There are actually several possible explanations for this behavior which I've listed below. I agree with your vet in that if Thomas is rewarded by either your attention or food every time he vocalizes, you may be inadvertently reinforcing this behavior; however, I'd have to wonder if more is going on if this is something that he hasn't done his entire life. Even if he has and it seems to be worse, I wouldn't be surprised if more is going on with him which is why it's more intense.
1. Cats with senility or cognitive dysfunction (CD) can excessively vocalize; I think it reflects the confusion and/or anxiety that they are experiencing. Many of these cats will also suffer memory loss (when it comes to food, they forget that they just ate), possibly inappropriate elimination, staring off into space or acting like they don't quite know where they are at times. Signs can be intermittent but the condition does tend to progress.
Treatment options are limited, unfortunately.
a) Feliway diffusers or a spray which are natural pheromones that are intended to reduce anxiety and instill a sense of calm may be helpful. There a similar oral product called Composure Chews. These products are available on the internet or at most pet stores
b) Fish oil supplements such as Welactin may help some cats because of their anti-oxidant properties.
c). Specific cognitive supplements such as Neutricks, SAMe (Novifit) and Senilife may be useful as well as NuCat Senior supplement. They should be available on the internet
d) Evidence exists that daily and sustained exercise has positive effects in reducing progression of CD although it's difficult to exercise a cat. But, playing with them several times a day may suffice.
e. Sensory stimulation such as touching, brushing, and massage therapy may also reduce progression of CD.
2. Cats with hyperthyroid disease will often excessively vocalize. I don't have a good explanation for this (probably secondary to hypertension....see below) but I see it all the time. Blood work would diagnose this problem and there are good treatments for this disease.
3. Some cats with arthritis pain or other pain in their bodies will vocalize. We are also somewhat limited in treating cats with this problem but options to consider would include:
a. Cosequin for Cats which is a joint supplement.
b. Occasional use of anti-inflammatory drugs such as Onisor which is licensed for use in cats but can only be given for three days in a row.
There is a drug called Metacam but it is somewhat controversial in veterinary medicine. It's use can cause significant damage to the kidneys and should be used with great caution in older cats.
c. Adequan which is basically a stronger joint supplement but is an injection and needs to be given by your vet.
d. Fish oil supplements as I mentioned above
If you think this might be the problem, you could discuss trying drugs for a week or so with your vet to determine if there is improvement in the vocalization. Some cats will also benefit from acupuncture believe it or not.
4. Cats with hypertension can behave in some odd ways. This is rarely a primary problem in cats but usually secondary to Hyperthyroid Disease (#2 above) or kidney issues or Diabetes. Blood work would help diagnose either one of these conditions.
And blood pressure measurements are routinely done in cats these days and they can be treated for it, similar to a human.
5. She might be losing her hearing. I think these cats meow louder to hear themselves.
6. I always worry about a brain mass when older cats start to behave in odd ways. I only include this to be complete but not to alarm you.
In addition to the supplements which I've mentioned above, I often suggest that owners give their cats over the counter, human Melatonin which can help some of them sleep at night and may mellow them out during the day; it also has anti-oxidant properties which may be of value.
The dose would be 3-12 mg once or twice a day; I usually start with the lower dose. For some patients, it can take several weeks before improvement is seen. Nature's Bounty is a good manufacturer since what's in the bottle is not necessarily what's on the label....which is true for all supplements.
I hope this helps and provides options for you to consider. Deb