How would you grade the "degree" of biological plausibility? All deep learning is somewhat plausible, since they capture hierarchical structure in feature learning. Generally what people wonder about is whether the learning is biologically plausible. RBM's use local learning rules, rather than backprop. Taylor, P., et al. (2015). The global landscape of cognition: hierarchical aggregation as an organizational principle of human cortical networks and functions. Scientific Reports, 5(November), 18112. Bengio et al. (2015) arxiv.org/abs/1502.04156