Brain-imaging techniques create a window into the
effects of alcohol on the brain.
Using these techniques, researchers have observed shrinkage of brain tissue in people after long-term use of
alcohol. But there is also recovery
of brain tissue volume in people who stop drinking and remain abstinent, so this "shrinking" effect
appears not to be due exclusively to the
loss of brain cells. Interestingly, some studies indicate that certain parts of
the brain may be more vulnerable to damage by alcohol than others, such as the cortex—the folded, lumpy
surface of the brain (it gets its name
because of its resemblance to the bark of a tree), which endows us with
consciousness and controls most of our mental functions. One region of the cortex that appears to be
particularly vulnerable is the frontal
lobe. The frontal lobes are unique in that they act like a kind of executive manager for the rest of the brain. They
monitor and help to coordinate the
actions of the other cortical lobes—much like an executive does in a corporation. The analogy is so apt
that the functions of the frontal
lobes are often called "executive functions." They endow us with the
ability to bring together our mental abilities to solve complex problems, to make and execute plans of action, and to
use judgment in service of those
plans. Even in people who have never been diagnosed with an alcohol use disorder, chronic drinking can
contribute to frontal lobe damage.
Another vulnerable region is the mammillary bodies, which are very important for memory. (These small, round
structures near the base of the brain
got their name from the neuroanatomists who first noticed them and thought that they looked like
breasts. Actually, their resemblance
to breasts is quite remote, but neuroanatomists do have good imaginations!)
Although many of the studies of brain shrinkage
have been done with alcoholics, some
of the more recent ones have assessed social drinkers and found similar effects, though less severe. The
shrinkage occurs while the person is
still using alcohol. If she stops drinking for a prolonged period, her brain
will recover somewhat—not because new nerve cells grow but because support cells, or parts of the
remaining nerve cells, grow.
Therefore, the regrowth of brain size does not mean that the deficits in mental functioning that many alcoholics
experience will be erased simply by
abstaining from alcohol.
It is not known if there is a safe level of chronic
drinking. Clearly many people who
drink do not appear to suffer any damage to their mental functioning. Still, as with acute
intoxication, the lack of any obvious impairment does not mean that there is
none. Studies using animals instead of
humans can look more closely at nerve-cell damage. Such studies have shown that more moderate alcohol
exposure can damage and kill brain
cells. A number of these studies have shown large areas of nerve-cell loss in a region of the brain called the
hippocampus, which is known to be
critical for the formation of new memories. This could be one reason why people who drink chronically can end
up with relatively poor memory
function, though of course this will vary with the person's drinking history.
Another study in animals has shown that in the
case of very heavy drinking, brain
damage may occur much sooner than previously thought. Using a model in which animals are exposed to a
heavy "binge" of alcohol around
the clock for four days, it was discovered that cells in some of these same regions started to die off after the first
two days of the binge. If this holds
true for humans, it will show that even one very heavy episode of binging across a couple of days could damage the
brain. These effects were
particularly
pronounced in adolescent animals, raising some concern that teenage binge drinking may have more serious
long-term consequences than we once
thought.
Wilke Wilsion
