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How does sensitization strengthen the reflex response in Aplysia californica?

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neuroplasticity The fundamental cell of the nervous system is the neuron. Neurons in a human brain are shown here.

In Aplysia californica, sensitization is a form of nonassociative learning where a reflex response increases in strength following exposure to a significant stimulus. Unlike habituation, which involves a decline in synaptic efficacy, sensitization is characterized by an increase in the magnitude of postsynaptic potentials at the synapse.12

The underlying physiological mechanism is known as presynaptic facilitation. This process is driven by an increase in the second messenger cAMP within the terminals of the sensory neurons. This molecular change enhances the strength of the synaptic connection, allowing the animal to respond more robustly to stimuli.21

Furthermore, this neuroplasticity can lead to structural changes over the long term; while habituation may reduce the number of active zones at nerve terminals, long-term sensitization has been shown to increase them. These cellular and molecular mechanisms demonstrate how simple organisms adapt to their environments through changes in synaptic efficacy, providing insights into processes that may be conserved across the phylogenetic tree.2