Re: Do organisms learn, lose and then relearn lessons due to memory capacity?

Hi Gordon-

     Good question! I understand your question to be: 'Do organisms have limited memory storage capacity, and does this limited storage capacity mean that the fish and cats are always forgetting about noxious stimuli/ chastisement?" I'll answer these two questions separately below.

     To first address the question " do organisms have limited memory capacity?" I think the answer has to be yes! We only have so much hardware in our heads to remember things. However, there is a LOT of hardware, so we are capable of remembering quite a bit of information. The brain has 100 billion neurons with an average of 1000 synapses per neuron. And we think that memories are encoded at the synapse level (probably at the level of 10s of synapses), so if we even use 50% of our neurons in memory-associated functions, we have the ability to remember lots and lots and lots. You can read about the models of memory formation at the synapse level here.
     Even though fish and cats have significantly fewer neurons than we do, they can probably still remember a lot. Cats' brains are more evolutionarily developed than that of fish, so they may have a greater capability for storage. But the point is that though storage is not limitless, it's quite expansive. The animals you mention are probably not running out of room.

     Now to address the second question "why is it that these organisms can't remember these events?" This question is a pretty complicated one. If you think to your own anecdotal experiences, you tend to remember things in association with contexts, and only if the experience is behaviorally important. What I would surmise is that the noxious stimuli (if we consider chastisement of the kitties noxious) is not nearly noxious enough. Now, I'm not suggesting that you attempt to hurt the animals in any way, but a more painful or aversive stimulus would lead to behavior change. And it would also have to be paired with a context. I'll describe what I mean below.
     Let's say I have an electrical lead that can give you a shock, and a pretty good one at that. If I randomly shock you and you can't make a connection about why you're being shocked, you won't learn anything. If I gave you that strong shock every time you swim into a particular part of a tank, or every time you sat on the couch, you'd probably stay away from those locations. If I shocked you 10 minutes after going to that location, you may or may not make the connection. If you do make the connection - it'll take a while to make it.
     However, if there were something desirable in those locations, such as potential food, a good view of squirrels outside, or even a hard-to-quantify sense of freedom, it might get trickier. A weak shock might prevent you from going to that part of the tank if there were nothign there, but since there's food there, you can tolerate a weak shock to get some food. A stronger shock, though, might make you think twice. This is getting into economics - perceived value at perceived cost, etc...

     Again - let's not start shocking cats or anything like that. But in the strange mind of cats, your chastisement is probably only viewed as a temporary nuisance. And then they end up doing what they're not supposed to again because they derive more pleasure from doing what it is they've been doing than pain when you reprimand them about it.

     In terms of our own abilities (or inabilities, as the case may be), we follow similar principles. (consider many people's relationship with beer and hangovers... apparently our hangovers just aren't bad enough) The flip side is that our brain is made remember lots of random things, as long as they are relevant to what we do - we can forget things. If you take spanish class, but aren't forced to use it to communicate, you'll probably lose quick access to your spanish vocabulary. But if you moved to Mexico after taking that class, you'd not forget a thing (and probably learn even more). Again, our memory acquisition and retention is context dependent.

     I hope this adequately answers your questions!
cheers,
Alex