The physical brain must be distinguished from the mind. The physical brain appears to think, in that it takes material (perceptions, memories) and processes them, shooting up 'thoughts', as images, words, or clouds of dread, to the mind. But there is no one in there. There is no little man inside the Chinese Room. These 'thoughts' are not thoughts in the real sense of extensions, creations by the conscious, will-powered mind. They are downstream of the mind, not upstream. They are no different than physical sensations of heat or cold. Worse than that: they are highly faulty. At least sensations of heat and cold are largely accurate.
All anxiety, all gloom, all fretting, all resentment is coming from the physical brain, downstream of the mind, given credence by the mind, and treated as its guiding force, its god.
None of this is real, and none of this need be.
From ACIM:
LESSON 10.My thoughts do not mean anything.W-pI.10.1. This idea applies to all the thoughts of which you are aware, or become aware in the practice periods. 2 The reason the idea is applicable to all of them is that they are not your real thoughts. 3 We have made this distinction before, and will do so again. 4 You have no basis for comparison as yet. 5 When you do, you will have no doubt that what you once believed were your thoughts did not mean anything. ...W-pI.10.3. This aspect of the correction process began with the idea that the thoughts of which you are aware are meaningless, outside rather than within; and then stressed their past rather than their present status. 2 Now we are emphasizing that the presence of these "thoughts" means that you are not thinking. 3 This is merely another way of repeating our earlier statement that your mind is really a blank. 4 To recognize this is to recognize nothingness when you think you see it. 5 As such, it is the prerequisite for vision.
Any 'thoughts' that do not come from above, that are not inspiration, intuitive thoughts, and decisions that use me as their material, are not thoughts at all. I must be receptive to what comes from above, not from what comes below.
From Find And Use Your Inner Power (Emmet Fox)
... but we should be careful to see that we shut out negative things only and still leave ourselves open to the True, the Beautiful, and the Good. Here is an affirmation that, intelligently used, will save you much unnecessary bombardment by negative thoughts:I am positive to everything but the action of God.In an electric circuit, any given point is said to be positive to any point below it and negative to any point above it. Current passes always from the positive to the negative and never the other way. Now, if you are positive in this sense to everything but the action of God, no negative things can come back at you. On the other hand, you are receptive (or "negative") in the purely electrical sense of this ambiguous word) to all good—the direction inspiration of God, the prayers of other people, and all the beautiful and interesting vibrations in the universe.