Brain is directory connected to mind. Examining the differences of wave patterns that emit from brain when someone is mad or meditating explains there is a direct connection. What if someone achieved nirvana or a lower state of the path to nirvana, and met in an accident and lost all his memories or had permanent brain damage due to a disease . As an example in alzheimer’s disease brain shrinks and it losses its memories and abilities to think . So in a situation like this , can someone loose his state in the path to nirvana ?
"Will permanent brain damage can cause someone to loose their Arihathness ?
So in a situation like this , can someone loose his state in the path to nirvana ?"
In Theravada Buddhism the attainment of Nibbana is enumerated into 4 stages, also known as the Four stages of Enlightenment.
There are a total of 10 fetters (roots) that has to be broken in order to attain Nibbana.
The destruction of those roots comes in stages;
As seen in the illustration below, the Arahant is free from the 5 lower fetters and the 5 higher fetters. When a fetter has been broken it does not come back. It is done away with for good. It is permanently destroyed.
So to answer your question: No, an arahant cannot loose his attainment.
Brain damage might reduce mental capacity.
An Arahat is free from the unwholesome roots, i.e., they have stopped reacting to sensual stimuli. Brain damage or not unwholesome roots do not arise again.
So they do not lose their attainment.
Arahathhood does not depend on the ability to remember. It depends on whether there are defilements in the mind or not. You can slice and dice and french fry the brain, but if there's something missing in the mind, it's never going to magically appear from nowhere.
At our place there was discourse by Geshela Navang Samatenji and he had told there are neurologists studying Buddhist monk's brain for understanding science behind tranquility.
They find changes in their brains.
Brain controls body by nervous system that neurons send signals from one cell to others, or from one part of the body to others. And that's why we get if mosquito bite us.
We get sense. We weren't get sense of it if there's problem in our nervous system. And that wouldn't affect mind.
Mind also handle body but we can see two different people minds i.e. Consider there are two people one who is criminal and another is monk whose brain damaged. What we could say both of their mind. That criminal's mind is already malicious and monk is Arahat so even if they'll be cure, criminal not going to be monk and monk to be criminal that brain can't change state of mind.
Mind can control body by desire.
Just take a look Brains of Buddhist monks scanned in meditation study.
They explained good, so you can see that mind (meditation) changed their brains and not brain did changed mind.
The scanner tracks blood flow within the monks' heads as they meditate inside its clunky walls, which echoes a musical rhythm when the machine is operating.
Dr Josipovic, who also moonlights as a Buddhist monk, says he is hoping to find how some meditators achieve a state of "nonduality" or "oneness" with the world, a unifying consciousness between a person and their environment.
When one relaxes into a state of oneness, the neural networks in experienced practitioners change as they lower the psychological wall between themselves and their environments, Dr Josipovic says.
And this reorganisation in the brain may lead to what some meditators claim to be a deep harmony between themselves and their surroundings.
Further they explained Shifting attention that brain appears to be organised into two networks: the extrinsic network and the intrinsic, or default, network.
Brain is just matter(rupa) not nama. Brain is just like the something recording what is happening. Not to mention Arahantship, once Sotappana, this attainment of Noble truth never get destroyed not only in this life, it will be beyond life. So all Arya never lost their dhamma, even brain(mere rupa) is destroyed.