Studies have shown that newborns and nonhuman animals innately estimate quantities using the

approximate number system (ANS), raising questions about whether the ANS is a precursor to

advanced computational abilities or an independent cognitive function. Professional board game Go

players, who can quickly judge territory sizes without explicit calculations, provide a unique insight

into the ANS. Using fMRI, we investigated the neural correlates of the approximate number system in

professional Go players. Results showed that during the difficult task, professional Go players exhibited

significantly increased activity in the right cerebellum compared to the controls, while several parts

of the cerebrum were activated during the easy task. The observed activation in the right cerebellum

was inversely correlated with the number of years of training required to become professional players.

The findings indicate that the ANS is either facilitated by training or reflects an inherent, exceptional

ability in certain individuals, suggesting a cerebellar-based alternative to the computational role of the

cerebral cortex.

Keywords Approximate number system, Expert brain, Cerebellum, Game of Go (Baduk)