There is a amino acid called methionine...and it is necessary for our bodies to make SAM...which is a methyl donor for neurotransmitter synthesis. Methionine is usually found in animal food sources. If you get low in this, you could fail to make enough for your brain to run on.
http://www.drlam.com/opinion/methionine.asp

MethylB12 is only pennies a day orally. You could start at the lower dosage, 1000mcg a day on an empty stomach.

Online discount vitamin sources, have it, but stores most likely not. I've used iherb.com and Puritan's pride with good results.
I would use the methyl for the reasons, that are posted here at the beginning of this thread.

Check the content of your food choices for nutrients at this site:
http://nutritiondata.self.com/

Japan has high standards for their B12 because they had a huge accident involving a common drug used there that depleted B12 and left many dead and disabled as a result. So they tend to be more aggressive with the blood levels they use. The drug was clioquinol (aka Vioform).