Foerster's syndrome is the name used by Arthur Koestler in his account[1] of the compulsive punning first described[2] by the German neurosurgeon Otfrid Foerster.
In 1929, Foerster was operating on a patient suffering from a tumor in the third ventricle – a small cavity deep down in the phylogenetically ancient regions of the midbrain, adjacent to structures intimately concerned with the arousal of emotions.
When the surgeon began to manipulate the tumor, affecting those sensitive structures, the (conscious) patient burst into a manic flight of puns.
He exhibited typical sound associations, and with every word of the operator broke into a flight of ideas.
This gruesome humour, Koestler noted, all came "from a man tied face down to the operating table with his skull open".