Final answer:
The frontal lobe, specifically the primary motor cortex within it, is activated when preparing to execute limb movements, as it is responsible for motor functions.
Step-by-step explanation:
When a participant is preparing to execute a limb movement, the area of the brain that is activated is the frontal lobe. The frontal lobe is responsible for motor functions, which includes everything from planning movements to executing commands that are sent to the spinal cord and peripheral muscles. The precentral gyrus, located in the frontal lobe, acts as the primary motor cortex and is directly involved in controlling voluntary movements by connecting to cranial and spinal motor neurons.