If the brain is like a muscle, then the onset of addiction is like rheumatism -- a growing stiffness and pain with movement. That, at least, is the finding of a group of international researchers based in France, and published in a recent issue of Science.
The scientists studied what happens in the brains of rats when exposed to various addictive substances. Rats and scores of other species from the great apes down to tiny worms and fruit flies, can be turned into addicts by infusing their bloodstreams with the addictive substance. Researchers either hook up the animals to intravenous tubes that inject the drug, or they confine the animals in a vapor chamber where the air is infused with the substance. It doesn't take long before the animals display a set of behaviors and physiological symptoms that we humans know all too well, if we have alcoholics or other drug addicts in our family or friendship circles.
The fact that animals can readily be turned into addicts, by the way, is important evidence that it's the substance, and not some qualities in the person's psychology, that makes addicts of us. Despite the creative work of Walt Disney's animators, rodents don't have human personality profiles, and they probably don't suffer from spiritual maladjustment. Quite a few theories blame the person's emotional and spiritual deficiencies for the onset of addiction. The animal experiments teach that there's a neurobiological process at work. The molecules in the substance are like so many little vandals in the brain, hammering, bending, mutilating and wrecking the intricate circuits of the most complex apparatus on earth -- one that we all carry between our ears.
What long-term use of the addictive substances does, the researchers found, is to decrease synaptic plasticity. Synapses, of course, are the connections between brain cells. Connections are the rails on which our thoughts and feelings run. When we process a new experience, the brain cells rewire themselves to integrate the new elements into our existing web of ideas and emotions. The power of brain cells to form new connections, their plasticity, is the foundation of all kinds of learning. A brain with high synaptic plasticity is like a body that's flexible, loose, limber, toned -- the kind we love to see jogging in the park or performing acrobatic feats on television.
So, the next time you hear somebody use slang terms like "let's get hammered" or "stupid" or "stoned," take it as a neurobiological reality. The chronic use of addictive substances such as alcohol, cocaine, etc. creates stiffness in the brain cells, even while it tends to take away men's stiffness elsewhere in the anatomy (but that's another story). A kind of mental rigidity sets in; the ability to learn and to adapt declines; the person's mind becomes unresponsive to new ideas and feelings. Does this describe anyone you know?
[For more details, read Kasanetz et al., "Transition to Addiction is Associated with a Persistent Impairment in Synaptic Plasticity," Science 328:5986 pp. 1709-1712.
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