Using the brain for any of the "seven deadly sins" is, perhaps, too easy. Any sin could come from the brain. Instead, I suggest the following:
- Pride: Heart
- Envy: Ears
- Greed: Eyes
- Gluttony: Mouth
- Sloth: Gut (belly)
- Lust: Hands
- Wrath: Kidneys (adrenal glands)
Pride comes from the heart; it's an emotion, though often confused for "fact". Just because you feel you should be proud, doesn't mean there is actually a reason. It's even an involuntary reaction to stick out your chest as you inflate with pride.
Envy - desiring what others have - could come from eyes, but more often is a result of someone else bragging; thus, ears. Listening too long to braggarts will cause envy, more so than simply seeing someone's possessions.
Greed is the urge to collect, and keep, things for yourself. There is no use in the collecting; be it money, power, or otherwise, greed is about having, not using. Thus, the eyes, because the eyes can be pleased and not use a thing up, and eyes can experience vast wealth, and still want more.
Gluttony is about using something, and using it far past what would ever be needed. Be it overeating, binge-watching television, or exercising past the point of health, gluttony is about extremes. The mouth can eat all day; the jaw will chew and the tongue will taste, even if the stomach is full, even to the point of throwing up just to enjoy more food.
Sloth is the gut, the fat of the belly. The more energy goes unused, the more the gut grows; fat cells will expand indefinitely, overwhelming the rest of the body. Worse, that stored energy makes people less likely to get rid of it, as slothfulness promotes slothfulness.
Lust, beyond sex, is an unclean desire, a want for something unwholesome. More than a desire to simply see or hear, it is a need to experience, to feel, to be immersed. The more one experiences, the more one lusts for more. Just as we wash our hands to get rid of germs, ancient cultures would ritually wash their hands to show that they had cleansed themselves, purging the filth from their hands; what sin is more filthy than lust?
Wrath causes an immediate spike of adrenaline, turning peace into violence, turning anger into rage. Even silent and hidden, wrath burns in your mind and ignites your muscles, screaming, no matter how silently, to bring pain to others. The kidneys host the adrenal glands, which in turn regulate adrenaline; without them, wrath would quickly turn to apathy. Instead, they add fuel to the fires...