Contingency awareness refers to an observer’s ability to identify the association between a conditioned and an unconditioned stimulus (US). A widely held belief in human fear conditioning is that this form of associative learning may occur independently of contingency awareness. To test this hypothesis, in this preregistered study (https://osf.io/vywq7), we recorded electroencephalography during a task, where participants were presented with compounds of a word (drawn from two semantic categories) and tactile stimulation (vibration), followed by either a neutral sound (US−) or a loud noise (US+). Based on interviews, participants were divided into an aware (N = 50) and an unaware (N = 31) group. Only the aware group showed evidence of learning at the neural level, notably a larger stimulus-preceding negativity developing before US+ and a stronger theta response to vibrations predicting the US+. The aware group also showed stronger alpha and beta suppression around the vibrations and a weaker theta response to US+, possibly indicating heightened attention to the cue and the violation/confirmation of expectation. Group differences in alpha and beta suppression were already present before the aversive learning began, suggesting that elevated attention may precede and facilitate awareness. Personality tests showed that elevated anxiety, neuroticism, higher intolerance of uncertainty, or harm avoidance is not predictive of the acquisition of contingency awareness. Our findings support the notion that fear conditioning, as reflected in cortical measures, cannot occur without contingency awareness.

For individuals with sound-touch synesthesia, sounds consistently evoke strong, localized sensations on the body. We systematically investigated the relationship between sound frequency and the characteristics of induced tactile experiences in synesthetes (n = 19) and controls (n = 23). Sound frequency strongly predicted the location of tactile sensations in synesthetes and controls. Synesthetes experienced touch more frequently and tended to report sensations in more spatially focused regions of the body, reflecting a sharper mapping between sound frequency and somatotopy. This spatial distribution of touch according to sound frequency reflects a behavioral mapping between tonotopy and somatotopy suggesting the involvement of early, tonotopically- and somatotopically-organized brain areas. These findings highlight a strong similarity between auditory-tactile mappings in synesthetic and ordinary perception, suggesting that synesthesia only differs in the strength of the mappings and therefore may be on a spectrum with ordinary perception. Furthermore, these findings offer insights into the neural mechanisms of sound-touch mappings, suggesting they rely on cross-modal neural pathways utilized in ordinary perception.

While the beneficial impacts of meditation are increasingly acknowledged, its underlying neural mechanisms remain poorly understood. We examined the electrophysiological brain signals of expert Buddhist monks during two established meditation methods known as Samatha and Vipassana, which employ focused attention and open-monitoring technique. By combining source-space magnetoencephalography with advanced signal processing and machine learning tools, we provide an unprecedented assessment of the role of brain oscillations, complexity, and criticality in meditation. In addition to power spectral density, we computed long-range temporal correlations (LRTC), deviation from criticality coefficient (DCC), Lempel–Ziv complexity, 1/f slope, Higuchi fractal dimension, and spectral entropy. Our findings indicate increased levels of neural signal complexity during both meditation practices compared to the resting state, alongside widespread reductions in gamma-band LRTC and 1/f slope. Importantly, the DCC analysis revealed a separation between Samatha and Vipassana, suggesting that their distinct phenomenological properties are mediated by specific computational characteristics of their dynamic states. Furthermore, in contrast to most previous reports, we observed a decrease in oscillatory gamma power during meditation, a divergence likely due to the correction of the power spectrum by the 1/f slope, which could reduce potential confounds from broadband 1/f activity. We discuss how these results advance our comprehension of the neural processes associated with focused attention and open-monitoring meditation practices.

Visual imagery is a dynamic process recruiting a network of brain regions. We used electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) fusion to investigate the dynamics of category selective imagery in medial parietal cortex (MPC), ventral temporal cortex (VTC), and primary visual cortex (V1). Subjects attended separate EEG and fMRI sessions where they created mental images of personally familiar people and place stimuli. The fMRI contrast comparing people and place imagery replicated previous findings of category-selectivity in the medial parietal cortex. In addition, greater activity for places was found in the ventral and lateral place memory areas, the frontal eye fields, the inferior temporal sulcus, and the intraparietal sulcus. In contrast, greater activity for people was found in the fusiform face area and the right posterior superior temporal sulcus. Using multivariate decoding analysis in fMRI, we could decode individual stimuli within the preferred category in VTC. A more complex pattern emerged in MPC, which represented information that was not restricted to the preferred category. We were also able to decode category and individual stimuli in the EEG data. EEG–fMRI fusion indicated similar timings in MPC and VTC activity during imagery. However, in the VTC, fusion was higher in place selective regions during an early time window, and higher in face selective regions in a later time window. In contrast, fusion correlations in V1 occurred later during the imagery period, possibly reflecting the top-down progression of mental imagery from category-selective regions to primary visual cortex.

How is it that psychedelics so profoundly impact brain and mind? According to the model of “Relaxed Beliefs Under Psychedelics” (REBUS), 5-HT2a agonism is thought to help relax prior expectations, thus making room for new perspectives and patterns. Here, we introduce an alternative (but largely compatible) perspective, proposing that REBUS effects may primarily correspond to a particular (but potentially pivotal) regime of very high levels of 5-HT2a receptor agonism. Depending on both a variety of contextual factors and the specific neural systems being considered, we suggest opposite effects may also occur in which synchronous neural activity becomes more powerful, with accompanying “Strengthened Beliefs Under Psychedelics” (SEBUS) effects. Such SEBUS effects are consistent with the enhanced meaning-making observed in psychedelic therapy (e.g. psychological insight and the noetic quality of mystical experiences), with the imposition of prior expectations on perception (e.g. hallucinations and pareidolia), and with the delusional thinking that sometimes occurs during psychedelic experiences (e.g. apophenia, paranoia, engendering of inaccurate interpretations of events, and potentially false memories). With “Altered Beliefs Under Psychedelics” (ALBUS), we propose that the manifestation of SEBUS vs. REBUS effects may vary across the dose–response curve of 5-HT2a signaling. While we explore a diverse range of sometimes complex models, our basic idea is fundamentally simple: psychedelic experiences can be understood as kinds of waking dream states of varying degrees of lucidity, with similar underlying mechanisms. We further demonstrate the utility of ALBUS by providing neurophenomenological models of psychedelics focusing on mechanisms of conscious perceptual synthesis, dreaming, and episodic memory and mental simulation.

The role of the prefrontal cortex (PFC) in consciousness is hotly debated. Frontal theories argue that the PFC is necessary for consciousness, while sensory theories propose that consciousness arises from recurrent activity in the posterior cortex alone, with activity in the PFC resulting from the mere act of reporting. To resolve this dispute, we re-analysed an electroencephalography (EEG) dataset of 30 participants from a no-report inattentional blindness paradigm where faces are (un)consciously perceived. We performed source reconstruction on the EEG data to first establish the robustly active regions, which were then used to build the networks in the dynamic causal modelling analysis. Dynamic causal modelling was used to estimate the effective connectivity between the key contended brain regions, the prefrontal and the posterior cortices. Then, a second-level parametric empirical Bayesian model was conducted to determine how connectivity was modulated by awareness and task-relevance. While an initial data-driven search could not corroborate neither sensory nor frontal theories of consciousness, a more directed hypothesis-driven analysis revealed strong evidence that both theories could explain the data, with a very slight preference for frontal theories. Specifically, a model with backward connections switched off within the posterior cortex explained awareness better (53%) than a model without backward connections from the PFC to sensory regions. Our findings provide some support for a subtle, yet crucial, contribution of the frontal cortex in consciousness, and highlight the need to revise current theories of consciousness.

A Ganzfeld is a homogeneous, unstructured visual field that is known to induce visual hallucinations. Aside from visual percepts emerging in participants’ awareness, Ganzfeld viewing is characterized by decays of color and brightness. The studies dedicated to this topic from the 20th century have focused on these decays, although they have been reported in a confusing way, with different terms for these decaying experiences. This paper synthesizes the current state of the Ganzfeld literature going back to the 1930s with the purpose of clarifying the terminology of the phenomena that have largely retained their mysterious aspects. We built a Ganzfeld space to study the phenomenology without the restricted feeling of a confined space that translucent Ganzfeld goggles cause. Employing a multi-method approach, we combined quantitative and qualitative measures to better grasp the number, kind and temporal dynamics of the experienced phenomena as well as their experiential characteristics. We offer more insight into the different kinds of visual percepts that emerge in participants’ awareness, induced by the Ganzfeld, and we identified three distinct types of decays of color and brightness. Based on previously used terminology, we propose to employ the terms ‘fade-out’, ‘black-out’ and ‘blank-out’, and present both the prevalence as well as the qualitative characteristics of these decays. Finally, we shed some light onto the role of eye movements and blinks on the experienced phenomena. All of this is relevant groundwork to be able to study the dynamics of different Ganzfeld experiences, in relation to different states of consciousness and their neural correlates in future work.

During the wake–sleep cycle, consciousness waxes and wanes, and this is thought to be reflected in varying levels of integration between brain areas. Recent studies challenged the notion that consciousness is homogeneously present or absent in a brain state, as exemplified by conscious reports found in otherwise unconscious Non-rapid eye movement (NREM) sleep. Here, we tested if functional connectivity (FC) between neurons varies within brain states in a way compatible with a fluctuating level of consciousness. We examined directed FC between neurons across the wake–sleep cycle in rats, at a scale of a few seconds. We observed that NREM sleep contains epochs in which patterns of inter-areal FC are comparable to those observed in wakefulness and REM sleep, and vice versa. Thus, circuit-level connectivity patterns are not univocally determined by the brain state in which they occur, but could rather reflect other factors such as the fluctuation in the level of consciousness that takes place not only between but also within brain states.

This paper explores the limitations of neurobiological approaches to human emotional experience, focusing on the case of grief. We propose that grief is neither an episodic emotion nor a longer-term mood but instead a heterogeneous, temporally extended process. A grief process can incorporate all manner of experiences, thoughts, and activities, most or all of which are not grief-specific. Furthermore, its course over time is shaped in various different ways by interpersonal, social, and cultural environments. This poses methodological challenges for any attempt to relate grief to the brain. Grief also illustrates wider limitations of approaches that conceive of emotions as brief episodes, abstracted from the dynamic, holistic, longer-term organization of human emotional life.

Auto-induced cognitive trance (AICT) is a modified state of consciousness derived from shamanic tradition that can be practised by individuals after specific training. The aim of this work was to characterize the phenomenological experiences of AICT, using text mining analysis. Free recalls of subjective experiences were audio-recorded in 27 participants after five pseudo-randomized experimental sessions: ordinary conscious resting state, with auditory stimulation and with an imaginary mental task, as well as during AICT with and without auditory stimulation. Recordings were transcribed, normalized total word counts were calculated for each condition, and analyses of content were performed using IRaMuTeQ software. Results showed that the length of the participants' reports was higher for AICT compared to the other conditions, and that the content could be categorized into four classes of discourse: AICT memory, AICT, ordinary conscious states, and AICT with and without stimulation. AICT was also characterized by specific content compared to rest, auditory stimulation, and imagination conditions. Content analysis of the narrative revealed nine categories encompassing the presence of nature, people, animals, positive and negative features, sensory perceptions, body modifications, metacognition, and difficulty of describing thoughts. Among these categories, AICT is specifically characterized by reports related to the presence of nature, animals, body modifications, as well as the difficulty of describing thoughts. These results suggest that a richer phenomenology was reported during AICT, compared to the other conditions, and that AICT constitutes a class of discourse on its own, with a clear dissociation from the other conditions.