Do Cats Hallucinate?

I have two cats. One is about four, and he is a psychopath. The other is sixteen - elderly, in cat terms - and I've recently noticed some changes in her behaviour.

For one, she's become a lot more affectionate, and she demands constant attention - she meows at people on sight, follows you around, and almost always comes and sits on top of you, or on top of whatever you're doing/reading/typing.

But on top of that, she's started pausing in the middle of whatever she's doing and staring at empty corners, or walls. All cats sit down and gaze into space a lot of the time, but this is different - it happens in the middle of normal actions, like eating or walking around. What does this mean?

Could she be hallucinating? Hallucinations are unfortunately not uncommon in elderly people. Seeing and hearing things that aren't there is a major symptom of Alzheimer's, and other forms of dementia. Do cats get Alzheimer's? The internet says: yes. In terms of scientific research there doesn't seem to have been much, but a few studies have found Alzheimer's-like changes (amyloid-beta protein accumulation) in the brains of old cats. Whether these cause the same symptoms as they do in people is unclear, but, why not?

How would you know if an animal was hallucinating? They can't talk about it, and unlike say hunger or pain, they don't have specific ways of communicating it through body language or cries. A hallucinating animal would, presumably, react fairly normally to whatever it thought it saw or heard: so hallucinations would manifest as normal behaviours, but in inappropriate situations. Whether this is what's happening to my cat, I'm not sure, but again, it's possible.

A more philosophical issue is whether we can conclude that this kind of out-of-context behaviour means the animal is experiencing a hallucination. But this is really just the age old question of whether animals have conciousness at all. If they do, then they can presumably hallucinate: if you can be concious of sensations, you can be concious of false sensations.

For what its worth, my view is that animals, at any rate for mammals, are concious. Humans are (although technically we only know for sure that we personally are, and have to assume the same is true of others.) Mammalian brains are structured in a similar way to our own; they're made of the same cells; they use the same neurotransmitters and the same drugs interfere with them in the same ways; pretty much all of the brain regions are there, although the sizes differ.

There's of course a big difference between us and other mammals: we have language, and conceptual thinking, and so forth. But does conciousness depend on that? It seems unlikely, just because most of what we're concious of at any one time isn't anything to do with those specifically human things.

Right now, I'm concious of what I can see, what I can hear, what I can feel with my fingertips, and the thoughts I'm writing down. Only 1/4 of that (to put it crudely) is unique to humans. And I'm not always aware of thoughts or words; there are plenty of times when I'm only aware of sensations and perceptions.

Probably the closest we get to animal conciousness is in strong, primitive experiences like pain, panic and anger, in which we "take leave of our senses" - not meaning that we become unconscious, but that we temporarily stop being able to "think straight" i.e. like a human. That doesn't mean that animals spend all their time in some extreme emotional state, but it's harder for us to know what it's like to be a relaxed cat because generally when we're relaxed, we're thinking (or daydreaming, etc. Although who's to say cats don't? They dream, after all...)