Consciousness has long been a subject of fascination across neuroscience, philosophy, psychology, and more recently, artificial intelligence. It encompasses the subjective experience of “what it is like” to have a mind, as well as the brain processes and behaviors associated with awareness. This study provides an in-depth look at consciousness from multiple perspectives – examining how it’s defined, the enduring mystery of subjective experience (Chalmers’ “hard problem”), scientific theories of brain mechanisms, philosophical debates, psychological descriptions, and implications for AI. We balance historical context with cutting-edge findings, drawing on insights from leading thinkers (David Chalmers, Anil Seth, Daniel Dennett, Giulio Tononi, etc.) and influential research. Critiques of major theories are noted throughout. A conversational summary is provided after the detailed analysis, followed by a proposal of new questions to push the discourse on consciousness and AI beyond its current boundaries.
Consciousness is notoriously difficult to define, and each discipline emphasizes different aspects ( Understanding consciousness - PMC ). Common sense definitions describe it as the state of sentience and wakeful awareness that starts when we awake from dreamless sleep and continues until we fall asleep again or lose consciousness ( Understanding consciousness - PMC ). In philosophy, consciousness often refers to subjective experience – the qualia or “what it feels like” aspect of mind (Microsoft Word - facing.doc) ( Understanding consciousness - PMC ). For example, Thomas Nagel famously said an organism is conscious “if there is something that it is like to be that organism” (Microsoft Word - facing.doc), highlighting the intrinsic first-person perspective. Psychology traditionally views consciousness as the stream of thoughts, feelings, and perceptions flowing through the mind. William James coined the term “stream of consciousness” to describe how mental life appears as a continuous flow rather than discrete bits: “Consciousness… does not appear to itself chopped up in bits… it flows. A ‘river’ or a ‘stream’ are the metaphors by which it is most naturally described.” (Stream of consciousness (psychology) - Wikipedia). This emphasizes the continuous, unified nature of conscious experience. Neuroscience definitions tend to be more operational, often equating consciousness with brain-integrated information processing that enables reportable awareness of self and environment ( Understanding consciousness - PMC ) ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ). For instance, a neuroscientist might define a conscious state as one in which widespread neural networks are active and information is globally available in the brain (as we’ll see in Global Workspace theory) ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ). Crucially, no single definition is universally accepted – “consciousness is hard to define, and no single definition is apt” ( Understanding consciousness - PMC ) – but broadly it involves being awake, aware, and having subjective experiences.
Rather than an all-or-nothing property, consciousness can vary by level and state. Clinically, levels of consciousness range from full wakefulness and alertness down through drowsiness, sleep, and into states of impaired consciousness like stupor or coma (Level of Consciousness - Clinical Methods - NCBI Bookshelf) (Level of Consciousness - Clinical Methods - NCBI Bookshelf). The normal conscious state is being awake or in light sleep (from which one can be easily awakened) (Level of Consciousness - Clinical Methods - NCBI Bookshelf). In contrast, altered states include deep sleep, anesthesia, or disorders of consciousness (e.g. vegetative state, minimally conscious state), where awareness is greatly diminished or absent (Level of Consciousness - Clinical Methods - NCBI Bookshelf) (Level of Consciousness - Clinical Methods - NCBI Bookshelf). Even within sleep, there are stages: during REM sleep we often experience vivid dreams – a form of consciousness with imagined sensory experiences – whereas in deep non-REM sleep, conscious experience can fade to nearly nothing. Transitions between these states (wake ↔ sleep, etc.) intrigue researchers because they illustrate consciousness turning “on” or “off” in the brain. Neuroscientist Ralph Adolphs points out the puzzle of why “being conscious” produces a distinctive experience that “vanishes in a coma or dreamless sleep” and is absent in inanimate objects ([Where Does Consciousness Come From? | Caltech Science Exchange
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Caltech Science Exchange](<https://scienceexchange.caltech.edu/topics/neuroscience/consciousness#:~:text=Despite%20advances%20in%20our%20understanding,coined%20by%20philosopher%20David%20Chalmers>)).
Modern theories suggest consciousness may be better viewed as a continuum rather than a binary. Philosopher-neuroscientist Kathinka Evers, for example, argues there is no sharp boundary between unconscious and conscious processes – the brain may be inherently conscious at some basic level, with gradually increasing degrees of complexity and awareness ( A continuum of consciousness: The Intrinsic Consciousness Theory ) ( A continuum of consciousness: The Intrinsic Consciousness Theory ). In this “Intrinsic Consciousness Theory”, even low-level brain activity carries primitive conscious qualities, and higher-level reflective consciousness emerges from the same continuum ( A continuum of consciousness: The Intrinsic Consciousness Theory ). This perspective aligns with ideas of graded consciousness, where animals, infants, or even simple neural networks might possess rudimentary forms of awareness. It also complements scientific efforts to measure consciousness level objectively. A recent advancement is the perturbational complexity index (PCI), a metric combining brain stimulation and EEG response complexity. Casali et al. (2013) showed that PCI reliably distinguishes levels of consciousness: in awake or dreaming brains the PCI is high (indicating rich, integrated activity), whereas in deep sleep, anesthesia, or vegetative states it is low (A theoretically based index of consciousness independent of sensory processing and behavior - PubMed) (A theoretically based index of consciousness independent of sensory processing and behavior - PubMed). Such findings support the idea that integrated complexity of brain activity correlates with “how conscious” a state is, providing empirical footing for the concept of a continuum of consciousness.
Across disciplines, then, consciousness can be defined in content (the subjective “feel”), in function (information access and responsiveness), and in degree (level or clarity of awareness). These multiple angles set the stage for the deeper questions: why does consciousness exist at all, and how do physical processes generate it?
One of the most profound challenges is what philosopher David Chalmers dubbed “the hard problem of consciousness.” Simply put, the hard problem asks: How and why do physical processes in the brain give rise to subjective experience? (Hard problem of consciousness - Wikipedia). In other words, even if we map every neural mechanism of perception or behavior (the “easy problems”), we still owe an explanation for why those brain processes feel like something from the inside (Hard problem of consciousness - Wikipedia). Chalmers contrasted this with the “easy problems” – which are not trivial, but are considered tractable – such as explaining how we discriminate stimuli, integrate information, or produce verbal reports (Hard problem of consciousness - Wikipedia) (Microsoft Word - facing.doc). Those easier questions deal with functions that neuroscience can address by identifying neural circuits and computational mechanisms. In fact, Chalmers noted we have a “clear idea” how to approach such phenomena via cognitive science (e.g. explaining how the brain focuses attention or the difference between wake vs. sleep in terms of neural activity) (Microsoft Word - facing.doc) (Microsoft Word - facing.doc). But none of those functional explanations inherently tell us why there is an inner life accompanying them. As he wrote: “There is also a subjective aspect… as Nagel put it, there is something it is like to be a conscious organism… Why should physical processing give rise to a rich inner life at all? It seems objectively unreasonable that it should, and yet it does.” (Microsoft Word - facing.doc) (Microsoft Word - facing.doc). This encapsulates the mystery of qualia (raw subjective sensations like the redness of red or the pain of a headache) – why don’t all those neural firings go on in the dark, without any felt experience?
Chalmers’ formulation in 1995 galvanized a debate. The implications are deep: if subjective experience cannot be derived straightforwardly from physical explanations, some argue we might need new fundamental principles or a form of dualism (e.g., treating consciousness as a basic property of nature, or as arising from unknown physics). Others suggest the hard problem is a misleading or even pseudo-problem. For instance, neuroscientist Daniel Dennett contends that once we thoroughly explain all the cognitive and behavioral functions of the brain (the “easy” problems), there is nothing extra left to explain – the sense of an unaddressed mystery is an illusion ( Understanding consciousness - PMC ) ( Understanding consciousness - PMC ). Dennett famously denies that ineffable qualia exist as separate mystical entities; he argues consciousness “is an illusion or an epiphenomenon”, analogous to a “virtual machine” running on the neural hardware ( Understanding consciousness - PMC ). In Dennett’s view, the brain is a massively parallel processor with no single locus of experience, and what we call consciousness is the brain’s user interface, a narrative the brain tells itself ( Understanding consciousness - PMC ). This “illusionism” (also espoused by philosophers like Keith Frankish and psychologist Susan Blackmore) doesn’t claim consciousness isn’t real, but that it isn’t what it feels like – e.g. it feels like a continuous stream of rich experience, but that may be a constructed narrative (Stream of consciousness (psychology) - Wikipedia). Illusionists thus try to dissolve the hard problem by saying the subjective magic is a cognitive trick. Not everyone is convinced by this dismissal – critics argue that describing consciousness as an illusion still begs the question “an illusion to whom?”, implying a conscious observer of the illusion.
Most scientists take a pragmatic approach: they acknowledge the hard problem (the explanatory gap between mechanism and experience) but focus on what can be tackled empirically. Cognitive neuroscientist Anil Seth suggests reframing the question: instead of asking “Why does consciousness exist?” as an unsolvable mystery, we should study its properties and mechanisms systematically (Anil Seth: "Reality is a controlled hallucination" | CCCB LAB) (Anil Seth: "Reality is a controlled hallucination" | CCCB LAB). He urges moving past seeing consciousness as an unfathomable enigma, likening it to how we approach life or the universe – we study how it works, even if the ultimate “why” remains open. In Seth’s own research, he describes perception as a “controlled hallucination” – our brains actively predict sensory inputs and thus essentially construct the world we experience (Anil Seth: "Reality is a controlled hallucination" | CCCB LAB). This perspective doesn’t solve the hard problem, but it offers a framework: the brain’s predictive models account for the content of experience (why this color looks like this, etc.), even if the fact that it is felt still amazes us. Other researchers attempt to chip away at the hard problem by bridging psychology and neurobiology. For example, neural correlates of consciousness (NCC) are being mapped – identifying the brain activity that reliably corresponds with conscious experience. The hope is that by narrowing down exactly which circuits and firing patterns accompany consciousness, we inch closer to understanding how brains generate experience ([Where Does Consciousness Come From? | Caltech Science Exchange
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Caltech Science Exchange](<https://scienceexchange.caltech.edu/topics/neuroscience/consciousness#:~:text=the%20neural%20correlates%20of%20consciousness,temporal%20lobe%20of%20the%20brain>)).
Still, a full answer to the hard problem remains elusive. Some philosophers (like Chalmers later on) have entertained panpsychism – the idea that consciousness might be a fundamental feature of matter, so that even simple systems have tiny rudiments of experience, which complex brains amplify. This would radically reframe the hard problem by eliminating a stark line between physical and phenomenal. Others like neuroscientist Antonio Damasio maintain optimism that standard science can eventually explain consciousness: he notes that investigating consciousness is “condemned to some indirectness” (since we can’t directly observe subjective experience), but so are many other areas of science, and this indirect approach can still yield understanding ( Understanding consciousness - PMC ). In summary, the hard problem highlights a conceptual gap in our understanding – one that current science acknowledges but largely brackets off. As we advance, researchers continue to debate whether this gap will close through conventional brain science or require a fundamentally new paradigm.
Despite the difficulties of the hard problem, neuroscience has made significant progress in explaining many aspects of consciousness. Several major theories propose how brain activity gives rise to the features of conscious experience (at least in terms of information processing and behavior). Here we focus on two influential frameworks – Global Workspace Theory and Integrated Information Theory – along with related findings on neural correlates of conscious states.
Originally proposed by cognitive scientist Bernard Baars and later developed neurally by Stanislas Dehaene and colleagues, Global Workspace Theory treats the brain as a collection of specialized processors with a central information exchange ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ). The Global Neuronal Workspace model posits that a mental content becomes conscious if it is broadcast globally to multiple brain systems (memory, attention, decision-making, etc.) ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ). In Baars’ analogy, unconscious processes are like numerous parallel “processors” working in the dark, and consciousness is like a spotlight on a “theater stage” (the global workspace) where information is illuminated and made available to the whole audience (the many brain modules). In neural terms, when a particular perception or thought attains a certain level of salience and connectivity, it ignites a broad network of high-level cortical neurons with long-range connections – especially linking frontal (executive) and posterior (sensory) areas ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ) ( The Neuroscience of Consciousness (Stanford Encyclopedia of Philosophy) ). This ignition – often correlated with a burst of synchronous activity (e.g., gamma oscillations) or a characteristic late brain-wave (the P3 wave) – makes the information accessible to memory, language, and decision circuits, hence “conscious.”