Researchers discovered that the neuronal activity in the brain of a monkey who simply watched another monkey pick up and eat a peanut was the same as the brain activity of the monkey actually performing these actions. These researchers are investigating:

The correct answer to the following question will be "mirror neurons".

Explanation:

The most popular hypothesis behind all the emergence or roots of mirror neurons seems to be the genetic explanation that indicates those neurons are mainly attributable to inherited environmental factors, and also the genetic tendency to grow neuron has developed because it enhances comprehension of behavior.Researchers have found that perhaps the neural function in a monkey's brain that had been merely watching other monkeys picking up and serve a nut is even worse than or same as the monkey's brain function performing those acts.

So that the above is the right answer.