The correct answer is gate-control theory of pain.
The gate control theory of pain assume that non-painful input closes the "gates" to painful input. As a consequence, pain sensation cannot travel to the central nervous system (CNS) and thus, stimulation by non-noxious input can suppress pain.
The gate control theory states that non-painful sensations can overcome the effect of painful sensations and thus reduce the sensation of pain traveling to the central nervous system by closing the nerves carrying the painful sensation.
Here, the nerves act as the gates and since the non-painful sensations are directions these nerves to not carry the painful sensations, it is said to be exerting the control over the "gates", i.e the nerves.
Therefore, in the given question, the argument presented by Dr. Gannon that the incoming pain sensations need to pass through the openings in the spinal cord which can also be closed, the argument is based on the gate control theory.
