Selective Brain Lesion Results in Loss of Drug Addiction

The American Journal of Psychiatry has this very interesting case, but first you should know some background. There is a pathway in the brain that is commonly referred to as the reward pathway. It is referred to as the reward pathway because if I were to -- for instance -- implant an electrode into parts of it and train a rat to press a lever to zap himself there, he would do so more or less in perpetuity. This ability to very rapidly train self-stimulatory behavior (keep your mind out of the gutter) suggests that these areas of the brain are involved in learning reward.

Here is a diagram from the case report showing the reward pathway:

It was also known that if you lesion parts of this pathway in a rat, you can remove this reward seeking behavior. You can also prevent the animals from becoming addicted to drugs.

This we knew, but I have never seen a case report that showed what would happen if parts of this pathway were lesioned in a human.

Cue the case report. A 34-year old long-time drug-user is taken to the ER after he starts acting freaky at a party. He has a bunch of methadone (an opiate like heroin) with him that he downs on the way in to avoid detection. He proceeds to OD.

There are areas of the brain called watershed regions. These are areas in the brain where the blood supply of the major arteries is at its sparsest -- at the overlapping edges of two arteries. When you overdose, you sometimes have strokes in these regions. It turns out that the globus pallidus -- an area in the pathway listed above -- is one such watershed region, and the patient described had a bilateral stroke in this brain area. Here is an MRI that the initiated will know shows that this is selective (the white bits would be in the globus pallidus):

This gets us to the really interesting part. When the guy comes to, he has something called anhedonia. Anhedonia is one of the symptoms of depression. It is the inability to feel joy. More interestingly, he ALSO has lost his drug addiction:

After this overdose, Mr. A became acutely depressed. He endorsed a depressed mood, anhedonia, low energy, difficulties concentrating and remembering, feelings of hopelessness and guilt, poor self-esteem, social isolation, increased sleep, and a 20-lb weight gain over the ensuing year. He reported the disappearance of drug cravings and remained abstinent from all recreational drugs other than an occasional glass of wine with dinner. He reported that he no longer experienced pleasure from drinking alcohol. Four serial urine toxicology screens were negative over 6 months. (Emphasis mine.)

I thought I would point out this article because it is a very compelling case showing the parallels between lab science and medicine. Neurology is unfortunately often a science where you need cases like this to prove that we are not totally off base with how we think the brain works.

Hat-tip: Faculty of 1000.