|
Neuroscience has shown us that experience alters brain structure and
that learning can create physical changes and affect cognition and
behavior. New research from the University of Lethbridge in Canada
published in the Proceedings of the National Academy of Sciences
shows that exposure to stimulant drugs such as amphetamine or cocaine
can impair the ability of specific brain cells to change as a
consequence of experience.
The researchers hypothesized that exposure to psychostimulant drugs
might influence later experience-dependent structural plasticity. Their
targets were the neuronal dendrites and spines particularly in the
nucleus accumbens which is involved in motivation and reward, and the
parietal cortex that is important for sensory-motor function. A series
of experiments examined how drugs of abuse and experience might
interact to produce changes in brain structure. Individually housed
rats were administered amphetamine, cocaine, or saline repeatedly for
20 days. This pattern of drug administration was previously shown by
these investigators to produce both behavioral changes in response to
the drugs and structural changes in several brain regions. The current
study went one step further. After the 20-day drug exposure, the rats
were housed in a new environment with a variety of stimuli for 3 to 3.5
months.
The scientists found as in their previous studies, that amphetamine
increased dendritic branching and spine density in the nucleus
accumbens, and decreased spine density in the parietal cortex. Exposure
to the complex environment also increased the dendritic branching and
spine density in the nucleus accumbens, and, in contrast to
amphetamine, increased dendritic branching and spine density in the
parietal cortex as well. Interestingly, those that had been given
amphetamine and then placed in the complex environment did not show the
same environmental-induced structural changes in the nucleus acccumbens
and parietal cortex as did saline-treated animals in the complex
environment.
These findings suggest that at least some of the cognitive and
behavioral advantages that accrue with experience may be diminished by
prior exposure to psychostimulant drugs. This impairment of the ability
of specific brain circuits to change in response to experiences can
also possibly explain some of the behavioral and cognitive deficits
seen in people who are addicted to drugs.
A direction for future research should be to explore whether certain
types of new cognitive experiences might possibly counteract the
effects of psychostimulant drugs.
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.1834271100
11:22:45 PM 
|
