You are free to research what you feel you need.

The vitamins are different than the Omega-3s in the brain.

Omega-3s are incorporated into cell structures. DHA forms nerves and receptor locations. Consider them as building blocks.
They are best consumed as grams in amount.

The B's are mostly metabolic. They are cofactors in enzymes that the body uses for tissue repair and growth and maintenance. So these are needed in smaller milligram amounts.

Thiamine for example B1, when low causes a form of psychosis.

B6 has many many functions, and this site goes into some of them:
http://www.meschinohealth.com/Articl...matory_effects

B6 is activated by B2 to its active biological form P5P.

Low niacin causes pellegra-- which one symptom of which is dementia.
http://www.foodforthebrain.org/nutri...psychosis.aspx

The well known and famous biochemist Dr. Ames, believes there are many potential genetic errors in Bcomplex vitamins and that these errors, account for human suffering in many ways.
This is a nice interview with Dr. Ames:
http://www.drpasswater.com/nutrition...uce_Ames2.html

This is a good site by Dr. Hyman MD...explaining the foibles of vitamin research:
http://drhyman.com/blog/2011/10/18/w...itamins/#close