Terms used to describe changes in speech

Mutism
This is the complete loss of speech. It could occur in depression,schizophrenia, dissociative disorders, disturbed children and patient with coarse brain disease. For example, a severely depressed patient may be mute. Some children may have elective mutism - i.e. the child speaks in certain environments only. For example he speaks normally at home, but does not speak at all at the school.
In motor aphasia, the patient's use of words may be severely restricted, but he may not be completely mute, i.e. he may be able to use 1 to 2 words. In akinetic mutism the patient appears to be aware of their environment, but is mute.

Pressure of speech
A state where there is an increased flow of speech. This speech is difficult to interrupt or stop. Pressure of speech is common in mania, where it is often associated with flight of ideas. Pressure of speech may also be seen in schizophrenia.

Flight of ideas
Flight of ideas are changes in the flow of speech which is typically seen in mania. In flight of ideas, the patient's thoughts occur very fast. The patient is very distractible, and the thoughts change very quickly, but there is an understandable association or connection between one thought and the next. These rapidly changing thoughts are manifested in the way the patient speaks very rapidly, jumping from subject to subject.