* 612.8 - Nervous System - This is the most general category encompassing the brain.
* 150 - Psychology - Brain function and behavior are studied here.
* 591.18 - Nervous System (Zoology) - This covers the brain from a biological and animal perspective.
* 616.8 - Diseases of the Nervous System - This includes conditions that affect the brain.
You'd need to be more specific about what aspect of the brain you're interested in to find the most relevant Dewey Decimal number. For example:
* Brain anatomy - 612.81
* Brain development - 612.82
* Brain disorders - 616.8
* Brain imaging - 616.805
* Brain function and psychology - 152, 153
The best way to find the most precise Dewey Decimal number is to use an online Dewey Decimal classification tool or consult a librarian.