 More recent studies using fMRI have demonstrated that V4 is more active in both word → color and grapheme → color synesthetes (; ; ).However, these neuroimaging studies do not have the spatial and temporal resolution to distinguish between the pruning and disinhibited feedback theories.Future research will continue to examine these questions using not only fMRI but also diffusion tensor imaging (DTI), which allows researchers to directly investigate neural connectivity in the human brain and magnetic resonance spectroscopy (MRS) which allows researchers to measure the amounts of different neurotransmitters in the brain.