Psychiatric illness may be associated with objective or subjective motor disorders. This chapter is chiefly devoted to objective motor disorders. However, it is important to note at the outset that subjective motor disorders may also occur.

Subjective motor disorders: the alienation of motor acts

Normally humans experience their actions as being their own and as being under their own control, although this sense of personal control is never in the forefront of consciousness, except when a particular effort is made to overcome the effects of fatigue or toxic substances that are clouding our consciousness and making it difficult for us to control our bodies. In obsessions and compulsions the sense of possession of the thought or act is not impaired, but the patient experiences the obsession as appearing against their will, so that although they have lost control over a voluntary act they still retain personal possession of the act.

In schizophrenia the patient may not only lose the control over their thoughts, actions or feelings, but may also experience them as being foreign or manufactured against their will by some foreign influence. These symptoms are known as ideas or delusions of passivity. The patient may also develop secondary delusions that explain this foreign control as the result of radio waves, X-rays, television, witchcraft, hypnosis, the internet, and so on. This can be described as a delusion of passivity. There is some evidence that delusions of passivity are related to anomalies of the parietal lobe (Maruff et al, 2005), but this association requires further study to clarify the precise anomalies that may underlie these phenomena.

Some individuals with severe anxiety may feel they cannot think clearly or are unable to carry out ordinary volitional activity. They may therefore feel ‘as if’ they are being controlled by foreign influences. As they have difficulty in thinking and putting their thoughts into words they may give the impression that they know that their thoughts are under foreign control, so it may be difficult to distinguish these ‘as if’ experiences from true passivity phenomenon, as seen in schizophrenia. This distinction is, however, crucial if misdiagnosis is to be avoided.

Classification of motor disorders

It is difficult to classify motor disorders, because although clear-cut individual motor signs, such as stereotypies, can be treated as if they were neurological symptoms, it is much more difficult to classify more complicated patterns of behaviour.