Ngược lại, sau khi quen thuốc lâu dài, chỉ có 30% các tế bào thần kinh cảm giác kết nối phát hiện vào các tế bào thần kinh vận động, và hiệu ứng này kéo dài trong hơn một tuần, những kết nối này chỉ phục hồi một phần tại 3 tuần. Như vậy, đầy đủ chức năng kết nối khớp thần kinh | Psychotherapy and the Single Synapse 19 cells Figure 1-5 . By contrast after long-term habituation only 30 of the sensory neurons produced detectable connections onto the motor cell and this effect lasted for over a week these connections were only partially restored at 3 weeks. Thus fully functioning synaptic connections were inactivated for over a week as a result of a simple learning experience several brief sessions of habituation training of 10 trials each. Thus whereas short-term habituation involves a transient decrease in synaptic efficacy long-term habituation leads to prolonged and profound functional inactivation of a previously existing connection. These data provide direct evidence that long-term change in synaptic efficacy can underlie a specific instance of long-term memory. Moreover at a critical synapse such as this one relatively few stimuli produce long-term synaptic depression. Sensitization Sensitization the opposite of habituation is the process whereby an animal learns to increase a given reflex response as a result of a noxious or novel stimulus. Thus sensitization requires the animal to attend to stimuli that potentially produce painful or dangerous consequences. Like habituation sensitization can last from minutes to days and weeks depending on the pattern of stimulation Pinsker et al. 1973 . In this discussion I will focus on the short-term form. At the cellular level sensitization also involves altered transmission at the synapses made by the sensory neurons on their central target cells. Specifically sensitization involves a mechanism called presynaptic facilitation whereby the neurons mediating sensitization end on the terminals of the sensory neurons and enhance their ability to release transmitter Figure 1-6 . Thus the same synaptic locus is regulated in opposite ways by opposing forms of learning it is depressed by habituation and enhanced by sensitization. The transmitter released by the neurons that mediate presynaptic .
