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Background Neuroimaging studies have just begun to explore the acute effects of psychedelics on large-scale brain networks’ functional organization. Even less is known on the neural correlates of subacute effects taking place days after the psychedelic experience. This study explores the subacute changes of primary sensory brain networks and networks supporting higher-order affective and self-referential functions 24h after a single session with the psychedelic ayahuasca. Methods We leveraged task-free functional magnetic resonance imaging data one day before and one day after a randomized placebo-controlled trial exploring the effects of ayahuasca in naïve healthy participants (21 placebo/22 ayahuasca). We derived intra- and inter-network functional connectivity of the salience, default mode, visual, and sensorimotor networks, and assessed post-session connectivity changes between the ayahuasca and placebo groups. Connectivity changes were associated with Hallucinogen Rating Scale scores assessed during the acute effects. Results Our findings revealed increased anterior cingulate cortex connectivity within the salience network, decreased posterior cingulate cortex connectivity within the default mode network, and increased connectivity between the salience and default mode networks one day after the session in the ayahuasca group compared to placebo. Connectivity of primary sensory networks did not differ between-groups. Salience network connectivity increases correlated with altered somesthesia scores, decreased default mode network connectivity correlated with altered volition scores, and increased salience-default mode network connectivity correlated with altered affect scores. Conclusion These findings provide preliminary evidence for subacute functional changes induced by the psychedelic ayahuasca on higher-order cognitive brain networks that support interoceptive, affective, and self-referential functions.
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Title
Subacute effects of the psychedelic ayahuasca on the salience and default mode networks
Authors
Lorenzo Pasquini PhD1*, Fernanda Palhano-Fontes PhD2*, Draulio B. Araujo PhD2
Affiliations
1 University of California San Francisco Memory and Aging Center, University of California San
Francisco, San Francisco, California
2 Brain Institute, Federal University of Rio Grande do Norte (UFRN), Natal-RN, Brazil
* These authors contributed equally to the manuscript
Corresponding author:
Draulio B. Araujo
Brain Institute (UFRN)
Av. Nascimento Castro, 2155
Natal, RN 59056 - Brazil
draulio@neuro.ufrn.br
Running title: Subacute effects of ayahuasca on brain networks
Keywords: Ayahuasca, default mode network, functional connectivity, interoception, salience
network, psychedelics.
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Abstract
Background: Recent years have seen a growing interest in the therapeutic use of psychedelic
substances for the treatment of anxiety and depression in patients with affective and mood
disorders. Neuroimaging studies have just begun to explore how brain networks supporting
perceptual and higher-order cognitive and emotional functions are affected during the acute
effects of psychedelics. Even less is known on the neural correlates of the subacute effects
taking place one to a few days after the psychedelic experience. This study explores the
subacute changes of primary sensory brain networks and networks supporting higher-order
affective and self-referential functions after a single session with the psychedelic ayahuasca.
Methods: We leveraged task-free functional magnetic resonance imaging data one day before
and one day after a randomized placebo-controlled trial exploring the effects of ayahuasca in
naïve healthy participants (21 placebo/22 ayahuasca). We derived functional connectivity maps
of the salience, default mode, visual and sensorimotor networks using a seed-to-whole brain
connectivity approach, and statistically assessed post-session functional connectivity changes
between the ayahuasca and placebo groups. Connectivity changes were subsequently
associated with scores of the Hallucinogen Rating Scale assessed during the acute session.
Results: Our findings revealed increased functional connectivity in the anterior cingulate cortex
of the salience network and decreased functional connectivity in the posterior cingulate cortex of
the default mode network one day after the session in the ayahuasca group. No connectivity
changes between groups were found in primary sensory networks. Subacute increased
connectivity of the salience network correlated positively with altered somesthesia scores
assessed during the acute effects of ayahuasca, while decreased connectivity of the default
mode network correlated negatively with altered volition scores.
Conclusion: These findings provide preliminary evidence for subacute functional changes
induced by the psychedelic ayahuasca on higher-order cognitive brain networks known to
support interoceptive, affective, and self-referential processes.
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Introduction
Classic psychedelics belong to a family of substances that lead to altered states of
consciousness, with a broad range of effects on sensory, cognitive, autonomic, interoceptive,
self-referential, and emotional systems (Nichols, 2016). Assisted sessions with psychedelic
substances such as ayahuasca and psilocybin have recently gained prominent use for the
treatment of affective and mood disorders (Carhart-Harris, Bolstridge, et al., 2016; Griffiths et
al., 2016; Grob et al., 2011; Osório et al., 2015; Palhano-Fontes et al., 2019; Ross et al., 2016;
Sanches et al., 2016).
Ayahuasca is an indigenous preparation that contains leaves of Psychotria viridis and
the bark of Banisteriopsis caapi, two plants vastly found in the Amazon (Mckenna et al., 1984).
The admixture contains the psychedelic tryptamine N,N-dimethyltryptamine (N,N-DMT) and
monoamine oxidase inhibitors, which has a particularly high affinity to serotonin and sigma-1
receptors (Barker, 2018; Fontanilla et al., 2009; Mckenna et al., 1984; Riba, Rodríguez-Fornells,
et al., 2001). Recent clinical trials have explored the antidepressant effects of ayahuasca
(Osório et al., 2015; Palhano-Fontes et al., 2019; Sanches et al., 2016). In an open-label trial,
17 patients with treatment-resistant depression were submitted to a single session with
ayahuasca. Significant antidepressant effects were observed one day after the session and
persisted for 21 days (Osório et al., 2015; Sanches et al., 2016). Consistent results were found
in a separate randomized placebo-controlled trial, where a significant rapid antidepressant effect
of ayahuasca was observed already one day after the session, compared to placebo (Palhano-
Fontes et al., 2019). Yet, little is known about the underlying mechanisms by which ayahuasca
may modulate affect, mood, and internal representations of oneself.
Neuroimaging techniques provide a powerful tool to explore brain changes elicited by
psychedelic agents (Dos Santos et al., 2016). Task-free functional magnetic resonance imaging
(tf-fMRI) measures synchronous, low frequency (<0.1 Hz) fluctuations in blood oxygen level-
dependent (BOLD) activity among distant gray matter regions (Allen et al., 2011; Fox et al.,
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2005; Smith et al., 2009) and has been used to delineate distinct intrinsic large-scale brain
networks supporting primary sensory and higher cognitive and emotional functions (Fox et al.,
2005; Grayson and Fair, 2017; Smith et al., 2009; van den Heuvel and Hulshoff Pol, 2010).
Importantly, human emotions and social behavior are modulated by a distributed set of brain
regions including the anterior cingulate cortex, bilateral anterior insula, and subcortical and
limbic structures that regulate affect, interoception, and self-awareness by interacting with the
autonomic nervous system (Craig, 2009; Critchley and Harrison, 2013; Zhou and Seeley, 2014).
These regions coactivate and are structurally connected, cohesively forming the salience
network, a large-scale brain system involved in homeostatic behavioral guidance and supporting
socioemotional functions by integrating visceral and sensory information (Rankin et al., 2006;
Seeley et al., 2007; Sturm, Brown, et al., 2018; Uddin, 2015). A second prominent large-scale
brain system is the default mode network , which is primarily composed of the posterior
cingulate cortex, precuneus, inferior parietal lobe, parahippocampal gyrus, and medial prefrontal
cortex (Buckner et al., 2008). This network has been repeatedly associated with self-referential
processes such as mind-wandering, introspection, and memory retrieval under healthy and
pathological conditions (Buckner et al., 2008; Raichle et al., 2001).
Recent neuroimaging studies have explored the acute effects of psychedelics on human
brain network functional organization (Carhart-Harris et al., 2012; Carhart-Harris,
Muthukumaraswamy, et al., 2016; Palhano-Fontes et al., 2015; Roseman et al., 2014; Viol et
al., 2017, 2019), with reports of increased functional integration at the global brain level (Petri et
al., 2014; Tagliazucchi et al., 2016; Viol et al., 2017), and connectivity increases primarily
affecting the primary visual cortex and frontal areas (Carhart-Harris, Muthukumaraswamy, et al.,
2016; De Araujo et al., 2012). Only one study has reported salience network connectivity
decreases under acute conditions (Lebedev et al., 2015), while most studies report decreased
connectivity in important hubs of the default mode network, such as the posterior cingulate
gyrus (Carhart-Harris et al., 2012; Lebedev et al., 2015; Palhano-Fontes et al., 2015).
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A recent study assessing the subacute effect of ayahuasca reported decreased negative
connectivity between the anterior cingulate cortex, a salience network hub, and key default
mode network regions such as the posterior cingulate cortex and medial temporal lobes,
whereas connectivity changes correlated with increased self-compassion scores (Sampedro et
al., 2017). Likewise, the subacute effects of psilocybin in patients with treatment-resistant
depression led to increased connectivity one day after dosing, which correlated with decreased
depressive symptoms (Carhart-Harris et al., 2017). Little is known, however, on within-network
subacute changes induced by ayahuasca on the salience and default mode networks on naïve
healthy participants hours to days after a psychedelic session, and how functional changes may
relate to the altered state of consciousness elicited by the psychedelic experience.
To address this critical gap, we leveraged tf-fMRI data assessed before and 24 hours
after a randomized placebo-controlled trial exploring the subacute effects of ayahuasca in naïve
healthy participants. We hypothesized subacute effects of ayahuasca for higher-order affective
and self-referential networks but not primary sensory networks and predicted that the former
would relate to the acute effects of ayahuasca. We applied a seed-based connectivity approach
to map the salience, default mode, visual, and sensorimotor networks and assess subacute
functional connectivity changes one day after the session with ayahuasca compared to placebo.
Methods and Materials
We recruited 50 participants from local media and the Internet. All individuals included in
the study were cognitively and physically healthy and naïve to ayahuasca. The following
exclusion criteria were adopted: (i) diagnosis of current clinical disease based on anamnesis,
physical, and laboratory examination; (ii) pregnancy; (iii) history of neurological/psychiatric
diseases; (iv) substance abuse; (v) restrictions to magnetic resonance imaging assessment. All
procedures took place at the Onofre Lopes University Hospital (UFRN), Natal-RN, Brazil. The
study was approved by the University Hospital Research Ethics Committee (# 579.479). All
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subjects provided written informed consent before participation. The study was registered at
http://clinicaltrials.gov (NCT02914769).
Half of the participants (n=25) received a single dose of 1 ml/kg of ayahuasca adjusted
to contain 0.36 mg/kg of N,N-DMT and the other half (n=25) received 1 ml/kg of a placebo
substance, designed to simulate organoleptic properties of ayahuasca, and to produce low to
modest gastrointestinal distress (Palhano-Fontes et al., 2019). A single ayahuasca batch was
used throughout the study. The batch was prepared and provided by a branch of the Barquinha
church, Ji-Paraná, Brazil. Baseline tf-fMRI assessments occurred one day before dosing, and a
second tf-fMRI assessment occurred 24h after dosing (Figure 1A).
To assess the acute psychedelic experience, we used the Hallucinogenic Rating Scale
(HRS), which was initially designed to assess the psychedelic effects of N,N-DMT (Strassman
et al., 1994). It is divided into six subscales: (i) intensity, which reflects the strength of the overall
experience; (ii) somaesthesia, which assesses somatic effects including interoception, visceral,
and tactile effects; (iii) affect, which assesses comfort, emotional, and affective changes; (iv)
perception, which assesses visual, auditory, gustatory, and olfactory effects; (v) cognition, which
assesses changes in thoughts; and (vi) volition, which is related to the subject’s capacity to
willfully interact with his/her ‘self’ (Riba, Rodrı, et al., 2001; Strassman et al., 1994). We used
the HRS version translated to Brazilian Portuguese (Mizumoto et al., 2011). Participants
completed the HRS at the end of the dosing session (approximately 4h after ayahuasca or
placebo ingestion).
Neuroimaging data acquisition. tf-fMRI scanning was performed on a 1.5 Tesla scanner
(General Electric, HDxt). Functional MRI data were acquired using an EPI sequence with the
following parameters: TR = 2000 ms; TE = 35 ms; flip angle = 60˚; FOV = 24 cm; matrix = 64 x
64; slice thickness = 3 mm; gap = 0.3 mm; number of slices = 35; volumes = 213. T1-weighted
images were also acquired using a FSPGR BRAVO sequence with the following parameters:
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TR = 12.7 ms, TE = 5.3 ms, flip angle = 60˚, FOV = 24 cm, matrix = 320 x 320; slice thickness =
1.0 mm; number of slices = 128.
Neuroimaging data preprocessing. The first three volumes were discarded to allow T1
saturation. Preprocessing steps were performed using CONN (https://web.conn-toolbox.org/)
(Whitfield-Gabrieli and Nieto-Castanon, 2012) and included: head motion correction, slice timing
correction, and spatial smoothing (6-mm FWHM Gaussian kernel). Functional images were
coregistered to the subject's anatomical image, normalized into the Montreal Neurological
Institute (MNI) template, and resampled to 2 mm3 voxels. Motion artifact was examined using
the Artifact Detection Toolbox (ART; http://www.nitrc.org/projects/artifact_detect/). Volumes
were considered outliers if the global signal deviation was superior to five standard deviations
from the mean signal or if the difference in frame displacement between two consecutive
volumes exceeded 0.9 mm. Physiological and other spurious sources of noise were removed
using the CompCor method (Behzadi et al., 2007). Residual head motion parameters (3 rotation
and 3 translation parameters), outlier volumes, white matter, and cerebral spinal fluid signal
were regressed out. Finally, a temporal band-pass filter of 0.01 Hz to 0.1 Hz was applied. After
data quality check, three participants in the ayahuasca group and four in the placebo group
were excluded due to excessive motion artifact (inter-frame translations greater than 3 mm,
inter-frame rotations greater than 3 degrees) (Power et al., 2012; Satterthwaite et al., 2012).
For each subject, average BOLD activity time courses were extracted using bilateral
regions-of-interest from the Brainnetome Atlas (seed numbers 187 and 188 for the anterior
cingulate cortex, seed numbers 175 and 176 for the posterior cingulate cortex, seed numbers
203 and 204 for the occipital cortex, and seed numbers 59 and 60 for the precentral cortex,
http://atlas.brainnetome.org/) (Fan et al., 2016). Salience, default mode, visual, and
sensorimotor network functional connectivity maps were generated through voxel-wise
regression analyses using the extracted time-series as regressors (Seeley et al., 2007). After
visual inspection, baseline one-sample t-test maps derived from the seed-based approach were
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spatially correlated with publicly available maps of the visual (Rseed=0.44), sensorimotor
(Rseed=0.49), default mode (Rseed=0.69) and salience networks (Rseed=0.64) (Smith et al., 2009),
and interactively compared to maps available on NeuroVault (https://neurovault.org)
(Gorgolewski et al., 2015). To control for our method of choice, the seed-based approach, we
replicated the analysis using group independent component analysis (ICA) implemented
through the GIFT toolbox (http://icatb.sourceforge.net). Briefly, preprocessed tf-fMRI data of all
subjects were decomposed into 20 spatially independent components within a group-ICA
framework (Calhoun et al., 2001; Pasquini et al., 2015). Data were concatenated and reduced
by two-step principal component analysis, followed by independent component estimation with
the infomax-algorithm. This procedure results in a set of averaged group components, which are
then back reconstructed into the subject's space. As in the seed-based approach, baseline one-
sample t-test maps derived from the ICA-based approach were spatially correlated with publicly
available maps of the default mode network(RICA=0.63) (Buckner et al., 2008) and salience
network (RICA=0.56) (Smith et al., 2009).
Statistical analyses. Using individual brain network connectivity maps at baseline, a
voxel-wise one-sample t-test was implemented in SPM12
(https://www.fil.ion.ucl.ac.uk/spm/software/spm12/) to assess significant functional connections
to our seeds of choice (t=6.5, extent probability threshold of p<0.01 FWE corrected, voxel-wise
threshold of p<0.001 FWE corrected for multiple comparisons; Figure 1B). These maps were
used as masks for subsequent voxel-wise statistical analyses. Change maps of brain network
functional connectivity were derived by individually subtracting the functional connectivity maps
post-dosing from the ones at baseline. Voxel-wise two-sample t-tests were used to assess
differences in brain network functional connectivity between placebo and ayahuasca. If not
reported otherwise, all voxel-wise findings are reported at the joint cluster and extent probability
thresholds of p<0.05 and p<0.01.
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Since the use of liberal statistical thresholds in neuroimaging studies has been recently
shown to be prone to inflate false positives results (Eklund et al., 2016), we additionally
assessed group differences in functional connectivity through nonparametric permutation tests
as implemented using the FSL package Randomise
(https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/Randomise) (p<0.05 threshold-free cluster enhancement
uncorrected and FWE corrected for multiple comparisons) (Smith and Nichols, 2009; Winkler et
al., 2014). Two-sample t-tests were used to assess group differences in demographic variables,
mean framewise head displacement, and HRS subscales (p<0.005 if not specified otherwise).
Average functional connectivity changes were derived from clusters identified with the voxel-
wise two-sample t-tests using a joint cluster and extent probability threshold of p<0.05 for the
default mode network and a more stringent joint cluster and extent probability threshold of
p<0.01 for the salience network. Partial correlation coefficients corrected for the difference in
framewise head displacement between the second and first scan were used to associate
averaged functional connectivity changes in clusters of brain networks with HRS subscale
scores (p<0.05 if not specified otherwise).
Results
Forty-three (43) ayahuasca naïve participants assigned either to ayahuasca (n = 22) or
placebo (n = 21) passed our neuroimaging data quality check (Table 1). All participants were
assessed with tf-fMRI one day before and one day after dosing (Figure 1A), and salience,
default mode network, visual, and sensorimotor networks maps were individually derived by
seeding bilateral regions-of-interest (Figure 1B, Supplementary Table S1). Participants were
comparable in terms of age, gender distribution, and mean framewise head displacement at
both scans (Table 1). We found significant between-group differences for all HRS subscales,
with significant increases in the ayahuasca compared to the placebo group in levels of altered
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somesthesia (p<0.0005), affect (p<0.005), perception (p<0.0005), cognition (p<0.0005), volition
(p<0.009), and intensity (p<0.0005) (Table 2).
Subacute salience and default mode connectivity changes. We next explored differences
in brain network functional connectivity between the ayahuasca and the placebo groups. A
voxel-wise two-sample t-test revealed significant increased functional connectivity in the
ayahuasca compared to the placebo group for the salience network (t=1.3; joint cluster and
extent probability thresholds of p<0.05 and p<0.01) (Figure 2A red and yellow maps,
Supplementary Table S2). Functional connectivity increases were located bilaterally within the
anterior cingulate cortex and superior frontal gyrus, with a tendency towards the left hemisphere
(Figure 2A first three brain slides and Supplementary Table S2). Conversely, we found default
mode network functional connectivity decreases in the ayahuasca group compared to placebo,
located within the posterior cingulate cortex (Figure 2C and Supplementary Table S2). Average
levels of functional connectivity changes derived from the clusters identified in Figures 2A and C
are schematized as box plots (Figure 2B and D).
Similar functional connectivity differences for the salience network and default mode
network were also found when using nonparametric permutation-based tests (Supplementary
Figure S1 and Supplementary Table S3). Furthermore, consistent with our seed-based findings,
ICA revealed patterns of increased anterior cingulate cortex and superior frontal gyrus functional
connectivity for the salience network (t=1.7; joint cluster and extent probability thresholds of
p<0.05, Supplementary Figure S2 A-B and Supplementary Table S4) and a trend in decreased
posterior cingulate cortex functional connectivity of the default mode network in the ayahuasca
group (t=1.3; joint cluster and extent probability thresholds of p<0.1, Supplementary Figure S2
C-D and Supplementary Table S4). Finally, the functional connectivity of primary sensory
networks (visual and sensorimotor) did not differ significantly between ayahuasca and placebo,
suggesting some level of specificity of subacute functional changes elicited by ayahuasca on
the salience and default mode networks.
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Ayahuasca induced subacute changes in functional connectivity correlate with acute
alterations in somesthesia and volition. Average functional connectivity changes were derived
from the previously identified clusters in the salience network and default mode network. Partial
correlation analyses corrected for the difference in framewise head displacement between the
second and first scanning session revealed significant positive associations between increases
in salience network functional connectivity and somesthesia in the ayahuasca group but not in
the placebo group (PRaya=0.55, p<0.01; PRpla=0.01, p=0.95) (Figure 3). Positive trend
correlations were found between increased salience network functional connectivity and affect
in the ayahuasca group and volition in the placebo group (Supplementary Table S5). Subacute
changes in default mode network functional connectivity showed a significant negative
correlation only with volition in the ayahuasca group and a trend in placebo (PRaya= -0.59,
p<0.005; Rpla= -0.43, p=0.06) (Figure 3, Supplementary Table S5).
Discussion
Neuroimaging techniques provide a unique opportunity to study the neural correlates of
altered states of consciousness induced by psychedelic agents (Carhart-Harris et al., 2012;
Carhart-Harris, Muthukumaraswamy, et al., 2016; De Araujo et al., 2012; Palhano-Fontes et al.,
2015; Riba et al., 2004; Viol et al., 2017; Vollenweider et al., 1997). In this study, ayahuasca
naïve participants were randomly assigned to a single session with either ayahuasca or
placebo, and functional connectivity of different large-scale brain networks was assessed with tf-
fMRI one day before and one day after the dosing session. We found salience network
connectivity increases in the anterior cingulate cortex and superior frontal gyrus in ayahuasca
compared to placebo, while default mode network connectivity was decreased in the posterior
cingulate cortex in the ayahuasca group. Ayahuasca induced subacute functional connectivity
increases in the salience network correlated with altered levels of somesthesia, which reflects
somatic changes including interoceptive, visceral, and tactile effects induced by psychedelics
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(Riba, Rodrı, et al., 2001). Reduced default mode network connectivity correlated with altered
levels of volition, proposed to reflect the subject’s capacity to willfully interact with his/her ‘self’
during the psychedelic experience (Riba, Rodrı, et al., 2001). Critically, no subacute differences
were detected in primary sensory brain networks, suggesting specificity of the observed
changes in the salience network and default mode network. Although little is known on the long-
term functional impact of psychedelics on large-scale brain networks, these findings suggest
that ayahuasca has sustained effects on neural systems supporting interoceptive and self-
referential processes (Brewer et al., 2013; Craig, 2009; Critchley and Harrison, 2013; Raichle,
2015; Seeley et al., 2007; Uddin, 2015).
Effects of psychedelic substances on the salience network and default mode network.
N,N-DMT, one of the major constituents of ayahuasca, has high affinity to the 5HT2A
serotonergic receptor (Barker, 2018), while other constituents such as harmine, harmaline and
tetrahydroharmine act as MAOi and serotonin reuptake inhibitors partially by interacting with the
serotonin transporter (5-HTT) (Mckenna et al., 1984; Riba, Rodríguez-Fornells, et al., 2001). A
recent molecular neuroimaging study involving positron emission tomography acquired in a
large sample of healthy individuals revealed in vivo multimodal density maps of serotonin
transporter and major serotonin receptors in the human brain (Beliveau et al., 2017). 5HT2A
receptors displayed a widespread pattern of distribution spanning the visual cortex, temporal,
parietal and frontal regions overlapping with major hubs of the salience, default mode, and task-
control networks (Buckner et al., 2008; Raichle et al., 2001; Seeley et al., 2007), with density of
serotonin transporter being highest within frontotemporal regions overlapping with the insula
and anterior cingulate cortex. Previous studies investigating psychedelics have reported
decreased within salience network functional coupling during the acute effects of psilocybin
(Lebedev et al., 2015). Psilocybin-induced reduced functional connectivity was associated with
“ego-dissolution”, a construct frequently reported as altered by psychedelics, characterized by
the feeling that the border between one's self and the external world is dissolving (Goodman,
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2002; Griffiths et al., 2011; Lyvers and Meester, 2012; Trichter et al., 2009). Similar studies
have reported increased salience network entropy levels during the acute effects of LSD
(Lebedev et al., 2016) and with ayahuasca (Viol et al., 2017). A study investigating the structural
correlates of long-term ayahuasca use found increased cortical thickness within the anterior
cingulate cortex (a region standing out throughout our analyses) of regular ayahuasca users
compared to controls, while cortical thickness of default mode network regions such as the
precuneus and posterior cingulate cortex was decreased in long-term ayahuasca users (Bouso
et al., 2015). The salience network has been proposed to orchestrate dynamic switching
between mentalizing states anchored on the default mode network and externally-driven
attentional states anchored on the task-control network in order to guide behavior by
segregating relevant internal and extrapersonal stimuli (Menon and Uddin, 2010; Uddin, 2015;
Zhou and Seeley, 2014). Intriguingly, increased global coupling and functional connectivity
between the salience and default mode network nodes have been found under acute psilocybin
administration (Carhart-Harris et al., 2013) and subacutely with ayahuasca (Sampedro et al.,
2017), but future work, ideally combining multimodal molecular and functional neuroimaging, is
needed in order to elucidate how mid- and long-term functional interactions of both networks are
changed by psychedelic agents.
Impact of psychedelics on interoception, affect, and self-referential processes.
Psychedelic substances modulate blood pressure, body temperature, and heart rate by
interacting with the sympathetic and parasympathetic autonomic nervous system, and have
shown to impact emotional and affective functions by improving clinical symptoms in mood
disorders (Carhart-Harris, Bolstridge, et al., 2016; Griffiths et al., 2016; Grob et al., 2011;
Palhano-Fontes et al., 2019; Ross et al., 2016; Sanches et al., 2016). By which mechanisms
may ayahuasca mediate changes in interoception, affect, and self-referential processes? Hubs
of the salience network, such as the insula and the anterior cingulate, have been consistently
associated with emotional processing (Craig, 2009; Critchley and Harrison, 2013; Etkin et al.,
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author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
2011; Ochsner and Gross, 2005; Seeley et al., 2007; Touroutoglou et al., 2012) and
dysfunctions in these regions underlie depression and anxiety in various affective disorders
(Williams, 2016). Increased connectivity in the salience network has been associated with early
heightened emotional contagion in preclinical Alzheimer’s disease (Fredericks et al., 2018;
Sturm et al., 2013), while widespread salience network functional and structural degeneration is
observed in behavioral variant frontotemporal dementia, a neurodegenerative disease
characterized by loss of empathy, socioemotional symptoms, and autonomic dysfunctions
(Rankin et al., 2006; Seeley et al., 2012; Sturm, Sible, et al., 2018). Based on these studies, the
salience network is believed to support socioemotional-autonomic processing through its
interoceptive afferents in the anterior insula processing autonomic activity streams regarding the
“moment-to-moment” condition of the body (Craig, 2009; Critchley and Harrison, 2013; Uddin,
2015; Zhou and Seeley, 2014). The anterior cingulate cortex subsequently receives integrated
anterior insula input and serves to mobilize visceromotor responses to salient socioemotional
stimuli in order to guide behavior (Craig, 2009; Critchley and Harrison, 2013; Uddin, 2015; Zhou
and Seeley, 2014). Critically, our findings of subacute default mode network functional
connectivity decreases with ayahuasca are in contrast with a previous study reporting subacute
default mode network connectivity increases with psilocybin in treatment-resistant depression
(Carhart-Harris et al., 2017). Previous works have reported both default mode network
connectivity increases and decreases in major depression (Berman et al., 2011; Greicius et al.,
2007; Sheline et al., 2009; Yan et al., 2019), with heightened connectivity being associated with
altered self-referential thoughts such as rumination and negative internal representations
(Berman et al., 2011; Sheline et al., 2009). Although in healthy subjects, our findings provide
preliminary evidence that ayahuasca may have a sustained dampening on functional
connectivity of systems involved in self-referential processes associated with characteristic
symptoms of depression (Brewer et al., 2013; Sheline et al., 2009). We propose that future
studies combining longitudinal tf-fMRI and autonomic recordings in healthy and neuropsychiatric
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author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
populations could shed light on the acute and long-term impact of psychedelic agents on brain
networks supporting interoceptive, affective, and self-referential processes.
Limitations. An important limitation of our study consists of the use of liberal voxel-wise
statistical thresholds when assessing group differences in subacute functional connectivity
across distinct brain networks. Recent research has shown that liberal cluster-extend thresholds
are prone to inflate false-positive results, questioning the validity of weakly significant
neuroimaging findings (Eklund et al., 2016). The low power attained in our study may have been
caused by the small number of participants involved in the study and by the moderate strength
of the MRI scanner (1.5 Tesla). Further, weak effects on functional connectivity were to expect
after a single ayahuasca session in a sample of cognitively healthy participants, urging for future
studies implementing repeated sessions and the inclusion of neuropsychiatric populations.
However, we performed several control analyses in order to mitigate methodological and
statistical concerns. First, we assessed the reliability of our findings by controlling for the used
methodological approach, which revealed similar functional connectivity changes when
comparing findings from the seed-based versus ICA approach. Finally, in order to address
concerns related to the liberal statistical threshold, we applied nonparametric permutation tests
replicating the main findings in this study. Second, we assessed the impact of head movement
on the association between altered states of consciousness and subacute functional
connectivity changes through the use of partial correlation coefficients. These analyses revealed
that head movement, a common confounder in tf-fMRI studies, did not impact our findings.
However, findings of decreased functional connectivity in the default mode network need to be
interpreted with a grain of salt, since these did not survive more stringent statistical thresholds.
Further, the volition subscale of the HRS has been shown to have a low internal consistency
(Riba, Rodrı, et al., 2001) advising caution in interpreting the association between altered acute
levels in the volition scale and subacute default mode network functional connectivity decreases
induced by ayahuasca.
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author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
Conclusions
Psychedelic substances have sustained effects on mood, affect, and self-referential
processes in healthy and clinical populations days to weeks after dosing. The novelty of our
study resides in elucidating the subacute effects of the psychedelic ayahuasca on functional
organization of the salience network and default mode network, two brain systems distinctly
involved in interoceptive, affective, and self-referential functions. While primary sensory
networks did not show subacute changes in functional connectivity, increased functional
connectivity of the salience network one day after the session with ayahuasca related to altered
acute somesthesia levels, while decreases in default mode network functional connectivity
related to altered levels of volition. Our findings suggest that ayahuasca may have long-lasting
effects on affect and mood by modulating those neural circuits supporting interoceptive,
affective, and self-referential functions.
Acknowledgments
L.P. was supported by the German Academic Foundation. The study was funded by the
Brazilian federal agencies CNPq (grants #466760/2014 & #479466/2013) and CAPES (grants
#1677/2012 & #1577/2013).
Financial Disclosures
The authors have no conflict of interest to declare.
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Tables
Ayahuasca
(N = 22)
Placebo
(N = 21)
t
p
Age (s.d.) in years
30.8 (8.4) 31.0 (10.5) 0.06 0.95
Gender (F/M)
12/10 11/10 0.02
&
0.89
Before dosing
-
mean
framewise head
displacement (s.d) in mm
0.14 (0.03) 0.13 (0.05) 0.56 0.57
After dosing
-
mean
framewise head
displacement (s.d) in mm
0.15 (0.05)
A
0.14 (0.05)
B
1.01 0.31
Table 1. Sample characteristics. &Chi-square statistics, chi-square test used to test group
differences in gender distribution. Paired t-test used to test differences in head motion between
the first and second sessions: At = 1.43, p = 0.17; Bt = 0.41, p = 0.69.
Mean (
s.d.)
Ayahuasca
Placebo
t
p
Somesthesia
1.0 (0.6) 0.2 (0.1) 6.3 < 0.0005
Affect
0.9 (0.6) 0.4 (0.2) 3.6 < 0.005
Perception
1.2 (0.6) 0.0 (0.1) 10.0 < 0.0005
Cognition
0.9 (0.6) 0.1 (0.1) 6.2 < 0.0005
Volition
1.2 (0.5) 0.8 (0.5) 2.8 < 0.009
Intensity
2.4 (0.9) 0.5 (0.4) 8.9 < 0.0005
Table 2. Hallucinogenic rating scale (HRS). Subscales assessed during the
ayahuasca/placebo sessions.
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author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
Figures and Legends
Figure 1. Study pipeline. (A)
Participants were randomly assigned to the placebo (n=21; 1
ml/kg of ayahuasca adjusted to contain 0.36 mg/kg of DMT) or ayahuasca group (n=22; 1 ml/kg
of a placebo). Subscales of the Hallucinogenic Rating Scale (HRS) were assessed during the
acute effects of ayahuasca/placebo. All participants were assessed with tf-
fMRI one day before
and one day after dosing. (B)
Map of the salience, default mode, visual, and sensorimotor
networks at baseline overlaid onto the MNI template (warm colors; extent probabilit
y threshold
1
kg
he
re
tor
ld
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author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
of p<0.01 FWE corrected, voxel-wise threshold of p<0.001 FWE corrected for multiple
comparisons). Individual brain network maps were derived by seeding bilateral region-of-interest
(in blue). Left is on the left, bar reflects t-values.
. CC-BY-NC-ND 4.0 International licenseIt is made available under a
author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the(which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/19007542doi: medRxiv preprint
Figure 2. Functional connectivity changes. (A)
Significant salience network functional
connectivity increases in the anterior cingulate cortex for the ayahuasca compared to the
placebo group. Joint extent and cluster probability thresholds of p<0.05 (red) and
p<0.01
(yellow). Left is on the left, bar reflects t-values. (B)
Box plot schematizing group differences in
functional connectivity (average functional connectivity levels derived from the cluster identified
in panel A with a joint cluster and extent probability thresholds of p<0.01). (C)
Significant default
mode network functional connectivity decreases in the posterior cingulate cortex for the
ayahuasca compared to the placebo group. Joint cluster and extent probability thresholds of
p<0.05 (red). Left is on the left, bar reflects t-values. (D)
Box plot schematizing group
differences in functional connectivity (average functional connectivity levels derived from the
cluster identified in panel C with a joint cluster and extent probability thresholds of p<0.05).
al
he
01
in
ed
ult
he
of
up
he
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Figure 3. Ayahuasca induced suba
cute changes in functional connectivity correlate with
altered somesthesia and volition. Boxplot showing group differences in (A)
somesthesia and
(B) volition assessed with the HRS during the acute effects of aya
huasca (in red) and placebo
(in cyan). Scatter plots and partial correlation coefficients corrected for the difference in
framewise head displacement between the second and first scan associating (C)
somesthesia
or (D) volition with averaged levels of func
tional connectivity changes identified in the salience
network and default mode network (ayahuasca red circles and line, placebo cyan triangles and
line).
+
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With the aim of further advancing the understanding of the human brain’s functional connectivity, we propose a network metric which we term the geodesic entropy. This metric quantifies the Shannon entropy of the distance distribution to a specific node from all other nodes. It allows to characterize the influence exerted on a specific node considering statistics of the overall network structure. The measurement and characterization of this structural information has the potential to greatly improve our understanding of sustained activity and other emergent behaviors in networks. We apply this method to study how the psychedelic infusion Ayahuasca affects the functional connectivity of the human brain in resting state. We show that the geodesic entropy is able to differentiate functional networks of the human brain associated with two different states of consciousness in the awaking resting state: (i) the ordinary state and (ii) a state altered by ingestion of the Ayahuasca. The functional brain networks from subjects in the altered state have, on average, a larger geodesic entropy compared to the ordinary state. Finally, we discuss why the geodesic entropy may bring even further valuable insights into the study of the human brain and other empirical networks.
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Background: Recent open-label trials show that psychedelics, such as ayahuasca, hold promise as fast-onset antidepressants in treatment-resistant depression. Methods: To test the antidepressant effects of ayahuasca, we conducted a parallel-arm, double-blind randomized placebo-controlled trial in 29 patients with treatment-resistant depression. Patients received a single dose of either ayahuasca or placebo. We assessed changes in depression severity with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Hamilton Depression Rating scale at baseline, and at 1 (D1), 2 (D2), and 7 (D7) days after dosing. Results: We observed significant antidepressant effects of ayahuasca when compared with placebo at all-time points. MADRS scores were significantly lower in the ayahuasca group compared with placebo at D1 and D2 (p = 0.04), and at D7 (p < 0.0001). Between-group effect sizes increased from D1 to D7 (D1: Cohen's d = 0.84; D2: Cohen's d = 0.84; D7: Cohen's d = 1.49). Response rates were high for both groups at D1 and D2, and significantly higher in the ayahuasca group at D7 (64% v. 27%; p = 0.04). Remission rate showed a trend toward significance at D7 (36% v. 7%, p = 0.054). Conclusions: To our knowledge, this is the first controlled trial to test a psychedelic substance in treatment-resistant depression. Overall, this study brings new evidence supporting the safety and therapeutic value of ayahuasca, dosed within an appropriate setting, to help treat depression. This study is registered at http://clinicaltrials.gov (NCT02914769).
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Psilocybin with psychological support is showing promise as a treatment model in psychiatry but its therapeutic mechanisms are poorly understood. Here, cerebral blood flow (CBF) and blood oxygen-level dependent (BOLD) resting-state functional connectivity (RSFC) were measured with functional magnetic resonance imaging (fMRI) before and after treatment with psilocybin (serotonin agonist) for treatment-resistant depression (TRD). Quality pre and post treatment fMRI data were collected from 16 of 19 patients. Decreased depressive symptoms were observed in all 19 patients at 1-week post-treatment and 47% met criteria for response at 5 weeks. Whole-brain analyses revealed post-treatment decreases in CBF in the temporal cortex, including the amygdala. Decreased amygdala CBF correlated with reduced depressive symptoms. Focusing on a priori selected circuitry for RSFC analyses, increased RSFC was observed within the default-mode network (DMN) post-treatment. Increased ventromedial prefrontal cortex-bilateral inferior lateral parietal cortex RSFC was predictive of treatment response at 5-weeks, as was decreased parahippocampal-prefrontal cortex RSFC. These data fill an important knowledge gap regarding the post-treatment brain effects of psilocybin, and are the first in depressed patients. The post-treatment brain changes are different to previously observed acute effects of psilocybin and other ‘psychedelics’ yet were related to clinical outcomes. A ‘reset’ therapeutic mechanism is proposed.
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Background: Ayahuasca is a plant tea containing the psychedelic 5-HT2A agonist N,N-dimethyltryptamine (DMT) and harmala monoamine-oxidase inhibitors. Acute administration leads to neurophysiological modifications in brain regions of the default mode network (DMN), 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 sixteen healthy volunteers ayahuasca-induced post-acute neurometabolic and connectivity modifications, and their association with mindfulness measures. Methods: Using 1H-magnetic resonance spectroscopy (MRS) and functional connectivity, we compared baseline and post-acute neurometabolites and seed-to-voxel connectivity in the posterior (PCC) and anterior (ACC) cingulate cortex after a single ayahuasca dose. Results: MRS showed post-acute reductions in Glx (glutamate+glutamine), creatine and NAA-NAAG (N-acetylaspartate+N-acetylaspartylglutamate) in the PCC. Connectivity was increased between the PCC and the ACC, and between the ACC and limbic structures in the right medial temporal lobe (MTL). Glx reductions correlated with increases in the "Non-Judging" subscale of the Five Facets Mindfulness Questionnaire. Increased ACC-MTL connectivity correlated with increased scores on the Self-Compassion questionnaire. Post-acute neural changes predicted sustained elevations in "Non-Judging" two 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 PCC, a key region within the DMN, and increased connectivity between the ACC and MTL structures involved in emotion and memory, potentially underlie the post-acute psychological effects of ayahuasca.
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Background: Clinically significant anxiety and depression are common in patients with cancer, and are associated with poor psychiatric and medical outcomes. Historical and recent research suggests a role for psilocybin to treat cancer-related anxiety and depression. Methods: In this double-blind, placebo-controlled, crossover trial, 29 patients with cancer-related anxiety and depression were randomly assigned and received treatment with single-dose psilocybin (0.3 mg/kg) or niacin, both in conjunction with psychotherapy. The primary outcomes were anxiety and depression assessed between groups prior to the crossover at 7 weeks. Results: Prior to the crossover, psilocybin produced immediate, substantial, and sustained improvements in anxiety and depression and led to decreases in cancer-related demoralization and hopelessness, improved spiritual wellbeing, and increased quality of life. At the 6.5-month follow-up, psilocybin was associated with enduring anxiolytic and anti-depressant effects (approximately 60-80% of participants continued with clinically significant reductions in depression or anxiety), sustained benefits in existential distress and quality of life, as well as improved attitudes towards death. The psilocybin-induced mystical experience mediated the therapeutic effect of psilocybin on anxiety and depression. Conclusions: In conjunction with psychotherapy, single moderate-dose psilocybin produced rapid, robust and enduring anxiolytic and anti-depressant effects in patients with cancer-related psychological distress. Trial registration: ClinicalTrials.gov Identifier: NCT00957359.
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The entropic brain hypothesis holds that the key facts concerning psychedelics are partially explained in terms of increased entropy of the brain's functional connectivity. Ayahuasca is a psychedelic beverage of Amazonian indigenous origin with legal status in Brazil in religious and scientific settings. In this context, we use tools and concepts from the theory of complex networks to analyze resting state fMRI data of the brains of human subjects under two distinct conditions: (i) under ordinary waking state and (ii) in an altered state of consciousness induced by ingestion of Ayahuasca. We report an increase in the Shannon entropy of the degree distribution of the networks subsequent to Ayahuasca ingestion. We also find increased local and decreased global network integration. Our results are broadly consistent with the entropic brain hypothesis. Finally, we discuss our findings in the context of descriptions of "mind-expansion" frequently seen in self-reports of users of psychedelic drugs.
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In the behavioral variant of frontotemporal dementia (bvFTD), left-lateralized salience network dysfunction reduces basal activity in the parasympathetic nervous system, a branch of the autonomic nervous system that reduces arousal and fosters empathy and prosociality. Here we examined whether resting parasympathetic deficits in bvFTD related to diminished prosocial behavior. Eighty participants [30 with bvFTD, 25 with Alzheimer's disease (AD), and 25 healthy controls] completed a “helping task” in which we quantified participants' spontaneous reactions to an experimenter who struggled to find a lost key. Participants also underwent an assessment of baseline autonomic nervous system activity and structural magnetic resonance imaging. An exploratory factor analysis of participants' behaviors during the helping task revealed four factors: empathic concern, consolation, disengagement, and impatience. Patients with bvFTD had lower empathic concern and greater disengagement and impatience than the AD and healthy control groups. Patients with bvFTD had lower resting respiratory sinus arrhythmia and faster respiration and heart rates than patients with AD and healthy controls, a pattern consistent with parasympathetic dysfunction. Skin conductance level was also lower in bvFTD than in the other groups. Lower baseline respiratory sinus arrhythmia and faster baseline respiration rates, but not skin conductance level, predicted lower prosocial helping behaviors. Voxel-based morphometry analyses revealed that atrophy in the bilateral medial pulvinar nucleus of the thalamus, midcingulate cortex, and caudate was associated with lower empathic concern and consolation, and atrophy in the bilateral medial pulvinar nucleus of the thalamus, left frontoinsula, and left ventral striatum was associated with greater disengagement and impatience. Left-lateralized frontoinsula atrophy was associated with not only lower respiratory sinus arrhythmia but also with lower consolation and greater disengagement. This study offers evidence for prosocial behavior deficits in bvFTD and suggests that left-lateralized salience network atrophy reduces patients' resting parasympathetic activity and motivation to help others in need.
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The salience network is a distributed neural system that maintains homeostasis by regulating autonomic nervous system activity and social-emotional function. Here we examined how within-network connectivity relates to individual differences in human (including males and females) baseline parasympathetic and sympathetic nervous activity. We measured resting autonomic nervous system physiology in 24 healthy controls and 23 patients with behavioral variant frontotemporal dementia (bvFTD), a neurodegenerative disease characterized by baseline autonomic deficits. Participants also underwent structural and task-free functional magnetic resonance imaging. First, we used voxel-based morphometry to determine whether salience network atrophy was associated with lower baseline respiratory sinus arrhythmia (RSA; a parasympathetic measure) and skin conductance level (SCL; a sympathetic measure) in bvFTD. Next, we examined whether functional connectivity deficits in 21 autonomic-relevant, salience network node-pairs related to baseline autonomic dysfunction. Lower baseline RSA was associated with smaller volume in left ventral anterior insula (vAI), weaker connectivity between bilateral vAI and bilateral anterior cingulate cortex (ACC), and stronger connectivity between bilateral ACC and bilateral hypothalamus/amygdala. Lower baseline SCL, in contrast, was associated with smaller volume in inferior temporal gyrus, dorsal mid-insula, and hypothalamus; weaker connectivity between bilateral ACC and right hypothalamus/amygdala; and stronger connectivity between bilateral dorsal anterior insula and periaqueductal gray. Our results suggest that baseline parasympathetic and sympathetic tone depend on the integrity of lateralized salience network hubs (left vAI for parasympathetic and right hypothalamus/amygdala for sympathetic) and highly calibrated ipsilateral and contralateral network connections. In bvFTD, deficits in this system may underlie resting parasympathetic and sympathetic disruption.SIGNIFICANCE STATEMENTThe salience network maintains homeostasis and regulates autonomic nervous system activity. Whether within-network connectivity patterns underlie individual differences in resting parasympathetic and sympathetic nervous system activity, however, is not well understood. We measured baseline autonomic nervous system activity in healthy controls and patients with behavioral variant frontotemporal dementia, a neurodegenerative disease characterized by resting autonomic deficits, and probed how salience network dysfunction relates to diminished parasympathetic and sympathetic outflow. Our results indicate that baseline parasympathetic and sympathetic tone are the product of complex, opposing intra-network nodal interactions and depend on the integrity of highly tuned, lateralized salience network hubs (i.e., left ventral anterior insula for parasympathetic activity and right hypothalamus/amygdala for sympathetic activity).
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The serotonin (5-hydroxytryptamine, 5-HT) system modulates many important brain functions and is critically involved in many neuropsychiatric disorders. Here, we present a high-resolution, multidimensional, in vivo atlas of four of the human brain's 5-HT receptors (5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4) and the 5-HT transporter (5-HTT). The atlas is created from molecular and structural high-resolution neuroimaging data consisting of positron emission tomography (PET) and magnetic resonance imaging (MRI) scans acquired in a total of 210 healthy individuals. Comparison of the regional PET binding measures with postmortem human brain autoradiography outcomes showed a high correlation for the five 5-HT targets and this enabled us to transform the atlas to represent protein densities (in picomoles per milliliter). We also assessed the regional association between protein concentration and mRNA expression in the human brain by comparing the 5-HT density across the atlas with data from the Allen Human Brain atlas and identified receptor-and transporter-specific associations that show the regional relation between the two measures. Together, these data provide unparalleled insight into the serotonin system of the human brain.