A lack of B12 can result of analytical thought.
^

I assume there is a "in lack" lacking there! Or something similar.

As a sufferer of Pernicious Anaemia, I know lack of B12 can affect nerve
function, hence I suppose brain function. But my (slight) nerve symptoms
were in my arms and legs. I'd always put down the slight depression
before disgnosis as related to exhaustion due to the anaemia.