They would cut the major pathway between the the hemispheres. This was a last resort treatment. It slows and or stops the wave of seizure "signals" from propagating through the whole brain and overwhelming it.

It was effective and people were able to have mostly normal lives, with a few interesting side effects, including possible split consciousness...

Split brain patients. Some cool experiments with fascinating results to be seen there.

Yeah, there was also a thing called an ice-pick lobotomy. It was very popular throughout the mid 1900s (think 40s and 50s) as a way of (if we're being cynical) making peoblematic mental illness cases go away, as well as a way of treating seizures.

The procedure was pretty simple and "safe": it's just a small tool they inserted through the eye socket on the inner side of your eye (your eye would be fine) to reach the connective tissue between your hemispheres, and they'd swich it arround until large portions of this connective tissue (and also your frontal lobe) were severely damaged.

This was done in essentially outpatient settings, and the doctor that invented it was highly prolific, and did like thousands of these procedures over the years: most to people who shouldn't be treated with brain surgery. It usually left people halfway between mildly impared and vegetable, but it did frequently "cure" the worst symptoms of a lot of mental illnesses by essentially erasing half their personality.

I'm grossly oversimplifying here but it was nasty business. Not medicine's best chapter

Edit: more ethical versions of this survived the ice pick lobotomy era, for specifically only seizure treatments that had fewer adverse side effects, although it's a very radical treatment for pretty severe cases as I understand it

Yes. While over simplified, think of the brain as 3 major parts. Left, right, and lower. Think of the brain as a giant circle with the connections. Left and right are connected, and both are connected to the lower part.

We have cut the connection between the left and right parts. From it some pretty interesting experiments, studies, and realization have shown up.

Like the theory that each of your brain hemispheres are both conscious in some way, having their own likes and dislikes. Like experiments where they would be asked to reach out with both hands and pick their favorite color... And yet each hand would choose a different color.

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They did and for those that didnt die it often really stopped epilepsy.

So yes. If we hadnt stopped researching it cuz its "inhumane" we might have a solution to epilepsy as a whole now.

They would cut their corpus callosum (I probably botched that spelling). It's the biggest and most important communication network between the hemispheres. Without it they struggle to/can't communicate in real time. However, it can cure epilepsy.

It creates a ton of interesting quirks. For instance, the hemispheres can't share everything about what they're seeing with their respective eyes. Sometimes one hand can do something without the opposite hemisphere even knowing about it. The person will generally attempt to explain away the behavior, but the truth is that they don't know exactly what their left hand was doing when they couldn't see it with their right eye.