Modern Methods and Experiments in the Study of Consciousness

Philosophical Framework

The study of consciousness, especially its “hard problem” — the question of why and how physical processes give rise to subjective experience — is deeply rooted in the philosophy of consciousness. This problem, tracing back to Leibniz and Dubois-Reymond [Schleim, 2022], challenges the possibility of fully explaining phenomenal experience solely through neurobiological mechanisms. Contemporary approaches, such as neurophenomenology [Varela, 1996], seek to bridge this gap by integrating first-person data (subjective experience) with third-person data (neurobiological measurements). This allows not only describing the neural correlates of consciousness but also investigating how experience itself shapes our understanding of the world and ourselves.

Introduction

Modern consciousness research lies at the intersection of philosophy, psychology, and cognitive sciences, attempting to unravel one of the most fundamental mysteries of human existence. The key challenge is the so-called “hard problem of consciousness,” formulated by David Chalmers, which concerns explaining subjective experience, or qualia. Unlike the “easy problems” related to functional aspects of consciousness, such as attention or memory, the hard problem requires understanding why physical processes produce “something that feels like” [Block, 1995].

In recent decades, significant progress has been made in developing experimental methods aimed at studying the neural correlates of consciousness (NCC) — the minimal set of neural mechanisms sufficient for conscious experience [Lamme, 2010]. These methods include functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and transcranial magnetic stimulation (TMS), which allow investigation of brain activity in various states of consciousness, from wakefulness to sleep and altered states induced by meditation or psychedelics [Atad et al., 2025]. However, despite these advances, the question remains open as to how well these methods can bridge the gap between objective neural data and subjective phenomenal experience, or, as Dennett put it, what happens when some content reaches consciousness? [Dennett, 2018].

Research Overview

How to Define and Measure Consciousness?

The question of how to define and measure consciousness remains one of the most fundamental and arguably elusive in modern science. We can talk about consciousness, but as soon as we try to grasp it, it slips away like sand through fingers. This is not merely an academic dispute; the answer to this question determines whether we will ever understand the nature of subjective experience, develop artificial intelligence with genuine self-awareness, or even determine the presence of consciousness in coma patients.

One of the most influential attempts to provide a quantitative assessment of consciousness belongs to Giulio Tononi, who proposed the Integrated Information Theory (IIT). According to Tononi, consciousness is not merely the presence of information but the system’s ability to integrate that information. He states: “Consciousness poses two main problems. The first is to understand the conditions that determine the degree to which a system has conscious experience.... The second problem is to understand the conditions that determine what kind of consciousness a system has.... This paper presents a theory of what consciousness is and how it can be measured. According to the theory, consciousness corresponds to the system’s ability to integrate information” [Tononi, 2004]. Tononi introduces the metric Φ (phi), which is intended to quantitatively express the degree of information integration in a system. The higher the Φ, the higher the level of consciousness. This theory suggests that consciousness arises from causal relationships within the system, not merely from its complexity.

However, not everyone agrees with this approach. David Chalmers, for example, introduced the famous distinction between “easy” and “hard” problems of consciousness. The “easy” problems concern explaining cognitive functions such as information processing, attention, and memory, which, although complex, can in principle be explained by neurophysiological mechanisms. But the “hard problem,” according to Chalmers, is explaining why and how physical processes give rise to subjective experience, i.e., what it is like to be something [Brogaard et al., 2016]. Tononi’s theory, despite its elegance, is criticized for possibly addressing only the “easy” problem by proposing a metric for information integration but not explaining the phenomenal aspect of experience itself.

An equally important perspective is offered by Ned Block, who distinguishes phenomenal consciousness (P-consciousness) and access consciousness (A-consciousness). He writes: “Consciousness is a hybrid concept: there are several very different ‘consciousnesses.’ Phenomenal consciousness is experience; the phenomenally conscious aspect of a state is what it is like to be in that state. Access consciousness, by contrast, is characterized by availability for use in reasoning and rational guidance of speech and action” [Block, 1995]. For Block, phenomenal consciousness is the directly experienced sensations and feelings, whereas access consciousness is information available for cognitive processing and behavioral control. Measuring access consciousness is probably more feasible since it is linked to observable brain functions. But how to measure “what it is like”? This remains an open question.

Some researchers, such as Axel Cleeremans and Catherine Tallon-Baudry, propose viewing consciousness as a function possessing intrinsic value. They ask: Why do we do anything at all if the action does nothing to us? [Cleeremans et al., 2022]. They suggest that subjective experience, i.e., “what it tastes like,” has intrinsic value, and it is this value that agents associate with their experience that explains why they perform certain actions and avoid others. In this context, consciousness is not merely an epiphenomenon but an active participant in shaping behavior, giving meaning and motivation. This shifts the focus from passive observation to the active role of consciousness in adaptation and survival.

Another position, presented by Colin Klein and Andrew B. Barron, proposes that phenomenal consciousness results from how mobile animals with spatial senses and goal-directed behavior solve the complex problem of action selection [Klein et al., 2020]. They argue that the brain solves this problem by transforming heterogeneous information into a common structure — a “phenomenal interface” — and then using it to compute multi-objective Q-values. This, in their view, naturally generates the distinction between self and non-self, as well as a first-person perspective in which external stimuli have subjective value. This approach offers a functional role for consciousness even in relatively simple organisms such as insects.

However, when it comes to measurement, neurobiological methods provide some tools. For example, studies using transcranial magnetic stimulation (TMS) and electroencephalography (EEG) can help assess cortical excitability and information integration in the brain. Sleep deprivation studies, for instance, have shown that it affects cortical excitability by reducing cortical inhibition and enhancing excitation [Zhang et al., 2025]. This may be an indirect indicator of changes in the state of consciousness, although it does not explain the subjective experience itself.

Another approach to measuring consciousness is related to studying its complexity. Daniel Andrew Atad and colleagues note a growing interest in using complexity science-inspired metrics to study consciousness [Atad et al., 2025]. Their review shows that higher complexity of neural activity often correlates with conscious states, as well as with altered states of consciousness, for example, after taking psychedelics or during meditation. This suggests that the complexity of neural patterns may serve as one of the measurable parameters of consciousness.

Nevertheless, despite all these approaches, we face a fundamental problem: how to relate objective measurements of neural activity to subjective, internal experience? Even if we can measure information integration or neural network complexity, this does not provide a direct answer to what it is like to be conscious. This brings us to the “hard problem of consciousness,” which, as we will see further, is not merely a philosophical curiosity but a real challenge for scientific research.

Is the “Hard Problem of Consciousness” a Real Scientific Problem?

In the previous section, we discussed the difficulties of defining and measuring consciousness, emphasizing that even basic concepts remain subjects of active debate. Now we face an even more fundamental question: is the so-called “hard problem of consciousness” a real scientific problem at all, or is it rather a philosophical artifact distracting us from more productive research? This question, first formulated by David Chalmers, concerns explaining why physical processes in the brain give rise to subjective experience, or qualia.

Daniel Dennett, for example, takes a rather radical position, arguing that the so-called hard problem of consciousness is a chimera distracting from the hard question of consciousness [Dennett, 2018]. For him, the true difficulty lies not in why subjective experience arises, but in what happens after some content reaches consciousness. In other words, Dennett shifts the focus from the phenomenological “what it is like” to the functional “what it does.” If we can explain all functions of consciousness — attention, memory, decision-making — then, in his view, there is no “hard” problem requiring separate explanation. This is a kind of reductionist approach aiming to dissolve the phenomenal aspect into the functional.

Similar arguments are put forward by Stephen Sloman, who considers the “hard problem” a “fictional problem” due to its reliance on a semantically mistaken concept of “phenomenal consciousness” (P-C) [Sloman, 2010]. Sloman argues that P-C, in the sense defined by Ned Block, is unsuitable for scientific investigation or modeling because it is not amenable to objective description. Instead, he proposes focusing on “access consciousness” (A-C), which, in his opinion, relates to phenomena that can be described and explained within a future scientific theory. This shifts the emphasis from the inexplicable subjective to the measurable and functional.

However, not everyone agrees with this approach. For many researchers, the hard problem remains central. Klein and Barron, for example, emphasize that for a materialist, the hard problem is fundamentally an explanatory problem [Klein et al., 2020]. They argue that its solution requires explaining why the brain-experience connection is as it is and not otherwise. It is not merely a question of how the brain processes information but why this process is accompanied by the feeling of something. Why, for example, does activation of certain neural circuits lead to the sensation of red color and not something else? This question goes beyond purely functional description.

Wolf Singer proposes a naturalistic approach to solving the hard problem, arguing that it cannot be solved by considering only the neural bases of cognition [Singer, 2019]. He suggests that its solution requires considering not only biological but also sociocultural dimensions of evolution. Singer believes perception is the result of a constructivist process dependent on prior knowledge, applicable both to perception of the external world and self-perception. Social interactions, in his view, generate immaterial realities that become preconditions for perceiving oneself and the surrounding world, which in turn produce a dualistic classification of phenomena into material and immaterial. Singer expands the problem’s framework to include social and cultural context.

Interestingly, even within the naturalistic approach, which seeks to explain consciousness through physical processes, questions remain difficult to ignore. For example, Thomas Metzinger, although a proponent of naturalism, acknowledges that we do not perceive the world directly but rather create an internal “model of self” and “model of the world.” This model, in his view, forms the basis of our subjective experience. However, the question of how this model generates the feeling of “being” or “owning” this experience remains open.

Evan Thompson, in turn, criticizes reductionist approaches, arguing that consciousness cannot be fully explained through neural correlates. He proposes an enactivist approach, where consciousness is seen as the result of dynamic interaction between organism and environment. In this context, subjective experience is not something that simply “happens” in the brain but rather arises from active interaction and meaning-making. This means that the “hard problem” may be less a problem of explanation and more a problem of understanding how we conceptualize consciousness.

Lisa Feldman Barrett also offers an alternative view, arguing that emotions, often considered an integral part of subjective experience, are not innate or universal but constructed by the brain based on sensory data and prior experience. If even such basic aspects of experience as emotions are constructs, this calls into question the very idea of irreducible qualia underlying the “hard problem.” Perhaps the problem lies in seeking an entity that does not actually exist in the form we imagine.

The discussion about the “hard problem” boils down to whether subjective experience is something that can be fully explained through physical processes or whether it represents a fundamentally different category. Dennett and Sloman lean toward the former, proposing to reformulate the problem to make it accessible to scientific investigation. Klein and Barron, as well as Singer, insist on its uniqueness, though they propose different paths for its resolution within a naturalistic paradigm.

Perhaps, as Alva Noë notes, the “hard problem” arises from incorrect assumptions about the nature of consciousness. If we stop considering consciousness as something that happens “inside” the brain and begin to perceive it as a dynamic interaction between organism and world, the problem itself may change or even disappear. This does not mean consciousness becomes less mysterious, but the nature of the questions we ask changes.

Ultimately, the question of the reality of the “hard problem of consciousness” remains open and depends on the philosophical and scientific framework we choose. If we adopt a reductionist approach, it may seem a chimera. If we insist on the uniqueness of subjective experience, it remains a central mystery. However, regardless of what we call it, the task of understanding how physical processes give rise to our inner world continues to stimulate research. Perhaps the key to further understanding lies in studying how various states of consciousness, for example, those achieved through meditation, can alter our subjective experience and the complexity of neural activity.

How Does Meditation Affect the Complexity of Neural Activity and the State of Consciousness?

If the “hard problem of consciousness” is indeed a problem, as we discussed earlier, its solution may lie not only in searching for neural correlates but also in understanding how we can actively modify these correlates and associated phenomenological experiences. Meditation, as a practice aimed at altering states of consciousness, offers a unique experimental ground for such research. The question is how exactly this practice affects the complexity of neural activity and, consequently, our subjective perception of the world.

Studies show that meditation not only calms the mind but also induces profound changes in brain function. One key aspect of these changes is the influence on the complexity of neural activity. Atad and colleagues [Atad et al., 2025], in their review, emphasize that regardless of the measures used, their overview reveals convergence toward identifying higher complexity during the meditative state compared to wakeful rest or mind wandering. This means that the brain during meditation exhibits more diverse and unpredictable activity patterns, often associated with greater flexibility and adaptability of the system.

However, an interesting paradox arises here: although the meditative state is characterized by increased complexity, long-term meditation practice may lead to a decrease in baseline complexity of neural activity at rest. Atad et al. [Atad et al., 2025] note a reduction in baseline complexity as a feature after regular meditation practice. How is this possible? Possibly, this reflects a kind of “optimization” of brain activity: the brain becomes more efficient in managing its resources, allowing it to achieve states of high complexity on demand while maintaining a lower level of background activity. This resembles the idea that a well-tuned instrument does not make noise unnecessarily but can produce complex music when required.

Besides neural complexity, meditation significantly influences phenomenological experiences. Venkatesh and colleagues [Venkatesh et al., 1997] conducted a structural analysis of consciousness patterns during meditative states and found altered experience in perception (percentile rank PR = 90), meaning (PR = 82), and sense of time (PR = 87), while measures of positive affect showed increases in joy (PR = 73) and love (PR = 67). These data indicate that meditation not only changes quantitative parameters of brain activity but qualitatively transforms subjective experience, affecting fundamental aspects of our being.

These changes in perception and affect are not random. They may be related to how the brain processes information about itself and the surrounding world. For example, studies show that meditation can influence activity of the default mode network (DMN), associated with self-referential thinking and mind wandering. Reduced DMN activity during meditation may contribute to decreased self-focus and expanded perception, consistent with phenomenological reports of a sense of unity or ego dissolution.

It is important to note that different types of meditation may affect the brain and consciousness differently. For example, mindfulness meditation is often associated with improved emotion regulation and attention, while other practices may focus on developing compassion or concentration. D’Andrea and colleagues showed that mindfulness meditation styles differentially modulate microstate dynamics and MEG complexity at the source level. This highlights the need for more nuanced analysis of specific practices and their neural correlates.

From the perspective of theoretical models of consciousness, such as Integrated Information Theory (IIT) or predictive processing theory, changes in neural complexity during meditation may have profound implications. If consciousness is linked to information integration, as IIT suggests, increased complexity may indicate a higher degree of integration and thus richer conscious experience. On the other hand, if the brain constantly generates and updates predictive models of the world, meditation may alter these models, reducing “prediction errors” and leading to more immediate and less mediated perception of reality.

However, as in any consciousness research, there are methodological challenges. As Rebecca Nicholls-Clow and colleagues note [Nicholls-Clow et al., 2024] in the context of another study, study quality was a key variable examined in this systematic review and meta-analysis; this summary has a fundamental limitation due to the limited quality and quantity of published studies. This caveat is relevant to meditation research as well. Insufficient standardization of practices, differences in meditators’ experience, and subjectivity of reports may introduce significant variability in results.

Nevertheless, meditation provides a unique opportunity to study consciousness, as it allows exploration of changes in phenomenology and neural activity under controlled conditions. It challenges traditional notions of consciousness stability and offers a path to understanding its plasticity. If we can systematically alter the state of consciousness through practice, this opens new horizons for understanding its nature and mechanisms. The open question remains how exactly these changes in neural complexity and phenomenology relate to subjective experience and how we can use this knowledge for deeper understanding of consciousness overall.

What Is the Role of Neurophenomenology in the Study of Consciousness?

In the previous section, we discussed how meditation affects the complexity of neural activity and the state of consciousness. This question inevitably leads us to a broader methodological problem: how to study subjective experience, which by its nature is inaccessible to direct observation? Here neurophenomenology comes into play, offering a radical approach to bridging the gap between objective neuroscience data and subjective reports of experience.

Francisco Varela, one of the pioneers of this direction, argued that the “hard problem of consciousness” is not just a theoretical challenge requiring a “theoretical fix” or “additional ingredient” [Varela, 1996]. He saw in it a fundamental methodological problem requiring a new way of investigation. Varela proposed neurophenomenology as a methodological tool aiming at articulation through mutual constraints between phenomena present in experience and the correlational field of phenomena established by cognitive sciences [Varela, 1996]. In other words, it is about creating a dialogue between first-person reports (phenomenology) and third-person data (neuroscience), where each side serves as a check and complement for the other.

This approach implies that to fully understand consciousness, it is not enough to measure neural activity or behavioral responses. It is also necessary to systematically and rigorously investigate subjective experience itself. Varela emphasized that phenomenology, in this context, is not mere introspection in the everyday sense but represents a strict method inspired by the continental phenomenological tradition, particularly the works of Edmund Husserl [Varela, 1996]. The goal is to develop self-observation skills enabling people to describe their inner experiences with high precision and detail, which can then be correlated with objective neurophysiological data.

Meditation, as we have already seen, becomes an ideal paradigm for neurophenomenological research. Long-term meditators, thanks to years of practice, develop exceptional ability for sustained and detailed self-observation. Aviva Berkovich-Ohana and colleagues note a recent surge in neuropsychological studies of meditation in general and long-term meditators in particular [Atad et al., 2025]. These subjects are presumably capable of generating stable conscious states over extended periods, making experiments with them an interesting paradigm for consciousness research [Atad et al., 2025]. Their ability to provide precise phenomenological reports allows researchers to match specific subjective states with measurable brain changes, for example, increased overall gamma synchronization, as shown in one of Berkovich-Ohana’s studies.

However, neurophenomenology faces several challenges. One of the main problems is the subjectivity of phenomenological reports. How to ensure their reliability and validity? Here, methods borrowed from psychophysics and experimental psychology, as well as rigorous methodological training of subjects, come to aid. For example, to assess neural complexity, metrics such as Permutation Entropy (PE), Sample Entropy (SE), and Multiscale Entropy (MSE) are used. These methods allow quantitative evaluation of the unpredictability and diversity of patterns in neural time series data, which can be correlated with subjective experiences.

Other complexity measures, such as Higuchi’s fractal dimension (HFD) or the Hurst exponent, are also used to analyze neural system dynamics [Atad et al., 2025]. These metrics allow assessment of how complex and nonlinear brain activity is in various states of consciousness. For example, studies show that meditation can lead to changes in these indicators, correlating with changes in subjective experience.

It is important to note that neurophenomenology does not aim to reduce subjective experience to neural processes. On the contrary, it acknowledges its irreducibility but seeks ways to establish “mutual constraints” between these two domains [Varela, 1996]. This means phenomenological data can help interpret neural data, and neural data, in turn, can serve as a check for phenomenological reports. For example, if a meditator reports a state of deep calm and clarity, and neural data show decreased complexity or synchronization in certain areas, this creates a basis for further investigation of the relationship between these phenomena.

However, as in any interdisciplinary approach, difficulties arise. For example, how to ensure that phenomenological reports are not biased by expectations or preconceptions? Here, the role of “unbiased raters” and standardized measures is important, as emphasized in methodological reviews [Nicholls-Clow et al., 2024]. Although these reviews concern other fields, principles of ensuring research quality, such as using representative samples and adequate measures, remain universal.

Neurophenomenology also offers a new perspective on the problem of “levels of consciousness.” Instead of simply classifying states as “conscious” or “unconscious,” it allows exploration of subtle gradations and qualitative differences in subjective experience, correlating them with corresponding neural patterns. This is especially relevant for understanding altered states of consciousness induced by meditation or other practices.

Ultimately, neurophenomenology represents an ambitious attempt to create a more complete picture of consciousness, combining the rigor of scientific method with the richness of human experience. It acknowledges that consciousness cannot be fully understood either solely through objective measurements or solely through subjective reports. Instead, it proposes a path to synthesis, where each approach informs and enriches the other. This dialogue between the inner and outer worlds of consciousness opens new perspectives for understanding how attention shapes our perception and how these processes manifest at the neural level.

How Are Attention and Conscious Perception Related?

After discussing the role of neurophenomenology in bridging the gap between subjective experience and objective measurements, it is logical to move to one of the most fundamental questions in consciousness studies: how exactly does attention interact with conscious perception? After all, if neurophenomenology seeks to understand what we experience, the question of attention concerns how we experience it and what exactly makes our perception conscious. This is not merely an academic dispute but an attempt to understand the mechanisms underlying our interaction with the world.

Attention and consciousness are often used interchangeably, but this is not entirely accurate. Attention can be viewed as a mechanism that directs our cognitive resources to certain aspects of the environment or internal thought processes. Conscious perception, however, is the result of this directed attention, i.e., what we ultimately become aware of. However, their relationship is much more complex than a simple cause-effect link. For example, Giulio Tononi in his Integrated Information Theory (IIT) suggests that consciousness corresponds to the system’s ability to integrate information, which implies some level of attention to this information but is not reducible to it [Tononi, 2004].

Different types of attention have different effects on conscious perception. The study by Chica and Bartolomeo shows that endogenous, or top-down, attention, which we direct consciously, has a relatively weak influence on subsequent conscious perception of near-threshold stimuli [Chica et al., 2012]. This means that even if we try to focus on something barely noticeable, it does not guarantee that we will be aware of it. On the other hand, exogenous, or bottom-up, forms of spatial attention, triggered by external, unexpected stimuli, appear to be a necessary, though insufficient, step in developing distinct visual experiences [Chica et al., 2012]. That is, something bright or sudden can attract our attention and potentially lead to conscious perception, but this alone is not perception. This emphasizes that attention is not a monolithic process but rather a set of different mechanisms, each playing its role.

Interestingly, even with attention present, conscious perception can be limited. Nelson Cowan, revisiting George Miller’s concept of the “magical number 7,” argues that the actual capacity of short-term memory, closely linked to conscious perception, is only three to five “chunks” of information [Cowan, 2001]. This means that even with full attention, we can consciously perceive only a limited number of elements simultaneously. This limit is not rigid but indicates a fundamental constraint on our ability for simultaneous conscious perception, even when attention is focused.

Moreover, our attention is not always directed at external stimuli. The phenomenon of mind wandering is a vivid example of the dynamic aspect of consciousness, when attention shifts from the current task to unrelated thoughts and feelings [Smallwood et al., 2014]. This is not merely distraction but an active process in which consciousness generates internal experiences. Phenomenological studies of mind wandering emphasize the importance of its content and connection with metacognition for determining its functional outcomes [Smallwood et al., 2014]. That is, not all internal distractions are equally useless; some may contribute to creativity or future planning, as noted by Smallwood and Schooler.

In the context of mind wandering, attention essentially “disconnects” from the external world to focus on internal processes. This phenomenon, which Smallwood and Schooler call “perceptual decoupling,” allows us to free ourselves from the constraints of the present moment and immerse in episodic memories or affective states [Smallwood et al., 2014]. Here attention acts as a kind of switch between external and internal worlds, determining what will dominate our conscious experience.

The relationship between attention and consciousness also manifests in neural networks. For example, William Seeley and colleagues identified two dissociable intrinsic networks: the salience network and the executive-control network [Seeley et al., 2007]. The salience network, associated with the dorsal anterior cingulate cortex and orbitofrontal insular cortex, is responsible for detecting relevant stimuli and directing attention. The executive-control network, linking dorsolateral prefrontal and parietal neocortices, participates in maintaining attention and cognitive control. These networks work in tandem, determining which stimuli become the focus of our attention and, consequently, enter our conscious perception.

However, despite the obvious interrelation, attention is not synonymous with consciousness. One can imagine a situation where attention is directed at an object but conscious perception does not occur, for example, with very rapid stimulus presentation when the brain registers information but does not have time to become aware of it. Conversely, we may be aware of something we did not actively attend to, such as background noise suddenly becoming noticeable. This indicates that consciousness may be a broader phenomenon than merely the result of directed attention.

In this context, works by researchers such as Thomas Metzinger, who considers consciousness as the “phenomenal self,” or Evan Thompson, who explores the interrelation between consciousness, attention, and selfhood, offer deeper understanding of these processes. They suggest that consciousness does not passively register information to which attention is directed but actively constructs our experience, using attention as one of the tools of this construction.

Attention can be viewed as a dynamic process that modulates conscious perception but does not fully determine it. Different forms of attention — endogenous and exogenous, external and internal — differently influence what we become aware of. However, even with optimal attention, there are fundamental limitations on the amount of information we can consciously perceive. This leads us to question the reliability of our methods for measuring and interpreting these complex interrelations and the limitations inherent in our current approaches to studying consciousness.

Criticism and Limitations

Methodological Limitations in Studying Subjective Experience

A major weakness of many modern consciousness studies lies in their methodological limitations, especially regarding subjective experience. We can measure neural activity with unprecedented precision, but how to relate these objective data to the internal, ineffable feeling? Neurophenomenology, proposed by Varela [Varela, 1996], attempts to bridge this gap, but even it faces the problem of verifying subjective reports. If we could directly “read” phenomenal experience, there would be no need for complex methods based on self-reports, which by their nature are prone to distortions, biases, and expectation effects. For example, in meditation studies where phenomenological reports play a key role, there is a risk that subjects describe their experience according to expected results or cultural narratives rather than their true inner state [Schleim, 2022]. This calls into question the universality and reproducibility of such data, which is a cornerstone of the scientific method.

The Problem of Interpreting Neural Correlates of Consciousness

Even if we successfully identify neural correlates of consciousness (NCC), i.e., the minimal set of neural mechanisms associated with conscious experience, this does not solve the “hard problem.” Knowing where and when conscious information processing occurs does not explain why it is accompanied by subjective experience. As Dennett notes, the hard problem of consciousness is a chimera distracting from the hard question of consciousness, which is what happens when some content reaches consciousness [Dennett, 2018]. We can observe increased complexity of neural activity during meditation [Atad et al., 2025], but this is only a correlation, not a causal relationship. What exactly in this complexity generates the feeling of “clarity” or “unity” reported by meditators [Venkatesh et al., 1997]? Without understanding this mechanism, neural correlates remain merely “footprints” of consciousness, not its explanation.

Limitations in Generalizability and Representativeness of Studies

Many consciousness studies, especially those concerning altered states, are often conducted on small samples, such as experienced meditators or people taking psychedelics. This creates a problem of generalizing results to a broader population. As Nicholls-Clow and colleagues emphasize in the context of another study, study quality was a key variable examined in this systematic review and meta-analysis; this summary has a fundamental limitation due to the limited quality and quantity of published studies [Nicholls-Clow et al., 2024]. Applied to consciousness, this means that conclusions drawn from specific groups may not reflect universal principles of consciousness functioning. For example, changes in neural complexity observed in long-term meditators may result from years of practice and may not manifest in novices or people without meditation experience. This raises the question of how applicable these findings are to understanding consciousness in general and how we can develop more inclusive and representative experimental designs.