Well, if they are adamant, I doubt they can back it up.
Having said that, you might read Eben Alexander, an academic neurosurgeon, who would have also agreed that consciousness is the brain.
But one day he fell ill with a severe case of bacterial meningitis, and whilst in a coma, he had vivid complex hallucinations.
When he woke up, he had a problem. His brain had been ill and could not, as far as he knew as a neurosurgeon, his brain could NOT have allowed him to hallucinate anything. His complex brain was in a mush of bacteria, so how come he experienced vivid bright complex dreamscapes with music and people and valleys and thoughts? Where in his brain was that being produced, if his brain was basically shut down, as he understands it?
So now he thinks that consciousness exists also on other levels apart from the physical here.
If you can possibly stomach the titles of his books, at least then you can see what he is basing his views on.
But also don't forget that the consciousess-brain link is considered a hard problem, at least by those who don't wave it off. We know that consciousness and the brain are related, neurones fire when you see shapes, but we don't know how something like sentience ever just emerges out of the brain.
Imagine you build a robot which is as complex as a human, and has software which can respond to its environment and make social interactions and basically be as sophisticated as a human. I think this is quite possible. But here is the issue: it would not need to be sentient. If it is just a machine running a program, why does it need to be sentient? It could do everything, physically process inputs and create outputs, without any need for an observer, someone experiencing the show all the time.
Why are you sentient? What possible advantage is there to you having an experience of existing? The machine, your body, doesn't need an "experiencer". Why aren't you just a machine responding to the environment, "in the dark" as it were. My camera does not need to be sentient to recognise faces, why do I need to be sentient?
So the thing is that, sentience is just strange and we don't know what it is, even though it is our most basic quality.
But anyway, all claims need high scepticism, and an open mind.