lead to measurable decreases of glutamate-glutamine and energy
metabolites in the post-acute phase. Second, that neurometabolic
changes would parallel enhanced connectivity between the PCC
and the ACC by decreasing the normal pattern of anticorrelated
brain activity existing between these brain regions. Third, that the
measured neurometabolic and connectivity changes would cor-
relate with increased mindfulness capacities in the immediate
post-acute phase and at follow-up 2months later.
Materials and Methods
Ethics
The study was approved by the Ethics Committee at Hospital
de Sant Pau (Barcelona, Spain). All participants provided written
informed consent to participate in the study.
Participants
The study included 16 healthy volunteers (6 females) with
prior experience with ayahuasca. Exclusion criteria included a
current or past history of psychiatric disorders, alcohol or other
substance dependence, evidence of signicant illness, and preg-
nancy. Detailed information on the recruitment procedure and
the characteristics of study participants is provided in the sup-
plementary le.
Drug
A single ayahuasca batch was used in the study. All participants
ingested ayahuasca from this single batch, so alkaloid concen-
trations were the same for all subjects. The ayahuasca used
was analyzed and the total volume ingested by each participant
was recorded. Alkaloid concentrations were determined using
a previously described method implementing liquid chroma-
tography-electrospray ionization-tandem mass spectrometry
(McIlhenny etal., 2009). Based on the analysis, the ayahuasca
used in the session contained 0.3 mg/mL DMT, 0.86 mg/mL
harmine, 0.17mg/mL tetrahydroharmine, and 0.04mg/mL har-
maline. Participants took a mean ± SD volume of ayahuasca
during the session of 148±29mL. Thus, the mean ± SD alkaloid
amounts ingested were: 45±9mg DMT, 126±25mg harmine,
26±5mg tetrahydroharmine, and 5± 1mg harmaline. For a
70-kg person, the dose would be equivalent to 0.64mg DMT/
kg, within the range found to be psychoactive in laboratory
studies by our group (Riba etal., 2001, 2003). In the present
study, we conducted post- vs. pre-ayahuasca comparisons of
the dependent variables. No placebo was used in the present
investigation.
StudyDesign
Participants were assessed twice in an MRI scanner. The rst
measurement was conducted in the 24h prior to an ayahuasca
session. The baseline assessment included the acquisition of
anatomical high-resolution T1 images, 1H-MR spectroscopy data,
and resting-state BOLD activity. Participants also completed 3
mindfulness questionnaires before the rst scan. The post-acute
assessment was conducted in the 24 hours after the ayahuasca
session. It involved again obtaining structural T1 images, 1H-MR
spectroscopy, resting-state BOLD data, and the same mindful-
ness questionnaires. The second MRI assessment was conducted
for each participant at approximately the same time of the day
as the rst assessment, with a variation of about 30 minutes.
The meals ingested by participants were equivalent on each
assessment day. Participants were asked to ll out the mindful-
ness questionnaires indicating how they felt during the post-
acute stage. Additionally, participants were asked to ll out the
Hallucinogen Rating Scale, a subjective effects questionnaire, to
indicate retrospectively how they had felt during the acute psy-
chedelic phase. Two months later, a follow-up was conducted.
Participants were requested to ll out again the mindfulness
questionnaires they had been administered at baseline and in
the post-acute phase.
Image Acquisition and Analysis
Images were acquired on a 3T Siemens Magneto TIM Trio scan-
ner using a 32-channel phased-array head coil. The assessment
protocol involved obtaining: (1) high resolution T1 structural
images; (2) spectroscopy data in 3 volumes of interest (VOIs);
and (3) resting state BOLD data for functional connectivity anal-
ysis. Each measurement is described briey below and in depth
in the supplementary information.

4 | International Journal of Neuropsychopharmacology, 2017
MR Spectroscopy: Neurometabolite Assessment
Single voxel spectra were obtained from 3 VOIs placed in the
PCC, ACC, and cerebellum, as shown in Figure1 (top panel) for
one of the participants.
Metabolite concentrations were quantied for total cre-
atine plus phosphocreatine (Cr), total choline containing
compounds (glycerophosphocholine plus phosphocholine;
Cho), inositol (Ins), combined glutamate plus glutamine (Glx),
and total N-acetylaspartate plus N-acetylaspartylglutamate
(NAA-NAAG). We used absolute metabolite levels, since ratios
with creatine have been found to be a potential confounding
factor and the source of increased variability (Li etal., 2003).
See the supplementary materials for further details on VOI
placement, quality assurance of measurements, and tissue
corrections.
The obtained millimolar (mM) metabolite concentrations
were compared at each VOI using repeated-measures ANOVA
with ayahuasca intake (post- vs. pre-ayahuasca) and metabolite
type as factors (Cr, Cho, Ins, Glx, and NAA-NAAG). When a sig-
nicant effect of ayahuasca intake or the interaction ayahuasca
intake by metabolite type was found, pair-wise comparisons
were conducted using Student’s t tests. Results were considered
signicant for P < .05. Statistical results are presented in tabu-
lated form showing uncorrected P values and values corrected
for multiple comparisons using the false discovery rate (FDR).
Effect size is provided using Cohen’s d (see supplementary le
for details).
Resting State BOLD Signal Acquisition and Functional
Connectivity Analysis
Resting state functional images were collected using a 7-min-
ute sequence during which participants stayed awake with
eyes closed. The functional connectivity analysis was con-
ducted using the CONN software (Whiteld-Gabrieli and Nieto-
Castanon, 2012). The analysis included several preprocessing
steps (see supplementary le), followed by a rst-level statis-
tical analysis calculating seed-to-voxel connectivity maps for
each subject and condition (pre-ayahuasca and post-acute).
Individual z-maps were used in the subsequent random-effects
second-level analysis to assess drug-induced changes in con-
nectivity (post- vs. pre-ayahuasca intake) using paired-samples
Student’s ttests.
Post-acute ayahuasca-induced changes in seed-to-voxel
connectivity were assessed using 3 spherical seeds with 10-mm
radius. The rst was placed in the PCC at MNI coordinates x=0,
y=-56, z=28, based on previously published data (Whiteld-
Gabrieli and Nieto-Castanon, 2012). The 2 additional seeds were
placed in the ACC. The rst seed was placed in the dorsal ACC
(dACC) at MNI coordinates x=5, y=14, z=42, over BA 32, a sub-
region of the ACC involved in executive top-down control, and
positive task activation (Kelly etal., 2009). Asecond more ros-
tral seed (here denoted as “superior rostral ACC” or srACC) was
placed at MNI coordinates x=0, y=15, z=30) in BA 24 (Dixon
etal., 2014). This subregion of the ACC has extensive connectiv-
ity with limbic structure in the medial temporal lobe (Vogt, BA,
Figure1. Location of the 1H-MRS voxels (top) and a representative spectrum (bottom). The top panel shows sagittal views of voxel placement over the anterior cingulate
(left), posterior cingulate (center), and cerebellum (right). The dimensions of the respective voxels were: 25 x 25 x 25mm3 in the anterior cingulate cortex (ACC) and
posterior cingulate cortex (PCC) and 20 x 40 x 20mm3 in the cerebellum.

Sampedro et al. | 5
2009) and has been found to be hypoactive in depressed patients
(Fales etal., 2008).
The signicance maps obtained in the second-level analy-
sis were corrected for multiple comparisons at the cluster level
using the family wise error correction (FWE). Signicance level
was set at FWE < 0.05 for a spatial extension of at least 20 con-
tinuous voxels. Further details on image acquisition and analy-
sis can be found in the supplementary le.
Mindfulness Measures
Assessment Instruments and Statistical Analysis
Scores on mindfulness facets were assessed before and after
ayahuasca intake using the Spanish versions of the follow-
ing instruments: (1) the Five Facet Mindfulness Questionnaire
(FFMQ) (Cebolla etal., 2012); (2) the Experiences Questionnaire
(EQ) (Soler etal., 2014b); and (3) the short version of the Self-
Compassion (SC) questionnaire (Garcia-Campayo etal., 2014).
Additionally, the Mindsens Composite Index was calculated
with items from the FFMQ and EQ. This index is most sen-
sitive to meditation practice and accurately discriminates
between meditators and nonmeditators (Soler etal., 2014a). The
Mindsens index was used to assess to what extent the changes
induced by ayahuasca were comparable with those induced by
meditation practice.
Scores on mindfulness facets (FFMQ, EQ, and SC) were
obtained before and after ayahuasca intake. Baseline assess-
ment was conducted in the 24 hours prior to ayahuasca intake,
and the second was conducted within the 24 hours after intake,
before going into the MRI scanner. Participants were contacted
by email 2months after participation to conduct a follow-up
assessment. Fourteen of the 16 participants responded and
returned the completed questionnaires. This follow-up analysis
had consequently less power to detect changes and should be
thus considered exploratory. In all instances, participants were
asked to ll out the questionnaires indicating how they felt at
the moment of completion. Further details on the instruments
used are provided in the supplementaryle.
Ayahuasca-induced changes in mindfulness measures were
assessed using paired-samples t tests. Scores at follow-up were
compared with pre-ayahuasca values. Results were considered
signicant for P < .05. Statistical results are presented visually as
bar graphs and in tabulated form (supplementary material). The
supplementary table shows uncorrected P values and values
corrected for multiple comparisons using the FDR.
Acute Subjective Effects
Assessment Instruments and Statistical Analysis
To establish that participants had experienced psychoactive
effects during the acute phase, the intensity of the psychedelic
effects during the acute inebriation were retrospectively assessed
using a Spanish version of the Hallucinogen Rating Scale (HRS).
The HRS was administered only once, in the course of the post-
ayahuasca assessment, before the MRI scan. Participants were
requested to ll out the questionnaire indicating how they had
felt during the acute effects of ayahuasca.
To statistically verify that the dose ingested was indeed psy-
choactive, scores obtained in the 6 HRS subscales (see supplemen-
tary materials) were compared with scores obtained previously
in a laboratory study from a sample of 12 healthy volunteers
who received a placebo and an ayahuasca dose equivalent to
0.75 mg DMT/kg body weight (Valle et al., 2016). The statisti-
cal comparison was carried out using independent-samples
Student’s t tests. Results were considered signicant for P < .05.
Results are shown in a gure with signicance symbols denoting
P values after multiple comparisons correction using the FDR.
Exploratory Correlation Analysis
Correlation analyses were conducted to explore potential asso-
ciations between neurometabolic and functional connectivity
changes on the one hand and scores on subjective effects meas-
ures and mindfulness questionnaires on the other. In all calcula-
tions, difference values (post- minus pre-ayahuasca) were used.
For connectivity data, the difference in z-values (post- minus
pre-ayahuasca) was calculated for clusters showing ayahuasca-
induced signicant changes in connectivity in the paired-sam-
ples comparison between normalized statistical maps (post- vs.
pre-ayahuasca). Correlations with mindfulness measures at
follow-up were calculated using the difference values between
follow-up scores and pre-ayahuasca values. Correlations were
considered signicant for P < .05. Given the exploratory nature
of this analysis, we did not implement corrections for multiple
comparisons, and results should be interpreted with caution.
Results
All 16 participants completed the baseline and post-acute
assessments. There were no drop-outs in thestudy.
MR Spectroscopy: Neurometabolite Assessment
Average metabolite concentrations in the baseline and post-
acute assessments in the 3 VOIs examined are shown in Table1.
Data from several participants were below the signal-to-noise
threshold either in the pre- or post-ayahuasca assessment and
had to be excluded from further analysis. Usable data for Glx
assessment in the PCC were obtained from 12 participants, 13
for the ACC, and 11 for the cerebellum. Inositol in the PCC could
be adequately measured in 13 participants. All other metabo-
lites could be quantied in the PCC, ACC, and cerebellum in 14
participants.
In the PCC VOI, the 2-factor repeated-measures ANOVA
showed a signicant effect of metabolite type [F(4,44) = 761,
P < .001], a trend for ayahuasca intake [F(1,12) = 3.88, P = .075], and
signicant interaction between ayahuasca intake and metabo-
lite type [F(4,44) = 4.11, P < .023]. As shown in Table1, the pair-wise
comparisons showed signicant decreases in Cr and NAA-NAAG
levels in the post-intake assessment. Glx levels were signi-
cantly decreased in the initial t test (P = .041), but this effect was
marginally signicant following the FDR correction (P = .068). Ins
and Cho concentrations remained unchanged.
In the ACC VOI, only an effect of metabolite type was
observed [F(4,48) = 997, P < .001], but not effect of ayahuasca intake
[F(1,12) = 0.32, P = .860] or the interaction [F(4,48) = 0.55, P = .606].
In the cerebellum VOI, the ANOVA yielded a signicant effect
of metabolite type [F(4,44) = 321, P < .001], but no effects of aya-
huasca intake [F(1,11) = 1.44, P = .255] or the interaction between
intake and metabolite type [F(4,44) = 0.54, P = .632]. Mean metabo-
lite concentrations at baseline assessment and in the post-acute
phase for these 3 VOIs are also shown in Table1.
Functional Connectivity Assessment
Usable pre-ayahuasca and post-acute resting-state functional
connectivity scans were obtained from all 16 participants. No
subjects had to be eliminated due to excessive movement (see
the supplementary information le for further details). Figure2

6 | International Journal of Neuropsychopharmacology, 2017
shows brain maps corresponding to the analysis of functional
connectivity between the PCC seed (0, -56, 28)and the rest of
the brain. The top panels display the results of the rst-level
statistical analysis separately for the pre-ayahuasca and the
post-acute assessments. The bottom panels display the results
of the second-level comparison between post-acute vs. pre-aya-
huasca correlation maps. The statistical maps are shown cor-
rected for multiple comparisons at the cluster level (FWE P < .05).
Table1. Neurometabolite Levels at Baseline and in the 24 Hours after Ayahuasca Intake for the 3 Examined Regions of Interest
Brain Region and Metabolite Baseline Post-Ayahuasca n df t Value P Value P FDR Cohen’ d
PCC
Inositol 8.26 (1.06) 8.32 (0.95) 13 12 -0.24 0.817 0.817 –
Glx 6.60 (0.64) 6.25 (0.57) 12 11 2.31 0.041** 0.068* 0.67
Cr 8.88 (0.50) 8.61 (0.46) 14 13 3.03 0.010** 0.043** 0.81
Cho 1.79 (0.19) 1.77 (0.18) 14 13 0.83 0.421 0.526 –
NAA-NAAG 12.83 (0.70) 12.03 (0.93) 14 13 2.74 0.017** 0.043** 0.73
ACC
Inositol 8.75 (0.82) 8.57 (0.79) 14 – – – – –
Glx 5.38 (0.39) 5.51 (0.50) 13 – – – – –
Cr 8.39 (0.40) 8.40 (0.44) 14 – – – – –
Cho 2.22 (0.20) 2.20 (0.20) 14 – – – – –
NAA-NAAG 11.20 (0.41) 11.22 (0.36) 14 – – – – –
Cerebellum
Inositol 10.67 (2.19) 10.05 (1.51) 14 – – – – –
Glx 6.79 (0.65) 6.76 (0.75) 12 – – – – –
Cr 13.58 (1.73) 13.19 (1.28) 14 – – – – –
Cho 3.38 (0.53) 3.32 (0.36) 14 – – – – –
NAA-NAAG 13.02 (1.80) 12.98 (0.94) 14 – – – – –
Abbreviations: ACC, anterior cingulate cortex; Cho, glycerophosphocholine+phosphocholine; Cr, creatine+phosphocreatine; Glx, glutamate+glutamine; NAA-NAAG,
N-acetylaspartate+N-acetylaspartylglutamate; PCC, posterior cingulate cortex.
Pair-wise comparisons between baseline and post-acute values were carried out for the PCC only, based on results from the ANOVA, which
were signicant only for this region. Comparisons were carried out using paired-samples Student’s t tests. Values are expressed as mean (SD)
in millimolar concentration units. *P < .01; **P < .05; P FDR, FDR corrected P value.
Figure2. Seed-to-voxel connectivity maps between the posterior cingulate cortex (PCC) seed (green circle) at MNI coordinates x=0, y=-56, z=28, and the rest of the
brain. The top panels show statistically signicant positive (hot colors) and negative (cold colors) correlations in the pre-ayahuasca and post-acute assessments. The
bottom panels show the results of the second-level random effects analysis (post-acute vs. pre-intake). Only signicant increases in connectivity were found, located
in 2 main clusters: the anterior cingulate cortex (ACC) (left brain map) and the visual cortex (right brain map). In all statistical maps results are shown corrected for
multiple comparisons at the cluster level (FWE < 0.05, z > 2.5, 20 contiguous voxels).

Sampedro et al. | 7
Uncorrected maps can be found in the supplementary informa-
tion le (supplementary Figure1)
As shown in the upper section of Figure2 and the supple-
mentary le, prior to ayahuasca intake the BOLD time series
in the PCC seed showed a pattern of positive correlations with
brain regions known to participate in the DMN (Raichle etal.,
2001). On the other hand, the PCC seed showed negative cor-
relations with the ACC and other regions participating in the
task-positive networks (TPNs) (Fox et al., 2005). In the post-
acute phase, the negative correlation with the ACC was strongly
reduced, suggesting a decrease in the orthogonality of BOLD
activity between the PCC and theACC.
The second-level random effects analysis conrmed the
orthogonality decreases seen in the post-acute assessment
maps. Brain areas demonstrating statistically signicant
changes in PCC seed-to-voxel connectivity are shown in the
lower section of Figure 2 and are listed in Table 2. A cluster
of signicantly increased connectivity (reduced anticorrela-
tion) was found in the ACC. Alarge signicant cluster was also
found over visual areas in the occipital lobe, where connectivity
changed from negative to positive (see supplementary Figure1).
Additional clusters of increased connectivity were found in the
pre- and post-central gyri and in the superior temporal gyrus
and the insula. No areas of functional connectivity decrease
were found in the second-level analysis.
Figure3 shows the results of the second-level random effects
statistical comparison between post-acute vs. pre-intake seed-
to-voxel connectivity for the dACC seed (dorsal ACC, x=5, y=14,
z = 42). Uncorrected maps for the rst-level and second-level
analyses can be found in supplementary Figure2.
Signicant connectivity increases were seen between the
seed and voxels in the medial parietal cortex corresponding
to the precuneus and posterior cingulate cortex. On the other
hand, functional connectivity was decreased between the dACC
Table2. Brain Areas Showing Post-Ayahuasca Statistically Signicant Changes in Seed-to-Voxel PCC Resting-State Functional Connectivity
Brain area BA MNI (x, y, z) Number of voxels Maximum t value
Areas showing increased connectivity
Cuneus (occipital lobe) 18/19 (2, -88, 24) 3824 6.80
Anterior cingulate gyrus 24/32 (-10, 8, 38) 605 6.80
Precentral gyrus/ postcentral gyrus 6/4 (-54, -2, 32) 1301 5.23
Superior temporal gyrus/ insula 22/13 (-32, -8, -2) 1401 5.10
Data shows results for the pair-wise comparison (post- vs. pre-intake) corrected for multiple comparisons at the cluster level (FWE < 0.05, z > 2.5, 20 contiguous
voxels). The MNI coordinates indicate the location of the voxel with the maximum t value.
The PCC seed was located at (0, -56, 28) MNI coordinates. Data shows results of the pair-wise comparison (post- vs. pre-intake) corrected for multiple comparisons at
the cluster level (FWE < 0.05, z > 2.5, 20 contiguous voxels). The MNI coordinates indicate the location of the voxel with the maximum t value. No areas were found
showing signicant decreases in connectivity with the PCC seed.
Figure3. Statistical map showing the results of the second-level analysis (post- vs. pre-intake) of changes in connectivity between the dorsal anterior cingulate (dACC)
seed (green circle) at MNI coordinates x=5, y=14, z=42, and the rest of the brain. As shown in the top panel a signicant increase in connectivity was found with vox-
els in the precuneus/posterior cingulate cortex. As shown in the bottom panel, signicant decreases (cold colors) were found with voxels located in the cuneus (visual
association cortex: BA 18 and 19). Results are shown corrected for multiple comparisons at the cluster level (FWE < 0.05, z > 2.5, 20 contiguous voxels).

8 | International Journal of Neuropsychopharmacology, 2017
seed and visual association areas (BA 18 and 19)in the occipital
lobes. Cluster details are provided in Table3.
Finally, Figure4 shows the statistical maps corresponding to
the second-level random effects statistical comparison of seed-
to-voxel changes between post-acute and pre-intake connectiv-
ity for the srACC seed (superior rostral ACC, x=0, y=15, z=30).
Cluster data are presented in Table3, and uncorrected maps for
the rst-level and second-level analyses can be found in sup-
plementary Figure3.
As shown therein, in the post-acute stage, this subregion of
the ACC increased its connectivity with limbic structures within
the right MTL, including areas of the parahippocampal gyrus,
the hippocampus, and the amygdala. Increased connectiv-
ity was also found in the left parietal lobe and in the medial
parietal lobe, over the posterior cingulate cortex. As shown in
the rst-level maps (supplementary Figure 3), this increase
reected a reduction of the anticorrelation between the ACC
and the PCC. Finally, connectivity between the srACC and the
visual cortex was signicantly reduced in the post-acute stage.
The inspection of the rst-level maps shows that BOLD activity
in this area changed from being positively to negatively coupled
with that in the srACC.
Table 3. Brain Areas Showing Ayahuasca-Induced Statistically Signicant Changes in Seed-to-Voxel Resting-State Functional Connectivity for
the dACC Seed at MNI Coordinates (5, 14, 42) and the srACC Seed at (0, 15, 30)
Brain Area BA MNI (x, y, z) Number of voxels Maximum t value
dAAC seed (5, 14, 42)
Areas showing increased connectivity
Precuneus, posterior cingulate cortex 31 (-6, -42, 40) 864 3.76
Areas showing decreased connectivity
Cuneus (occipital lobe) 18/19 (28, -82, 0) 739 5.56
srACC seed (0, 15, 30)
Areas showing increased connectivity
Parahippocampal gyrus, hippocampus, amygdala (R) 35/28 (24, -18, -24) 660 6.04
Angular gyrus, inferior parietal lobule (L) 7/40/39 (-32, -74, 54) 633 6.02
Precuneus, posterior cingulate cortex (L&R) 31/7 (14, -54, 28) 1436 5.02
Areas showing decreased connectivity
Cuneus (occipital lobe) 18/19 (-2, -94, 6) 790 4.76
Abbreviations: dACC, dorsal anterior cingulate cortex; srACC, superior rostral anterior cingulate cortex.
Data shows results for the pair-wise comparison (post- vs. pre-intake) corrected for multiple comparisons at the cluster level (FWE < 0.05, z > 2.5, 20 contiguous
voxels). The MNI coordinates indicate the location of the voxel with the maximum t value.
Figure4. Statistical maps showing the results of the second-level analysis (post- vs. pre-intake) of changes in connectivity between the superior rostral anterior cingu-
late (srACC) seed (green circle) at MNI coordinates x=0, y=15, z=30, and the rest of the brain. As shown in the top panel, decreases in connectivity (cold colors) were
found with voxels located in the cuneus (visual cortex: BA 18 and 19). Increases in connectivity were found with 3 separate clusters (bottom panel): (a) the right medial
temporal lobe (left brain map); (b) the precuneus and posterior cingulate cortex (center brain map); and (c) the left angular gyrus and left parietal lobule (right brain
map). Results are shown corrected for multiple comparisons at the cluster level (FWE < 0.05, z > 2.5, 20 contiguous voxels).

Sampedro et al. | 9
Mindfulness Measures
Figure5 shows bar graphs of scores on those subscales of the
FFMQ, EQ, and SC questionnaires that showed statistically sig-
nicant differences from pre-intake values in the post-acute
assessment or at follow-up. Tabulated data for all subscales can
be found in supplementary Tables 1 and 2. As shown in sup-
plementary Table1, participants already scored higher than the
general population in several facets and higher than meditators
in the 3 subscales of the SC questionnaire.
Despite high baseline values, further increases were
observed in the post-acute assessment. The paired-samples
comparison (post-acute vs. pre-ayahuasca) of the 5 subscales
of the FFMQ showed statistically signicant increases in scores
on: nonjudging: [t(15)=-2.92, P = .011, P (FDR)=0.021]; and non-
reacting: [t(15)=-2.61, P = .020, P (FDR)=0.031]. The other 3 sub-
scales were not signicantly modied. At follow-up 2months
later, the nonjudging score remained signicantly higher than
baseline: [t(13)=-2.22, P = .045], but this effect did not survive
multiple comparisons correction using FDR (P = .495). Scores
on the other 4 scales were not different from baseline values.
The EQ questionnaire also showed signicant effects of aya-
huasca, with higher scores in the post-acute stage [t(15)=-3.58,
P = .003, P (FDR) = .011]. At follow-up, scores were not different
from baseline values.
The Mindsens composite score was signicantly increased
relative to baseline [t(15)=-3.63, P=.002, P (FDR)=.011]. Again,
at follow-up, scores were not signicantly different from those
at baseline.
Analysis of scores on the SC questionnaire showed statisti-
cally signicant increases [t(15)=-3.00, P = .009, P (FDR) = .020].
At follow-up 2 months later, values were not different from
baseline.
Acute Subjective Effects
The analysis of scores on the different HRS subscales showed
that ayahuasca intake led to signicant psychoactive effects
during the acute stage (supplementary Figure4). The compara-
tive analysis with data from a previous laboratory study by our
group (using independent samples Student’s t tests) showed
signicant differences from placebo for all subscales, except for
volition. Scores in the present study on somaesthesia, affect,
perception, volition, and intensity were not different from those
we had obtained after a medium 0.75-mg DMT/kg ayahuasca
dose (Valle etal., 2016). Only cognition was signicantly differ-
ent, with higher scores obtained here: t(26)=4.25, P (FDR) <.01.
Exploratory Correlation Analyses
We examined potential association between neurometabolic
and functional connectivity changes, and scores on mindful-
ness measures and subjective effects. In all correlations, differ-
ence values (post-acute minus pre-ayahuasca) were used. For
Figure5. The graph bars shows mean scores on mindfulness measures that showed statistically signicant post- vs. pre-ayahuasca intake changes. Data from n=16
participants at the pre- and post-acute assessments, and from n=14 participants at follow-up 2months later. FFMQ, Five Facets Mindfulness Questionnaire; EQ, Expe-
riences Questionnaire; MINDSENS, Mindsens composite index; SC, Self-Compassion Questionnaire. The error bars denote 1 standard error of mean. Signicant differ-
ences in the statistical comparison (post-acute or follow-up vs. pre-intake) are denoted as *P < .05 after FDR correction. #Signicance lost after FDR correction. Scores on
nonsignicant subscales are provided in the supplementary information le.

10 | International Journal of Neuropsychopharmacology, 2017
follow-up measures, the difference values from pre-ayahuasca
scores were used. Scatter plots for the nonjudging subscale are
shown in Figure6. Additional scatter plots are included in sup-
plementary Figure5.
Associations between neurometabolic and connectivity
measures, and acute psychedelic effects
Scores on the cognition subscale of the HRS correlated with Cr
decreases (n = 14; r = –0.735; r2 = 0.540; P = .003) and NAA-NAAG
decreases in the PCC (n = 14; r = –0.622; r2 = 0.387; P = .018). No
other signicant correlations were found.
Associations between neurometabolic and connectivity
measures, and post-acute mindfulness effects
Glx decreases in the PCC correlated with increases in the non-
judging FFMQ subscale (n = 12; r = –0.589; r2 = 0.506; P = .044).
Increased srACC-PCC connectivity correlated with increases
in the nonjudging (n = 16; r = 0.604; r2 = 0.365; P = .013) and Non-
Reacting (n = 16; r = 0.522; r2 = 0.272; P = .038) subscales of the
FFMQ. Increased srACC-MTL connectivity similarly correlated
with increases in the nonjudging (n = 16; r = 0.637; r2 = 0.406;
P = .008) and nonreacting (n = 16; r = 0.656; r2 = 0.430; P = .006)
subscales of the FFMQ, and with the SC score (n = 16; r = 0.514;
r2 = 0.264; P = .042).
Association between neurometabolic and connectivity measures,
and mindfulness effects at follow-up
Glx decreases in the PCC correlated with difference in the non-
judging subscale 2 months after baseline assessment (n = 11;
r = –0.740; r2 = 0.548; P = .009). Positive correlations with sustained
effects on nonjudging were also found for post-acute increases
in srACC-PCC (n = 14; r = 0.584; r2 = 0.341; P = .028) and ACC-MTL
(n = 14; r = 0.566; r2 = 0.320; P = .035) connectivity.
Discussion
Here we investigated the neural correlates of the psychedelic
“after-glow” induced by ayahuasca in healthy volunteers. Using
2 different MRI techniques, we evidenced signicant neuromet-
abolic and functional connectivity changes hours after the acute
effects of ayahuasca had disappeared. These modications were
associated with immediate changes in the psychological sphere
Figure6. Scatter plots showing signicant correlations between difference scores at the post-acute and follow-up assessments (relative to baseline values) for the
FFMQ nonjudging subscale and changes in neuroimaging measures (post-acute minus pre-intake). The top panels show the correlations with changes (Δ) in Glx
(glutamate+glutamine) concentrations (millimolar) in the posterior cingulate cortex (PCC) voxel as measured using MRS. The middle panels show the correlations with
changes in functional connectivity (Δ in z values) between the superior rostral anterior cingulate (srACC) seed and the precuneus/PCC cluster. The lower panels show
the correlations with changes in functional connectivity (Δ in z values) between the srACC seed and the right medial temporal lobe (MTL) cluster. The left column
shows correlations with FFMQ nonjudging difference scores in the post-acute assessment and the right column shows correlations with difference scores at follow-up.
R and P values are reported in the main text.

Sampedro et al. | 11
that were marginally maintained 2 months later. Our results
replicate previous ndings of enhanced mindfulness capacities,
including increased “decentering,” and decreased judgmental
and reactive attitudes during the post-acute phase of ayahuasca
(Soler et al., 2016). Ayahuasca had the power to increase FFMQ,
EQ, and Mindsens scores in individuals with already high base-
line scores (Soler et al., 2014a). We also found increases in self-
compassion, a previously unexplored facet in this context.
MRS showed neurometabolic changes in the PCC, a region
rich in 5-HT2A receptors (Carhart-Harris et al., 2012; Beliveau
etal., 2016) and a target region of psychedelics (Palhano-Fontes
etal., 2015; Carhart-Harris et al., 2016a; Valle etal., 2016). Glx
levels in the PCC were lower in the post-acute assessment com-
pared with baseline values, an effect that was however only
marginally signicant when corrected for multiple comparisons.
We thus obtained partial evidence for the previously postulated
involvement of glutamate neurotransmission in the effects of
psychedelics (Kłodzinska etal., 2002; Moreno etal., 2011).
While we did not measure Glx levels during the acute psyche-
delic phase, our MRS ndings are compatible with increased glu-
tamate levels during the acute stage. Cortical glutamate levels
increase in periods of external perceptual stimulation or during
active cognitive tasks, while they fall below baseline levels dur-
ing stimulation- or task-free periods (Mangia etal., 2007; Huang
etal., 2015; Terhune etal., 2015). Also, acute psilocybin decreases
brain aspartate (Preller etal., 2016), a neurotransmitter whose
levels vary in an anticorrelated fashion with those of glutamate
(Mangia etal., 2007). The post-acute Glx decreases in the PCC
may result from increased excitatory activity during the acute
phase. EEG and MEG studies in humans have shown a decrease
of alpha oscillations, an inhibitory rhythm, in the parieto-occip-
ital cortex during the acute effects of psychedelics (Kometer
etal., 2013; Carhart-Harris etal., 2016a; Valle etal., 2016).
The post-acute Glx reductions in the PCC are also consist-
ent with the observed reductions in Cr, NAA, and NAAG. Cr
and N-acetyl compounds have been associated with metabolic
activity, and NAAG has been directly linked to glutamater-
gic pathways (Rae, 2014). Additionally, the inverse correlation
found between Cr and NAA-NAAG variations and scores on
the HRS-Cognition subscale suggest a relationship between
the intensity of acute effects and subsequent neurometabolic
reductions. Neurometabolic changes may have contributed to
the antidepressant effects reported for ayahuasca (Osório etal.,
2015; Sanches etal., 2016). Depressed patients show abnormally
high glutamate levels in the parieto-occipital cortex (Bhagwagar
etal., 2007). Glutamate reductions in these areas correlate with
clinical improvement in depression (Abdallah etal., 2014).
The functional connectivity analysis also evidenced post-
acute changes. Activity in the PCC and associated areas within
the DMN (Raichle etal., 2001) has been associated with the per-
sonal sense of “self.” Psychedelics acutely loosen the bounda-
ries of the “self” and increase the cross-talk between networks
(Carhart-Harris etal., 2012, 2016a). Here, we found a post-acute
increase in coupling between the PCC and a subregion of the
ACC pertaining to theTPNs.
While DMN and TPN activity are typically anticorrelated (Fox
etal., 2005), psilocybin and LSD acutely increase DMN-TPN con-
nectivity (Carhart-Harris etal., 2013), and general inter-network
connectivity (Roseman et al., 2014; Tagliazucchi et al., 2016).
Our results suggest that cross-talk lingers beyond the acute
stage and contributes to the “after-glow,” reected as enhanced
mindfulness capacities. Increased DMN-TPN connectivity cor-
related with reduced judgmental processing, inner reactivity,
and increased self-kindness, providing a neurobiological basis
for these modications. Conventional mindfulness training also
increases DMN-TPN connectivity (Doll etal., 2015).
Visual areas showed increased coupling with the PCC but
reduced with the ACC. This pattern suggests a greater interplay
between internally generated visual information and sponta-
neous mind-wandering, and a reduction in cognitive control.
These effects could explain increased phosphenes or “entop-
tic activity” persisting days after ayahuasca use (Frecska etal.,
2012). Aprevious neuroimaging study found increased activity
in the visual cortex under ayahuasca (de Araujo etal., 2012).
The superior rostral ACC (srACC) seed also demonstrated
increased functional coupling with parahippocampal, hip-
pocampal, and amygdalar areas of the MTL. Prior studies had
identied these areas as targets of acute ayahuasca (Riba etal.,
2004, 2006; de Araujo etal., 2012). LSD acutely decreases fear rec-
ognition (Dolder etal., 2016), an effect mediated by the amyg-
dala, and psilocybin increases synchronization between the
hippocampus and the ACC (Tagliazucchi etal., 2014).
Our data suggest that during the “after-glow” there is an
enhanced interplay between the ACC, participating in execu-
tive tasks and in the binding of cognitive and emotional infor-
mation, with limbic structures with key roles in emotion and
memory processes. This nding is particularly relevant in the
interpretation of the antidepressant effects of ayahuasca. Other
researchers have found abnormal interactions between the
srACC and the amygdala in depressed patients, possibly indi-
cating decreased cognitive control over negative emotions (Fales
etal., 2008).
Our data show for the rst time that the modication
induced by psychedelics on brain dynamics leads to changes
in its neurometabolic, functional, and psychological balance
beyond the acute stage. As previously reported (Grifths etal.,
2011; Lebedev etal., 2016), the post-acute phase in our study
showed positive psychological effects, highlighting the paradox-
ical nature of psychedelics (Carhart-Harris etal., 2016c). While
the acute inebriation shares features with psychosis (Schmid
etal., 2015; Carhart-Harris et al., 2016c), psychedelics may lead
to mid-term increases in psychological well-being. Increasing
mindfulness capacities is clearly a desirable effect, especially in
a psychotherapeutic context. Here post-acute scores were above
values reported for meditators (Soler etal., 2014a), a population
that also shows a pattern of decreased DMN-TPN anticorrela-
tion (Brewer etal., 2011; Froeliger etal., 2012). Considering that
maladaptive ruminations in depression have been associated
with greater DMN “dominance” over TPN activity (Hamilton
etal., 2011), our results provide another interesting link between
psychedelic-induced neural modications and the therapeutic
potential of ayahuasca.
The post-acute phase of the psychedelic experience had
received little attention from modern neuroscience. Although
investigators had postulated the capacity of psychedelics to
modulate brain plasticity (Vollenweider and Kometer, 2010),
most research had assessed mid- and long-term effects only
from a psychological perspective. The changes in personal-
ity and life attitudes reported in the 1960s (Savage etal., 1966;
Pahnke, 1969) have recently been replicated as increases in trait
openness (Grifths etal., 2006; Carhart-Harris etal., 2016c). Also,
in a structural neuroimaging study of regular ayahuasca users,
we found a cortical thinning of the PCC, the area showing neu-
rometabolic decreases in the present study. PCC thinning was
inversely correlated with increased self-transcendence, a per-
sonality trait closely related to openness (Bouso etal., 2015).
Our MRS and connectivity data provide a biological basis for
the therapeutic effects of ayahuasca (Osório etal., 2015; Sanches

12 | International Journal of Neuropsychopharmacology, 2017
etal., 2016). Its potential to inuence brain dynamics at multiple
levels suggests its usefulness to treat disorders that are highly
refractory to therapeutic intervention. Its combined effect on
the psychological and neural spheres may be particularly well
suited to treat addiction disorders (Fernández and Fábregas,
2014), where high impulsivity and self-centeredness coexist
with alterations in brain function and structure (Vaquero etal.,
2016).
Our study has several limitations that need to be men-
tioned. We assessed a small sample of individuals before and
after ayahuasca intake, with no control for placebo or time
effects. The difculties associated with Glx quantication
allowed measurement in an even smaller sample. All partici-
pants had previous experience with ayahuasca, which may
have biased our sample to individuals who usually experience
positive effects after intake. Additionally, participants showed
high baseline scores on several mindfulness facets. While
this could be considered a limitation, it is also true that these
capacities show “ceiling” effects and are difcult to increase
in high scorers (Montero-Marin etal., 2016). The correlation
analysis should be considered exploratory and interpreted
with caution. Finally, our study investigated only the sub-
acute stage of ayahuasca effects. The observed connectivity
modications cannot be interpreted as indicating persistent
network changes. Future studies should consider using larger
samples and double-blind, placebo-controlled designs. Also,
the role of prior exposure to ayahuasca could be better estab-
lished by recruiting less experienced or even ayahuasca-naive
individuals
To conclude, the present results indicate that ayahuasca
and potentially other psychedelics induce neural modications
beyond the time frame of the acute inebriation. Neurometabolic
decreases in the PCC and the increased inter-network connec-
tivity were associated with enhanced mindfulness facets. These
associations provide hints to a potential biological basis for the
therapeutic effects of ayahuasca.
Acknowledgments
The authors thank Alexander Lebedev for performing the Frame
Displacement analysis of the fMRI data. We are also grateful to
Anna Ermakova for her critical reading of the manuscript; Núria
Bargalló, Anna Calvo, and Cesar Garrido for technical assistance;
and the study volunteers for their participation.
This study was funded by the Beckley Foundation. Marta
Valle was supported by FIS through a grant (CP04/00121) from
the Spanish Health Ministry in collaboration with Institut de
Recerca de l’Hospital de la Santa Creu i Sant Pau, Barcelona. José
Alexandre S.Crippa and Jaime E.C. Hallak are recipients of CNPq
Research fellowship awards.
Statement of Interest
None.
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