Why can a repeated regular stimulus lead to habituation?

Habituation is a form of learning characterized by a decline in an animal's behavioral response to a stimulus following its repeated presentation. This phenomenon serves an important adaptive function: by ignoring familiar, non-threatening stimuli, an animal can conserve energy and time for vital activities like foraging, rather than wasting resources on reactions that provide no benefit.12

The mechanism behind this waning response is not due to sensory adaptation or effector fatigue, but rather to changes in the nervous system. Research on the marine snail Aplysia has shown that repeated stimulation leads to a decrease in excitatory postsynaptic potential, which effectively short-circuits the neural pathway between the stimulus and the response. This can occur through the closing of calcium channels, which reduces the influx of calcium into presynaptic terminals and subsequently decreases neurotransmitter release. Additionally, long-term habituation may involve a reduction in the number of active zones at nerve terminals, demonstrating the plasticity of the nervous system.23