@L a Farme / Anne Bown Vitamin B12 deficiency will cause your brain to shrink, you may lose memory or experience confusion. One indication that you might be deficient is the appearance of lines or ridges on your fingernails and/or the disappearance of the moons at the bottoms of your fingernails. Methylcobalamin is the bioactive form, so look on your label to make sure you have that form of B12. Also, watch your peripheral neuropathy start to ease with B12, it is nerve food!