Drugs and Diseases
The impressive connections between mental processes such as perception, learning, memory, and
reading and specific brain processes are evidence for the identification of mind and brain only if
brain changes cause mental changes. But perhaps there is only correlation here rather than causation.
The fact that ice cream consumption and drowning frequency are correlated does not show that one
causes the other, as they have a common cause in high temperatures. A dualist could argue that all the
empirical studies described above merely show that brain processes correlate with mental ones
without brain's being the exclusive cause of mind. In scientific reasoning, the best way to show
causation rather than mere correlation is to introduce an intervention, showing that manipulating one
factor leads to a change in another factor. In psychology and neuroscience, there are both technical
and ethical reasons why it is often hard to show that manipulating the brain can produce mental
changes.
However, people frequently engage in such manipulations when they take drugs that have
psychological effects. If you use recreational drugs such as alcohol or therapeutic drugs such as
antidepressants, you are producing a physical change in your brain that changes your mental state in
predictable ways. A quick review of how drugs affect the brain and thereby change mental states
provides evidence that the connection between brain and mind is causal and not just correlational.
Much is now known about the neural and molecular mechanisms that draw people to recreational
drugs. When you have a glass of beer, wine, or whiskey, the alcohol quickly affects your brain
chemistry. Because of increased concentrations of the neurotransmitter dopamine, there is increased
activity in the nucleus accumbens, a brain area associated with feelings of pleasure. Alcohol also
increases activity of the neurotransmitter GABA, which enables some neurons to inhibit the firing of
other neurons. You then get greater inhibition of neural firing, which in small doses of alcohol can
produce relaxation but in large doses can lead to lack of coordination, slurring of words, and even
passing out. Other neurotransmitters that are altered by alcohol include serotonin and norepinephrine.
Extensive studies with animals and humans support the following causal chain: drinking alcohol
changes your brain processes and thereby changes your thinking. Similarly, we know that people
become addicted to smoking cigarettes because nicotine stimulates acetylcholine receptors and
increases dopamine levels, producing a physical dependency.
The neuropsychological mechanisms triggered by illegal drugs are also well understood.
Stimulants such as cocaine and amphetamines, including the popular drug Ecstasy, increase brain
concentrations of the pleasure-inducing neurotransmitter dopamine, as well as other energizing
neurotransmitters such as norepinephrine. Dependency on such drugs can arise because depletion of
these neurotransmitters produces cravings for more of the drug. Opiates such as heroin stimulate
special receptors in the brain leading to release of dopamine and subsequent feelings of pleasure and
relaxation, producing strong inclinations toward addiction. Enough is known about how such
powerfully addictive drugs work that we can confidently say that people use them to manipulate
mental states by changing their brain states.