Ring, common (requires attunement)
A dull brass ring with seemingly no special qualities. When a creature adorns this ring, all of their ability scores are temporarily set to 10. The ring cannot be removed from their finger for 1 hour unless a remove curse spell is cast on the ring or the creature wearing it. If this happens, that creature can freely wear and remove the ring to gain its effect. This ring has no effect on creatures with a value of 4 or lower in any ability score.
Notes: Cursed, Jewelry, Handwear
So I could force this on some interrogation target with only 5 int as to boost it enough for normal conversation.
You could definitely get some more intelligent conversation out of a target who wears this ring, but a creature's ability to be interrogated ultimately relies on the languages it knows. It may also not help to make it intelligent enough to want to keep its secrets!
This ring is actually perfect: If you manage to find two of them, you can set balanced duels of honor. Similarly, a character, like, say, a demigod or other high level character that is pretending to be much weaker than they actually are can wear one of these to avoid anyone else from detecting their true strength. Kind of like a limiter ring.
Fantastic idea!