Final answer:
During painting, the central nervous system's activation of motor neurons occurs to control the fine motor skills and precise hand movements needed for creating art.
Step-by-step explanation:
When Idris is painting portraits, the process of the central nervous system that most likely occurs during this activity is the activation of motor neurons. Painting requires fine motor skills and precise hand movements which are controlled by motor neurons.
These neurons transmit signals from the brain to the muscles in the hand and arm, directing the motions needed to create the artwork. The release of adrenaline and production of insulin are not primarily associated with the act of painting, and sensory perception is not inhibited during such a creative task.