Final answer:
Stimulating DA neurons can cause behavioral choice preference even without a reward, through the use of causal methods.
Step-by-step explanation:
The researchers used causal methods to stimulate DA neurons and found that this caused behavioral choice preference even in the absence of a reward. The specific method used was not mentioned in the provided information, but the study emphasized the role of the dopamine (DA) and the reward system in associative learning and memory encoding.