This study examined the neuronal correlates of reading Roman numerals and the changes that occur with extensive practice. Subjects were scanned by functional Magnetic Resonance Imaging (fMRI) three times the first day of the experiment and once following two to three months of practice. This allowed comparison of brain activations with varying levels of practice on the same day and across the two to three months of training. The results revealed that upon learning that the alphabetical symbols had numeric meaning subjects immediately activated a network of brain areas, many of which have been previously implicated in numerical processing. Subsequent practice led to a change in the pattern of neuronal activity in only a single region of the mid-dorsolateral prefrontal cortex in the left hemisphere. Implications of these findings are argued with regard to the prevalent neuronal model for the implementation of elementary numerical abilities.