It is easy to understand tolerance: the brain adapts so that the person no longer gets the same buzz from two beers and now needs three or four. But what explains the experience of an alcoholic who can no longer “tolerate” a single sip of alcohol without going into a drinking binge. Or what explains the experience of a sex addict who experiences such a strong pull by a single image of a sexy woman on the computer screen that he binges on porn? Norman Doidge writes the following in his excellent book, The Brain That Changes Itself:
“Eric Nestler, at the University of Texas, has shown how addictions cause permanent changes in the brains of animals. A single dose of many addictive drugs will produce a protein, called ΔFosB (pronounced ‘delta Fos B’), that accumulates in the neurons. Each time the drug is used, more ΔFosB accumulates, until it throws a genetic switch, affecting which genes are turned on or off. Flipping this switch causes changes that persist long after the drug is stopped, leading to irreversible damage to the brain’s dopamine system and rendering the animal far more prone to addiction. Nondrug addictions, such as running and sucrose drinking, also lead to the accumulation of ΔFosB and the same permanent changes in the dopamine system.”
Years earlier that sexually-addicted man did not have the build-up of ΔFosB. After repeatedly viewing porn, different genes were turned on. Later in life he has a far lower tolerance of visual stimulation without that stimulation pulling him toward an obsessive cycle of sexual acting out. The AA saying “One drink is too many and a thousand isn’t enough” captures both of these phenomena: tolerance and the increased pull toward the addictive drug.