Miller Lab alumnus, Andreas Nieder, shows number tuned neurons in pefrontal and parietal cortices of naive (untrained) subjects.
Viswanathan and Nieder 2013 

Andreas Nieder’s Miller Lab work on the neural substrates for numerosity:

Nieder, A., Freedman, D.J., and Miller, E.K. (2002) Representation of the quantity of visual items in the primate prefrontal cortex.  Science. 297:1708-1711. View PDF »

Nieder, A. and Miller, E.K. (2003) Coding of cognitive magnitude: Compressed scaling of numerical information in the primate prefrontal cortex. Neuron. 37:149-157. View PDF »

Nieder, A. and Miller, E.K. (2004) A parieto-frontal network for visual numerical information in the monkey. Proceedings of the National Academy of Sciences, 101:7457-7462. View PDF »

Nieder, A. and Miller, E.K. (2004) Analog numerical representations in rhesus monkeys: Evidence for parallel processing. Journal of Cognitive Neuroscience. 16:889-901. View PDF »