thought disorder

n. disorder that affects the thought processes where connections between ideas are lost, loosening of associations (Psychiatry)

In psychiatry, thought disorder or formal thought disorder is a term used to describe a pattern of disordered language use that is presumed to reflect disordered thinking. It is usually considered a symptom of psychotic mental illness, although it occasionally appears in other conditions.It describes a persistent underlying disturbance to conscious thought and is classified largely by its effects on speech and writing. Affected persons may show pressure of speech (speaking incessantly and quickly), derailment or flight of ideas (switching topic mid-sentence or inappropriately), thought blocking, rhyming, punning, or 'word salad' when individual words may be intact but speech is incoherent.
See more at Wikipedia.org...