Please read this important disclaimer. Robert, I haven't heard of seasonal fluctuations in dementia. Dementia symptoms can fluctuate due to minor changes in environment and a host of metabolic changes.
Symptoms sometimes worsen at night.
Seasonal depression is a well documeted occurance for many and I'dl be curious to know if your wife evidenced symptoms of seasonal depression in the past. Having dementia doesn't buffer us from prior conditions. Also, you should know that many of the symptoms of depression minic dementia. At any rate, I'll do a literature review to see if I can find anything on seasonal fluctuations in dementia symptoms. In the meantime, I'ld suggest you talk to your wife's doctor and discuss light therapy - a very effective treatment for seasonal depression.