Impulses

Brian Stewart is a respected professional man, liked by his colleagues and friends and loved by his wife Marcia and their two young children. He has never been the kind of man who would lose his sense of propriety or do anything on an impulse.
Until, that is, the day he starts to go off the rails. Alarmed at the change in her husband, Marcia is horrified to discover that he has incurred tens of thousands of pounds in debts after starting to gamble compulsively. Soon afterwards, he is arrested for alleged sexual offences, including rape. Marcia stands by Brian but is unable to understand or explain this profound change in her husband's behaviour. Surely, he is not in his right mind. But what sort of affliction could lead to such serious loss of control over his basic impulses?