Final answer:
Withdrawal from addictive drugs increases the reward threshold because long-term drug use alters the brain's dopamine system, leading to fewer dopamine receptors and reduced dopamine levels. This adaptation raises the threshold for achieving pleasure, making rewards less attainable during withdrawal, which can lead to intense cravings.
Step-by-step explanation:
Understanding Drug Addiction and Reward Threshold
Withdrawal from addictive drugs can increase the reward threshold due to changes in the brain's chemistry and functioning. When a person uses drugs that increase dopamine levels, such as cocaine or nicotine, the neurotransmitter dopamine acts more intensely in the brain, stimulating the pleasure centers and creating a sense of euphoria. Over time, as drug use continues, the synaptic membrane's ratio of stimulatory to inhibitory receptors may change, resulting in a reduced number of dopamine receptors as seen in PET scans of addicted individuals' brains.
This reduction means that it takes more of the drug or a more intense experience to achieve the same pleasurable effects, thereby raising the reward threshold. When the drug is no longer present, as in withdrawal, the depleted dopamine levels and the lack of adequate receptors leave the individual in a state of diminished pleasure or dysphoria, which is often accompanied by cravings for more of the drug to compensate for the deficit. Therefore, the experience of reward becomes less accessible during withdrawal, necessitating greater effort or drug intake to achieve previously attainable levels of satisfaction.