system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do migraines generally only put pressure on one side of the head/ in one eye and not the other?
gpt
The neurovascular theory of migraines suggests that there is some trigger that activate a neuron system. After that, there will be vascular changes, with dilation of brain vessels which will cause pain. 

As you know, people that have strokes are usually only affected on one side of the body. That's because the vascular system is very well divided between the left and right brain hemisphere. For the migraine is the same. Only one side will suffer the change of perfusion, thus you only feel pain on one side.