When Picard was captured by the Kardassians he was tortured and they attempted to brainwash him. He was shown 4 bright lights and continuously told there were 5 (I think 5) of he said there were 4. The sequence ends with a final over the top amount of torture and he the last thing he said before being returned to federation was there are only 4 lights (I think). Later he is talking to someone and says he actually saw 5 the last time I believe.