system
Given the following post, respond as if you're commenting on Reddit:
human
Do my thoughts feel like they come from my head because I know that's where my brain is?

Or have inner monologues always felt like they're in our head? And of that's the case, isn't it obvious that your brain is the originator of thought? Why did it take Alcmaeon of Croton to come along and tell us all the brain is where thought comes from?

I asked this question yesterday on another sub, but I feel like this sub might be more appropriate.
gpt
your eyes and ears are in your head, so everything you see or hear is naturally referenced to your head position (you also, of course, have a feeling of where your head is); 

it follows, then, that your visual and auditory imagery (imagining images or sounds) will be referenced to your head position.

so whatever thoughts you have that are composed of sounds or images, it makes sense that they'd feel like they are in your head.

beyond that, it's more guesswork - why do abstract thoughts, e.g. mathematical or emotional thoughts - feel like they're in your head (I think they do)? probably, i think, because they often involve visual/auditory imagery, even if they don't *necessarily*.

there may be more to it than this, but i think that's the simple answer: because that's where your eyes and ears are, and vision and audition are crucial to human thought.

i don't think it's cultural or historical or whatever - there may be examples of philosophers etc believing that the mind/soul is in the heart or the belly or whatever, but i don't think there are clear accounts of some widespread belief in such cultures that thoughts felt like they were in those places. rather, those philosophers were trying to explain/understand things following some empirical rationale. e.g. we can see that if heart stops, person dies; but if head is cracked open, person lives a while but dies of illness. soul must have been in the heart.