Aplysia californica (marine mollusk) contains only 20,000 neurons. Some of the neurons can be isolated to study the neural circuits.
The two basic forms of learning mediated by the Aplasia’s synaptic function are,
• Habituation
• Sensitization
Habituation response is a stimulus that weakens with repeated exposure to the same stimulus. For example, adaptation to traffic sounds by the people living in crowded cities.
Sensitization response is the enhanced response to some stimulus, which is opposite of habituation.
Thus, the blanks can be filled with habituation; sensitization.