Addiction is a complex phenomenon that involves the brain's reward circuitry. It's often described as a continuum, with different substances and behaviors having varying degrees of addictive liability. For instance, substances like cocaine or opioids have a very high addictive liability, while others like caffeine, despite causing tolerance, don't typically lead to destructive behaviors associated with addiction.
In the context of neurobiology, addiction involves powerful changes in the connections between nerve cells, or synapses, in the reward circuitry of the brain. These changes can make the brain more sensitive to certain experiences. It's also important to note that addiction can be influenced by a combination of underlying genetics and environmental factors.
In a broader sense, I've described addiction as a progressive narrowing of the things that bring you pleasure. This means that as addiction progresses, fewer and fewer things are able to bring the individual pleasure, often leading to a focus on the addictive substance or behavior.