Talk:Apartment 4A/@comment-23.251.66.62-20150112231541/@comment-24176508-20150130024020

It's a drawing of a brain cell by microbiologist Santiago Ramon y Cajal. Sheldon's assistant Alex picks it out as a potential Valentine's Day gift for Sheldon to give to Amy, but Sheldon ends up keeping it for himself. See Season 6, Episode 16; The Tangible Affection Proof.

For samples of Cajal's artistry, see:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845060/