I see absolutely no reason to hypothesize that Neandertals had anything to do with this art, given the clear evidence for an earlier presence of AMH in Europe before this time. Indeed, the latest evidence may suggest that not even all modern humans who entered Europe had highly developed art, and indeed such art is lacking in many contexts associated with modern humans outside Europe. In short, rather than hypothesize that art was a pastime of not only modern humans, but also Neandertals, we must rather accept the most plausible idea that art was a cultural innovation that began with a subset of anatomically modern humans.
Science 15 June 2012:
Vol. 336 no. 6087 pp. 1409-1413
U-Series Dating of Paleolithic Art in 11 Caves in Spain
A. W. G. Pike et al.
Paleolithic cave art is an exceptional archive of early human symbolic behavior, but because obtaining reliable dates has been difficult, its chronology is still poorly understood after more than a century of study. We present uranium-series disequilibrium dates of calcite deposits overlying or underlying art found in 11 caves, including the United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage sites of Altamira, El Castillo, and Tito Bustillo, Spain. The results demonstrate that the tradition of decorating caves extends back at least to the Early Aurignacian period, with minimum ages of 40.8 thousand years for a red disk, 37.3 thousand years for a hand stencil, and 35.6 thousand years for a claviform-like symbol. These minimum ages reveal either that cave art was a part of the cultural repertoire of the first anatomically modern humans in Europe or that perhaps Neandertals also engaged in painting caves.