The most common approach is to use Summon Monster spells to heal. You can increase your options for this with the "Summon Good Monster" feat. Here's a list from reddit; I've added an [SGM] tag to the options that require the feat:
Summon Monster III:
[SGM] Silvanshee Agatheon - Lay on Hands 1d6 1/day, at-will Stabilize
Summon Monster V:
Bralani Azata - Cure Serious Wounds 2/day
[SGM] Vulpinal Agathion - Lay on Hands 3d6 6/day, Remove Disease, Calm Emotions Aura
[SGM] Unicorn - Cure Light Wounds 3/day, Cure Moderate Wounds 1/day, Neutralize Poison 1/day
Summon Monster VI:
[SGM] Kirin - Lesser Restoration 7/day, Cure Light Wounds 8/day, Stabilize At Will
Lillend Azata - Cure Serious Wounds 2/day, Cure Light Wounds 5/day, Bardic Performance as 7th-level bard
Summon Monster VII:
[SGM] Movanic Deva - Remove Curse, Disease, and Fear at will, Cure Serious Wounds 7/day
[SGM] Shedu - Empowered Cure Moderate Wounds 3/day, Dispel Magic 3/day, Remove Disease 3/day, Shield Other 3/day, Restoration 1/day
Summon Monster VIII:
[SGM] Monadic Deva Angel - Dispel Magic at will, Remove Curse, Disease, Fear at will, Cure Serious Wounds 3/day, Heal 1/day
[SGM] Lammasu - Cure Moderate Wounds or Lesser Restoration 7/day, Cure Light Wounds 7/day, stabilize at will
Summon Monster IX:
Astral Deva - Remove Curse, Disease, Fear at will, Dispel Magic at will, Cure Light Wounds 7/day, Heal 1/day
[SGM] Couatl - Cure Moderate Wounds 7/day, Stabilize at will
Azata Ghaele - Cure Light Wounds at will, Dispel Magic at will, Heal 1/day, Restoration 1/day, Cure Serious Wounds 3/day, Lesser Restoration 2/day, Stabilize at will
[SGM] Leonal Agathion - Cure Critical Wounds 3/day, Neutralize Poison 3/day, Remove Disease 3/day, Heal 1/day
Trumpet Archon - Mass Cure Serious Wounds 2/day, Heal 2/day, Mass Cure Light Wounds 1/day, Neutralize Poison 1/day, Cure Serious Wounds 1/day, Cure Moderate Wounds 2/day, Lesser Restoration 2/day, Cure Light Wounds 3/day, Stabilize at will.
Best Answer
Regenerate for this DM
I took a few minutes to learn about strokes here, and the general gist is that due to a combination of ruptured/blocked blood vessels a bunch of brain cells die. This progressing to full death depends on how far it gets, but regardless the creature in question effectively has severed body parts by virtue of brain cells being dead and effectively disconnected from the overall organ.
Given that Regenerate states:
Natural healing could include stem cells, reinvigorating the dead brain cells back to life, or growing new ones. Whichever logic works for you.
As a 7th level spell, this would finally make me happy to see some reason for it to be as high level as it is. Using this spell, this DM would permit the caster to fully restore mental faculties to someone who has degenerated from a stroke, dementia, etc.