I know I say, "My brain is being dumb," or, "I am having a case of the braindumbs," when I am having Fun Anxiety Times. I tend to refer to autism things more as "my brainstuff" since it is kinda my brain but it's more the way my brain is rather than my brain being an anxious piece of shit who needs to quit it. I mean autism sucks sometimes and I get angry at my brain for being the way it is on occasion, but like @Acey said, it's a part of who I am so I can't be that angry at it because I would probably be a totally different person without it (also I can do cool stuff like recognise patterns and notice details other people don't notice! That is a cool thing!) I think, in a way, maybe personifying my brain gives me something to attribute blame to. Like, it's not me that's having an anxious self-hate spiral that is causing me to be unable to get out of bed, it's my stupid brain! Damn you, brain! Or, "Goddammit brain, get your executive functioning together, we have shit that we gotta do." Does that make sense?
Before I had any treatment, I never did the brain vs. me split because I was sitting in a narrative of "I am a complete failure at all life things." After I got on meds I started to do that a lot, because there was a me at top functionality when the meds were working and I was having a good day, and there was a me when the meds were wearing off and I had just done a huge homework assignment and I had paperwork to fill out and the world was terrible and oppressive. Stuff like "my anxiety wants me to just curl up in a ball and cry because there are so many things in the world" and "my brain would like to remind us that in fact everything is pointless and we should stop trying to accomplish anything and just go back to sleep." It was kind of a shorthand for "part of me wants this, but I've already decided that I shouldn't, and it doesn't seem particularly rational." These days? I'm honestly trying not to do that. Even with optimal meds-and-therapy situation, I think there's always going to be some level of brainweird going on. I was chronically depressed from puberty until just a couple years ago and I don't know if I'll ever be in full remission; my ADHD is something I'm getting better at working with (and around) but it's never going to go away; my anxiety disorder is slowly improving but I imagine it's going to be there a long time yet. For me, I feel like trying to separate those things from myself... it's something like a Chinese finger trap. The harder I try to pull these things away from myself, the more they're stuck right there. Or maybe this is better: there's a joke in my family about reading the instructions so that we can make sure we're ignoring them properly. If you're reading the instructions, you're categorically not ignoring them. If you decide you're not going to do anything the instructions say, you're still not ignoring them, you're just purposefully opposing them. Maybe I'm anxious because something really is wrong with the situation. Maybe I'm bored with an activity because I really don't need to be doing it. Maybe resisting the urge to get up and move around and think with my hands is just taking up brainspace, and if I just let myself do those things, I could get more done. I wouldn't recommend this kind of thinking to everyone. It would have completely wrecked me when I didn't really understand a lot of things about my mental illnesses and I was just starting to get better. It's just what I've moved to now.
Hm. I think I use "my brain" to refer to anxious things - and music too, I think, like "yeah haha my brain was all like 'no one's gonna come and you'll be sitting in the restaurant alone' or 'this song is good. like, really good. my brain likes it." In the first example, I think it's more the level of distancing myself from negative thoughts, and/or being unsure of a thing. It's what I like to call first thoughts vs second thoughts (which, yeah, i stole cheerfully from the Tiffany Aching books), where my first (surface) thoughts will be freaking out, and my second (undercurrent) thoughts will be going "annnnd breathe. come on, dude, this isn't a thing.". The second example probably goes more with the deal that while I like certain songs all the time, some songs are very soothing for some reason, and some make me want to itch out of my skin. so - my brain likes them, because they're soothing. Sometimes when I'm being flippant about depression, I'll say something like "yeah, my brain hates me and wants me to die sometimes". ...Maybe flippancy marks the border between me/my brain as well?