Neuroscience & Biobehavioral Reviews
December 17, 2011
Jaan Aru, Talis Bachmann, Wolf Singer et al.
612 citations
Identifying the neural correlates of consciousness (NCC) is a major goal in neuroscience, typically pursued by comparing brain activity when a person is conscious of a stimulus versus when they are not. This review argues that such contrastive analyses are problematic because they can capture not only the true NCC but also neural prerequisites for conscious processing and consequences that follow it. Previous findings may therefore be ambiguous. The authors propose experimental strategies to isolate the NCC from these confounds, aiming to refine the contrastive approach.
Neuron
May 15, 2024
Johan F Storm, P Christiaan Klink, Jaan Aru et al.
108 citations
Consciousness may be explained by multiple, partly compatible theories rather than a single winner. A group of scientists representing different theories argue that various accounts often address different aspects or mechanistic levels of conscious experience, so they do not necessarily contradict each other. Instead, several theories may converge on fundamental neuronal mechanisms and be complementary, allowing multiple perspectives to simultaneously advance understanding. The authors advocate for unifying, integration-oriented approaches that combine valuable elements from diverse theories, an approach that has so far been largely neglected.
Brain : a journal of neurology
September 14, 2022
James M Shine, Claire O'Callaghan, Ishan C Walpola et al.
63 citations
Serotonin in the brain can be understood as an extension of the gut's serotonergic system, which controls digestion. Central serotonin activity mimics a digestion/satiety circuit, where low serotonergic tone facilitates cognitive automaticity and higher tone helps identify flexible solutions when initial responses fail. This perspective explains serotonin's roles in reward processing, exploration, and psychedelic experiences, and clarifies links between serotonergic dysfunction and psychiatric symptoms.
Consciousness and cognition
August 1, 2017
Jaan Aru, Talis Bachmann
42 citations
Conscious experience depends on attention and expectation, but some argue it can occur without attention. Experiments on iconic memory (IM) are often cited as evidence for attention-independent consciousness. A prior study found that when attention is diverted from an IM letter display, people fail to notice missing letters. This work replicates and extends that finding by measuring subjective visibility and testing post-cue effects. Results show that participants who do not realize letters are absent perceive illusory letters, indicating phenomenal consciousness persists even without attention. Expectation generates illusory content that overwrites valid IM content, suggesting this experimental paradigm cannot reliably assess iconic memory content.
Front Psychiatry
March 1, 2023
Karl Kristjan Kaup, Madis Vasser, Kadi Tulver et al.
22 citations
An open-label feasibility study tested whether a virtual reality simulation designed to replicate aspects of the psychedelic experience could be used as a therapeutic tool. Participants reported that the VR experience produced subjective effects resembling those of psychedelics, including altered perception and a sense of oceanic boundlessness. The findings suggest that VR-based psychedelic replications are feasible and acceptable, and may offer a scalable, non-pharmacological approach for mental health interventions. The study did not assess clinical outcomes, but participants showed reduced negative affect after the session. The authors indicate that further controlled research is needed to determine therapeutic efficacy.
November 26, 2021
Kadi Tulver, Karl Kristjan Kaup, Ruben Laukkonen et al.
16 citations
preprint
Insight, the sudden understanding of a solution or idea, is not only central to creative problem-solving but also plays a key role in psychotherapy, meditation, the emergence of delusions in schizophrenia, and the therapeutic effects of psychedelics. This integrative review draws on literature from multiple fields to examine the event of insight, its prerequisites, and its consequences. It highlights commonalities and differences across these domains, aiming to bridge gaps between disparate research traditions and inspire interdisciplinary efforts to understand this core cognitive process.
Neuroscience and biobehavioral reviews
February 1, 2026
Borjan Milinkovic, Jaan Aru
7 citations
Consciousness in biological systems arises from two fundamental computational features absent in current artificial intelligence: scale-inseparable, substrate-dependent multiscale processing as a metabolic optimization strategy, and continuous-valued computations performed by the fluidic substrate alongside discrete operations. These features are essential to the brain's mode of computation. The absence of consciousness in artificial systems reflects a deeper divide between digital and biological computation, not merely missing functional organization. The authors outline foundational principles of a biological theory of computation and explain why current AI systems are unlikely to replicate conscious processing as it arises in biology.
July 5, 2022
Kristjan Kaup, Madis Vasser, Kadi Tulver et al.
7 citations
preprint
A 2-day virtual reality intervention called Psyrreal, designed to mimic the phenomenological components of psychedelic experiences, combined with psychological support, led to significant decreases in depressive symptoms at a 2-week follow-up in ten participants with mild-to-moderate depression. The intervention also appeared to promote insight and alterations in the sense of self in some people, based on thematic analysis of semi-structured interviews. These preliminary results suggest potential for VR experiences in treating depressive symptoms and warrant further research.
Frontiers in psychiatry
January 1, 2023
Karl Kristjan Kaup, Madis Vasser, Kadi Tulver et al.
3 citations
correction
No Summary
May 28, 2023
Timo Siimon, Kadi Tulver, Kristjan Kaup et al.
2 citations
preprint
A psychedelic virtual reality environment, which replicates visual content experienced under the influence of psychedelics, helped people stuck on a real-life creative problem reach new insights more effectively than a control VR environment. The thematic analysis indicated that the psychedelic VR supported several aspects of creative insight, likely by relaxing the person's fixed assumptions about their problem. The results are encouraging but need to be tested in larger studies.
Neuroscience and biobehavioral reviews
June 1, 2026
Javier Hidalgo Jiménez, Karl Kristjan Kaup, Jaan Aru
1 citation
Psychedelics such as LSD and NBOH produce complex, heterogeneous effects on brain cells, challenging the idea that they simply increase cortical excitability. A systematic review of 23 in vitro and 26 in vivo electrophysiological studies found that these compounds modulate both excitatory and inhibitory processes in a cell-type- and compartment-specific manner, with biphasic, dose-dependent, and context-sensitive responses. Activation of 5-HT2A receptors triggers intricate calcium signaling, downregulating excitatory currents and firing rates in many neurons while enhancing glutamate release and activating a subset of projection fibers. Modulation of presynaptic and extrasynaptic GluN2B-containing NMDA receptors appears central to these effects.
Journal of Psychopharmacology
February 16, 2026
Marten Kase, Karl Kristjan Kaup, Jaan Aru
1 citation
A systematic review of 32 placebo-controlled studies from 1990 to 2025 examined the acute and post-acute effects of LSD, DMT, and psilocybin on cognitive and psychological functions. Psychedelics tended to enhance emotional empathy but had no effect on cognitive empathy. Effects on memory varied by task and timing, with some impairments, enhancements, or no change. Dose-dependent impairments occurred in reaction time, attention, and inhibition tasks, though some studies found no effects. Recognition of negative stimuli was impaired under acute effects. Findings on cognitive flexibility were mixed. Many studies had small samples, and finding a reliable placebo is challenging due to psychedelics' unique subjective effects.
Philosophical Psychology
January 1, 2026
Juensung J. Kim, Kadi Tulver, Jaan Aru et al.
1 citation
Mystical-type experiences and insight problem solving both belong to a family of "realization experiences" where information suddenly becomes experienced as real or true. Both can be modeled using behavioral entropy and graph theory. When novel information conflicts with prior representations, the mind destabilizes its representational network, entering a state of altered salience and enhanced associations. After restructuring sensitive to environmental cues, the agent forms new beliefs or revises its entire framework. The phenomenology depends on the size and content of the updated network and environmental affordances. This shared vocabulary aims to facilitate discussion across these phenomena.
September 2, 2025
Zefan Zheng, Robert Chis-Ciure, Peter Thestrup Waade et al.
1 citation
preprint
Consciousness science is fragmented, with theories operating orthogonally and accumulating anomalies. The principle of recurrency—functional and architectural feedback loops—offers a unifying scaffold. All theories tacitly invoke feedback loops and can be re-expressed along a single axis of recursion. Four nested levels (cellular, local inter-areal, global, and lateral) map onto state, phenomenal content, manipulative access, and experiential similarity, tying evolved anatomy to phenomenon. The phenomenal-versus-access distinction dissolves into a graded cascade where deeper recursion expands reportable variables. Recurrence is evolutionarily favored, rebutting feed-forward objections, while brain-body loops ground selfhood. Clinically, targeting recurrent pathways promises new biomarkers and alleviation in disorders of consciousness.
Frontiers in neuroscience
January 1, 2025
Albert Gidon, Jaan Aru, Matthew E. Larkum
1 citation
Simulating a simple computation in an artificial neural network, researchers recorded neuron activity during visual stimulation and replayed those signals back into the same neurons. This replay degraded the computation by erasing counterfactual activity patterns—alternative neural states that could have occurred—while leaving ongoing brain activity unchanged. This outcome reveals a disconnect between neural activity and computational structure, challenging the computational functionalist view that consciousness emerges from the right computations, whether in machines or biological brains.
February 12, 2024
Kadi Tulver, Kristjan Kaup, Jaan Aru
preprint
A new framework proposes that diverse mental breakthroughs—from everyday problem-solving insights to profound personal transformations—share common mechanisms of representational change. The model identifies three core components—tension, altered salience, and enhanced flexibility—as prerequisites for cognitive restructuring, interacting in an iterative cycle that influences insight emergence. The intensity and impact of an 'aha-moment' depend on how central the conflict is within one's conceptual landscape and the degree to which existing mental models are challenged. Drawing on psychotherapy, contemplative science, and psychedelic research, this theoretical account aims to unify explanations of insight phenomena across disciplines.
arXiv Preprint Archive
June 26, 2025
Jaan Aru
The science of consciousness has made progress, but key questions remain unanswered. Moving forward may require revising fundamental assumptions rather than relying on the same theoretical commitments. A key assumption is that neural correlates of consciousness are found at the level of spiking responses, but this should not be taken for granted. Another assumption is that the computations underlying consciousness are close to being understood, yet they may be far more complex than current theories envision, and there is little reason to think consciousness is an abstract computation. Consciousness research could benefit from investigating internal changes like aha-moments. The piece questions what theories the science of consciousness truly needs.
Trends in Neurosciences
June 1, 2023
Jaan Aru, M. Larkum, J. Shine
Claims that large language models may soon be conscious are difficult to defend from a neuroscience perspective. The inputs to these models lack the embodied, embedded information content that characterizes sensory contact with the world. Present-day AI architectures also miss key features of the thalamocortical system linked to conscious awareness in mammals. Furthermore, the evolutionary and developmental trajectories that produced living conscious organisms have no parallels in current artificial systems. The existence of living organisms depends on actions and survival, which are linked to multi-level cellular, inter-cellular, and organismal processes that culminate in agency and consciousness.
Consciousness and Cognition
February 1, 2023
T. Bachmann, Jaan Aru
The science of consciousness depends on experimental paradigms that compare conscious and unconscious processing. This review highlights a class of paradigms called "conscious interpretation," in which an object is consciously perceived as a set of features, but the interpretation of that set alternates in consciousness. The authors compare these paradigms with other types and review past and recent studies. They propose that for certain stimuli with a hierarchy of interpretations, conscious experience is drawn toward the higher-level interpretation and cannot revert to the lower level. The paper discusses how theories of consciousness might incorporate constraints arising from conscious interpretation.
Frontiers in Systems Neuroscience
August 30, 2019
Jaan Aru, Mototaka Suzuki, R. Rutiku et al.
A fundamental feature of consciousness is that its contents depend on its state. The authors propose that both state and contents depend on the activity of cortical layer 5 pyramidal (L5p) neurons. These neurons couple cortico-cortical and thalamo-cortical loops, forming a thalamo-cortical broadcasting system where L5p cells are central. This coupling corresponds to the coupling between state and contents of consciousness. The perspective predicts that cortical processing without L5p neurons will be unconscious, suggesting L5p neurons have a central role in the mechanisms underlying consciousness.
Advances in Consciousness Research
June 17, 2015
Jaan Aru, Talis Bachmann, Wolf Singer et al.
Identifying the neural correlates of consciousness (NCC) is considered a key step toward understanding consciousness. Typical experiments contrast conditions with and without conscious perception, but this contrast captures not only neural activity directly tied to conscious experience but also prerequisites and consequences of that perception. To isolate the true neural basis of conscious experience, researchers must disentangle the NCC from these confounding processes. This review discusses recent experimental developments and proposes new empirical approaches to more precisely isolate the neural activity underlying conscious perception.