Adam Marblestone on whether different areas of the brain optimize diverse cost functions using specialized structures [2, 3, 1]: (PDF), (PDF), (PDF), (SLIDES), (VIDEO).

You might also want to check out Geoff Hinton on YouTube talking about possible neural correlates for backpropagation: (VIDEO)

References

[1]	Alexander A. Chubykin, Emma B. Roach, Mark F. Bear, and Marshall G. Hussain Shuler. A cholinergic mechanism for reward timing within primary visual cortex. Neuron, 77:723--735, 2012.
[2]	Adam H. Marblestone, Greg Wayne, Konrad P. Kording, and Kenneth J Hayworth. Do brain areas optimize diverse cost functions using specialized structures? CoRR, arXiv:NNNN.NNNN, 2016.
[3]	Shimon Ullman, Daniel Harari, and Nimrod Dorfman. From simple innate biases to complex visual concepts. Proceedings of the National Academy of Sciences, 109(44):18215--18220, 2012.