This further analysis of data from a single-blind, placebo-controlled study (n=20) on the effects of LSD (75µg) finds that the context (eyes closed/open, silence/music/video) modulates the level of brain entropy. The study finds that eyes-closed elicited the biggest response, and that video (external stimuli) disrupts the correlation between brain entropy and subjective ratings of the experience.
Recent findings have shown that psychedelics reliably enhance brain entropy (understood as neural signal diversity), and this effect has been associated with both acute and long-term psychological outcomes, such as personality changes. These findings are particularly intriguing, given that a decrease of brain entropy is a robust indicator of loss of consciousness (e.g., from wakefulness to sleep). However, little is known about how context impacts the entropy-enhancing effect of psychedelics, which carries important implications for how it can be exploited in, for example, psychedelic psychotherapy. This article investigates how brain entropy is modulated by stimulus manipulation during a psychedelic experience by studying participants under the effects of lysergic acid diethylamide (LSD) or placebo, either with gross state changes (eyes closed vs open) or different stimuli (no stimulus vs music vs video). Results show that while brain entropy increases with LSD under all of the experimental conditions, it exhibits the largest changes when subjects have their eyes closed. Furthermore, brain entropy changes are consistently associated with subjective ratings of the psychedelic experience, but this relationship is disrupted when participants are viewing a video─potentially due to a “competition” between external stimuli and endogenous LSD-induced imagery. Taken together, our findings provide strong quantitative evidence of the role of context in modulating neural dynamics during a psychedelic experience, underlining the importance of performing psychedelic psychotherapy in a suitable environment.
Papers cited by this study that are also in Blossom
Carhart-Harris, R. L., Bolstridge, M., Rucker, J. et al. · Lancet Psychiatry (2016)
Carhart-Harris, R. L., Goodwin, G. M. · Neuropsychopharmacology (2017)
Kyzar, E. J., Nichols, C. D., Gainetdinov, R. R. et al. · Trends in Pharmacological Sciences (2017)
Wacker, D., Wang, S., Mccorvy, J. D. et al. · Cell (2017)
Recent work has shown that classic psychedelics reliably increase measures of brain entropy, understood here as the informational complexity or diversity of neural signals, and that these increases relate to acute phenomenology and longer-term psychological change. However, a robust decrease in entropy is also a marker of reduced conscious level (for example during sleep), raising questions about how entropy relates to different facets of consciousness. The Entropic Brain Hypothesis (EBH) proposes that the rich altered states induced by psychedelics reflect an enrichment of spontaneous, population-level neural dynamics, but it remains unclear how contextual factors such as sensory environment and eye state (components of "set and setting") modulate this entropy-enhancing effect. Mediano and colleagues set out to test how external stimulation and eye opening interact with LSD to shape neural entropy and its relation to subjective experience. Using MEG recordings and subjective ratings collected while participants received intravenous LSD or placebo, the study compares four environmental conditions (eyes closed, music with eyes closed, eyes open fixation, and watching a silent nature video) to determine whether and how context alters both the magnitude of entropy changes and their correspondence with phenomenology. The work is framed as a proof-of-principle translational investigation in healthy volunteers with implications for the practice of psychedelic-assisted therapy.
The analysis reuses data from a previously reported experiment in which twenty healthy participants attended two sessions each: one with intravenous LSD (75 μg) and one with intravenous saline placebo. Session order was randomised and sessions were separated by two weeks; participants were blind to order (single-blind design). During each session whole-brain magnetoencephalography (MEG) was recorded while participants experienced four conditions: resting with eyes closed (closed), listening to instrumental ambient music with eyes closed (music), resting with eyes open fixating a dot (open), and watching a silent nature documentary (video). Visual Analog Scale (VAS) questionnaires were administered at the end of each session to capture subjective dimensions including intensity, emotional arousal, ego dissolution, positive mood, and simple and complex imagery (the imagery items were only rated in eyes-closed conditions). MEG data were acquired with a 271-gradiometer CTF system and structural MRI scans were obtained for source reconstruction. After excluding three participants for incomplete recording or excessive movement, data were preprocessed using FieldTrip: artefacts were removed by visual inspection and ICA to eliminate muscle and line noise, a second-order low-pass Butterworth filter at 100 Hz was applied, and data were split into 2 s epochs. Source time series (virtual sensors) were estimated using a regularised LCMV beamformer at the centroids of the AAL-90 atlas; Lempel-Ziv complexity (LZ), an algorithmic measure of signal diversity, was computed on these source time series and mapped to a standard template for group analysis. Statistical analysis combined non-parametric tests (Kruskal-Wallis and post-hoc t-tests) with linear mixed-effects (LME) models to assess predictors of LZ and VAS scores. LME models treated average LZ (or VAS items) as the dependent variable, included fixed effects such as drug condition (LSD vs placebo), presence of stimulus (none/music/video), and eye opening, and modelled subject identity as a random effect; model selection used the Bayesian Information Criterion (BIC). Between-subject Pearson correlations (with false discovery rate correction where reported) were used to probe relationships between regional LZ changes and VAS items. Multivariate regression and a conditional predictive power analysis were also employed: the latter builds a directed network indicating whether the predictive information a brain region provides about a VAS item is mediated by another region.
Across all analyses the administration of LSD produced a clear increase in Lempel-Ziv complexity relative to placebo. In the placebo sessions external stimuli and eye opening themselves modulated LZ: richer stimuli produced higher LZ and eye opening increased LZ, with a Kruskal-Wallis test showing significant differences across conditions and post-hoc tests indicating consistent increases with richer stimuli. In an LME model using stimulus presence and eye opening as predictors (with subject as a random effect), stimulus had a positive effect on LZ (β = 0.013, SE = 0.005, p = 0.017) and eye opening had a larger positive effect (β = 0.025, SE = 0.005, p < 0.001). Adding drug as a fixed effect revealed a substantial further increase in LZ under LSD, larger than those associated with stimulus or eye opening. Crucially, the interaction between drug and eye opening was significant and negative: increased external stimulation (in particular opening the eyes or viewing richer stimuli) reduced the magnitude of the drug-induced LZ increase. The authors interpret this as a form of competition between endogenous, drug-induced neural dynamics and exogenous, stimulus-driven dynamics. This negative interaction was robust to alternative analyses (for example using stricter signal filters) and was spatially widespread across brain regions. Subjective VAS measures were strongly affected by LSD, with the drug producing much larger effects than stimulus or eye opening across the assessed dimensions. Correlations between LSD-induced changes in regional LZ and VAS ratings were present in several conditions but differed markedly by context. In the eyes-closed condition significant positive correlations were observed, for example between ego dissolution and posterior default mode network (pDMN) entropy, positive mood and amygdala entropy, and simple/complex imagery and visual/auditory ROIs. These neural–psychometric correlations persisted in eyes-closed, music, and eyes-open fixation conditions but largely disappeared when participants watched the video: correlations fell to near zero (none exceeding |r| > 0.1). A multivariate regression showed that the interaction of stimulus and eye opening was associated with smaller VAS–LZ correlation values (β = -0.21, SE = 0.08, p = 0.006). Analyses of inter-regional LZ correlations showed that external stimulation increased the correlation between ROIs, which the authors characterise as potential "complexity matching" whereby neural dynamics become more entrained by the stimulus and thus more similar across regions. Regression models of ROI–ROI correlation yielded eye opening associated with smaller values (β = -0.10, SE = 0.04, p = 0.011), while stimulus presence (β = 0.15, SE = 0.04, p < 0.001) and the stimulus-by-eye-open interaction (β = 0.18, SE = 0.05, p = 0.001) predicted larger correlations. Conditional predictive power analyses indicated that lower-level sensory regions tend to mediate the predictive relationships between higher-level areas and subjective reports: once changes in visual and auditory region entropy are known, the entropy changes in pDMN or insula add little extra predictive information about reported complex imagery. Ego dissolution was a notable exception, where pDMN, auditory cortex, and insula each provided complementary, unmediated predictive information about the subjective report.
Mediano and colleagues interpret the findings as quantitative evidence that environmental context substantially shapes both the neural dynamics and subjective phenomenology of the psychedelic state. The data show that while LSD robustly increases neural signal diversity, this effect is attenuated by external stimulation and eye opening, and the close correspondence between entropy and subjective experience is strongest with eyes closed. The authors propose a competition model in which exogenous stimuli can overwrite or mask endogenous, drug-driven dynamics, reducing the capacity to detect relationships between entropy measures and specific aspects of reported experience. In relation to the Entropic Brain Hypothesis, the results qualify a straightforward reading that higher brain entropy uniformly indexes richer conscious content. The authors note that Lempel-Ziv complexity, computed at the level of individual source time series, may preferentially reflect lower-level, sensory aspects of the brain–mind relation rather than higher-order cognitive phenomena. They therefore advocate for complementary approaches that consider network-level entropy and other multidimensional metrics of brain dynamics, while recognising that increasing model complexity can reduce interpretability and statistical power. Implications for psychedelic-assisted therapy are emphasised: the stronger drug–entropy effects and tighter LZ–phenomenology correlations when eyes are closed support therapeutic practices that encourage eyes-closed, introspective states and the selective use of music rather than visual stimulation. The work is presented as a proof-of-concept in healthy volunteers that establishes LZ as a neuroimaging marker sensitive to interactions between drug and context, paving the way for clinical studies. The authors acknowledge limitations and avenues for future research. The sample comprised healthy participants and the design was single blind; three participants were excluded due to incomplete or artefact-laden recordings. Several analyses and controls are reported in supplementary material, and the authors call for replication and extension in clinical cohorts, with other pharmacological agents, dosages, and stimulus modalities to further disentangle the relationships between entropy, phenomenology, and therapeutic outcomes.
Recent findings have shown that psychedelics reliably enhance brain entropy (understood as neural signal diversity), and this effect has been associated with both acute and long-term psychological outcomes such as personality changes. These findings are particularly intriguing given that a decrease of brain entropy is a robust indicator of loss of consciousness (e.g. from wakefulness to sleep). However, little is known about how context impacts the entropy-enhancing effect of psychedelics, which carries important implications for how it can be exploited in, for example, psychedelic psychotherapy. This article investigates how brain entropy is modulated by stimulus manipulation during a psychedelic experience, by studying participants under the effects of LSD or placebo, either with gross state changes (eyes closed vs. open) or different stimulus (no stimulus vs. music vs. video). Results show that while brain entropy increases with LSD in all the experimental conditions, it exhibits largest changes when subjects have their eyes closed. Furthermore, brain entropy changes are consistently associated with subjective ratings of the psychedelic experience, but this relationship is disrupted when participants are viewing video -potentially due to a "competition" between external stimuli and endogenous LSD-induced imagery. Taken together, our findings provide strong quantitative evidence for the role of context in modulating neural dynamics during a psychedelic experience, underlining the importance of performing psychedelic psychotherapy in a suitable environment. Additionally, our findings put into question simplistic interpretations of brain entropy as a direct neural correlate of conscious level. Complexity | Psychedelics | Neuroscience | Consciousness P sychedelic substances, such as LSD and psilocybin, are known to induce profound changes in subjects' perception, cognition, and conscious experience. In addition to their role in ancestral spiritual and religious practices, and their recreational use related to introspection and self-exploration, there is promising evidence that psychedelics can be used therapeutically to treat multiple mental health conditions. However, despite the increasingly available evidence of the neurochemical action of psychedelics at the neuronal and sub-neuronal level, the mechanisms associated with their therapeutic efficacy are not yet completely understood. Some of the factors at play during psychedelic therapy can be related to the Entropic Brain Hypothesis (EBH), a simple yet powerful theory which posits that the rich altered state of consciousness experienced under psychedelics depends on a parallel enriching effect on the dynamics of spontaneous population-level neuronal activity. * The hypothesis that in-17 creased brain entropy -as captured e.g. by Lempel-Ziv (LZ)
The effectiveness of psychedelic therapy is thought to de-30 pend not only on direct neuropharmacological action, but 31 also on contextual factors -commonly referred to as set 32 and setting. These include the subject's mood, expectations, 33 and broader psychological condition (set) prior to the "trip", 34 together with the sensorial, social, and cultural environment 35 (setting) in which the drug is taken. For example, there is 36 direct physiological evidence that (visual) stimuli affect the 37 * Entropy is understood here not as a thermodynamic but as an informational property, measuring the complexity of neural dynamics and the diversity of their configuration repertoire (see Methods).
The effects of psychedelic substances on conscious experience can be substantially affected by contextual factors, which play a critical role in the outcomes of psychedelic therapy. This study shows how context can modulate not only psychological, but also neurophysiological phenomena during a psychedelic experience. Our findings reveal distinctive effects of having eyes closed after taking LSD, including a more pronounced change on the neural dynamics, and a closer correspondence between brain activity and subjective ratings. Furthermore, our results suggest a competition between external stimuli and internal psychedelic-induced imagery, which supports the practice of carrying out psychedelic therapy with patients having their eyes closed. expression of serotonergic receptor genes, and that spe-weeks, and participants were blind to the order (i.e. single blind design). Whole-brain magnetoencephalography (MEG) data were collected under four conditions: resting state with eyes closed, listening to instrumental ambient music with eyes closed, resting state with eyes open (focusing on a "fixation dot"), and watching a silent nature documentary videohenceforth referred to as closed, music, open, and video. The music tracks were taken from the album "Eleusian Lullaby" by Alio Die, and the video was composed of segments of the "Frozen Planet" documentary series produced by the BBC. More information about the experimental design can be found in Ref.. Studying the whole-brain average LZ from the placebo sessions showed that external stimuli yield significant differences in LZ (Kruskal-Wallis test, p < 0.001). Post-hoc t-tests, shown in Figure, revealed that richer stimuli induce consistent significant increases across conditions, with large effect sizes (Cohen's d). To disentangle the effect of the stimuli over the effect of eye opening, a linear mixed-effects (LME) model was constructed using the presence of stimulus and eye opening as predictor variables, and subject identity as random effect (see Methods). This model showed significant positive effects of both stimulus (β = 0.013, SE = 0.005, p = 0.017) and eye opening (β = 0.025, SE = 0.005, p < 0.001). The statistical significance of both effects suggests that the measured LZ cannot be explained added the drug as fixed effect. This analysis shows a dramatic 96 increase in LZ under the effects of LSD, much larger than that 97 associated with eye opening or stimulus (Fig.and Table).
Post-hoc analyses showed that the effect of drug is substantial 99 in all stimulus conditions (Fig.).
Crucially, the LME model revealed a significant interaction 101 between drug and eye opening as predictors of LZ (Table).
Importantly, this interaction effect was negative -i.e. in-103 creased external stimulation reduced the effect of the drug.
Alternatively, this can be interpreted as the drug reducing the 105 effect of external stimulation on brain entropy -which, either way, points towards a "competition" between endogenous, drug-induced, and exogenous, stimulus-induced, effects on neural dynamics. This negative interaction was confirmed by ordering the four experimental conditions with integer values from 1 to 4 (Fig.), and with multiple statistical hypothesis tests (e.g. 2-way ANOVA). Furthermore, we confirmed that the results still hold with stricter filters (e.g. a low-pass filter at 30 Hz on the MEG signals), and when controlling for order effects between the stimulus and non-stimulus sessions (see Supplementary Material). Both the effect of the drug and its interaction with external conditions are spatially widespread (Fig.) .
In addition to MEG measurements, Visual Analog Scale (VAS) subjective ratings were collected at the end of each session. The questionnaires were designed to capture central features of the subjective effects of LSD. They included assessments of the intensity of the experience, emotional arousal, ego dissolution, positive mood, and simple and complex internal visual imagery. The imagery items were only rated for the eyes-closed conditions. The effects of LSD on VAS ratings varied widely between conditions (Fig.). A quantitative analysis with LME models showed the effect of the drug to be much larger than that of the stimulus or eye opening on all the VAS measures (Fig.). Additionally, stimulus effects tended to be more specific than , in all four experimental conditions. As external stimulation is increased, there is a large decrease in correlation between subjective ratings and entropy, but an increase in the correlation in entropy between different brain regions (see Supplementary Material). Bottom right panels show example correlations between ego dissolution and posterior DMN entropy (two left panels) and positive mood and amygdala entropy (two right panels). In both cases, correlation is strong and significant with eyes closed, but vanishes when subjects watch a video. other specific aspects of experience such as its visual quality. 156 However, given that -as we show here -setting interacts with neural dynamics, then it is natural to ask whether it also affects the relationship between phenomenology and its neural correlates. To address this question, we analysed the relationship between LZ and VAS changes induced by LSD, in each one of the four experimental conditions. Between-subjects Pearson correlation coefficients were calculated between changes in VAS ratings and LZ measured in different regions of interest (ROI). Motivated by the nature of the study and known brain effects of LSD, we focused on areas associated with sensory processing (visual and auditory), interoception (insula), emotional processing (amygdala), and self-monitoring (mPFC and posterior DMN; see Methods for details). Analyses revealed multiple significant relationships between subjective ratings and LZ changes during the eyes-closed, music, and eyes-open conditions (Fig.). For example, we observed significant (p < 0.05, FDR-corrected) positive correlations between ego dissolution and DMN, positive mood and amygdala, and simple and complex imagery and visual and auditory ROIs, all in the eyes-closed condition -supporting the suitability of the eyes-closed resting condition for assessing the neural correlates of these experiences. Strikingly, all the observed neural-psychometric correlations vanish when subjects watched a video, with none exceeding an absolute value of |r| > 1/10. This observation was verified by building a multivariate regression model, using the correlation coefficients between VAS and LZ changes as target variables, and stimuli and eye opening as predictors. Results showed that neither stimuli (p = 0.17) nor eyes-open (p = 0.13) had significant effects by themselves, but their interaction was strongly associated with smaller VAS-LZ correlation values (β = -0.21, SE = 0.08, p = 0.006; see Supplementary Material). As a complementary analysis, we also studied how the four environmental conditions affect the relationship between the LSD-induced LZ changes across different ROIs. To do this, we evaluated the Pearson correlation coefficient between the LZ changes measured in the various ROIs across subjects. It was observed that the correlation between ROIs is substantially increased when subjects perceive an external stimulus (either music or video; see Supplementary Material), which could be indicative of a form of "complexity matching"in which neural dynamics are entrained by the external stimulus, obscuring the relationship between neurodynamics and subjective experience. This observation was also verified via multivariate regression modelling, this time using ROI-ROI correlation values as target. In this case, eye opening was associated with smaller correlation values (β = -0.10, SE = 0.04, p = 0.011), while stimuli (β = 0.15, SE = 0.04, p < 0.001) and the interaction between stimuli and eyes-open (β = 0.18, SE = 0.05, p = 0.001) were both associated with significantly larger correlation values (see Supplementary Material). These findings suggest that the increased within-brain correlation driven by external stimulation may obfuscate potential correlations between entropy and individual VAS ratings -which are most apparent e.g. in the eyes closed condition.
we analysed the relationship between changes in LZ and behavioural reports as they were exposed to the different experimental conditions. For this, we constructed LME models using VAS ratings as target; average LZ, eye opening, and stimulus as fixed effects; and subject identity as random effect (see Methods). These models revealed multiple associations between brain entropy and subjective reports (Fig.), including some widespread correlations with LZ averaged across the whole brain (most strongly with ego dissolution and simple imagery), as well as more specific correlations (e.g. between positive mood and amygdala). In contrast, stimulus and eye opening show small effect sizes in all models, as well as strong negative interactions with LZ (see Supplementary Material). This negative interaction suggests that the relationship between LZ and VAS is broken when stimuli are present, in line with the results in Fig.. To explore the correlations between behavioral ratings and LZ in various ROIs in more detail, we performed a conditional predictive power analysis (see Methods). This method allows us to build a directed network representing the predictive ability of the various ROIs with respect to a given VAS item, such that a ROI R1 is connected to a VAS item V via a another ROI R2 if, once the entropy change in R2 is known, there is no further benefit in knowing the entropy change in R1 for improving the prediction of the change in V (Fig.). Results show that, in general, "low-level" regions (i.e. closer to the sensory periphery, like visual areas) tend to "mediate" the associations between subjective reports and high-level regions (like the DMN). For example, visual and auditory 243 areas mediate the predictive information that the pDMN and 244 insula have about reported complex imagery. † Put simply: 245 once the change in entropy in auditory and visual regions is 246 known, knowing the change in entropy in the pDMN provides 247 no extra information about the change in reported complex 248 imagery. A notable exception, however, is ego dissolution, for 249 which pDMN, auditory, and insula all provide unmediated 250 complementary information -in line with previous studies 251 linking self-related processing and the DMN.
We also performed a reciprocal analysis to assess the condi-253 tional predictive power of the various VAS items using LZ as 254 target (Fig.). Results show that, across brain regions and 255 VAS items, the predictive power of more abstract VAS scores 256 (e.g. ego dissolution, positive mood) tends to be mediated by 257 less abstract ones (e.g. simple and complex imagery). For 258 example, changes in ego dissolution scores become irrelevant 259 for predicting LZ in auditory areas once one knows the corre-260 sponding change in complex imagery. One interpretation of 261 these analyses is that brain entropy, as currently measured 262 with LZ, may most faithfully reflect "low-level" aspects of the 263 brain-mind relation (see Discussion).
The present study's findings provide strong quantitative evi-266 dence on how environmental conditions can have a substantial 267 influence on both subjective experience and on neural dynamics 268 during a psychedelic experience. Importantly, the entropy-269 enhancing effects of LSD were less marked when participants 270 opened their eyes or perceived external stimuli -such as 271 music or video. Furthermore, the differences in brain entropy 272 observed in various regions of the brain were found to be asso-273 ciated with behavioural reports about the subjects' perception, 274 emotion, and self-related processing -but the relationship 275 † Although note that the role of auditory regions and insula is reversed for simple and complex imagery, respectively. associations with high-level cognitive processing or subjective phenomena (such as ego dissolution) in the eyes-closed conditions because that relationship becomes more specific in the absence of the strong "driving" effects present in the eyes-open conditions -especially video. Future studies might distinguish between these hypotheses by exploring the reliability of relationships between LZ and various subjective phenomena, including ego dissolution, perceptual complexity, and alertness, involving different pharmacological agents (e.g. psychedelics and stimulants), dosages, and stimuli. Towards a refinement of the entropic brain hypothesis. A deeper understanding of the functional relevance of brain entropy will help us better understand how such measures can be refined, in order to shed clearer light on their relationship with reported phenomenology. The results presented in this paper, while grounded in and motivated by the EBH, also highlight some important qualifiers of it. Since brain entropy measures such as LZ depend only on the dynamics of individual loci (e.g., individual time series corresponding to single sources or sensors), they may only indirectly reflect the richer scope of brain dynamics, network and connectivity properties -although it is worth noting that LSD-induced entropy increases at the single-source level have been related to specific network properties of the human connectome. One potential way forward for the EBH may be to consider the entropy of network dynamics and other high-order brain features, rather than merely the entropy of individual sources. For example, examining increases in entropy at the level of emergent whole-brain states may prove particularly fruitful. We see this as part of a broader move towards multidimensional descriptions of brain activity, transcending "one-size-fits-all" scalar measures -including more complicated unidimensional ones like integrated information. In line with recent theoretical proposalsand experimental findings, a range of metrics may be necessary to provide a more complete, multi-dimensional representation of brain states. However, we also acknowledge that increasing model complexity can complicate interpretability and affect statistical power, and thus is only justified when it yields substantial improvement in explanatory power and is driven by reliable hypotheses. Implications for psychedelic psychotherapy. These findings can be regarded as neurobiological evidence for the importance of environmental context, or 'setting,' to the quality of psychedelic experiences -a matter of particular relevance to psychedelic therapy. In particular, the present findings support the principle that having one's eyes closed during a psychedelic experience may enhance the differential entropic effect of the drug (1), which is consistent with approaches fostering eyesclosed, introspective experiences during psychedelic therapy, as they may lead to beneficial therapeutic outcomes. In addition, our results suggest a differential effect between sensory modalities (visual versus auditory) on brain dynamics and subjective experience, with visual stimulation reducing the measured relationship between neural entropic changes and subjective reports. Together, these findings support the choice of music -in contrast to visual stimulation -to modulate and support psychedelic therapy. Importantly, this study reveals that the effects of contextual elements on brain dynamics can be effectively tracked via current neuroimaging techniques. Our results establish LZ as a marker that is sensitive to the interaction between drug and context, which opens the door to future studies that may assess the effect of contextual elements on the brain during psychedelic therapy. This study, therefore, serves as a proof-of-concept translational investigation in healthy subjects, setting a precedent for future studies in clinical populations. Accompanying extensions into clinical populations, future work is also needed to further clarify how interactions between drug and context manifest on a psychological and neurobiological level, and how they can be harnessed for best therapeutic outcomes.
Data pre-processing. Data was collected with a 271-gradiometer CTF MEG scan. In addition, structural MRI scans of every subject were obtained for later inter-subject co-registration. Three subjects could not complete all stages of recording, or had excessive movement artefacts and were removed from the analysis altogether. All pre-processing steps were performed using the FieldTrip toolbox. First, artefacts were removed by visual inspection and muscle and line noise effects were removed using ICA. Then we applied a 2 nd -order lowpass Butterworth filter at 100 Hz and split the data into 2 s epochs for subsequent analysis. For source reconstruction, we used the centroids of the AAL-90 400 atlas. The positions of these centroids were non-linearly inverse-401 warped to subject-specific grids using the subjects' structural MRI 402 scans, and source time series (a.k.a. virtual sensors) were estimated 403 with a regularised LCMV beamformer. We calculated Lempel-Ziv 404 complexity on these locations, and finally mapped them back onto 405 the standard template for statistical analysis and visualisation. In 406 addition, for the visualisation in Fig.we computed LZ in sources 407 reconstructed in a uniform 10 mm 3D grid.
Lempel-Ziv complexity. The main tool of analysis used in this study is 409 the Lempel-Ziv complexity (referred to as LZ), which estimates how 410 diverse the patterns exhibited by a given signal are. The method and subject identity as random effect. When constructing a model, 460 all possible pairwise interactions were considered; then model selection is performed using the Bayesian Information Criterion (BIC).
All the reported models correspond to the one selected by BIC.
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