In psychiatry, drugs used to treat mental illnesses also perform such manipulations. For depression,
millions of people take drugs like Prozac and Zoloft that inhibit the reuptake of the neurotransmitter
serotonin. How these drugs alleviate depression may involve the production of new neurons in the
hippocampus as well as increased availability of serotonin in the synaptic gaps between existing
neurons. Other antidepressants, such as MAO inhibitors, affect neurotransmitters in different ways.
Bipolar disorder, formerly known as manic depression, can be effectively treated with lithium, which
affects various neurotransmitters. The often devastating disease schizophrenia can sometimes be
treated with drugs like Thorazine and Risperdal that inhibit dopamine and also can affect levels of
other neurotransmitters. Increasing concentrations of dopamine can alleviate the symptoms of
Parkinson's disease.
Thus the use of recreational and therapeutic drugs provides overwhelming evidence that changing
brain processes causes changes in mental processes. Of course, the precise effects of drugs often
depend on expectations, as when people get more drunk than normal on a small amount of alcohol just
because of their social surroundings. So it is legitimate to say that mental processes cause brain
processes too. After all, the mind-brain identity theory just says that mental processes are brain
processes, and there is no problem in saying that brain processes cause other brain processes. More
importantly, these expectation effects provide no evidence for reintroducing the soul or other
nonmaterial substance into explanations of brain changes, because beliefs can be understood as neural
processes.
In this section I have only scratched the surface of the kinds of explanations that neuroscience is
increasingly able to give of diverse kinds of thinking. Those wanting more detail should consult
textbooks and journals in cognitive neuroscience and psychopharmacology, which will provide
pointers to thousands of experiments that investigate the neural bases of perception, memory, learning,
emotion, and other mental processes. The hypothesis that minds are brains is part of a highly
successful and rapidly expanding research program that has been generating neural explanations for a
wide range of mental phenomena. Experimental methods used by this research program include not
only brain scans that can identify correlations between thinking and neural activity, but also
transcranial magnetic stimulation that can cause changes in thinking by noninvasive alteration of the
electrical activity of neurons. In this technique, electromagnetic pulses are used to disrupt neural
firing, causing changes in cognitive processes such as vision and memory.
Later in this book I will provide more evidence supporting mind-brain identity. Chapters 4–6 will
provide fuller accounts of how brains know the world, have emotional experiences, and make
decisions. Proponents of the soul hypothesis cannot avoid the evidence that links such aspects of mind
with brain processes, but they have to say that the brain hypothesis is not by itself sufficient to explain
everything about thinking. Dualism maintains that people consist of both minds and bodies, or more
specifically souls and brains. Let us now consider some evidence that might support dualism over the
simpler identification of minds with brains.