Since that time, enormous advances in neuroscience have occurred, assisted by previously unimagined new capabilities in imaging technology and the computer technology that enables them. It is now mainstream, well-supported scientific consensus that consciousness is entirely biological in origin.
A specifically "conscious" part of the brain has never been identified, but consciousness is clearly exclusively associated with brain activity observed via fMRI. There are also these things called drugs which, when you put them in your brain, alter consciousness and make you think and feel differently, almost like you're a different person. Also it is well known that if the brain becomes injured, the way you think and feel and even your personality can completely change. Finally, if the brain breaks down and stops, like, brainalyzing or whatever, then you aren't conscious at all anymore.
It is clear from all evidence that without a brain, there is no consciousness, even if scientists can't agree on exactly what consciousness is. But an understanding is gradually emerging that consciousness may not be quite what we thought it was - an entity or an algorithm of some kind - but rather that it is really just a deep pile of competences layered upon one another from which the sense of being a Person emerges. As those competences are removed one by one, so fades the sense of Self and consciousness. Therefore it is less useful to ask, "what is consciousness?" and instead investigate neuro-biological competence, including the interesting question of what is required for Moral Competence.
Ants have about 250,000 neurons, and you can make them run around crazy by poking sticks at them. That is something they are competent at doing. Dogs have about 2.2 billion neurons, and they can count to three, but they also eat their own poops. Humans have about 86 billion neurons - not just the ones that can do calculus, but also including the ones that purchase whole life insurance and are dumb. It is therefore clearly not just the number of neurons, but how they are connected and how they function. In other words, the brain requires conditioning in order to have high levels of competence and therefore consciousness.
As an aside, we might wonder what would happen if we had a lot more neurons. Would we be super-duper intelligent? Would we develop, like, telekinesis or something? Well, elephants have about 250 billion neurons, about 3 times what we have. While they have pretty good memory, they evidently do not posses the power of telekinesis, or even the power of instagram. Although some of them are known to be exceptional artists.
So, we find that there is no single part of the brain that is "the consciousness." There are, however, specific parts, circuits, networks etc that are responsible for individual competencies. Consciousness is what emerges when all these competencies are combined, and consciousness is a kind of measure of the number and diversity of our competencies.
Neither is there any sharp line between conscious and not conscious. Lots of neurons = lots of neural competence; a few neurons = a few competencies; zero neurons = zero competence. Ants have fewer competencies than dogs, which have fewer than humans. Plants have a few limited competencies, and so might possibly be regarded as having a minimal degree of consciousness, even though they have no actual neurons. They do have some specialized cells called bundle sheath cells that behave somewhat like neurons.
Rocks have no competencies whatsoever, no internal functions or organized structure other than random crystallization grain structures, and are therefore in no way conscious at all by any measure or definition. Some may argue for the consciousness of ecosystems, but only to the extent that living systems have evolved any identifiable competencies. But there is absolutely no question of there being anything remotely like a "universal" consciousness in the sense of rocks or other inanimate objects being self-aware or having feelings or opinions.
Only the highest levels of competence endow a very few mammal species (notably humans) with a competence for self-awareness and the level of consciousness we associate with that sense of Self. Why did other species not get that even with far more evolutionary time under their belts? Well, they evidently did not need that particular competence for survival, or small evolutionary steps in that direction were of no advantage to them. Only humans are so physically regressive and degraded that we could only survive by being super aware, individual, and clever.
As early as 200,000 years ago, humans were basically physically as we are now, including our 86 billion neurons. If 190,000 years wasn't enough for us to invent Porsches and Breguet wrist-watches and Apple eye-phones, then what was so special about the last 10,000 years?
Software. It took a while, but once the ecosystem of human brains had become fertile enough ground for a new form of evolution to start taking place, bits and pieces of a new operating system began falling into place using a kind of fitness-for-survival driving force. Social orders developed, and our brains gained that competence. Language developed, and again 86 billion neurons were sufficiently large to accommodate languages. Crafts developed, using language as a stepping stone so that skills could be transmitted virally. Technologies developed which benefited success-driven software evolution by creating more human brains to infect. These include agriculture and animal husbandry, larger social structures, writing, fighting, money, irrigation, housing, clothing, etc. All these ideas form the suite of thinking tools that we use to think about ourselves - in other words, to be conscious.
Can there be consciousness without a brain? If you imagine seeing a ghost (that isn't actually there because you're hallucinating which is something brains are very competent at doing) and that ghost visibly has zero neurons in total because it's invisible and floating in the air, then what are the chances that the ghost is a conscious being that is super intelligent and has also magic ghost powers?
Zero. The answer is zero probability, to infinity decimal places. If there are no functioning neurons (a necessary but insufficient condition), then there is no functional competence and hence zero consciousness.
"But what if the ghost has Ghost Neurons? Huh?"
Ok - you exponentially amp up the improbability of this nonsense by suggesting that it requires the further existence an even more improbable thing.
Sure - why not.
So - do these ghost neurons of yours also use ghost chemical neurotransmitters? What are they? How do they work? What are they made of? Can you murder a ghost by spraying lysol on it? Do your ghost neurons produce electrical impulses using actual electrical charge? Or is it some kind of never-before-detected form of ghost electricity? What keeps these ghost neurons together in a body? Ghost velcro? What is the source of the ghost neuron's energy? Does the ghost have a respiratory and circulatory system as well? Or does it run on ghost batteries?
Keep in mind that every time you have to propose some stop-gap ad-hoc new thing to keep the hypothesis from unraveling, you exponentially increase the improbability that some thing exists which has never been observed (actually, positively observed to not be there) and which would require the invalidation of mountains of established fact. And don't try hiding in the gaps of scientific knowledge - these are small and dwindling. The Argument from Ignorance is basically, "you don't know some minor detail, therefore vast swathes of my imaginary nonsense are proved conclusively." Can we hold you to that when that knowledge gap is eventually filled? Or will you continually move the goalposts?
You've heard of Occam's Razor? Well - get ready for Newton's Flaming Laser Sword of Truth. It's just like Occam's razor, but way more dangerous and devastating to bullshit. It works like this. Anyone who asserts the existence of a Mind in the absence of a Brain is under the obligation to produce logical observable consequences of that assertion. If they fail to do so, the assertion must be dismissed as effectively proven false.
One such potential observable consequence of the existence of Mind without Brain is that dead people should be able to pass real information to the living. Also, that new, real, and accurate information should be able to be received by prophecy alone.
Unfortunately, no real, accurate, specific information has ever been received from the dead or from prophecy, at a rate distinguishable from random chance. All practitioners of "talking to the dead" have been proven to be frauds who use mere parlor tricks, and their "information" is so nonspecific it has become a generic cliche'. "Does anyone in the room have, perhaps, an elderly relative who has died?" Um, no - we're all AI robots here.
Also, no prophecy has ever produced reliable new information (not previously known), and "prophets" almost universally miss a lot of really important and obvious stuff. "Prophets" are also almost always known to be frauds and criminals, and are therefore most untrustworthy in the first place.
This state of affairs must be regarded as powerful positive evidence in condemning the notion of Mind without Brain. No brain, no mind. Of that we can be absolutely certain.