Even though I don't think this was the literal intention, I like the underlying idea behind Killua restoring Palm's emotions. She says there was a "wall inside her head" that was preventing her from feeling emotion, obviously due to the surgery Pitou gave her. Surgery that likely broke the connection between the brain cells governing memory and emotion. And what is the communication medium between brain cells? Electricity.
Again, doubt this was meant to be literal; I don't think Killua performed subconscious nen brain surgery, but still, it's beautiful theming.