The Schizophrenia Syndrome
Schizophrenia affects about 1% of people all over the world. The first symptoms typically appear in a person's mid-twenties, and many people never fully recover. Worse still, we know almost nothing about schizophrenia's causes.
On the one hand, there is strong evidence that schizophrenia has a biological basis, because it runs in families, which indicates a genetic component. There are also subtle abnormalities in brain structure. Treatment with drugs, particularly those that target the neurotransmitter dopamine, can reduce the symptoms, but the mechanism of this effect is unknown and unfortunate side effects can and do occur.
On the other hand, the characteristic symptoms of schizophrenia are firmly in the domain of the mind. Patients report hallucinations (false perceptions) and delusions (false beliefs). A patient may hear his own thoughts spoken aloud or hear voices discussing him. A patient may believe that alien forces are controlling his or her actions or inserting thoughts into his or her mind. The challenge for the neuropsychologist is to show how a disorder in the brain can lead to these bizarre experiences. My own starting point for understanding schizophrenia is the observation that, in some cases, the "voices" that patients hear are clearly their own. This observation puts the problem in a slightly different light: the question is not why patients hear voices, but why they mistake their own voice for that of someone else. This question applies to other symptoms as well. For example, patients with delusions of control report that their movements are alien; they feel as if they were being made by someone else. This is not as startling as it may at first appear. After all, every action we perform causes changes in our sensations. When we speak, we hear the sound of our own voice. When we move our arm, there are changes in kinesthetic and tactile sensations. But there is nothing in the nature of these sensations that distinguishes them from signals caused by external events - the sound of someone else's voice, someone else lifting our arm.