Final answer:
The neural circuit described is involved in sensitization and the component that enables this plasticity is the modulatory interneuron.
Step-by-step explanation:
option d is correct
The neural circuit described in the question is involved in sensitization and the component of the circuit that makes this form of plasticity possible is the modulatory interneuron.
Sensitization is a form of plasticity where an organism becomes more responsive to a repeated stimulus. In this case, the neural circuit is involved in sensitization because the animal responds to the tone as if it was a shock and avoids it, showing an increased response to the stimulus.
The modulatory interneuron is the component of the circuit that makes this form of plasticity possible. Modulatory interneurons release neuromodulators, such as serotonin or dopamine, which can change the sensitivity of other neurons in the circuit. In this case, the modulatory interneuron is likely releasing a neuromodulator that increases the sensitivity of the circuit to the tone stimulus, leading to sensitization.