Compared with environmentally impoverished rats, those rats housed in enriched environments experienced a dramatic increase in the number of their:

synapses

Explanation:

In mammals brain, synapse has the function to pass electric or chemical signals from one neuron to another. In an enriched environment, the rats would most likely encountered far more stimulus compared to environmentally impoverished rats. This will make their brain become used to conducting more activities compared to environmentally impoverished rats, which will lead to the dramatic increase in the number of their synapses.

answer law is not needed; /// (concurrent resolutions);