In a study on the biological bases of learning, lab rat A is given a drug that blocks dopamine activity in its brain. Thereafter, the rat is placed in an operant chamber where a lever-pressing task is shaped through positive reinforcement. We should expect that the rat will have .

more difficulty learning the task than a normal rat.                    

Explanation:

Positive reinforcement: In psychology, the term "positive reinforcement" is described as a process through a subject or participant is being provided with something when he or she performs the "desired action" in order to associate or connect a particular action with a specific reward and therefore does it more frequently. Here, in the given scenario the "reward" is considered as a "reinforcing stimulus".

In the question above, the rats will find more difficulty in learning a specific task rather than a normal rat because of the blockage of dopamine activity which is responsible for transmitting the different signal to nerves.