WASHINGTON — Uh-oh, the new year’s just begun and already you’re finding it hard to keep those resolutions to junk the junk food, get off the couch or kick smoking. There’s a biological reason a lot of our bad habits are so hard to break — they get wired into our brains.

Understanding how unhealthy behaviors become ingrained has scientists learning some tricks that may help good habits replace the bad.

“Why are bad habits stronger? You’re fighting against the power of an immediate reward,” says Dr. Nora Volkow, director of the National Institute on Drug Abuse and an authority on the brain’s pleasure pathway.

It’s the fudge vs. broccoli choice: Chocolate’s yum factor tends to beat out the knowledge that sticking with veggies brings an eventual reward of lost pounds.

“We all as creatures are hard-wired that way, to give greater value to an immediate reward as opposed to something that’s delayed,” Volkow says.

Just how that bit of happiness turns into a habit involves a pleasure-sensing chemical named dopamine. It conditions the brain to want that reward again and again — reinforcing the connection each time — especially when it gets the right cue from your environment.

People tend to overestimate their ability to resist temptations around them, thus undermining attempts to shed bad habits, says experimental psychologist Loran Nordgren.

“People have this self-control hubris, this belief they can handle more than they can,” says Nordgren, who studies the tug-of-war between willpower and temptation.

Researchers say there are some steps that may help counter your brain’s hold on bad habits:

• Repeat the new behavior — the same routine at the same time of day. Resolved to exercise? Doing it at the same time of the morning, rather than fitting it in haphazardly, makes the striatum recognize the habit so eventually, “if you don’t do it, you feel awful,” says Volkow.

• Exercise itself raises dopamine levels, so eventually your brain will get a feel-good hit even if your muscles protest.

• Reward yourself with something you really desire, Volkow stresses. You exercised all week? Stuck to your diet? Buy a book or a great pair of jeans.

• Stress can reactivate the bad-habit circuitry. “You see people immediately eating in the airport when their flight is canceled,” Volkow points out.

• And cut out the rituals linked to your bad habits. No eating in front of the TV, ever.