Aman was being treated for drug addiction. he was exposed repeatedly to drug paraphernalia, the people, money--all of things that he had learned to associate with the drug use and resulting drug high--without actually using the drug. this process, called desensitization, makes use of to treat addiction.

In the case of psychoactive drugs, drug tolerance is a condition in which repeated use of a drug leads to reductions in its psychological effects, thereby requiring progressively larger doses in order for similar effects to occur. many factors affect the development of drug tolerance, and learning is one of them. a classic study by siegel, hinson, krank, and mccully (1982) was one of the first to demonstrate this. the researchers found that rats can be classically conditioned to develop tolerance to heroin.

siegel, et al. (1982) wanted to understand why some addicts died after taking a dose of the drug that they had taken many times before. the official cause of death in these cases usually was said to be a “drug overdose” because the dose was high enough to kill most people not addicted to the drug. these addicts, however, had developed a high level of tolerance to the lethal effects of the drug, so ascribing their deaths to an overdose couldn’t be correct.

the researchers hypothesized that the addicts’ tolerance was due, in part, to classical conditioning. that is, the situation is which they typically took the drug had become a conditioned stimulus (cs) that elicited a conditioned response (cr) involving a change in biological processes that prepared their bodies to counteract the lethal effects of the drug. this explanation may be easier to understand by looking at a case study described in siegel (2001). the study was of a man suffering from severe pain because of pancreatic cancer. in order to reduce the pain, he received four injections of morphine per day. over time, the dosage had been increased to a high level because of the tolerance he had developed to morphine’s pain-reducing effects.

Urban growth invariably feeds increased commercialization and industrialization. it requires continually expanding land areas. when urbanization rates are high, and countries do not have the institutional and managerial capacities or economic wherewithal to manage such rapid growths, they exert intense pressure on the types and nature of the resulting settlements. they contribute to the development of overcrowded slums and shanty towns without adequate essential services and necessary infrastructure.-by asit k. biswas and cecilia tortajada