I found this last night in a book called Think Cat by David Taylor. Thought it might be of interest.
The night time yell of the cat, one of the most distinctive of the 16 vocalisations that behaviourists recognise in the species, is something that most often starts to occur as the cat gets older. These strident calls- summons would be a better word- are at first less commonly emitted during daylight hours. It`s all to do with the senior citizen feeling in need of a little reassurance and attention now that the nights of searching for a way out of the house to go clubbing in Cat Town are long gone. More and more it appreciates the value and companionship of its human friend so, in the still of the night, it calls out for them. Up you get to see what is amiss and find the cat sitting there, cool as a cucumber, with no sign of trouble in the offing. A pick-up, a cuddle, a stroke and a few words of affection and you pop him back in his sleeping place. All is well.
Of course, some cats prefer the added sense of security of sleeping on the owners bed and will yell again to make the point. Once curled up on the eiderdown, the cat doesn`t move till your alarm clock goes off. All of this is training - the cat training you. It quickly learns that the yell evokes an immediate response and so, as time passes, is gratified to find it can get the owner to come running whenever it cannot decide whether to sit in front of the fire or on the mantlepeice. The owners fussing, which involves making the yeller comfortable in one of the two places, or on an even better third location, proves it. The cat eventually has the owner perfectly conditioned to the point where the yell will work at any time of day or night. It is easier for an elderly animal to do than using energy going to find the owner and jumping on their lap or tapping them pitifully with a paw.
Much younger cats sometimes go in for night yelling. Again, the cause is normally a feeling of insecurity and anxiety after some change in their environment, such as moving house. The cat is calling for reassurance. If it persists for long after whatever change in circumstances triggered it, the cat has learned that it now has a way of demanding the owners attention. Whilst I would recommend tolerant acceptance of this behaviour in a venerable cat, I think it is important to try to eradicate it in younger exponents to the yell. To do this you must have an iron will, and ignore the attention seeking vocalizations. Combined with this, aversion treatment administered via a squirt from a water pistol or a sharp noise as soon as the yell begins is very effective. After but a few nighttime yells more, peace will descend once again upon the sleeping household.