Habituation is a simple form of learning in which the strength of a response to a certain stimulus becomes weaker with repeated presentation of that stimulus. Habituation is not a result of an inability of either sensory neurons or motor neurons to produce action potential. In habituation, the excitatory postsynaptic potential in motor neuron becomes smaller. This is due to the fact that motor neurons are receiving a less neurotransmitter across synapse. This decrease in neurotransmitter occurs because calcium channels have become less responsive to the voltage changes associated with action potentials, causing a reduction on the influx of calcium needed to release neurotransmitter. In habituation, changes take place in calcium channels. Sensitization is a process by which the response to a stimulus increases with repeated presentation of that stimulus. Serotonin interneuron that makes a pre-synaptic connection with a sensory neuron releases serotonin. Serotonin reduces K+ efflux through potassium channels, thus prolonging the action potential. The prolonged action potential results in a greater calcium influx and therefore increased release of neurotransmitter. In sensitization, changes take place in potassium channels. The duel process theory aims to explain both habituation and sensitization within one framework. S-R system is responsible for producing fixed response to a stimulus (i.e. reflex), where there is a direct connection between the stimulus input and the motor output. Habituation is believed to occur in the S-R system. The State System involves the sensory input and the response, but also the input is sent to the central nervous system for additional processing to modulate responses. Sensitization is thought to exist in the State system.
Long term enhancement (LTE) is a change in amplitude of an excitatory postsynaptic potential. The enhancement of postsynaptic potential can last for number of hours to number of days.