15A Concerned with part of the brain not working in image (6)
I have ?O?T?C and can see POETIC (OET in PIC, somehow) or NOETIC but can't make either work properly. Also, the last C comes from the letter clash, where the letter is G, but could only otherwise be an E, giving us the C.
Key phrase is "not working" which implies a rearrangement of "not" within a three letter word (or abbreviation) for image. I'm sure that you can now get the answer