I'm sorry to hear about Pichu. It seems a little early for dementia, he's not that old, but you never know. I read the links Catty posted... thanks! Some of it fits on Fister. He keeps me awake meowing half the night sometimes, but other than that, he seems to be OK - eats, drinks, pees and poops in his box and even want to go down now and again. Last week, he was meowing for me in the yard, though, which is very unusual.

"The change seen with senior dementia is one of increased or excessive vocalizations, and not just a simple meow. Some cats appear to develop a separation anxiety at night."

I hope you will find a diet that can slow down this and Pichu will be happy for years to come.