Additionally, drugs that affect monoamine transmission vary in their selectivity. For example, drugs with high selectivity for increasing dopamine and norepinephrine transmission relative to serotonin transmission tend to have highly addictive properties. Amphetamine and cocaine share this selectivity profile, and administration of these drugs generally results in a left-shift in M50 and θ0, indicating sensitization of the reward circuitry and high abuse potential. This characteristic leftward-shift of M50 in response to a moderate dose of cocaine is illustrated in a hypothetical data set in Figure 1. Note that the maximum response rate is reached at a lower frequency than it is at baseline, and there is a significant response rate at the lowest frequency, which did not produce responding under baseline conditions. Even following chronic administration of methamphetamine or cocaine, there is little to no tolerance to ICSS facilitation. After chronic treatment is stopped, however, there is a withdrawal-induced depression of ICSS responding, which can be reversed by re-administering the drug.