Determinism cannot exclude any event. It cannot exclude choosing any more than it can exclude a tree growing or the rain falling or anything else that happens.
Well, yes. It's how determinism is defined. Nothing within the system can be excluded.
Which of course has described implications for the notion of free will'
Only for the notion of "free will" defined as "a choice we make that is free from cause and effect".
But the implication for "free will" defined as "a choice we make that is free of coercion and undue influence" is quite different. This notion of "free will" is a deterministic event that is reliably caused by prior events, just like every other event. The implication of determinism for this notion of "free will" is that it must necessarily happen, exactly as it does happen, without deviation.
In other words, this operational free will is just as embedded in determinism as every other event that ever happens. And this is an entirely different implication than the one that applies to "freedom from cause and effect".
Implications that effectively rule out the idea of free will within a deterministic system.
The implication of determinism for "freedom from causal necessity" is that no such thing exists.
The implication of determinism for "freedom from coercion and undue influence" is that it inevitably exists.
The implications have been described too many times.
Indeed. But you insist upon defining free will as "freedom from causal necessity", while ignoring the ordinary free will which is nothing more than "freedom from coercion and undue influence".
And because you fail to recognize operational free will, you cavalierly claim that free will cannot exist within a deterministic system. And I must repeatedly explain to you why the ordinary notion of free will, the one that people understand and correctly use all the time, is a real event within a deterministic system.
But you choose not to hear this.
The brain, according to the definition, is subject to determinism.
Using the wrong metaphors can distort the truth. The brain is not "subject to determinism". The brain simply "functions deterministically". Everything that happens within our brain, every neuron firing, every thought and feeling we experience, is reliably caused by prior neurons firing, and prior thoughts and feelings.
The proper metaphor is not determinism being the "king" of the brain, but rather the brain itself being determinism exercising control over other objects. For example, I filled a cup with water to take my morning pills. My brain controlled these events, and it did so deterministically.
My brain is simply doing what it naturally does. Neither the laws of nature nor determinism are external "agents" controlling what I do. They are simply me, doing what I naturally do.
Quite simply, if the world is deterministic, the brain being inseparable from the world and its objects and events, is deterministic.
The brain is a separate object, just like every other object is a separate object. So, let's not start by smushing all of the objects together.
The brain, like every other object, operates deterministically as it interacts with other objects and forces to produce events. And even the events within the brain, the sequences of thoughts and feelings, occur deterministically.
Consequently, what it does, its abilities, faculties, thoughts and action is determined - basically - by environment, inputs and memory function, a system where free will plays no part in thought or response.
The brain's perception manages inputs. The brain's memory keeps track of things. The brain's intentions keep it on track. The brain's decision making controls every deliberate action.
The environment does not micromanage the brain's activities. The brain itself does that through its own perception, memory, intention, and decision making functions.
When the brain decides for us what we will do, while free of coercion and undue influence, it is a "freely chosen will", or simply "free will".
Free will is obviously not free from cause and effect, but only free from coercion and other forms of undue influence. And this operational free will is perfectly compatible with a world of perfectly reliable cause and effect.
The story you quoted, about people whose behavior was altered by a brain tumor, demonstrates the notion of undue influence. An undue influence is any extraordinary influence that prevents you from deciding for yourself what you will do. These are cases where a person is not acting of their own free will, and it is the operational notion of free will that is used precisely to make such distinctions.
Determinism itself never makes any meaningful or relevant distinction between events. Because determinism is such a useless notion, it seldom comes up when dealing with real-life scenarios. Determinism is a logical fact, derived from the presumption of a world of perfectly reliable causation. However, it is neither a meaningful nor a relevant fact. And this is why the intelligent human mind simply acknowledges it, and then ignores it.