A laboratory monkey observing a researcher lick an ice cream cone and showing brain activity in the same area as if the monkey had licked the ice cream itself is exhibiting the effects of:

Mirror neurons.

Explanation:

Mirror neurons can be defined as a kind of sensory-motor cell that is typically found in the brain which is being activated when a living organism such as a primate animal or human being performs an action and/or when it observes another living organism that is performing the same activity (action).

This ultimately implies that, the neurons of living organisms mirror or duplicate the actions (behaviors) of others, as though the observer is acting itself.

In this scenario, a laboratory monkey observing a researcher lick an ice cream cone and showing brain activity in the same area as if the monkey had licked the ice cream itself is exhibiting the effects of mirror neurons because the neuron of the monkey mirrored the action that was being performed by the researcher.