Directly, I have no experience (yet) with art and dementia, only with dementia, but a colleague of mine (Prof Brenda Roe) has recently published a paper in this field (just a month ago):
Not personally, but the question brought to mind a paper I have read that might be helpful:
Castora-Binkley, M., Noelker, L., Prohaska, T., & Satariano, W. (2010). Impact of arts participation on health outcomes for older adults. Journal of Aging, Humanities, and the Arts: Official Journal of the Gerontological Society of America, 4(4), 352-367.
Hi Tomi thank you for the reply. You may be interested in our ongoing study called Dementia and Imagaination evalauting the impact of attending a 12 week visual arts group for people living with Dementia.
I was going to refer you to the £1.2 million Dementia and visual Arts project of Bangor University (nb1), but I believe you may be well aware of it.
Other than that, Cela-Conde et al. 2011 (nb2) indicate that "artists with Alzheimer's disease seem to gradually lose the ability to represent the world with precision, but are able to use color and form in aesthetically appealing ways". The authors refer to some other references that may be relevant, including Miller & Hou 2004 (nb3) who worked with people with frontotemporal dementia and studied their new interests in art, for example, painting repetitive motifs that improved over time.
nb2. Cela-Conde, C. J., Agnati, L., Huston, J. P., Mora, F., & Nadal, M. (2011). The neural foundations of aesthetic appreciation. Progress in neurobiology, 94(1), 39-48.
nb3. Miller, B.L., Hou, C.E., 2004. Portraits of artists. Emergence of visual creativity in dementia. Arch. Neurol. 61, 842–844.