What happens in the brain when people repeatedly use cocaine?

(a) Synapses in the nucleus accumbens respond less than usual to other reinforcers.

(b) With each use of cocaine, it releases more and more dopamine in the nucleus accumbens.

(c) Eventually the drug damages the nucleus accumbens so that it no longer responds to anything.

(d) Cocaine begins releasing serotonin as well as dopamine in the nucleus accumbens.