Do you think a "brain in a vat," cut off from the body and outside world, could still be conscious?

Consciousness is simply defined as the ability to voluntarily choose a reaction to sensory input. An isolated brain in a jar is deprived of the five senses, and can therefore receive no sensory input. If there is no sensory input to react to, there can be no consciousness. The brain can still show activity and can conceptualize, akin to dreaming, but it can not be conscious.

It seems to me that "consciousness" is nothing but an epiphenomenon of sensations received by the brain from within and without the body.

The brain will try to create a world in which it can function. If it is to survive, it will build its functions "in a new environment." It will compensate for everything it can and learn everything it lacks to function. It's also worth remembering that this will require hormones. Without hormones, it may indeed be incapable of rapid action and learning.

Personally, I think a brain which Never had stimuli would remain Potentially conscious, but not. With no way to recognize an environment of some kind (even if its environment and itself is perceived as just one 'realm'), AND a way to interact with and alter it (or them), I cannot imagine a brain developing any way of developing! Less conscious than the organisms which simply react, with no awareness that they are actually separate from the world they are in.

A vat brain that had previous experiences of some kind would have developed an awareness dependent on the amount and type of awareness, and would then have something to think about...leading to the horror of "Where Did All That Go?!?!"

I can only hope that a completely input-free brain would lapse into something like very deep sleep. Anesthesia at its most powerful. If not, any real experimentation in the field could be unimaginable cruel.

From my perspective consciousness implies awareness of your surroundings so your brain can process the information and interact accordingly. If the brain in the vat has no sensory perception how can it decide on the appropriate interaction?

Very thought provoking. It’s hard to answer the question without more experimentation.

Brains seem to be as intrinsically excitable media that will naturally exhibit space-temporal waves.

What have we learned from the electrical and fMRI of intact brains under sensory deprivation? We know that people feel strange sensations and hallucinate.

Given the powerful arguments of Iain McGilcrist that the two hemispheres represent different ways of being, I wonder if there is any difference in the behavior for right or left hemisphere disconnection both in the electrical and fMRI of the severed half and indeed in the behavior of the person undergoing the treatment.

A brain in a vat must have a history. There must be a great difference between a brain removed from an adult and one grown in the vat. The former will likely become an extreme version of a sensory deprived human. There is no reason to suspect spontaneous recognizable consciousness in the grown brain unless it had the developmental opportunities of the fetal through childhood shaping by interaction with its environment.

This article offers a careful and illuminating empirical probe into the classic “brain in a vat” problem by examining hemispherotomy patients—cases in which one cerebral hemisphere is biologically alive yet functionally disconnected from the body and the external world. Its central finding is both subtle and significant: even when neural networks remain surprisingly well organized, the isolated hemisphere most likely enters a sleep-like state rather than sustaining an independent stream of conscious experience.

From the perspective of Advaita Vedānta, this conclusion is largely consonant with classical insights, while also revealing a deeper philosophical distinction. Advaita draws a sharp line between consciousness itself (cit or ātman) and the instruments through which experience is expressed—the body, senses, and mind. Consciousness, on this view, is not produced by neural or cognitive processes; it is self-luminous awareness, the unchanging witness in whose presence mental and sensory activities arise and subside. The brain–mind system functions as a medium for the manifestation of experience, not as its ontological source.

Seen in this light, the article’s finding that organized neural structure can persist without conscious experience strongly supports the Vedāntic insight that organization is not identity. Structural or functional integrity alone does not amount to awareness. Advaita has long articulated this point through its analysis of the three states of experience—waking, dream, and deep sleep. Waking experience depends on active engagement between senses, body, and world. Dream shows that experience can arise without external sensory input, generated by the mind alone. Deep sleep represents the withdrawal of mental activity altogether—not the annihilation of awareness, but the absence of experiential content.

By showing that neural structure can persist without conscious experience, the article clarifies the dependence of waking consciousness on bodily and environmental interaction, while unintentionally reinforcing Advaita’s distinction between awareness itself and the instruments through which it is expressed. Where the article and Advaita diverge is at the ontological level. Remaining within a physicalist framework, the article cautiously suggests that consciousness may fade when neural integration with body and world is lost. Advaita would reframe this claim: what fades is not consciousness itself, but its expression through the mind.

In this way, the article usefully delineates the limits of neural organization in accounting for awareness and, perhaps unintentionally, echoes a central Vedāntic insight: science can describe the conditions under which experience appears, but the nature of consciousness itself may not be reducible to the structures that express it.

When I read about the innumerable parts of the body sending and receiving signals to and from the brain, I have to wonder what the implications would be for consciousness emerging from a "brain in a vat." How would consciousness be altered? Aside from the five senses, my conscious state is aware of and monitors many other perceptions like proprioception. What would consciousness be if there was nothing to perceive? Would any perceptions now be phantom, perhaps painful as can happen with a phantom limb?

I think there is a great deal to learn about the fate of consciousness when these mind-body interactions suddenly ceased to exist?

Consciousness is the attention we pay to something. You can be aware of one thing and not another, and every organism needs this to be able to select from the input what it needs and what it doesn't. Cells are also aware of their environment in this way and only make the organism aware of a problem if they cannot solve it themselves. At a higher level, this also applies to people. An organization or nation only becomes aware of a problem if it cannot be solved by the individuals themselves (and if the government is not cut of of the body and only looks outside, the opposite of this experiment). People are very capable of shutting themselves off from their environment, and I believe this requires the sleep spindles, which switch off familiar stimuli (except light) with anti-stimuli. This ensures that a person, even when concentrating or in deep sleep (default network), is not distracted or awakened by familiar sounds. A person is awakened by, for example, a feeling, sound, or smell that is unfamiliar, but also by a sound that should come but doesn't (for example, a train). This experiment seems to fully confirm this. Also, there are no sleep spindles visible, because of course, no stimuli need to be switched off there. And at such a moment, someone can still "see" what you can also see in a dream: imaginations (which, by the way, are different from a dominant voice that you once had to switch off as a child because it pushed you to do things it couldn't handle, but which you suddenly hear later when you no longer hear that voice. That's the anti-voice, and of course, it sounds exactly like the real voice. That's called hearing voices.

The findings are striking in showing that neural organization can persist even when a brain is cut off from body and world—yet this very result underlines a classical Vedāntic distinction. The mind–brain apparatus may remain structurally intact and still lapse into a sleep-like state, but organization is not awareness. In Advaita Vedānta, consciousness (Ātman) is not produced by neural activity; what sleeps or wakes is the mind, not the witnessing awareness itself. The study thus supports the idea that sensory interaction sustains waking experience, while unintentionally echoing the deeper insight that consciousness is independent of its instruments.

The study shows that the brain can remain organized without being awake—precisely Advaita’s point that consciousness is not a function of neural structure but the witness of it.

The short answer is no. Consciousness requires awareness of self and other. However, it is possible, in fact likely, that an isolated brain would bifurcate in a way that would allow it to constitute itself as both self and other. In which case the answer would be yes.

I think the brain is a perceptual organ that would cease to have any meaningful function in the absence of external stimuli to interpret and respond to.

I think a brain in a vat would go into shock since the brain literally has a map of the body and is in constant contact with all parts of the body. People who loose a limb experience phantom pain — so just imagine when the brain doesn’t find a body. Of course, the response would be to just feed the brain body sensations; but that will probably be a lot more complicated than anticipated.

I would say yes, although I think of the word "conscious" as an adjective corresponding to having some threshold level of a continuously ranged property called "consciousness", and so as not being well defined until that threshold level is specified. The reason I would say "yes" is because I interpret the word "consciousness" as referring to a property of information processing systems which corresponds roughly to the extent to which the information being processed includes a description of the internal state of the processor (which of course can never be 100% for a finite system), and I see no reason why a brain in a vat should not be able to process (ie "think about") some aspects of its own thought processes. This might be more difficult if the brain had never been given any external data to process, but if it had any prior contact with an "external world" then I don't see why it could not continue to think about those experiences - and also to think about what it had been thinking.

A brain did not evolve isolated from a nervous system. Without a nervous system and sensory input, there is no way for a brain to differentiate itself from its surroundings and "know" that it is a brain. Plus, is this an old brain with memories of sensory input or is it a young brain with no memories? A brain with no sensory input has nothing to process except memories. Memories are also used to model and predict the future. The slow wave pattern may be the brain in idea mode waiting to process sensory input or communication from other parts of the brain. Or, I could be wrong.